A carbon dioxide capture and waste heat recovery system and its control method

Abstract

This invention discloses a carbon dioxide capture waste heat recovery system and its control method. The system includes: a stripping tower (1), a lean-rich liquid heat exchanger (2), a lean liquid pump (3), a waste heat recovery unit (4), a lean liquid cooler (5), an absorption tower (6), a rich liquid pump (7), and a regulating valve group. The lean liquid outlet of the stripping tower (1) is sequentially connected to the hot side of the lean-rich liquid heat exchanger (2), the lean liquid pump (3), the heat source side of the waste heat recovery unit (4), and the lean liquid cooler (5), and then connected to the lean liquid inlet of the absorption tower (6). The rich liquid outlet of the absorption tower (6) is sequentially connected to the rich liquid pump (7), the cold side of the lean-rich liquid heat exchanger (2), the heat sink side of the waste heat recovery unit (4), and then connected to the rich liquid inlet of the stripping tower (1). This invention, through the design of bypass pipelines and regulating valve groups, realizes flexible switching between waste heat recovery and the original system mode, solves the problems of waste heat waste in the lean liquid cooler and high-grade steam consumption for rich liquid heating, and significantly reduces external steam consumption of the stripping tower and cooling water consumption of the lean liquid cooler.

Description

Technical Field

[0001] This invention relates to the field of carbon dioxide capture technology, and in particular to a carbon dioxide capture waste heat recovery system and its control method. Background Technology

[0002] Carbon dioxide (CO2) emission reduction is receiving increasing attention, especially in various sectors in China. From carbon emissions to carbon trading, CO2 capture technology has become a key technological path to achieving the "dual carbon" goals, particularly playing a crucial role in the low-carbon utilization of fossil fuels. Through carbon capture, utilization, and storage (CCUS) technologies, CO2 emissions from industrial production processes can be efficiently captured and utilized for resource recovery, thereby reducing greenhouse gas emissions. Currently, central state-owned enterprises, state-owned enterprises, and universities are conducting research and trials on CO2 capture. By 2025, my country has planned and is operating over 120 CCUS demonstration projects, covering multiple industries such as power, steel, and cement, with a capture capacity of approximately 9.4 million tons per year. In these sectors, how to integrate CO2 capture with existing processes to reduce energy consumption costs and achieve energy conservation and efficiency has become a focus of industry attention.

[0003] Carbon capture (CC) processes have been used in the petroleum, chemical, and power industries for decades. Current methods primarily utilize chemical absorption, which has lower equipment costs compared to other methods but higher energy consumption. In CC processes, lean and rich solutions undergo heat exchange, heating the rich solution and cooling the lean solution. The heated rich solution then enters a stripping column, where it is indirectly heated by external steam heating of the reboiler, releasing carbon dioxide. It then returns to the stripping column to absorb carbon dioxide, thus fulfilling the system's cycle requirements. However, the lean solution, after cooling in the lean-rich solution exchanger, still has a relatively high temperature, necessitating a lean solution cooler. This cooler uses direct cooling water to lower the temperature to around 40-50°C to ensure optimal absorption of carbon dioxide. Therefore, the heat generated by the lean solution cooler is wasted, while the rich solution requires high-grade steam to reach the required temperature, resulting in inefficient energy utilization and increased steam consumption per ton of carbon dioxide. Research has revealed that the heat generated in existing CC technologies is not recovered, leading to resource waste.

[0004] Existing technologies have attempted to recover waste heat from carbon capture systems using heat pumps. One approach involves recovering the heat from the regenerated gas at the top of the tower to heat the circulating liquid in the bottom of the tower. In this approach, the top of the tower contains carbon dioxide, water vapor, and a small amount of amines, among other substances. The diverse composition and gaseous state of these components affect heat exchange, and the discharge of non-condensable gases (CO2) in the waste heat recovery equipment must be considered. This makes the unit design more challenging, and the cooling effect may not be sufficient, requiring further cooling in a heat exchanger, increasing gas resistance. Simultaneously, this approach requires increasing the circulation volume in the reboiler section, changing from natural circulation to forced circulation, increasing power consumption. Maintaining the outlet pressure of the waste heat recovery unit is also crucial; otherwise, two-phase flow will occur, making waste heat recovery impossible. Furthermore, the waste heat recovery equipment in this approach is primarily an absorption heat pump, requiring high steam pressure to drive the heating of the bottom liquid, and the design involves considerations for corrosion prevention of high-temperature solutions in the unit. Another option is to recover heat from the lean liquid cooler to heat the circulating liquid in the reboiler. This option also requires increasing the circulation volume in the reboiler section, changing from natural circulation to forced circulation, increasing power consumption, and maintaining the outlet pressure of the waste heat recovery unit. Otherwise, it will lead to two-phase flow of vapor and liquid, making waste heat recovery impossible. At the same time, the waste heat recovery equipment in this option is mainly an absorption heat pump, which needs to meet the high steam pressure required for heating the liquid in the reboiler and the unit design considerations for high-temperature solution corrosion prevention. In addition, the waste heat recovery temperature in this option is lower than the temperature of the amine liquid in the reboiler of the heating tower, which will greatly increase the unit cost. Moreover, due to the characteristics of the unit, only a portion of the waste heat can be recovered.

[0005] Therefore, recovering heat from the capture process to reduce the high-energy consumption (steam) in the capture process is beneficial to enterprises in terms of energy conservation, consumption reduction, and environmental protection, fully demonstrating the principle of returning to the process from the process. Summary of the Invention

[0006] The purpose of this invention is to provide a waste heat recovery system and control method for carbon dioxide capture. The system aims to achieve this by installing a waste heat recovery unit after the lean-rich liquid heat exchanger and before the lean liquid cooler. By utilizing bypass pipelines and regulating valve groups, the system introduces the medium-temperature lean liquid before the lean liquid cooler into the waste heat recovery unit as a heat source, and the rich liquid after the lean-rich liquid heat exchanger into the same waste heat recovery unit as a heat sink. Combined with proportional linkage control of the valve group, this achieves heat transfer from the lean liquid side to the rich liquid side. This solves the dual technical problems of waste heat loss due to cooling water carrying away from the lean liquid cooler in traditional carbon capture processes, and high overall energy consumption due to the need for high-grade steam to heat the rich liquid. The system achieves the effects of reducing external steam consumption of the stripping tower, reducing cooling water consumption of the lean liquid cooler, and synergistically reducing the overall energy consumption of the carbon capture process through closed-loop waste heat recovery.

[0007] To address the aforementioned problems, a first aspect of the present invention provides a carbon dioxide capture and waste heat recovery system. This system includes: a desorption tower 1, a lean-rich liquid heat exchanger 2, a lean liquid pump 3, a waste heat recovery unit 4, a lean liquid cooler 5, an absorption tower 6, a rich liquid pump 7, and a regulating valve group. The lean liquid outlet of the desorption tower 1 is sequentially connected to the hot side of the lean-rich liquid heat exchanger 2, the lean liquid pump 3, the heat source side of the waste heat recovery unit 4, and the lean liquid cooler 5, and then connected to the lean liquid inlet of the absorption tower 6. The rich liquid outlet of the absorption tower 6 is sequentially connected to the rich liquid pump 7, the cold side of the lean-rich liquid heat exchanger 2, and the heat sink side of the waste heat recovery unit 4, and then connected to the rich liquid inlet of the desorption tower 1. The regulating valve group includes a first valve group disposed on the bypass pipeline of the heat sink side of the waste heat recovery unit 4, a second valve group disposed on the main rich liquid pipeline, a third valve group disposed on the bypass pipeline of the heat source side of the waste heat recovery unit 4, and a fourth valve group disposed on the main lean liquid pipeline.

[0008] This invention, through innovative bypass piping and regulating valve group design, sets up a waste heat recovery unit after the lean and rich liquid heat exchanger and before the lean liquid cooler. This decouples the series-connected lean liquid cooling flow path and rich liquid heating flow path in the traditional carbon capture process, transforming them into two independently controllable heat exchange paths: the lean liquid is introduced to the heat source side of the waste heat recovery unit via the bypass piping to release heat and cool down, while the rich liquid is introduced to the heat sink side of the same waste heat recovery unit via the bypass piping to absorb heat and heat up. Heat transfer is achieved within the unit. Simultaneously, with the proportional linkage control of the first, second, third, and fourth valve groups, a new system that can achieve waste heat recovery and utilization without changing the main structure of the original process is constructed together in the primary network (original process piping) and the secondary network (bypass piping). This fundamentally solves the dual technical problems in the traditional carbon capture process: the waste heat of the lean liquid cooler is carried away by the cooling water, resulting in waste, and the high overall energy consumption caused by the consumption of high-grade steam for rich liquid heating. This significantly improves the system's energy utilization efficiency, operating economy, and process adaptability flexibility.

[0009] Furthermore, the first valve group includes a first regulating valve 11 and a third regulating valve 13, the second valve group includes a second regulating valve 12, the third valve group includes a fourth regulating valve 14 and a sixth regulating valve 16, and the fourth valve group includes a fifth regulating valve 15.

[0010] Furthermore, the first regulating valve 11 and the third regulating valve 13 are controlled in a proportional manner with the second regulating valve 12: when the first regulating valve 11 and the third regulating valve 13 are opened proportionally, the second regulating valve 12 is closed proportionally; and the fourth regulating valve 14 and the sixth regulating valve 16 are controlled in a proportional manner with the fifth regulating valve 15: when the fourth regulating valve 14 and the sixth regulating valve 16 are opened proportionally, the fifth regulating valve 15 is closed proportionally.

[0011] Furthermore, the waste heat recovery unit 4 is an absorption heat pump or an electric compression heat pump.

[0012] Furthermore, a reboiler 9 is provided at the bottom of the analytical tower 1 to supplement the heating of the analytical tower 1 when the heat supply from the waste heat recovery unit 4 is insufficient.

[0013] Furthermore, the top regenerated gas outlet of the analytical tower 1 is connected to a gas cooler 8 for cooling the analyzed regenerated gas.

[0014] Furthermore, the lean liquid cooler 5 is a cooling water heat exchanger used to cool the lean liquid.

[0015] Furthermore, the heat source side of the waste heat recovery unit 4 is an evaporator used to recover waste heat from lean liquid; the heat sink side of the waste heat recovery unit 4 is an absorber and / or a condenser used to heat rich liquid.

[0016] According to another aspect of the present invention, the present invention also provides a control method for a carbon dioxide capture waste heat recovery system, for use in the aforementioned carbon dioxide capture waste heat recovery system. The control method includes: when operating in waste heat recovery mode, opening the first valve group and the third valve group, and closing the second valve group and the fourth valve group, so that the lean liquid is cooled by passing through the heat source side of the waste heat recovery unit 4, and the rich liquid is heated by passing through the heat sink side of the waste heat recovery unit 4; when operating in the original system mode, closing the first valve group and the third valve group, and opening the second valve group and the fourth valve group, so that the lean liquid and the rich liquid bypass the waste heat recovery unit 4 and flow along the main pipeline respectively.

[0017] This invention employs an innovative proportional linkage control method to coordinate and couple the independently controlled lean liquor cooling flow path and rich liquor heating flow path in traditional carbon capture processes at the control level. This transforms them into two heat exchange channels that can respond to system demands in real time: When operating in waste heat recovery mode, the first and third valve groups are opened, while the second and fourth valve groups are closed, allowing the lean liquor to cool down at the heat source side of the waste heat recovery unit and the rich liquor to heat up at the heat sink side of the waste heat recovery unit; when operating in the original system mode, the first and third valve groups are closed, while the second and fourth valve groups are opened, allowing the lean and rich liquors to bypass the waste heat recovery unit. The valve groups flow along the main pipeline respectively; at the same time, in conjunction with the proportional linkage control between the first and second valve groups and between the third and fourth valve groups, a new control strategy that can realize waste heat recovery and utilization without changing the original process control framework is jointly constructed in the primary network (original process control logic) and the secondary network (bypass control logic). This fundamentally solves the technical problems in traditional carbon capture processes, such as the difficulty in balancing waste heat recovery and process safety, inflexible control mode switching, and inability to quickly switch back to the original system in the event of a fault. It significantly improves the system's control flexibility, operational safety, and adaptability to operating conditions.

[0018] Furthermore, when a fault or abnormal process parameter is detected in the waste heat recovery unit 4, it automatically switches back to the original system mode.

[0019] The above-described technical solution of the present invention has the following beneficial technical effects: 1. Waste heat recovery and reduced steam consumption: By installing a waste heat recovery unit after the lean-rich liquid heat exchanger and before the lean liquid cooler, and using a bypass pipeline to introduce the medium-temperature lean liquid before the lean liquid cooler into the heat source side of the waste heat recovery unit, and the rich liquid after the lean-rich liquid heat exchanger into the heat sink side of the same waste heat recovery unit, heat transfer from the lean liquid side to the rich liquid side is achieved. Thermal balance calculations have verified that after adopting this system, the heat consumption per ton of carbon dioxide can be reduced from approximately 3.5 GJ in the traditional process to 2.4-3.0 GJ, with a reduction of 15%-30% depending on the amine liquid (low temperature or high temperature), significantly reducing the external steam consumption of the stripping tower.

[0020] 2. Reduced cooling water consumption and energy waste: In traditional processes, the lean liquor still carries a large amount of low-grade waste heat after being cooled by the lean-rich liquor heat exchanger, which needs to be removed by cooling water through the lean liquor cooler. This system uses a waste heat recovery unit to pre-cool the lean liquor before it enters the lean liquor cooler, thereby reducing the inlet temperature of the lean liquor cooler and significantly reducing the cooling water consumption of the lean liquor cooler. The waste heat that would otherwise be removed by the cooling water is converted into useful thermal energy, realizing the cascade utilization of energy.

[0021] 3. Dual-mode switching ensures process safety: By setting up a first, second, third, and fourth valve group, this system can flexibly switch between waste heat recovery mode and the original system mode. When the waste heat recovery unit malfunctions or process parameters are abnormal, it can automatically switch to the original system mode to ensure the continuous and safe operation of the main carbon capture process, achieving a high degree of synergy between waste heat recovery and process safety.

[0022] 4. Wide applicability and flexible investment: Waste heat recovery units can be equipped with either absorption heat pumps or electric compression heat pumps, depending on site conditions and operational economics. Electric compression heat pumps can be selected when on-site electricity is readily available and electric heat pump operating costs are lower; absorption heat pumps can be used when on-site electricity is inconvenient or when there is available waste heat to drive a heat source. Both options achieve the same waste heat recovery function, providing customers with the flexibility to choose based on energy prices.

[0023] 5. Avoiding gas-liquid two-phase flow and reducing equipment design complexity: Both the heat source and heat sink sides of this system use liquid media (lean and rich solutions), eliminating the need for heat exchange with gaseous CO2 or water vapor. This fundamentally avoids the problems of reduced heat exchange efficiency, equipment vibration, and pipe corrosion caused by gas-liquid two-phase flow in existing solutions. Furthermore, this system utilizes existing lean and rich solution pumps for circulation, eliminating the need for forced circulation, thus reducing equipment investment and operating power consumption. It also eliminates the need for special high-temperature and corrosion-resistant materials, significantly reducing equipment design complexity and manufacturing costs. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of a carbon dioxide capture and waste heat recovery system according to an embodiment of the present invention.

[0025] Figure label: 1: Desorption tower; 2: Lean and rich liquid heat exchanger; 3: Lean liquid pump; 4: Waste heat recovery unit; 5: Lean liquid cooler; 6: Absorption tower; 7: Rich liquid pump; 8: Gas cooler; 9: Reboiler; 11: First regulating valve; 12: Second regulating valve; 13: Third regulating valve; 14: Fourth regulating valve; 15: Fifth regulating valve; 16: Sixth regulating valve. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments and the accompanying drawings. It should be understood that these descriptions are merely exemplary and not intended to limit the scope of the invention. Furthermore, descriptions of well-known structures and techniques are omitted in the following description to avoid unnecessarily obscuring the concept of the invention.

[0027] To address the problems in existing carbon capture processes, such as the waste caused by the removal of waste heat from the lean liquid cooler by cooling water and the high overall energy consumption due to the need for high-grade steam to raise the temperature of the rich liquid, this invention proposes a carbon dioxide capture waste heat recovery system and its control method. This system can achieve closed-loop recovery of waste heat and reduction of energy consumption within the carbon capture process without changing the main structure of the original process. This invention employs a waste heat recovery unit installed after the lean-rich liquid heat exchanger and before the lean liquid cooler. A bypass pipeline introduces the medium-temperature lean liquid before the lean liquid cooler into the heat source side of the waste heat recovery unit, while the rich liquid after the lean-rich liquid heat exchanger is introduced into the heat sink side of the same waste heat recovery unit. The lean liquid releases heat and cools down at the heat source side before returning to the lean liquid cooler, while the rich liquid absorbs heat and heats up at the heat sink side before entering the desorption tower. Simultaneously, a first valve group on the bypass pipeline on the heat sink side of the waste heat recovery unit, a second valve group on the main rich liquid pipeline, a third valve group on the bypass pipeline on the heat source side of the waste heat recovery unit, and a fourth valve group on the main lean liquid pipeline allow for flexible switching between the waste heat recovery mode and the original system mode. This invention can significantly reduce external steam consumption of the desorption tower and cooling water consumption of the lean liquid cooler while achieving waste heat recovery from the carbon capture process, reducing heat consumption per ton of carbon dioxide by 15%-30%. It provides stable, economical, and efficient technical support for low-carbon transformation in high-carbon emission industries such as power, steel, and cement.

[0028] The following is combined with Figure 1 The present invention describes the carbon dioxide capture waste heat recovery system and its control method.

[0029] Figure 1 This is a schematic diagram of a carbon dioxide capture and waste heat recovery system according to an embodiment of the present invention.

[0030] like Figure 1 As shown, in some embodiments, the carbon dioxide capture waste heat recovery system includes a stripping tower 1, a lean and rich liquid heat exchanger 2, a lean liquid pump 3, a waste heat recovery unit 4, a lean liquid cooler 5, an absorption tower 6, a rich liquid pump 7, and a regulating valve group.

[0031] The lean liquor outlet of the stripping tower 1 is sequentially connected to the hot side of the lean-rich liquor heat exchanger 2, the lean liquor pump 3, the heat source side of the waste heat recovery unit 4, and the lean liquor cooler 5, and then connected to the lean liquor inlet of the absorption tower 6, forming a lean liquor circulation loop. The rich liquor outlet of the absorption tower 6 is sequentially connected to the rich liquor pump 7, the cold side of the lean-rich liquor heat exchanger 2, and the heat sink side of the waste heat recovery unit 4, and then connected to the rich liquor inlet of the stripping tower 1, forming a rich liquor circulation loop. These two loops together constitute the core process flow path of this system.

[0032] The regulating valve group includes a first valve group installed on the bypass pipeline on the heat sink side of the waste heat recovery unit 4, a second valve group installed on the rich liquid main pipeline, a third valve group installed on the bypass pipeline on the heat source side of the waste heat recovery unit 4, and a fourth valve group installed on the lean liquid main pipeline. Specifically, the first valve group includes a first regulating valve 11 and a third regulating valve 13, the second valve group includes a second regulating valve 12, the third valve group includes a fourth regulating valve 14 and a sixth regulating valve 16, and the fourth valve group includes a fifth regulating valve 15. Through the coordinated control of the above valve groups, the system can flexibly switch between waste heat recovery mode and original system mode, while realizing proportional linkage regulation.

[0033] In waste heat recovery mode, the first regulating valve 11, the third regulating valve 13, the fourth regulating valve 14, and the sixth regulating valve 16 are open, while the second regulating valve 12 and the fifth regulating valve 15 are closed. The rich liquor from the absorption tower 6 is pumped by the rich liquor pump 7 to the cold side of the lean-rich liquor heat exchanger 2, where it exchanges heat with the high-temperature lean liquor from the desorption tower 1. The rich liquor is preheated, and the lean liquor is initially cooled. The preheated rich liquor enters the heat sink side of the waste heat recovery unit 4 via the first regulating valve 11 and is further heated before entering the desorption tower 1 via the third regulating valve 13. The initially cooled lean liquor is pumped by the lean liquor pump 3 and then via the fourth regulating valve 14 to the heat source side of the waste heat recovery unit 4, where it releases heat and cools down before entering the lean liquor cooler 5 via the sixth regulating valve 16. After further cooling, it returns to the absorption tower 6. Through the above process, this system recovers and transfers the waste heat of the lean liquor before the lean liquor cooler, which would otherwise be carried away by the cooling water, to the rich liquor, significantly reducing the external steam consumption of the stripping tower and the cooling water consumption of the lean liquor cooler. Thermal balance calculations have verified that, after adopting this system, the heat consumption per ton of carbon dioxide can be reduced from approximately 3.5 GJ in the traditional process to 2.4-3.0 GJ, with a reduction of 15%-30% depending on the type of amine liquor.

[0034] The first regulating valve 11 and the third regulating valve 13 are controlled proportionally with the second regulating valve 12: when the first regulating valve 11 and the third regulating valve 13 are opened proportionally, the second regulating valve 12 is closed proportionally. Similarly, the fourth regulating valve 14 and the sixth regulating valve 16 are controlled proportionally with the fifth regulating valve 15: when the fourth regulating valve 14 and the sixth regulating valve 16 are opened proportionally, the fifth regulating valve 15 is closed proportionally.

[0035] During system operation, when the amount of waste heat recovery needs to be increased, the second regulating valve 12 gradually closes, while the first regulating valve 11 and the third regulating valve 13 gradually open in the same proportion; when the amount of waste heat recovery needs to be decreased, the second regulating valve 12 gradually opens, while the first regulating valve 11 and the third regulating valve 13 gradually close in the same proportion. Similarly, when the amount of waste heat recovery needs to be increased, the fifth regulating valve 15 gradually closes, while the fourth regulating valve 14 and the sixth regulating valve 16 gradually open in the same proportion; when the amount of waste heat recovery needs to be decreased, the fifth regulating valve 15 gradually opens, while the fourth regulating valve 14 and the sixth regulating valve 16 gradually close in the same proportion.

[0036] The aforementioned gradual opening and closing actions are based on the heat required by the analytical tower 1 and the temperature of the analytical tower 1. When the temperature of the analytical tower 1 is too low, the action of increasing the waste heat recovery is executed accordingly; when the temperature of the analytical tower 1 reaches the target, the action of reducing the waste heat recovery is executed appropriately.

[0037] When a malfunction or abnormal process parameters are detected in waste heat recovery unit 4, the system automatically switches to the original system mode: the first regulating valve 11, the third regulating valve 13, the fourth regulating valve 14, and the sixth regulating valve 16 are closed, while the second regulating valve 12 and the fifth regulating valve 15 are opened, allowing the lean and rich solutions to bypass waste heat recovery unit 4 and flow along the main pipeline respectively. This dual-mode switching design ensures the continuous and safe operation of the main carbon capture process, achieving a high degree of synergy between waste heat recovery and process safety.

[0038] Waste heat recovery unit 4 is either an absorption heat pump or an electric compression heat pump, which can be flexibly selected according to site conditions and operating economy. When using an absorption heat pump, its heat source side is an evaporator for recovering lean liquid waste heat, and its heat sink side is an absorber and / or condenser for heating rich liquid. When using an electric compression heat pump, its heat source side is an evaporator for recovering lean liquid waste heat, and its heat sink side is a condenser for heating rich liquid. A reboiler 9 is installed at the bottom of the desorption tower 1 to supplement heating for the desorption tower 1 when the heat supply from waste heat recovery unit 4 is insufficient. A gas cooler 8 is connected to the regeneration gas outlet at the top of the desorption tower 1 to cool the desorbed regeneration gas. The lean liquid cooler 5 is a cooling water heat exchanger used to further cool the lean liquid to the required temperature at the inlet of the absorption tower 6.

[0039] The reboiler 9 has a lean liquid inlet, a lean liquid outlet, a steam inlet, and a condensate outlet. The bottom of the stripping column 1 is provided with a lean liquid outlet and a lean liquid return outlet. The lean liquid inlet of the reboiler 9 is connected to the lean liquid outlet, the lean liquid outlet of the reboiler 9 is connected to the lean liquid return outlet, the steam inlet of the reboiler 9 is connected to an external steam source, and the condensate outlet of the reboiler 9 is used to discharge steam condensate. The function of reboiler 9 is to supplement the heating of stripping tower 1 when the heat supply from waste heat recovery unit 4 is insufficient. When waste heat recovery unit 4 is working normally, the rich liquor, after preheating by waste heat recovery unit 4, can reach or approach the temperature required for stripping, and reboiler 9 can be idle or only maintain a minimum load, significantly reducing external steam consumption. When waste heat recovery unit 4 malfunctions, is under maintenance, experiences process fluctuations, or when the use of high-temperature amine liquor leads to insufficient preheating temperature rise, the control system opens the external steam valve, and steam enters reboiler 9 to heat the lean liquor in the tube side. The lean liquor temperature rises and partially vaporizes, and the heated lean liquor returns to the bottom of stripping tower 1. The generated steam rises and exchanges heat with the rich liquor, allowing the rich liquor to continue to strip CO2. Through the above settings, reboiler 9 and waste heat recovery unit 4 work together, with waste heat recovery unit 4 undertaking the basic preheating load and reboiler 9 undertaking the supplementary heating load.

[0040] This system utilizes the existing lean liquor pump 3 and rich liquor pump 7 to complete the circulation, eliminating the need for forced circulation as required by existing technologies. This reduces equipment investment and operating power consumption, and eliminates the need for special high-temperature and corrosion-resistant materials, significantly reducing equipment design complexity and manufacturing costs. Through this structure, the present invention achieves closed-loop recovery of waste heat within the carbon capture process, effectively solving the dual technical problems of waste heat from the lean liquor cooler and the consumption of high-grade steam for rich liquor heating. This results in a synergistic effect of reducing external steam consumption in the stripping tower, decreasing cooling water consumption, and improving the overall system energy efficiency.

[0041] This invention also provides a control method for the aforementioned carbon dioxide capture waste heat recovery system. The method includes: when operating in waste heat recovery mode, opening the first and third valve groups and closing the second and fourth valve groups, causing the lean liquor to cool down via the heat source side of the waste heat recovery unit 4, and the rich liquor to heat up via the heat sink side of the waste heat recovery unit 4. In this mode, the lean liquor from the lean liquor pump 3 is introduced into the heat source side of the waste heat recovery unit 4 to release heat and cool down, while the rich liquor from the lean-rich liquor heat exchanger 2 is introduced into the heat sink side of the waste heat recovery unit 4 to absorb heat and heat up. This achieves heat transfer from the lean liquor side to the rich liquor side, recovering the waste heat of the lean liquor before the lean liquor cooler that would otherwise be carried away by the cooling water and using it to preheat the rich liquor entering the tower, thereby significantly reducing the external steam consumption of the stripping tower 1 and simultaneously reducing the cooling water consumption of the lean liquor cooler 5.

[0042] The method also includes: when operating in the original system mode, closing the first and third valve groups and opening the second and fourth valve groups, allowing the lean and rich solutions to bypass the waste heat recovery unit 4 and flow along the main pipeline respectively. This mode serves as a backup channel for the waste heat recovery mode. When the waste heat recovery unit 4 malfunctions or requires maintenance, the system can switch to this mode to ensure uninterrupted carbon capture process and facilitate online maintenance of the waste heat recovery unit 4.

[0043] The method also includes automatically switching back to the original system mode when a fault is detected in the waste heat recovery unit 4 or abnormal process parameters are detected. Through this automatic fault switching design, the system can instantly switch back to the original carbon capture process without manual intervention, effectively avoiding the risk of process interruption caused by waste heat recovery unit malfunctions. This achieves a high degree of synergy between waste heat recovery and process safety, significantly improving the system's operational reliability and maintenance convenience.

[0044] The above control method, through flexible switching between waste heat recovery mode and original system mode, maximizes waste heat recovery and reduces energy consumption while ensuring process safety, and at the same time provides convenient conditions for online inspection and maintenance of equipment.

[0045] It should be understood that the term "and / or" in this article is merely a description of the relationship between related objects. For example, A and / or B indicates that there are three possible relationships: A exists alone, A and B exist simultaneously, and B exists alone. In addition, the character " / " in this article indicates that the related objects before and after it are in an "or" relationship.

[0046] It should be understood that the specific embodiments described above are merely illustrative or explanatory of the principles of the invention and do not constitute a limitation thereof. Therefore, any modifications, equivalent substitutions, improvements, etc., made without departing from the spirit and scope of the invention should be included within the protection scope of the invention. Furthermore, the appended claims are intended to cover all variations and modifications falling within the scope and boundaries of the appended claims, or equivalent forms of such scope and boundaries.

Claims

1. A carbon dioxide capture and waste heat recovery system, characterized in that, include: Analysis tower (1), lean and rich liquid heat exchanger (2), lean liquid pump (3), waste heat recovery unit (4), lean liquid cooler (5), absorption tower (6), rich liquid pump (7) and regulating valve group; The lean liquid outlet of the analytical tower (1) is connected in sequence to the hot side of the lean and rich liquid heat exchanger (2), the lean liquid pump (3), the heat source side of the waste heat recovery unit (4), the lean liquid cooler (5), and then to the lean liquid inlet of the absorption tower (6). The rich liquid outlet of the absorption tower (6) is connected in sequence to the rich liquid pump (7), the cold side of the lean and rich liquid heat exchanger (2), the heat sink side of the waste heat recovery unit (4), and then to the rich liquid inlet of the analytical tower (1). The regulating valve group includes a first valve group installed on the heat sink side bypass pipeline of the waste heat recovery unit (4), a second valve group installed on the rich liquid main pipeline, a third valve group installed on the heat source side bypass pipeline of the waste heat recovery unit (4), and a fourth valve group installed on the lean liquid main pipeline.

2. The carbon dioxide capture and waste heat recovery system according to claim 1, characterized in that, The first valve group includes a first regulating valve (11) and a third regulating valve (13), the second valve group includes a second regulating valve (12), the third valve group includes a fourth regulating valve (14) and a sixth regulating valve (16), and the fourth valve group includes a fifth regulating valve (15).

3. The carbon dioxide capture and waste heat recovery system according to claim 2, characterized in that, The first regulating valve (11) and the third regulating valve (13) are controlled by proportional linkage with the second regulating valve (12): when the first regulating valve (11) and the third regulating valve (13) are opened proportionally, the second regulating valve (12) is closed proportionally. Furthermore, the fourth regulating valve (14) and the sixth regulating valve (16) are controlled by proportional linkage with the fifth regulating valve (15): when the fourth regulating valve (14) and the sixth regulating valve (16) are opened proportionally, the fifth regulating valve (15) is closed proportionally.

4. The carbon dioxide capture and waste heat recovery system according to claim 1, characterized in that, The waste heat recovery unit (4) is an absorption heat pump or an electric compression heat pump.

5. The carbon dioxide capture and waste heat recovery system according to claim 1, characterized in that, The bottom of the analytical tower (1) is equipped with a reboiler (9) for supplementing heating of the analytical tower (1) when the heat supply from the waste heat recovery unit (4) is insufficient.

6. The carbon dioxide capture and waste heat recovery system according to claim 1, characterized in that, The top regenerated gas outlet of the analytical tower (1) is connected to a gas cooler (8) for cooling the regenerated gas extracted.

7. The carbon dioxide capture and waste heat recovery system according to claim 1, characterized in that, The lean liquid cooler (5) is a cooling water heat exchanger used to cool the lean liquid.

8. The carbon dioxide capture and waste heat recovery system according to claim 1, characterized in that, The heat source side of the waste heat recovery unit (4) is an evaporator, used to recover the waste heat of lean liquid; the heat sink side of the waste heat recovery unit (4) is an absorber and / or a condenser, used to heat rich liquid.

9. A control method for a carbon dioxide capture and waste heat recovery system, characterized in that, For use in the system according to any one of claims 1-8, comprising: When operating in waste heat recovery mode, the first valve group and the third valve group are opened, and the second valve group and the fourth valve group are closed, so that the lean liquid is cooled down by the heat source side of the waste heat recovery unit (4), and the rich liquid is heated up by the heat sink side of the waste heat recovery unit (4). When operating in the original system mode, the first valve group and the third valve group are closed, and the second valve group and the fourth valve group are opened, so that the lean liquid and the rich liquid bypass the waste heat recovery unit (4) and flow along the main pipeline respectively.

10. The control method according to claim 9, characterized in that, When a fault or abnormal process parameter is detected in the waste heat recovery unit (4), it will automatically switch to the original system mode.

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