A system and method for auxiliary carbon dioxide capture using the waste heat of the exhaust steam of a power plant steam turbine

Abstract

The present invention discloses a system and method for auxiliary carbon dioxide capture by utilizing the waste heat of the exhaust steam of a power plant steam turbine, belonging to the technical field of carbon dioxide capture. This system includes a carbon dioxide absorption system and a carbon dioxide desorption system; the carbon dioxide absorption system includes an absorption tower, a rich liquid transfer pump, a rich phase transfer pump, a lean phase transfer pump, a phase separation tank, an absorbent cooler and valves; the carbon dioxide desorption system includes a rich-lean liquid heat exchanger, a desorbed gas cooler, a dehydration cooler, a desorption tower, a lean liquid transfer pump, a forced circulation pump, a vacuum pump and a waste heat recovery system for the exhaust steam of the power plant steam turbine; the waste heat recovery system for the exhaust steam of the power plant steam turbine includes a steam mechanical recompression heat pump and a reboiler. The steam mechanical recompression technology is used to compress the exhaust steam of the power plant steam turbine, increase its pressure and temperature for heating the desorbed liquid in the carbon dioxide capture system and liquefying the exhaust steam, reducing the capture energy consumption of the carbon dioxide capture system and also reducing the operating load of the power plant circulating cooling device.

Description

Technical Field

[0001] The present invention belongs to the technical field of carbon dioxide capture, and particularly relates to a system and method for assisting carbon dioxide capture by using the waste heat of the exhaust steam of a power plant steam turbine. Background Art

[0002] CO2 capture is an important solution to solve the global climate problem and one of the important ways for China to achieve the "dual carbon" goal. According to the differences in CO2 capture principles, it can be divided into chemical absorption method, solid adsorption method, membrane separation method, cryogenic fractionation method, oxy-fuel combustion, chemical looping combustion, etc. The chemical absorption method is considered suitable for large-flow CO2 capture, with simple operation and high technical maturity, and has the most application prospects. It has been applied on a large scale of millions of tons at home and abroad. Currently, the energy consumption of the typical MEA chemical absorption method for carbon capture process is as high as 3.6 GJ / t CO2. After adopting the carbon capture process in traditional coal-fired power plants, the power generation loss is 20% - 30%, and the carbon capture cost is as high as 300 - 400 yuan / t CO2. The technical bottlenecks of high energy consumption and high cost severely limit the industrial application of carbon capture technology. Therefore, the innovation of low-energy-consumption carbon dioxide capture technology is extremely urgent.

[0003] In the power generation process of a thermal power plant, the high-temperature and high-pressure steam generated by the boiler enters the steam turbine to do work and drive the generator to generate electricity. The steam that has done work is called exhaust steam and enters the condenser. In the condenser, the exhaust steam is cooled to condensate by cooling circulating water. The condensate enters the feed water tank through the condensate pump and deaerator to form a cycle. The cooling circulating water is heated in the condenser and then enters the cooling device for cooling or is directly discharged into rivers, lakes, and seas to form a cooling water circulation system. A large amount of low-grade heat energy in the exhaust steam of the steam turbine is carried away by the cooling water in the condenser, accounting for more than 30% of the total energy. This not only causes waste of heat energy but also increases the operating load of the cooling device. A large amount of condensation heat is discharged into the environment, which also has a serious impact on the ecological environment. For cooling tower cooling, due to its evaporation heat dissipation and the influence of wind blowing, a large amount of heat and water droplets enter the atmospheric environment, which will increase the local temperature and humidity of the air; the dissipated heat and water droplets will have an impact on the local microclimate. Summary of the Invention

[0004] In view of the above-mentioned prior art, the present invention provides a system and method for assisting carbon dioxide capture by using the waste heat of the exhaust steam of a power plant steam turbine, which solves the problems of high energy consumption in the existing capture process, low coefficient of performance of the heat pump for heating due to the large temperature difference between the heat source end and the desorption end in the heat pump-assisted carbon dioxide capture process, and poor energy-saving effect, and alleviates the current situation that a large amount of low-grade heat energy in the exhaust steam of the steam turbine in a thermal power plant is carried away by the cooling water in the condenser, resulting in a large amount of waste of heat energy and an increase in the operating load of the cooling device.

[0005] To achieve the above object, the technical solution adopted by the present invention is: to provide a system for auxiliary carbon dioxide capture using the waste heat of the exhaust steam of a power plant steam turbine, including a carbon dioxide absorption system and a carbon dioxide desorption system;

[0006] The carbon dioxide absorption system includes an absorption tower, a rich liquid transfer pump, a rich phase transfer pump, a lean phase transfer pump, a phase separation tank, an absorbent cooler, a first valve, a second valve, a third valve, a fourth valve, a fifth valve, a sixth valve, a seventh valve, and an eighth valve;

[0007] The carbon dioxide desorption system includes a rich and lean liquid heat exchanger, a desorbed gas cooler, a dehydration cooler, a desorption tower, a lean liquid transfer pump, a forced circulation pump, a vacuum pump, and a waste heat recovery system for the exhaust steam of a power plant steam turbine;

[0008] The waste heat recovery system for the exhaust steam of a power plant steam turbine includes a steam mechanical recompression heat pump and a reboiler;

[0009] In the carbon dioxide absorption system, a gas inlet and a liquid outlet are provided at the bottom of the absorption tower, a gas outlet and a liquid inlet are provided at the top. The liquid inlet is connected to the outlet of the absorbent cooler, and the liquid outlet is connected to the inlet of the rich liquid transfer pump. The outlet of the rich liquid transfer pump is divided into two branches. The first branch is connected to the phase separation tank through the first valve, and the second branch is connected to the inlet of the fifth valve. The first outlet of the phase separation tank is connected to the inlets of the fourth valve and the sixth valve, and the second outlet is connected to the inlets of the second valve and the third valve. The outlets of the second valve and the sixth valve are merged and then connected to the inlet of the rich phase transfer pump. The outlets of the third valve and the fourth valve are merged and then connected to the inlet of the lean phase transfer pump. The outlet of the rich phase transfer pump is connected to the inlet of the eighth valve. The outlets of the fifth valve and the eighth valve are merged and then divided into two branches. The first branch is connected to the first inlet of the rich and lean liquid heat exchanger, and the second branch is connected to the inlet of the absorbent cooler. The outlet of the lean phase transfer pump is connected to the inlet of the seventh valve, and the outlet of the seventh valve is merged with the second branch after the merger of the outlets of the fifth valve and the eighth valve;

[0010] At the top of the desorption tower in the carbon dioxide desorption system, there are two liquid inlets and one gas outlet. The first outlet of the rich and lean liquid heat exchanger is connected to one of the liquid inlets at the top of the desorption tower. At the bottom of the desorption tower, there are two liquid outlets and one liquid inlet. One of the liquid outlets is connected to the inlet of the forced circulation pump. The outlet of the forced circulation pump is connected to the first inlet of the reboiler. The first outlet of the reboiler is connected to the liquid inlet at the bottom of the desorption tower; the other liquid outlet at the bottom of the desorption tower is connected to the inlet of the lean liquid transfer pump. The outlet of the lean liquid transfer pump is divided into two branches. One branch is connected to the second inlet of the rich and lean liquid heat exchanger. The second outlet of the rich and lean liquid heat exchanger is merged with the second branch after the merger of the fifth valve outlet and the eighth valve outlet. The other branch of the outlet of the lean liquid transfer pump is merged with the first outlet of the rich and lean liquid heat exchanger; the gas outlet at the top of the desorption tower is connected to the gas inlet of the desorbed gas cooler. The liquid outlet of the desorbed gas cooler is divided into a blowdown pipe and a reflux pipe. The blowdown pipe is connected outside the system. The reflux pipe is connected to the other liquid inlet at the top of the desorption tower. The gas outlet of the desorbed gas cooler is connected to the inlet of the vacuum pump. The outlet of the vacuum pump is connected to the inlet of the dehydration cooler. The liquid outlet of the dehydration cooler is connected outside the system. The gas outlet of the dehydration cooler is the trapped carbon dioxide;

[0011] The exhaust steam outlet pipe connected to the steam turbine of the thermal power plant is connected to the inlet of the steam mechanical recompression heat pump. The outlet of the steam mechanical recompression heat pump is connected to the second inlet of the reboiler. The second outlet of the reboiler is connected to the exhaust steam return pipe.

[0012] The beneficial effects of the present invention adopting the above technical solutions are as follows: Using the waste heat of the exhaust steam of the power plant steam turbine as the heat source in the carbon dioxide capture system can reduce the energy consumption of CO2 capture, reduce the cold source loss of the thermal power plant while reducing the CO2 emissions of the thermal power plant, and reduce the impact of waste heat on the environment; setting a group of valves and a phase separation tank that are convenient to open and close enables the entire system to be applicable to a variety of CO2 absorbents, expanding the application range of the system.

[0013] On the basis of the above technical solutions, the present invention can also be improved as follows.

[0014] Furthermore, the waste heat recovery system of the exhaust steam of the power plant steam turbine recovers the waste heat of the equipment of the thermal power plant. The equipment of the thermal power plant includes a boiler, a steam turbine, a generator, a condenser, a condensate pump, a deaerator, and a feed water tank;

[0015] The gas outlet of the boiler is connected to the gas inlet of the steam turbine. The steam turbine is connected to the generator. The gas outlet of the steam turbine is connected to the exhaust steam outlet pipe and the inlet of the condenser. The exhaust steam return pipe is merged with the inlet pipe of the condenser. The outlet of the condenser is connected to the inlet of the condensate pump. The outlet of the condensate pump is connected to the inlet of the deaerator. The outlet of the deaerator is connected to the inlet of the feed water tank. The outlet of the feed water tank is connected to the boiler. The condenser is also provided with a circulating cooling water inlet and a circulating cooling water outlet.

[0016] The beneficial effects of the present invention adopting the above further technical solutions are as follows: Through the exhaust steam outlet pipeline and the exhaust steam return pipeline, the waste heat of the exhaust steam of the power plant steam turbine is applied to the carbon dioxide desorption system, turning the waste heat of the exhaust steam of the power plant steam turbine into a useful resource, reducing the impact of the waste heat on the environment, and at the same time reducing the energy consumption for CO2 capture.

[0017] Further, the absorption tower is a plate tower, a packed tower, a series of rotating packed beds, or a combination of a tower device and a rotating packed bed.

[0018] The beneficial effects of the present invention adopting the above further technical solutions are as follows: The absorption tower can use ordinary commercial packing or surface-modified packing; if the packing is surface-treated, the absorbent can present a super-wetting state on the surface of the packing, which is beneficial to increasing the gas-liquid contact area and thus improving the absorption efficiency.

[0019] Further, the absorbent replenishment pipeline is merged with the second branch after the merger of the fifth valve outlet and the eighth valve outlet.

[0020] The beneficial effects of the present invention adopting the above further technical solutions are as follows: It is convenient to replenish the absorbent into the system.

[0021] Further, a method for capturing carbon dioxide by a system for assisting in capturing carbon dioxide using the waste heat of the exhaust steam of a power plant steam turbine includes the following steps:

[0022] S1: Feed the flue gas and the absorbent into the absorption tower from the bottom and the top of the absorption tower respectively, and the absorbent absorbs CO2 in the flue gas to obtain a rich absorbent solution;

[0023] S2: Transport 50% - 100% of the rich absorbent solution to the rich and lean liquid heat exchanger, preheat it and then enter the desorption tower from the top of the desorption tower. After desorption in the desorption tower, a desorbed solution, a regenerated absorbent, and a desorbed gas are obtained; the remaining rich absorbent solution is mixed with the regenerated absorbent from the rich and lean liquid heat exchanger and then enters the absorbent cooler; the desorbed solution is transported to the reboiler by a forced circulation pump, heated by the exhaust steam boosted by the steam mechanical recompression heat pump, and then returns to the bottom of the desorption tower; the regenerated absorbent is transported to the rich and lean liquid heat exchanger by a lean liquid transfer pump to preheat the rich absorbent solution;

[0024] Alternatively, the lean absorbent solution is transported to a phase separator for phase separation to obtain a CO2 lean phase and a CO2 rich phase; 50% - 100% of the CO2 rich phase is transported to a rich-lean solution heat exchanger, preheated, and then enters the desorption tower from the top of the desorption tower. After desorption in the desorption tower, a desorbed solution, a regenerated absorbent, and a desorbed gas are obtained; the remaining CO2 rich phase is mixed with the regenerated absorbent from the rich-lean solution heat exchanger and then enters an absorbent cooler; the desorbed solution is transported to a reboiler by a forced circulation pump, heated by the exhausted steam boosted by a steam mechanical recompression heat pump, and then returns to the bottom of the desorption tower; the regenerated absorbent is transported to the rich-lean solution heat exchanger by a lean solution transfer pump to preheat the CO2 rich phase; the CO2 lean phase is mixed with the regenerated absorbent from the rich-lean solution heat exchanger and then enters the absorbent cooler;

[0025] S3: The desorbed gas enters a desorbed gas cooler for cooling. The condensed water generated by the cooling flows back to the top of the desorption tower. The non-condensable gas enters a vacuum pump, and the tail gas of the vacuum pump enters a dehydration cooler for cooling. The non-condensable gas outlet of the dehydration cooler obtains the trapped carbon dioxide.

[0026] The beneficial effects of the present invention adopting the above further technical solutions are as follows: 0 - 50% of the lean absorbent solution returns to the absorption tower after being cooled by the absorbent cooler, which can improve the lean solution load and reduce the desorption energy consumption; the low-grade heat of the exhausted steam is effectively utilized for the regeneration of the lean absorbent solution, reducing the energy consumption of carbon dioxide capture from the flue gas of thermal power plants, also reducing the load on the exhausted steam condenser of thermal power plants and reducing the energy consumption of the cooling device.

[0027] Further, the molar ratio of the total amount of organic amine in the absorbent to the captured CO2 is 5 - 20:1, and the absorbent is a homogeneous absorbent or a phase change absorbent.

[0028] Further, the temperature of the flue gas is 35 - 50°C, the temperature of the absorbent entering the absorption tower is 35 - 40°C, and the temperature of the lean absorbent solution is 35 - 60°C.

[0029] The beneficial effects of the present invention adopting the above further technical solutions are as follows: A large amount of absorbent at a relatively low temperature of 35 - 40°C is used at the top of the absorption tower to absorb CO2 in the flue gas, which can significantly reduce the temperature and water vapor content of the tail gas at the top of the absorption tower, reducing the heat loss of absorption and amine loss in the absorption tower.

[0030] Further, the pressure of the exhausted steam boosted by the steam mechanical recompression heat pump is 35 - 60 kPa, the temperature of the desorbed solution heated by the reboiler is 65 - 80°C, and the temperature difference between the hot and cold fluid streams at both ends of the rich-lean solution heat exchanger is 2 - 10°C.

[0031] The beneficial effects of the present invention adopting the above further technical solutions are as follows: The steam mechanical recompression heat pump boosts the exhausted steam pressure to 35 - 60 kPa and enters the reboiler to provide the heat required for the desorption of the rich liquid. At the same time, the exhausted steam is condensed into liquid water, reducing the capture energy consumption of the carbon dioxide capture system and also reducing the operating load of the power plant circulating cooling device.

[0032] Further, the absolute pressure at the top of the desorption tower is 20 - 80 kPa.

[0033] Further, the desorbed gas cooler cools the gas to 15 - 40 °C, and the dehydration cooler cools the gas to 15 - 40 °C.

[0034] The beneficial effects of the present invention adopting the above further technical solutions are as follows: The desorption tower decompresses and desorbs under the operating pressure of 20 - 80 kPa absolute pressure, which can reduce the CO2 partial pressure in the desorption tower, lower the temperature of the desorbed liquid in the reboiler, reduce the temperature difference between the hot and cold ends of the heat pump, improve the heating performance coefficient of the heat pump, enhance the energy-saving effect, and also reduce the thermal degradation of the organic amine absorbent and extend the service life of the absorbent.

[0035] The beneficial effects of the present invention are as follows: The present invention uses a large amount of absorbent to absorb CO2 at the top of the absorption tower under low-temperature conditions, which can significantly reduce the temperature of the absorption tail gas at the top of the absorption tower, reduce the water vapor content in the tail gas, and reduce the absorption heat loss of the absorption tower; The absorption rich liquid with a large flow rate and high CO2 load can meet the requirements of CO2 capture volume at a low desorption rate, which can reduce the desorption energy consumption; By cooling a part of the rich liquid and returning it to the absorption tower to absorb CO2 again, the rich liquid load can be increased and the desorption energy consumption can be reduced; By adopting decompression desorption operation to reduce the CO2 partial pressure in the desorption tower, the temperature of the desorbed liquid in the reboiler can be reduced, that is, the outlet temperature of the condenser of the steam mechanical recompression heat pump MVR can be reduced, the outlet pressure of MVR can be reduced, the heating performance coefficient of MVR can be improved, the power consumption can be reduced, and the energy-saving effect can be enhanced. It can also reduce the thermal degradation of the organic amine absorbent and extend the service life of the absorbent. The steam mechanical recompression technology (MVR) is used to compress the exhausted steam of the power plant steam turbine, increase the temperature and pressure for regenerating the absorbent rich liquid in the reboiler of the carbon dioxide capture system, and at the same time liquefy the exhausted steam, reducing the capture energy consumption of the carbon dioxide capture system and also reducing the operating load of the power plant circulating cooling device. Brief Description of the Drawings

[0036] Figure 1 It is a schematic diagram of a system for utilizing the waste heat of the power plant steam turbine to assist in carbon dioxide capture;

[0037] Among them, 1. Boiler; 2. Steam turbine; 3. Generator; 4. Condenser; 5. Condensate pump; 6. Deaerator; 7. Feed water tank; 11. Rich and lean liquid heat exchanger; 12. Reboiler; 13. Absorbent cooler; 14. Desorbed gas cooler; 15. Dewatering cooler; 21. Absorption tower; 22. Desorption tower; 31. Phase separation tank; 41. First valve; 42. Second valve; 43. Third valve; 44. Fourth valve; 45. Fifth valve; 46. Sixth valve; 47. Seventh valve; 48. Eighth valve; 71. Rich liquid transfer pump; 72. Rich phase transfer pump; 73. Lean phase transfer pump; 74. Lean liquid transfer pump; 75. Forced circulation pump; 81. Vacuum pump; 91. Steam mechanical recompression heat pump. Detailed implementation manners

[0038] The following is a detailed description of the specific implementation manners of the present invention in conjunction with embodiments.

[0039] Embodiment 1

[0040] A system for utilizing the waste heat of the exhaust steam of a power plant steam turbine to assist in carbon dioxide capture according to the present invention, as Figure 1 shown, includes a carbon dioxide absorption system and a carbon dioxide desorption system.

[0041] The carbon dioxide absorption system includes an absorption tower 21, a rich liquid transfer pump 71, a rich phase transfer pump 72, a lean phase transfer pump 73, a phase separation tank 31, an absorbent cooler 13, a first valve 41, a second valve 42, a third valve 43, a fourth valve 44, a fifth valve 45, a sixth valve 46, a seventh valve 47, and an eighth valve 48; the top of the absorption tower 21 is provided with a gas outlet and a liquid inlet, and the bottom is provided with a gas inlet and a liquid outlet; the phase separation tank 31 is provided with a liquid inlet and two liquid outlets, and the two liquid outlets are respectively a heavy phase outlet and a light phase outlet.

[0042] The carbon dioxide desorption system includes a rich and lean liquid heat exchanger 11, a desorbed gas cooler 14, a dewatering cooler 15, a desorption tower 22, a lean liquid transfer pump 74, a forced circulation pump 75, a vacuum pump 81, and a waste heat recovery system for the exhaust steam of the power plant steam turbine; the rich and lean liquid heat exchanger 11 is provided with two outlets and two inlets, the first inlet of the rich and lean liquid heat exchanger 11 is a cold fluid inlet, the first outlet is a cold fluid outlet, the second inlet is a hot fluid inlet, and the second outlet is a hot fluid outlet; the reboiler 12 is provided with two outlets and two inlets; the top of the desorption tower 22 is provided with two liquid inlets and a gas outlet, and the bottom is provided with a liquid inlet and two liquid outlets.

[0043] The waste heat recovery system for the exhaust steam of the power plant steam turbine includes a steam mechanical recompression heat pump 91 and a reboiler 12.

[0044] In the carbon dioxide absorption system, the liquid inlet at the top of the absorption tower 21 is connected to the outlet of the absorbent cooler 13, and the liquid outlet at the bottom of the absorption tower 21 is connected to the inlet of the rich liquid transfer pump 71. The outlet of the rich liquid transfer pump 71 is divided into two branches. The first branch is connected to the phase separation tank 31 through the first valve 41, and the second branch is connected to the inlet of the fifth valve 45; the absorption tower 21 is a plate tower, a packed tower, a rotating packed bed connected in series and parallel, or a combination between a tower device and a rotating packed bed; taking the packed absorption tower as an example, the absorption tower 21 can use ordinary commercial packing or surface-modified packing. To improve the efficiency of the absorption tower, the packing can be surface-treated to make the absorbent present a super-wetting state on the surface of the packing, which is beneficial to increasing the gas-liquid contact area and improving the absorption efficiency; the method for surface-treating the packing is: soaking the stainless steel packing with an ammonium persulfate solution to corrode and oxidize the surface of the packing with ammonium persulfate to form Cr 3+ and Fe 3+ , and then adding a sodium hydroxide solution to convert Cr 3+ and Fe 3+ into Cr2O3 and Fe2O3, which are deposited on the surface of the stainless steel packing to form a dense oxide layer with a micro-nano structure.

[0045] The first outlet of the phase separation tank 31, i.e., the heavy phase outlet, is connected to the inlets of the fourth valve 44 and the sixth valve 46. The second outlet, i.e., the light phase outlet, is connected to the inlets of the second valve 42 and the third valve 43. The outlets of the second valve 42 and the sixth valve 46 are merged and then connected to the inlet of the rich phase transfer pump 72. The outlets of the third valve 43 and the fourth valve 44 are merged and then connected to the inlet of the lean phase transfer pump 73. The outlet of the rich phase transfer pump 72 is connected to the inlet of the eighth valve 48. The outlets of the fifth valve 45 and the eighth valve 48 are merged and then divided into two branches. The first branch is connected to the first inlet (cold fluid inlet) of the rich and lean liquid heat exchanger 11, and the second branch is connected to the inlet of the absorbent cooler 13. The outlet of the lean phase transfer pump 73 is connected to the inlet of the seventh valve 47. The outlet of the seventh valve 47 is merged with the second branch after the outlets of the fifth valve 45 and the eighth valve 48 are merged; the absorbent supplement pipeline is also merged with the second branch after the outlets of the fifth valve 45 and the eighth valve 48 are merged.

[0046] At the top of the desorption tower 22 in the carbon dioxide desorption system, there are two liquid inlets and one gas outlet. The first outlet (cold fluid outlet) of the rich and lean liquid heat exchanger 11 is connected to one of the liquid inlets at the top of the desorption tower 22. At the bottom of the desorption tower 22, there are two liquid outlets and one liquid inlet. One of the liquid outlets is connected to the inlet of the forced circulation pump 75. The outlet of the forced circulation pump 75 is connected to the first inlet (cold fluid inlet) of the reboiler 12. The first outlet (cold fluid outlet) of the reboiler 12 is connected to the bottom liquid inlet of the desorption tower 22. The other liquid outlet at the bottom of the desorption tower 22 is connected to the inlet of the lean liquid transfer pump 74. The outlet of the lean liquid transfer pump 74 is divided into two branches. One branch is connected to the second inlet (hot fluid inlet) of the rich and lean liquid heat exchanger 11. The second outlet (hot fluid outlet) of the rich and lean liquid heat exchanger 11 is merged with the second branch after the outlets of the fifth valve 45 and the eighth valve 48 are merged. The other branch of the outlet of the lean liquid transfer pump 74 is merged with the first outlet (cold fluid outlet) of the rich and lean liquid heat exchanger 11. The gas outlet at the top of the desorption tower 22 is connected to the gas inlet of the desorbed gas cooler 14. The liquid outlet of the desorbed gas cooler 14 is divided into a blowdown pipe and a reflux pipe. The blowdown pipe is connected outside the system, and the reflux pipe is connected to the other liquid inlet at the top of the desorption tower 22. The gas outlet of the desorbed gas cooler 14 is connected to the inlet of the vacuum pump 81. The outlet of the vacuum pump 81 is connected to the inlet of the dehydration cooler 15. The liquid outlet of the dehydration cooler 15 is connected outside the system. The gas outlet of the dehydration cooler 15 is the captured carbon dioxide.

[0047] The outlet pipeline of the exhaust steam of the steam turbine in the thermal power plant is connected to the inlet of the steam mechanical recompression heat pump 91. The outlet of the steam mechanical recompression heat pump 91 is connected to the second inlet of the reboiler 12. The second outlet of the reboiler 12 is connected to the exhaust steam return pipeline.

[0048] Example 2

[0049] The waste heat recovery system of the exhaust steam of the power plant steam turbine recovers the waste heat of the equipment in the thermal power plant, such as the equipment shown in the Figure 1 dashed box, including a boiler 1, a steam turbine 2, a generator 3, a condenser 4, a condensate pump 5, a deaerator 6, and a feed water tank 7. The gas outlet of the boiler 1 is connected to the gas inlet of the steam turbine 2. The steam turbine 2 is connected to the generator 3. The gas outlet of the steam turbine 2 is connected to the exhaust steam outlet pipeline and the inlet of the condenser 4. The exhaust steam return pipeline is merged with the inlet pipeline of the condenser 4. The outlet of the condenser 4 is connected to the inlet of the condensate pump 5. The outlet of the condensate pump 5 is connected to the inlet of the deaerator 6. The outlet of the deaerator 6 is connected to the inlet of the feed water tank 7. The outlet of the feed water tank 7 is connected to the boiler 1. The condenser 4 is also provided with a circulating cooling water inlet and a circulating cooling water outlet.

[0050] The high-temperature and high-pressure steam generated by the boiler 1 in the thermal power plant enters the steam turbine 2 to do work and drive the generator 3 to generate electricity. The steam that has completed the work is called exhaust steam. Part of it is transported to the inlet of the mechanical vapor recompression heat pump 91, and the other part is transported to the condenser 4. In the condenser 4, the exhaust steam is cooled to condensate by the cooling circulating water. The cooling circulating water is heated in the condenser 4 and then discharged from the system. The condensate enters the feed water tank 7 through the condensate pump 5 and the deaerator 6. The water in the feed water tank 7 is supplied to the boiler 1 to form a cycle.

[0051] Example 3

[0052] A method for capturing carbon dioxide in a system for capturing carbon dioxide by utilizing the waste heat of the exhaust steam of a power plant steam turbine according to the present invention includes the following steps:

[0053] The flue gas that has been dust-removed, denitrified and cooled to 35-50 °C enters the absorption tower 21 through the gas inlet at the bottom of the absorption tower 21. The absorbent is cooled to a temperature of 35-40 °C by the absorbent cooler 13 and then enters the absorption tower 21 through the liquid inlet at the top of the absorption tower 21. The absorbent is a homogeneous absorbent MEA (monoethanolamine). The total molar ratio of organic amine in the absorbent to the captured CO2 is 5-20:1. The flue gas flows upward from the bottom of the absorption tower 21, and the absorbent flows downward from the top of the absorption tower 21. The flue gas and the absorbent are in full contact, and the CO2 in the flue gas is absorbed by the absorbent. The gas purified by the absorption tower 21 is discharged from the system through the gas outlet at the top of the absorption tower 21. The rich absorbent liquid is transported to the rich liquid transfer pump 71 through the liquid outlet at the bottom of the absorption tower 21. The temperature of the rich absorbent liquid at the bottom of the absorption tower 21 is 35-60 °C.

[0054] The first valve 41, the second valve 42, the third valve 43, the fourth valve 44, the sixth valve 46, the seventh valve 47 and the eighth valve 48 are all closed, and the fifth valve 45 is opened. The rich liquid transfer pump 71 transports 50%-100% of the rich absorbent liquid to the rich and lean liquid heat exchanger 11 through the pipeline where the fifth valve 45 is located. After preheating, it enters the desorption tower 22 through a liquid inlet at the top of the desorption tower 22. After desorption in the desorption tower 22, desorbed liquid, regenerated absorbent and desorbed gas are obtained. The rich liquid transfer pump 71 also transports the remaining rich absorbent liquid to be mixed with the regenerated absorbent from the second outlet (hot fluid outlet) of the rich and lean liquid heat exchanger 11 and then enters the absorbent cooler 13 through the pipeline where the fifth valve 45 is located.

[0055] The desorbed liquid at the bottom of the desorption tower 22 is transported by the forced circulation pump 75 to the first inlet (cold fluid inlet) of the reboiler 12. In the reboiler 12, the latent heat of the exhausted steam from the power plant steam turbine boosted by the steam mechanical recompression heat pump 91 is used to heat the desorbed liquid to 65 - 80 °C and then it returns to the bottom of the desorption tower 22 to continue participating in the desorption of CO₂; the regenerated absorbent is transported from the bottom of the desorption tower 22 to the rich and lean liquid heat exchanger 11 by the lean liquid transfer pump 74 to preheat the rich absorbent liquid. After the regenerated absorbent recovers heat in the rich and lean liquid heat exchanger 11, it is transported to the absorbent cooler 13. The rich and lean liquid heat exchanger 11 maintains the temperature difference between the inlet and outlet of the hot and cold fluids at 2 - 10 °C; the desorption tower 22 operates under the condition of an absolute pressure of 20 - 80 kPa. The desorbed gas at the top of the desorption tower 22 enters the desorbed gas cooler 14 and is cooled to 15 - 40 °C. Part of the condensate water of the desorbed gas cooler 14 is discharged, and part of it returns to the top of the desorption tower 22. The non-condensable gas of the desorbed gas cooler 14 enters the vacuum pump 81, and the tail gas of the vacuum pump 81 enters the dehydration cooler 15 and is cooled to 15 - 40 °C. The condensate water of the dehydration cooler 15 is directly discharged outside the system, and the non-condensable gas outlet of the dehydration cooler 15 obtains the trapped CO₂.

[0056] The high-temperature and high-pressure steam of the thermal power plant enters the steam turbine 2 to drive the generator 3 to generate electricity. The steam that has done work is called exhausted steam. Part of it is transported to the inlet of the steam mechanical recompression heat pump 91, and the other part is transported to the condenser 4. The outlet of the steam mechanical recompression heat pump 91 is connected to the second inlet of the reboiler 12. The exhausted steam whose pressure has been increased by the work of the steam mechanical recompression heat pump 91 enters the reboiler 12 and is condensed into condensate water and then returns to the exhausted steam pipeline; in the condenser 4, the exhausted steam is cooled to condensate water by the cooling circulating water. The cooling circulating water is heated in the condenser 4 and then discharged from the system. The condensate water enters the feed water tank 7 through the condensate pump 5 and the deaerator 6. The water in the feed water tank 7 is supplied to the boiler 1 to form a cycle.

[0057] According to the differences in the steam turbine units of the thermal power plant, the temperature and pressure of the extracted exhausted steam are different: for the wet-cooled unit, the exhausted steam pressure of the steam turbine is 5 kPa (corresponding to the saturation temperature of 32 °C), for the indirect air-cooled unit, the exhausted steam pressure of the steam turbine is 10 kPa (corresponding to the saturation temperature of 45 °C), and for the direct air-cooled unit, the exhausted steam pressure of the steam turbine is 15 kPa (corresponding to the saturation temperature of 54 °C). The steam mechanical recompression heat pump 91 boosts the exhausted steam pressure to 35 - 60 kPa, and it enters the reboiler 12 and is condensed into condensate water and then returns to the exhausted steam pipeline of the thermal power plant. The low-grade heat of the exhausted steam is effectively utilized for the regeneration of the rich absorbent liquid, reducing the energy consumption of flue gas carbon dioxide capture in the thermal power plant, also reducing the load of the exhausted steam condenser in the thermal power plant, and reducing the energy consumption of the cooling device.

[0058] Example 4

[0059] A method for capturing carbon dioxide by a system for capturing carbon dioxide using the waste heat of the exhausted steam from a power plant steam turbine according to the present invention includes the following steps:

[0060] The flue gas that has been dedusted, denitrified and cooled to 35 - 50 °C enters the absorption tower 21 through the bottom gas inlet of the absorption tower 21. The absorbent is cooled to a temperature of 35 - 40 °C by the absorbent cooler 13 and then enters the absorption tower 21 through the liquid inlet at the top of the absorption tower 21. The absorbent is a phase change absorbent, and the molar ratio of the total organic amine in the absorbent to the captured CO2 is 5 - 20:1. The flue gas flows upward from the bottom of the absorption tower 21, and the absorbent flows downward from the top of the absorption tower 21. The flue gas and the absorbent are in full contact, and the CO2 in the flue gas is absorbed by the absorbent. The gas purified by the absorption tower is discharged from the system through the gas outlet at the top of the absorption tower 21. The rich absorbent liquid is transported to the rich liquid transfer pump 71 through the bottom liquid outlet of the absorption tower 21, and the temperature of the rich absorbent liquid at the bottom of the absorption tower 21 is 35 - 60 °C.

[0061] The first valve 41, the seventh valve 47 and the eighth valve 48 are opened, and the fifth valve 45 is closed; the rich liquid transfer pump 71 transports the rich absorbent liquid to the phase separation tank 31. The rich absorbent liquid is separated into a CO2 lean phase and a CO2 rich phase in the phase separation tank 31. If the density of the CO2 rich phase is greater than that of the lean phase, the second valve 42 and the fourth valve 44 are closed, and the third valve 43 and the sixth valve 46 are opened; if the density of the CO2 rich phase is less than that of the lean phase, the second valve 42 and the fourth valve 44 are opened, and the third valve 43 and the sixth valve 46 are closed; the CO2 lean phase and the CO2 rich phase are respectively transported to the lean phase transfer pump 73 and the rich phase transfer pump 72; the CO2 lean phase is transported by the lean phase transfer pump 73 through the seventh valve 47 to be mixed with the regenerated absorbent from the second outlet (hot fluid outlet) of the rich and lean liquid heat exchanger 11 and then enters the absorbent cooler 13. The rich phase transfer pump 72 transports 50% - 100% of the CO2 rich phase to the rich and lean liquid heat exchanger 11 through the pipeline where the eighth valve 48 is located, and after preheating, it enters the desorption tower 22 through a liquid inlet at the top of the desorption tower 22. After desorption in the desorption tower 22, desorbed liquid, regenerated absorbent and desorbed gas are obtained; the rich phase transfer pump 72 transports the remaining CO2 rich phase to be mixed with the regenerated absorbent from the second outlet (hot fluid outlet) of the rich and lean liquid heat exchanger 11 and then enters the absorbent cooler 13.

[0062] The desorbed liquid at the bottom of the desorption tower 22 is transported by the forced circulation pump 75 to the first inlet (cold fluid inlet) of the reboiler 12. In the reboiler 12, the latent heat of the exhaust steam from the power plant steam turbine boosted by the steam mechanical recompression heat pump 91 is used to heat the desorbed liquid to 65 - 80°C, and then it returns to the bottom of the desorption tower 22 to continue participating in the desorption of CO2; the regenerated absorbent is transported from the bottom of the desorption tower 22 to the rich and lean liquid heat exchanger 11 by the lean liquid transfer pump 74 to preheat the CO2-rich phase. After the regenerated absorbent recovers heat in the rich and lean liquid heat exchanger 11, it is transported to the absorbent cooler 13. The rich and lean liquid heat exchanger 11 maintains the temperature difference between the inlet and outlet of the hot and cold fluids at 2 - 10°C; the desorption tower 22 operates under the condition of an absolute pressure of 20 - 80 kPa. The desorbed gas at the top of the desorption tower 22 enters the desorbed gas cooler 14 and is cooled to 15 - 40°C. Part of the condensate water of the desorbed gas cooler 14 is discharged, and part of it returns to the top of the desorption tower 22. The non-condensable gas of the desorbed gas cooler 14 enters the vacuum pump 81, and the tail gas of the vacuum pump 81 enters the dehydration cooler 15 and is cooled to 15 - 40°C. The condensate water of the dehydration cooler 15 is directly discharged out of the system, and the non-condensable gas outlet of the dehydration cooler 15 obtains the trapped CO2;

[0063] The high-temperature and high-pressure steam of the thermal power plant enters the steam turbine 2 to drive the generator 3 to generate electricity. The steam after doing work is called exhaust steam. Part of it is transported to the inlet of the steam mechanical recompression heat pump 91, and the other part is transported to the condenser 4. The outlet of the steam mechanical recompression heat pump 91 is connected to the second inlet of the reboiler 12. The exhaust steam whose pressure is increased by the steam mechanical recompression heat pump 91 enters the reboiler 12 and is condensed into condensate water and then returns to the exhaust steam pipeline; in the condenser 4, the exhaust steam is cooled to condensate water by the cooling circulating water. The cooling circulating water is heated in the condenser 4 and then discharged from the system. The condensate water enters the feed water tank 7 through the condensate pump 5 and the deaerator 6. The water in the feed water tank 7 is supplied to the boiler 1 to form a cycle.

[0064] According to the differences of the steam turbine units in the thermal power plant, the temperature and pressure of the extracted exhaust steam are different: for the wet-cooled unit, the exhaust steam pressure of the steam turbine is 5 kPa (corresponding to the saturation temperature of 32°C), for the indirect air-cooled unit, the exhaust steam pressure of the steam turbine is 10 kPa (corresponding to the saturation temperature of 45°C), and for the direct air-cooled unit, the exhaust steam pressure of the steam turbine is 15 kPa (corresponding to the saturation temperature of 54°C). The steam mechanical recompression heat pump 91 boosts the exhaust steam pressure to 35 - 60 kPa, and then enters the reboiler 12 and is condensed into condensate water and then returns to the exhaust steam pipeline of the thermal power plant. The low-grade heat of the exhaust steam is effectively utilized for the regeneration of the absorbent rich liquid, reducing the energy consumption of the flue gas carbon dioxide capture in the thermal power plant, reducing the load of the exhaust steam condenser in the thermal power plant, and reducing the energy consumption of the cooling device.

[0065] Example 5

[0066] Theoretical calculation, the absolute pressure is 103 kPa, and the flow rate is 60000 Nm 3The flue gas from a coal-fired power plant with a flow rate of 1,000,000 Nm³ / h and a CO₂ content of 12% enters the bottom flue gas inlet of the absorption tower 21 after dust removal, denitrification, and cooling to 50°C. The flue gas flows upward from the bottom of the absorption tower 21 and comes into full contact with the absorbent at 40°C from the absorbent cooler 13 at the top of the absorption tower 21. The CO₂ in the flue gas is absorbed by the absorbent. An industrial MEA homogeneous absorbent with a concentration of 5 mol / L is used, and the molar ratio of the total amount of organic amine in the absorbent to the captured CO₂ is 16.7:1. The temperature of the tail gas at the top of the absorption tower 21 is 41.4°C, which greatly reduces the water vapor content in the tail gas and reduces the heat loss of absorption and amine loss in the absorption tower 21. The temperature of the rich absorbent at the bottom of the absorption tower 21 is 49.5°C.

[0067] There is no need to use a phase separation tank 31. The first valve 41, the second valve 42, the third valve 43, the fourth valve 44, the sixth valve 46, the seventh valve 47, and the eighth valve 48 are all closed, and the fifth valve 45 is open. The rich liquid transfer pump 71 transports 87.7% of the rich absorbent to the rich and lean liquid heat exchanger 11 through the pipeline where the fifth valve 45 is located, and after preheating, it enters the desorption tower 22. After desorption in the desorption tower 22, desorbed liquid, regenerated absorbent, and desorbed gas are obtained. 12.3% of the rich absorbent is transported to be mixed with the regenerated absorbent from the hot fluid outlet of the rich and lean liquid heat exchanger 11 and then enters the absorbent cooler 13.

[0068] The desorbed liquid at the bottom of the desorption tower 22 is transported to the reboiler 12 by the forced circulation pump 75, and the latent heat of the exhaust steam of the steam turbine in the thermal power plant boosted by the steam mechanical recompression heat pump 91 is used to heat the desorbed liquid to 70.9°C and then return it to the bottom of the desorption tower 22 to continue participating in the desorption of CO₂. The regenerated absorbent is transported from the bottom of the desorption tower 22 to the rich and lean liquid heat exchanger 11 by the lean liquid transfer pump 74 to preheat the rich absorbent. The temperature difference between the inlet and outlet of the hot and cold fluids in the rich and lean liquid heat exchanger 11 is 5°C. After the regenerated absorbent recovers heat in the rich and lean liquid heat exchanger 11, it is combined with the absorbent supplement pipeline and then enters the absorbent cooler 13 to be cooled to 40°C.

[0069] The desorption tower 22 operates under negative pressure, and the operating pressure is 40 kPa (absolute pressure), which can reduce the desorption temperature to 70.9°C. To reduce the operating load of the vacuum pump 81, the desorbed gas at the top of the desorption tower 22 enters the desorbed gas cooler 14 and is cooled to 40°C. The partial blowdown of the condensate water in the desorbed gas cooler 14 is 1474.9 kg / h. The non-condensable gas in the desorbed gas cooler 14 enters the inlet of the vacuum pump 81, and the tail gas of the vacuum pump 81 enters the dehydration cooler 15 and is cooled to 40°C to reduce the moisture in the enriched CO₂. The condensate water of the dehydration cooler 15 is directly discharged out of the system at a flow rate of 768.2 kg / h. The non-condensable gas outlet of the dehydration cooler 15 obtains the captured CO₂ product with a flow rate of 13318.1 kg / h, a CO₂ mole fraction of 90.7%, and a carbon capture rate of 90%.

[0070] The exhaust steam with a mass flow rate of 19400 kg / h, a pressure of 15 kPa, and a saturation temperature of 54°C is led from the exhaust steam pipeline of a direct air-cooled steam turbine unit in a thermal power plant to the inlet of a steam mechanical recompression heat pump 91. The steam mechanical recompression heat pump 91 boosts the pressure of the exhaust steam to 41 kPa and then enters a reboiler 12. The steam heating load is 13595 kW. After the steam in the reboiler 12 condenses into water, it enters the exhaust steam return pipeline of the thermal power plant. The low-grade heat of the exhaust steam is effectively utilized for the regeneration of the rich absorbent solution, reducing the energy consumption for carbon dioxide capture from the flue gas of the thermal power plant to 1.61 GJ / t CO2 (electricity consumption × 3), which is 55.3% lower than that of the traditional MEA absorption process. The 19400 kg / h of exhaust steam does not need to be condensed by the exhaust steam condenser of the thermal power plant, reducing the energy consumption of the cooling device.

[0071] Example 6

[0072] Theoretical calculation shows that the flue gas of a coal-fired power plant with an absolute pressure of 103 kPa, a flow rate of 60000 Nm 3 / h, and a CO2 content of 12% enters the bottom flue gas inlet of an absorption tower 21 after dust removal, denitrification, and cooling to 50°C. The flue gas flows upward from the bottom of the absorption tower 21 and fully contacts the absorbent at a temperature of 40°C from an absorbent cooler 13 at the top of the absorption tower 21. The CO2 in the flue gas is absorbed by the absorbent. An industrial MEA homogeneous absorbent with a concentration of 5 mol / L is used, and the molar ratio of the total amount of organic amine in the absorbent to the captured CO2 is 16.7:1. The temperature of the tail gas at the top of the absorption tower 21 is 41.4°C, significantly reducing the water vapor content in the tail gas and reducing the absorption heat loss and amine loss in the absorption tower 21. The temperature of the rich absorbent solution at the bottom of the absorption tower 21 is 49.6°C.

[0073] There is no need to use a phase separation tank 31. The first valve 41, the second valve 42, the third valve 43, the fourth valve 44, the sixth valve 46, the seventh valve 47, and the eighth valve 48 are all closed, and the fifth valve 45 is open. The rich liquid transfer pump 71 transports 87.7% of the rich absorbent solution through the pipeline where the fifth valve 45 is located to the rich and lean liquid heat exchanger 11, and after preheating, it enters the desorption tower 22. After desorption in the desorption tower 22, desorbed liquid, regenerated absorbent, and desorbed gas are obtained. 12.3% of the rich absorbent solution is transported to be mixed with the regenerated absorbent from the hot fluid outlet of the rich and lean liquid heat exchanger 11 and then enters the absorbent cooler 13.

[0074] The desorbed liquid at the bottom of the desorption tower 22 is transported by the forced circulation pump 75 to the reboiler 12, and the latent heat of the exhaust steam of the thermal power plant steam turbine pressurized by the steam mechanical recompression heat pump 91 is used to heat the desorbed liquid to 70.9 °C and then return it to the bottom of the desorption tower 22 to continue participating in the desorption of CO2; the regenerated absorbent is transported from the bottom of the desorption tower 22 to the rich and lean liquid heat exchanger 11 by the lean liquid transfer pump 74 to preheat the rich absorbent liquid. The temperature difference between the inlet and outlet of the hot and cold fluids in the rich and lean liquid heat exchanger 11 is 5 °C. After the regenerated absorbent recovers heat in the rich and lean liquid heat exchanger 11, it is combined with the absorbent makeup pipeline and then enters the absorbent cooler 13 to be cooled to 40 °C.

[0075] The desorption tower 22 operates under negative pressure, and the operating pressure is 40 kPa (absolute pressure), which can reduce the desorption temperature to 70.9 °C. To reduce the operating load of the vacuum pump 81, the desorbed gas at the top of the desorption tower 22 enters the desorbed gas cooler 14 and is cooled to 40 °C. The partial blowdown of the condensate water in the desorbed gas cooler 14 is 1474.9 kg / h. The non-condensable gas in the desorbed gas cooler 14 enters the inlet of the vacuum pump 81, and the tail gas of the vacuum pump 81 enters the dehydration cooler 15 and is cooled to 40 °C to reduce the moisture in the enriched CO2; the condensate water of the dehydration cooler 15 is directly discharged out of the system at a flow rate of 768.2 kg / h. The non-condensable gas outlet of the dehydration cooler 15 obtains the captured CO2 product with a flow rate of 13318.1 kg / h, a CO2 mole fraction of 90.7%, and a carbon capture rate of 90%.

[0076] Exhaust steam with a mass flow rate of 18760 kg / h, a pressure of 10 kPa, and a saturation temperature of 45.8 °C is led from the exhaust steam pipeline of the direct air-cooled steam turbine unit of the thermal power plant to the inlet of the steam mechanical recompression heat pump 91. The steam mechanical recompression heat pump 91 pressurizes the exhaust steam to 40 kPa and then enters the reboiler 12. The steam heating load is 13580 kW. After the steam in the reboiler 12 condenses into water, it enters the exhaust steam return pipeline of the thermal power plant; the low-grade heat of the exhaust steam is effectively utilized for the regeneration of the rich absorbent liquid, reducing the energy consumption of carbon dioxide capture from the flue gas of the thermal power plant to 2.00 GJ / t CO2 (electrical consumption × 3), which is 44.4% lower than the energy consumption of the traditional MEA absorption process. 18760 kg / h of exhaust steam does not need to be condensed by the exhaust steam condenser of the thermal power plant, reducing the energy consumption of the cooling device.

[0077] Example 7

[0078] Theoretical calculation, absolute pressure is 103 kPa, flow rate is 60000 Nm 3Flue gas from a coal-fired power plant with a flow rate of 1,000,000 m³ / h and a CO₂ content of 12% enters the bottom flue gas inlet of the absorption tower 21 after dust removal, denitrification, and cooling to 50°C. The flue gas flows upward from the bottom of the absorption tower 21 and comes into full contact with the absorbent at 40°C from the absorbent cooler 13 at the top of the absorption tower 21. The CO₂ in the flue gas is absorbed by the absorbent. An industrial MEA homogeneous absorbent is used, with a concentration of 5 mol / L. The molar ratio of the total amount of organic amine in the absorbent to the captured CO₂ is 16.7:1. The temperature of the tail gas at the top of the absorption tower 21 is 41.4°C, which significantly reduces the water vapor content in the tail gas, reduces the heat loss of absorption and amine loss in the absorption tower 21, and the temperature of the rich absorbent at the bottom of the absorption tower 21 is 49.6°C.

[0079] There is no need to use the phase separator 31. The first valve 41, the second valve 42, the third valve 43, the fourth valve 44, the sixth valve 46, the seventh valve 47, and the eighth valve 48 are all closed, and the fifth valve 45 is open. The rich liquid transfer pump 71 transports 87.7% of the rich absorbent to the rich and lean liquid heat exchanger 11 through the pipeline where the fifth valve 45 is located, and after preheating, it enters the desorption tower 22. After desorption in the desorption tower 22, desorbed liquid, regenerated absorbent, and desorbed gas are obtained. 12.3% of the rich absorbent is transported to be mixed with the regenerated absorbent from the hot fluid outlet of the rich and lean liquid heat exchanger 11 and then enters the absorbent cooler 13.

[0080] The desorbed liquid at the bottom of the desorption tower 22 is transported to the reboiler 12 by the forced circulation pump 75, and the latent heat of the exhaust steam of the steam turbine in the thermal power plant boosted by the steam mechanical recompression heat pump 91 is used to heat the desorbed liquid to 70.9°C and then return it to the bottom of the desorption tower 22 to continue participating in the desorption of CO₂. The regenerated absorbent is transported from the bottom of the desorption tower 22 to the rich and lean liquid heat exchanger 11 by the lean liquid transfer pump 74 to preheat the rich absorbent. The temperature difference between the inlet and outlet of the hot and cold fluids in the rich and lean liquid heat exchanger 11 is 5°C. After the regenerated absorbent recovers heat in the rich and lean liquid heat exchanger 11, it is combined with the absorbent supply pipeline and then enters the absorbent cooler 13 to be cooled to 40°C.

[0081] The desorption tower 22 operates under negative pressure, with an operating pressure of 40 kPa (absolute pressure), which can reduce the desorption temperature to 70.9°C. To reduce the operating load of the vacuum pump 81, the desorbed gas at the top of the desorption tower 22 enters the desorbed gas cooler 14 and is cooled to 40°C. The partial blowdown of the condensate water in the desorbed gas cooler 14 is 1474.9 kg / h. The non-condensable gas in the desorbed gas cooler 14 enters the inlet of the vacuum pump 81, and the tail gas of the vacuum pump 81 enters the dehydration cooler 15 and is cooled to 40°C to reduce the moisture in the enriched CO₂. The condensate water of the dehydration cooler 15 is directly discharged out of the system at a flow rate of 768.2 kg / h, and the non-condensable gas outlet of the dehydration cooler 15 obtains the captured CO₂ product, with a flow rate of 13318.1 kg / h, a CO₂ mole fraction of 90.7%, and a carbon capture rate of 90%.

[0082] The exhausted steam with a mass flow rate of 17610 kg / h, a pressure of 5 kPa, and a saturation temperature of 32.9 °C is led from the exhausted steam pipeline of the direct air-cooled steam turbine unit in the thermal power plant to the inlet of the steam mechanical recompression heat pump 91. The steam mechanical recompression heat pump 91 boosts the pressure of the exhausted steam to 40 kPa and then enters the reboiler 12. The steam heating load is 13580 kW. After the steam in the reboiler 12 condenses into water, it enters the exhausted steam return pipeline of the thermal power plant. The low-grade heat of the exhausted steam is effectively utilized for the regeneration of the rich absorbent solution, reducing the energy consumption for carbon dioxide capture from the flue gas of the thermal power plant to 2.72 GJ / t CO2 (electricity consumption × 3), which is 24.4% lower than that of the traditional MEA absorption process. 17610 kg / h of exhausted steam does not need to be condensed by the exhausted steam condenser of the thermal power plant, reducing the energy consumption of the cooling device.

[0083] Example 8

[0084] Theoretically calculated, the flue gas from a coal-fired power plant with an absolute pressure of 103 kPa, a flow rate of 60000 Nm 3 / h and a CO2 content of 12% enters the bottom flue gas inlet of the absorption tower 21 after dust removal, denitrification, and cooling to 35 °C. The flue gas flows upward from the bottom of the absorption tower 21 and comes into full contact with the absorbent at 35 °C from the absorbent cooler 13 at the top of the absorption tower 21. The CO2 in the flue gas is absorbed by the absorbent. An industrial MEA homogeneous absorbent is used, with a concentration of 5 mol / L. The total molar ratio of the organic amine in the absorbent to the captured CO2 is 5:1. The temperature of the tail gas at the top of the absorption tower 21 is 55 °C, and the temperature of the rich absorbent solution at the bottom of the absorption tower 21 is 55 °C.

[0085] There is no need to use the phase separation tank 31. The first valve 41, the second valve 42, the third valve 43, the fourth valve 44, the sixth valve 46, the seventh valve 47, and the eighth valve 48 are all closed, and the fifth valve 45 is opened. The rich liquid transfer pump 71 transports 100% of the rich absorbent solution through the pipeline where the fifth valve 45 is located to the rich and lean liquid heat exchanger 11, and after preheating, it enters the desorption tower 22. After desorption in the desorption tower 22, desorbed liquid, regenerated absorbent, and desorbed gas are obtained.

[0086] The desorbed liquid at the bottom of the desorption tower 22 is transported to the reboiler 12 by the forced circulation pump 75. The latent heat of the exhausted steam from the steam turbine of the thermal power plant boosted by the steam mechanical recompression heat pump 91 is used to heat the desorbed liquid to 79.7 °C and then return to the bottom of the desorption tower 22 to continue participating in the desorption of CO2. The regenerated absorbent is transported from the bottom of the desorption tower 22 to the rich and lean liquid heat exchanger 11 by the lean liquid transfer pump 74 to preheat the rich absorbent solution. The temperature difference between the inlet and outlet of the hot and cold fluids in the rich and lean liquid heat exchanger 11 is 5 °C. After the regenerated absorbent recovers heat in the rich and lean liquid heat exchanger 11, it is combined with the absorbent supplement pipeline and then enters the absorbent cooler 13 to be cooled to 35 °C.

[0087] The desorption tower 22 operates under negative pressure with an operating pressure of 40 kPa (absolute pressure), which can reduce the desorption temperature to 79.7 °C. To reduce the operating load of the vacuum pump 81, the desorbed gas at the top of the desorption tower 22 enters the desorbed gas cooler 14 and is cooled to 40 °C. All the condensate water of the desorbed gas cooler 14 flows back to the top of the desorption tower 22, and the non-condensable gas of the desorbed gas cooler 14 enters the inlet of the vacuum pump 81. The tail gas of the vacuum pump 81 enters the dehydration cooler 15 and is cooled to 40 °C to reduce the moisture in the enriched CO2. The condensate water of the dehydration cooler 15 is directly discharged out of the system at a flow rate of 756.8 kg / h, and the non-condensable gas outlet of the dehydration cooler 15 obtains the captured CO2 product with a flow rate of 13191.3 kg / h, a CO2 mole fraction of 92.1%, and a carbon capture rate of 90%.

[0088] The exhaust steam with a mass flow rate of 24867.5 kg / h, a pressure of 15 kPa, and a saturation temperature of 54 °C is led from the exhaust steam pipeline of the direct air-cooled steam turbine unit in the thermal power plant to the inlet of the steam mechanical recompression heat pump 91. The steam mechanical recompression heat pump 91 boosts the exhaust steam pressure to 57.5 kPa and then enters the reboiler 12. The steam heating load is 17823.2 kW. After the steam in the reboiler 12 condenses into water, it enters the exhaust steam return pipeline of the thermal power plant. The low-grade heat of the exhaust steam is effectively utilized for the regeneration of the absorbent rich solution, reducing the energy consumption for carbon dioxide capture from the flue gas of the thermal power plant to 2.33 GJ / t CO2 (electrical consumption × 3), which is 35.3% lower than that of the traditional MEA absorption process. The 24867.5 kg / h of exhaust steam does not need to be condensed by the exhaust steam condenser of the thermal power plant, reducing the energy consumption of the cooling device.

[0089] Example 9

[0090] Theoretically calculated, the flue gas from a coal-fired power plant with an absolute pressure of 103 kPa, a flow rate of 60000 Nm 3 / h and a CO2 content of 12% enters the bottom flue gas inlet of the absorption tower 21 after dust removal, denitrification, and cooling to 50 °C. The flue gas flows upward from the bottom of the absorption tower 21 and fully contacts the absorbent at 40 °C from the absorbent cooler 13 at the top of the absorption tower 21. The CO2 in the flue gas is absorbed by the absorbent. An industrial MEA homogeneous absorbent with a concentration of 5 mol / L is used, and the molar ratio of the total amount of organic amine in the absorbent to the captured CO2 is 20:1. The temperature of the tail gas at the top of the absorption tower 21 is 40 °C, significantly reducing the water vapor content in the tail gas and reducing the absorption heat loss and amine loss in the absorption tower 21. The temperature of the absorbent rich solution at the bottom of the absorption tower 21 is 48.2 °C.

[0091] There is no need to use the phase separation tank 31. The first valve 41, the second valve 42, the third valve 43, the fourth valve 44, the sixth valve 46, the seventh valve 47 and the eighth valve 48 are all closed, and the fifth valve 45 is open. The rich liquid transfer pump 71 transports 87.7% of the absorbent rich liquid to the rich and lean liquid heat exchanger 11 through the pipeline where the fifth valve 45 is located. After preheating, it enters the desorption tower 22. After desorption in the desorption tower 22, desorbed liquid, regenerated absorbent and desorbed gas are obtained. 12.3% of the absorbent rich liquid is transported to be mixed with the regenerated absorbent from the hot fluid outlet of the rich and lean liquid heat exchanger 11 and then enters the absorbent cooler 13.

[0092] The desorbed liquid at the bottom of the desorption tower 22 is transported to the reboiler 12 by the forced circulation pump 75. The latent heat of the exhaust steam of the thermal power plant steam turbine boosted by the steam mechanical recompression heat pump 91 is used to heat the desorbed liquid to 67.7 °C and then return it to the bottom of the desorption tower 22 to continue participating in the desorption of CO2. The regenerated absorbent is transported from the bottom of the desorption tower 22 to the rich and lean liquid heat exchanger 11 by the lean liquid transfer pump 74 to preheat the absorbent rich liquid. The temperature difference between the inlet and outlet of the hot and cold fluids in the rich and lean liquid heat exchanger 11 is 5 °C. After the regenerated absorbent recovers heat in the rich and lean liquid heat exchanger 11, it is combined with the absorbent make-up pipeline and then enters the absorbent cooler 13 to be cooled to 40 °C.

[0093] The desorption tower 22 operates under negative pressure, and the operating pressure is 40 kPa (absolute pressure). The desorption temperature can be reduced to 67.7 °C. To reduce the operating load of the vacuum pump 81, the desorbed gas at the top of the desorption tower 22 enters the desorbed gas cooler 14 and is cooled to 40 °C. The blowdown amount of the condensate water in the desorbed gas cooler 14 is 1669.9 kg / h. The non-condensable gas in the desorbed gas cooler 14 enters the inlet of the vacuum pump 81. The tail gas of the vacuum pump 81 enters the dehydration cooler 15 and is cooled to 40 °C to reduce the moisture in the enriched CO2. The condensate water of the dehydration cooler 15 is directly discharged out of the system at a flow rate of 774.8 kg / h. The non-condensable gas outlet of the dehydration cooler 15 obtains the captured CO2 product with a flow rate of 13391.9 kg / h, a CO2 mole fraction of 90%, and a carbon capture rate of 90%.

[0094] Exhaust steam with a mass flow rate of 20878 kg / h, a pressure of 15 kPa, and a saturation temperature of 54 °C is led from the exhaust steam pipeline of the direct air-cooled steam turbine unit of the thermal power plant to the inlet of the steam mechanical recompression heat pump 91. The steam mechanical recompression heat pump 91 boosts the exhaust steam to 35.1 kPa and then enters the reboiler 12. The steam heating load is 14471 kW. After the steam in the reboiler 12 condenses into water, it enters the exhaust steam return pipeline of the thermal power plant. The low-grade heat of the exhaust steam is effectively utilized for the regeneration of the absorbent rich liquid, reducing the energy consumption of carbon dioxide capture from the flue gas of the thermal power plant to 1.54 GJ / t CO2 (electricity consumption × 3), which is 57.2% lower than the energy consumption of the traditional MEA absorption process. 20878 kg / h of exhaust steam does not need to be condensed by the exhaust steam condenser of the thermal power plant, reducing the energy consumption of the cooling device.

[0095] Example 10

[0096] Theoretically calculated, the flue gas from a coal-fired power plant with an absolute pressure of 103 kPa, a flow rate of 60,000 Nm 3 / h and a CO2 content of 12% enters the bottom flue gas inlet of the absorption tower 21 after dust removal, denitrification and cooling to 35°C. The flue gas flows upward from the bottom of the absorption tower 21 and comes into full contact with the absorbent at 40°C from the absorbent cooler 13 at the top of the absorption tower 21. The CO2 in the flue gas is absorbed by the absorbent; an industrial phase change absorbent is used, with a concentration of 5 mol / L. The total molar ratio of organic amine in the absorbent to the captured CO2 is 10:1. The temperature of the tail gas at the top of the absorption tower 21 is 52.5°C, which greatly reduces the water vapor content in the tail gas and reduces the heat loss of absorption and amine loss in the absorption tower 21. The temperature of the rich absorbent liquid at the bottom of the absorption tower 21 is 58.5°C.

[0097] The fifth valve 45 is closed, and the seventh valve 47 and the eighth valve 48 are opened; because the density of the CO2 rich phase is smaller than that of the lean phase, the second valve 42 and the fourth valve 44 are opened, and the third valve 43 and the sixth valve 46 are closed; the CO2 lean phase is transported by the lean phase transfer pump 73 through the seventh valve 47 to be mixed with the regenerated absorbent from the hot fluid outlet of the rich and lean liquid heat exchanger 11 and then enters the hot fluid inlet of the absorbent cooler 13; 100% of the CO2 rich phase is transported by the rich phase transfer pump 72 to the rich and lean liquid heat exchanger 11, preheated and then enters the desorption tower 22. After desorption in the desorption tower 22, desorbed liquid, regenerated absorbent and desorbed gas are obtained.

[0098] The desorbed liquid at the bottom of the desorption tower 22 is transported to the reboiler 12 by the forced circulation pump 75, and the latent heat of the exhaust steam of the steam turbine in the thermal power plant pressurized by the steam mechanical recompression heat pump 91 is used to heat the desorbed liquid to 79.4°C and then return to the bottom of the desorption tower 22 to continue to participate in the desorption of CO2; the regenerated absorbent is transported from the bottom of the desorption tower 22 to the rich and lean liquid heat exchanger 11 by the lean liquid transfer pump 74 to preheat the CO2 rich phase. The temperature difference between the inlet and outlet of the hot and cold fluids in the rich and lean liquid heat exchanger 11 is 5°C. After the regenerated absorbent recovers heat in the rich and lean liquid heat exchanger 11, it is combined with the absorbent supplement pipeline and then enters the absorbent cooler 13 to be cooled to 40°C.

[0099] The desorption tower 22 operates under negative pressure with an operating pressure of 40 kPa (absolute pressure), and the desorption temperature can be reduced to 79.4 °C. To reduce the operating load of the vacuum pump 81, the desorbed gas at the top of the desorption tower 22 enters the desorbed gas cooler 14 and is cooled to 30 °C. The blowdown of the condensate in the desorbed gas cooler 14 is 101.1 kg / h. The non-condensable gas in the desorbed gas cooler 14 enters the inlet of the vacuum pump 81, and the tail gas of the vacuum pump 81 enters the dehydration cooler 15 and is cooled to 40 °C to reduce the moisture in the enriched CO2. The condensate of the dehydration cooler 15 is directly discharged outside the system at a flow rate of 376.5 kg / h. The non-condensable gas outlet of the dehydration cooler 15 obtains the captured CO2 product with a flow rate of 12954.2 kg / h, a CO2 mole fraction of 95.8%, and a carbon capture rate of 90%.

[0100] The exhausted steam with a mass flow rate of 13982 kg / h, a pressure of 15 kPa, and a saturation temperature of 54 °C is led from the exhausted steam pipeline of the direct air-cooled steam turbine unit in the thermal power plant to the inlet of the steam mechanical recompression heat pump 91. The steam mechanical recompression heat pump 91 boosts the exhausted steam to 57 kPa and then enters the reboiler 12. The steam heating load is 10016.2 kW. After the steam in the reboiler 12 condenses into water, it enters the exhausted steam return pipeline of the thermal power plant. The low-grade heat of the exhausted steam is effectively utilized for the regeneration of the rich absorbent solution, reducing the energy consumption for carbon dioxide capture from the flue gas of the thermal power plant to 1.46 GJ / t CO2 (electrical consumption × 3), which is 59.4% lower than that of the traditional MEA absorption process. The 13982 kg / h of exhausted steam does not need to be condensed by the exhausted steam condenser of the thermal power plant, reducing the energy consumption of the cooling device.

[0101] Example 11

[0102] Theoretically calculated, the flue gas from a coal-fired power plant with an absolute pressure of 103 kPa, a flow rate of 60000 Nm 3 / h and a CO2 content of 12% enters the bottom flue gas inlet of the absorption tower 21 after dust removal, denitrification, and cooling to 35 °C. The flue gas flows upward from the bottom of the absorption tower 21 and fully contacts the absorbent at 40 °C from the absorbent cooler 13 at the top of the absorption tower 21. The CO2 in the flue gas is absorbed by the absorbent. An industrial MEA homogeneous absorbent with a concentration of 5 mol / L is used, and the molar ratio of the total amount of organic amine in the absorbent to the captured CO2 is 20:1. The temperature of the tail gas at the top of the absorption tower 21 is 40 °C, significantly reducing the water vapor content in the tail gas and reducing the absorption heat loss and amine loss in the absorption tower 21. The temperature of the rich absorbent solution at the bottom of the absorption tower 21 is 46.1 °C.

[0103] There is no need to use the phase separation tank 31. The first valve 41, the second valve 42, the third valve 43, the fourth valve 44, the sixth valve 46, the seventh valve 47 and the eighth valve 48 are all closed, and the fifth valve 45 is open. The rich liquid transfer pump 71 transports 87.7% of the absorbent rich liquid to the rich and lean liquid heat exchanger 11 through the pipeline where the fifth valve 45 is located. After preheating, it enters the desorption tower 22. After desorption in the desorption tower 22, desorbed liquid, regenerated absorbent and desorbed gas are obtained; 12.3% of the absorbent rich liquid is transported to be mixed with the regenerated absorbent from the hot fluid outlet of the rich and lean liquid heat exchanger 11 and then enters the absorbent cooler 13.

[0104] The desorbed liquid at the bottom of the desorption tower 22 is transported to the reboiler 12 by the forced circulation pump 75. The latent heat of the exhaust steam of the thermal power plant steam turbine boosted by the steam mechanical recompression heat pump 91 is used to heat the desorbed liquid to 56°C and then return to the bottom of the desorption tower 22 to continue participating in the desorption of CO2; the regenerated absorbent is transported from the bottom of the desorption tower 22 to the rich and lean liquid heat exchanger 11 by the lean liquid transfer pump 74 to preheat the absorbent rich liquid. The temperature difference between the inlet and outlet of the hot and cold fluids of the rich and lean liquid heat exchanger 11 is 10°C. After the regenerated absorbent recovers heat in the rich and lean liquid heat exchanger 11, it is combined with the absorbent makeup pipeline and then enters the absorbent cooler 13 to be cooled to 40°C.

[0105] The desorption tower 22 operates under negative pressure, and the operating pressure is 20 kPa (absolute pressure). The desorption temperature can be reduced to 56°C. To reduce the operating load of the vacuum pump 81, the desorbed gas at the top of the desorption tower 22 enters the desorbed gas cooler 14 to be cooled to 15°C. The partial blowdown of the condensate water of the desorbed gas cooler 14 is 2368.2 kg / h. The non-condensable gas of the desorbed gas cooler 14 enters the inlet of the vacuum pump 81, and the tail gas of the vacuum pump 81 enters the dehydration cooler 15 to be cooled to 15°C to reduce the moisture in the enriched CO2; the condensate water of the dehydration cooler 15 is directly discharged out of the system at a flow rate of 409.7 kg / h. The non-condensable gas outlet of the dehydration cooler 15 obtains the captured CO2 product with a flow rate of 13071.6 kg / h, a CO2 mole fraction of 95.3%, and a carbon capture rate of 90%.

[0106] Exhaust steam with a mass flow rate of 28175 kg / h, a pressure of 15 kPa, and a saturation temperature of 54°C is led from the exhaust steam pipeline of the direct air-cooled steam turbine unit of the thermal power plant to the inlet of the steam mechanical recompression heat pump 91. The steam mechanical recompression heat pump 91 boosts the exhaust steam to 35 kPa and then enters the reboiler 12. The steam heating load is 19904 kW. After the steam in the reboiler 12 condenses into water, it enters the exhaust steam return pipeline of the thermal power plant; the low-grade heat of the exhaust steam is effectively used for the regeneration of the absorbent rich liquid, reducing the energy consumption of carbon dioxide capture from the flue gas of the thermal power plant to 2.07 GJ / t CO2 (electricity consumption × 3), a 42.5% reduction compared to the energy consumption of the traditional MEA absorption process. 28175 kg / h of exhaust steam does not need to be condensed by the exhaust steam condenser of the thermal power plant, reducing the energy consumption of the cooling device.

[0107] Example 12

[0108] Theoretically calculated, flue gas from a coal-fired power plant with an absolute pressure of 103 kPa, a flow rate of 60,000 Nm 3 / h, and a CO2 content of 12% enters the bottom flue gas inlet of the absorption tower 21 after dust removal, denitrification, and cooling to 35°C. The flue gas flows upward from the bottom of the absorption tower 21 and comes into full contact with the absorbent at 40°C from the absorbent cooler 13 at the top of the absorption tower 21. The CO2 in the flue gas is absorbed by the absorbent. An industrial MEA homogeneous absorbent with a concentration of 5 mol / L is used, and the molar ratio of the total amount of organic amine in the absorbent to the trapped CO2 is 20:1. The temperature of the tail gas at the top of the absorption tower 21 is 40°C, which significantly reduces the water vapor content in the tail gas and reduces the heat loss of absorption and amine loss in the absorption tower 21. The temperature of the rich absorbent liquid at the bottom of the absorption tower 21 is 46.1°C.

[0109] There is no need to use the phase separation tank 31. The first valve 41, the second valve 42, the third valve 43, the fourth valve 44, the sixth valve 46, the seventh valve 47, and the eighth valve 48 are all closed, and the fifth valve 45 is opened. The rich liquid transfer pump 71 transports 100% of the rich absorbent liquid to the rich and lean liquid heat exchanger 11 through the pipeline where the fifth valve 45 is located, and after preheating, it enters the desorption tower 22. After desorption in the desorption tower 22, desorbed liquid, regenerated absorbent, and desorbed gas are obtained.

[0110] The desorbed liquid at the bottom of the desorption tower 22 is transported to the reboiler 12 by the forced circulation pump 75, and the latent heat of the exhaust steam of the steam turbine in the thermal power plant boosted by the steam mechanical recompression heat pump 91 is used to heat the desorbed liquid to 78.8°C and then return it to the bottom of the desorption tower 22 to continue participating in the desorption of CO2. The regenerated absorbent is transported from the bottom of the desorption tower 22 to the rich and lean liquid heat exchanger 11 by the lean liquid transfer pump 74 to preheat the rich absorbent liquid. The temperature difference between the inlet and outlet of the hot and cold fluids in the rich and lean liquid heat exchanger 11 is 2°C. After the regenerated absorbent recovers heat in the rich and lean liquid heat exchanger 11, it is combined with the absorbent supply pipeline and enters the absorbent cooler 13 to be cooled to 40°C.

[0111] The desorption tower 22 operates under negative pressure with an operating pressure of 80 kPa (absolute pressure), and the desorption temperature can be reduced to 78.8 °C. To reduce the operating load of the vacuum pump 81, the desorbed gas at the top of the desorption tower 22 enters the desorbed gas cooler 14 and is cooled to 15 °C. The blowdown amount of the condensate water of the desorbed gas cooler 14 is 2753.8 kg / h. The non-condensable gas of the desorbed gas cooler 14 enters the inlet of the vacuum pump 81, and the tail gas of the vacuum pump 81 enters the dehydration cooler 15 and is cooled to 15 °C to reduce the moisture in the enriched CO2. The condensate water of the dehydration cooler 15 is directly discharged outside the system at a flow rate of 25.1 kg / h. The non-condensable gas outlet of the dehydration cooler 15 obtains the captured CO2 product with a flow rate of 13072.1 kg / h, a CO2 mole fraction of 95.3%, and a carbon capture rate of 90%.

[0112] The exhaust steam with a mass flow rate of 15155 kg / h, a pressure of 15 kPa, and a saturation temperature of 54 °C is led from the exhaust steam pipeline of the direct air-cooled steam turbine unit in the thermal power plant to the inlet of the steam mechanical recompression heat pump 91. The steam mechanical recompression heat pump 91 boosts the exhaust steam to 60 kPa and then enters the reboiler 12. The steam heating load is 10928.5 kW. After the steam in the reboiler 12 condenses into water, it enters the exhaust steam return pipeline of the thermal power plant. The low-grade heat of the exhaust steam is effectively used for the regeneration of the rich absorbent solution, reducing the energy consumption for carbon dioxide capture in the flue gas of the thermal power plant to 1.53 GJ / t CO2 (electricity consumption × 3), which is 57.5% lower than that of the traditional MEA absorption process. The 15155 kg / h of exhaust steam does not need to be condensed by the exhaust steam condenser of the thermal power plant, reducing the energy consumption of the cooling device.

[0113] Although the specific implementation manners of the present invention have been described in detail in combination with the embodiments, it should not be construed as a limitation on the protection scope of this patent. Within the scope described in the claims, various modifications and deformations that can be made by those skilled in the art without creative efforts still fall within the protection scope of this patent.

Claims

1. A system for assisting in carbon dioxide capture by utilizing the waste heat of the exhaust steam of a power plant steam turbine, characterized in that: It includes a carbon dioxide absorption system and a carbon dioxide desorption system; The carbon dioxide absorption system includes an absorption tower (21), a rich liquid transfer pump (71), a rich phase transfer pump (72), a lean phase transfer pump (73), a phase separation tank (31), an absorbent cooler (13), a first valve (41), a second valve (42), a third valve (43), a fourth valve (44), a fifth valve (45), a sixth valve (46), a seventh valve (47), and an eighth valve (48); The carbon dioxide desorption system includes a rich and lean liquid heat exchanger (11), a desorbed gas cooler (14), a dehydration cooler (15), a desorption tower (22), a lean liquid transfer pump (74), a forced circulation pump (75), a vacuum pump (81), and a power plant steam turbine exhaust heat recovery system; The power plant steam turbine exhaust heat recovery system includes a steam mechanical recompression heat pump (91) and a reboiler (12); In the carbon dioxide absorption system, the bottom of the absorption tower (21) is provided with a gas inlet and a liquid outlet, and the top is provided with a gas outlet and a liquid inlet. The liquid inlet is connected to the outlet of the absorbent cooler (13), and the liquid outlet is connected to the inlet of the rich liquid transfer pump (71). The outlet of the rich liquid transfer pump (71) is divided into two branches. The first branch is connected to the phase separation tank (31) through the first valve (41), and the second branch is connected to the inlet of the fifth valve (45). The first outlet of the phase separation tank (31) is connected to the inlets of the fourth valve (44) and the sixth valve (46), and the second outlet is connected to the inlets of the second valve (42) and the third valve (43). The outlets of the second valve (42) and the sixth valve (46) are merged and then connected to the inlet of the rich phase transfer pump (72). The outlets of the third valve (43) and the fourth valve (44) are merged and then connected to the inlet of the lean phase transfer pump (73). The outlet of the rich phase transfer pump (72) is connected to the inlet of the eighth valve (48). The outlets of the fifth valve (45) and the eighth valve (48) are merged and then divided into two branches. The first branch is connected to the first inlet of the rich and lean liquid heat exchanger (11), and the second branch is connected to the inlet of the absorbent cooler (13). The outlet of the lean phase transfer pump (73) is connected to the inlet of the seventh valve (47). The outlet of the seventh valve (47) is merged with the second branch after the merger of the outlets of the fifth valve (45) and the eighth valve (48); At the top of the desorption tower (22) in the carbon dioxide desorption system, there are two liquid inlets and one gas outlet. The first outlet of the rich and lean liquid heat exchanger (11) is connected to one of the liquid inlets at the top of the desorption tower (22). At the bottom of the desorption tower (22), there are two liquid outlets and one liquid inlet. One of the liquid outlets is connected to the inlet of the forced circulation pump (75). The outlet of the forced circulation pump (75) is connected to the first inlet of the reboiler (12). The first outlet of the reboiler (12) is connected to the liquid inlet at the bottom of the desorption tower (22). The other liquid outlet at the bottom of the desorption tower (22) is connected to the inlet of the lean liquid transfer pump (74). The outlet of the lean liquid transfer pump (74) is divided into two branches. One branch is connected to the second inlet of the rich and lean liquid heat exchanger (11). The second outlet of the rich and lean liquid heat exchanger (11) is merged with the second branch after the merger of the outlets of the fifth valve (45) and the eighth valve (48). The other branch of the outlet of the lean liquid transfer pump (74) is merged with the first outlet of the rich and lean liquid heat exchanger (11). The gas outlet at the top of the desorption tower (22) is connected to the gas inlet of the desorbed gas cooler (14). The liquid outlet of the desorbed gas cooler (14) is divided into a blowdown pipe and a reflux pipe. The blowdown pipe is connected outside the system. The reflux pipe is connected to the other liquid inlet at the top of the desorption tower (22). The gas outlet of the desorbed gas cooler (14) is connected to the inlet of the vacuum pump (81). The outlet of the vacuum pump (81) is connected to the inlet of the dehydration cooler (15). The liquid outlet of the dehydration cooler (15) is connected outside the system. The gas outlet of the dehydration cooler (15) is the captured carbon dioxide. The exhaust steam outlet pipe connected to the steam turbine of the thermal power plant is connected to the inlet of the steam mechanical recompression heat pump (91). The outlet of the steam mechanical recompression heat pump (91) is connected to the second inlet of the reboiler (12). The second outlet of the reboiler (12) is connected to the exhaust steam return pipe. A method for capturing carbon dioxide by a system for capturing carbon dioxide using the waste heat of the exhaust steam of a power plant steam turbine includes the following steps: S1: Feed the flue gas and the absorbent into the absorption tower (21) from the bottom and the top of the absorption tower (21) respectively. The absorbent absorbs CO2 in the flue gas to obtain a rich absorbent solution. S2: Transport 50% - 100% of the rich absorbent solution to the rich and lean liquid heat exchanger (11). After preheating, it enters the desorption tower (22) from the top of the desorption tower (22). After desorption in the desorption tower (22), a desorbed solution, a regenerated absorbent, and a desorbed gas are obtained. The remaining rich absorbent solution is mixed with the regenerated absorbent from the rich and lean liquid heat exchanger (11) and then enters the absorbent cooler (13). The desorbed solution is transported by the forced circulation pump (75) to the reboiler (12), and after being heated by the exhaust steam boosted by the steam mechanical recompression heat pump (91), it returns to the bottom of the desorption tower (22). The regenerated absorbent is transported by the lean liquid transfer pump (74) to the rich and lean liquid heat exchanger (11) to preheat the rich absorbent solution. Alternatively, the absorbent rich solution is transported to the phase separator tank (31) for phase separation to obtain a CO2 lean phase and a CO2 rich phase; 50% - 100% of the CO2 rich phase is transported to the rich-lean solution heat exchanger (11), preheated, and then enters the desorption tower (22) from the top of the desorption tower (22). After desorption in the desorption tower (22), a desorbed solution, a regenerated absorbent, and a desorbed gas are obtained; the remaining CO2 rich phase is mixed with the regenerated absorbent from the rich-lean solution heat exchanger (11) and then enters the absorbent cooler (13); the desorbed solution is transported to the reboiler (12) by the forced circulation pump (75), heated by the waste steam boosted by the steam mechanical recompression heat pump (91), and then returns to the bottom of the desorption tower (22); the regenerated absorbent is transported to the rich-lean solution heat exchanger (11) by the lean solution transfer pump (74) to preheat the CO2 rich phase; the CO2 lean phase is mixed with the regenerated absorbent from the rich-lean solution heat exchanger (11) and then enters the absorbent cooler (13). S3: The desorbed gas enters the desorbed gas cooler (14) for cooling. The condensed water generated by the cooling flows back to the top of the desorption tower (22), and the non-condensable gas enters the vacuum pump (81). The tail gas of the vacuum pump (81) enters the dehydration cooler (15) for cooling, and the non-condensable gas outlet of the dehydration cooler (15) obtains the trapped carbon dioxide. The pressure of the waste steam boosted by the steam mechanical recompression heat pump (91) is 35 - 60 kPa, the temperature of the desorbed solution heated by the reboiler (12) is 65 - 80 °C, and the temperature difference between the hot and cold fluid streams at both ends of the rich-lean solution heat exchanger (11) is 2 - 10 °C; the absolute pressure at the top of the desorption tower (22) is 20 - 80 kPa.

2. The system for utilizing the waste heat of the exhaust steam of a power plant steam turbine to assist in carbon dioxide capture according to claim 1, wherein: The waste heat recovery system of the power plant steam turbine recovers the waste heat of the equipment of the thermal power plant. The equipment of the thermal power plant includes a boiler (1), a steam turbine (2), a generator (3), a condenser (4), a condensate pump (5), a deaerator (6), and a feed water tank (7). The gas outlet of the boiler (1) is connected to the gas inlet of the steam turbine (2). The steam turbine (2) is connected to the generator (3). The gas outlet of the steam turbine (2) is connected to the waste steam outlet pipeline and the inlet of the condenser (4). The waste steam return pipeline is merged with the inlet pipeline of the condenser (4). The outlet of the condenser (4) is connected to the inlet of the condensate pump (5). The outlet of the condensate pump (5) is connected to the inlet of the deaerator (6). The outlet of the deaerator (6) is connected to the inlet of the feed water tank (7). The outlet of the feed water tank (7) is connected to the boiler (1). The condenser (4) is also provided with a circulating cooling water inlet and a circulating cooling water outlet.

3. The system for auxiliary carbon dioxide capture using the waste heat of the exhaust steam of a power plant steam turbine according to claim 1, wherein: The absorption tower (21) is a plate tower, a packed tower, a series-connected rotating packed bed, or a combination of a tower device and a rotating packed bed.

4. The system for auxiliary carbon dioxide capture using the waste heat of the exhausted steam of a power plant steam turbine according to claim 1, wherein: The absorbent makeup pipeline is merged with the second branch merged from the outlets of the fifth valve (45) and the eighth valve (48).

5. The system for utilizing the waste heat of the exhaust steam of a power plant steam turbine to assist in carbon dioxide capture according to claim 1, characterized in that: The molar ratio of the total amount of organic amine in the absorbent to the captured CO2 is 5 to 20:1, and the absorbent is a homogeneous absorbent or a phase change absorbent.

6. The method for capturing carbon dioxide by using the system for capturing carbon dioxide with the waste heat of the exhaust steam of a power plant steam turbine according to claim 1, characterized in that: The temperature of the flue gas is 35 to 50 °C, the temperature of the absorbent entering the absorption tower (21) is 35 to 40 °C, and the temperature of the rich absorbent is 35 to 60 °C.

7. The system for auxiliary carbon dioxide capture by utilizing the waste heat of the exhaust steam of a power plant steam turbine according to claim 1, characterized in that: The desorbed gas cooler (14) cools the gas to 15 to 40 °C, and the dehydration cooler (15) cools the gas to 15 to 40 °C.

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