A low-energy consumption heat pump assisted carbon dioxide capture system and capture process

Abstract

The present invention discloses a low-energy consumption heat pump-assisted carbon dioxide capture system and a capture process, belonging to the technical field of carbon dioxide capture by chemical absorption method. The carbon dioxide capture system includes a flue gas pretreatment system, a carbon dioxide absorption system, a carbon dioxide desorption system, and a heat pump system; the flue gas pretreatment system is used to remove SO x and dust from the flue gas, and at the same time cool the flue gas, which is beneficial to improving the rich liquid CO2 load of the carbon dioxide absorption system; the carbon dioxide absorption system uses a large amount of absorbent to absorb at a relatively low temperature of 35°C to 40°C, which can significantly reduce the temperature of the absorption tail gas at the top of the absorption tower, reduce the water vapor content, and reduce the heat loss of absorption in the absorption tower; the carbon dioxide desorption system is depressurized and desorbed under an operating pressure of 20 kPa (absolute pressure) to 80 kPa (absolute pressure), which improves the coefficient of performance of the heat pump, enhances the energy-saving effect, and prolongs the service life of the absorbent; the heat pump system realizes the recovery and utilization of waste heat and achieves energy saving.

Description

Technical Field

[0001] The present invention relates to the technical field of energy conservation and emission reduction, and particularly relates to a low-energy-consumption heat pump-assisted carbon dioxide capture system and a capture process. Background Art

[0002] CO2 capture technology refers to the process of separating and enriching CO2 generated during the utilization of fossil energy in industries such as power, steel, and cement. According to the differences in CO2 capture principles, it can be divided into solution absorption method, solid adsorption method, membrane separation method, cryogenic fractionation method, oxy-fuel combustion, chemical-looping combustion, etc.

[0003] Chemical absorption method is considered suitable for large-flow CO2 capture, with simple operation and high technical maturity, having the highest application prospect, and having achieved large-scale application of millions of tons at home and abroad. Currently, the energy consumption of the carbon capture process represented by industrial MEA is as high as 3.6 GJ / tCO2. After the carbon capture process is adopted 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 bottleneck of high energy consumption and high cost severely restricts the industrial application of carbon capture technology. Therefore, the innovation of low-energy-consumption carbon dioxide capture technology is extremely urgent. Summary of the Invention

[0004] In order to overcome the defects existing in the prior art, the purpose of the present invention is to provide a low-energy-consumption heat pump-assisted carbon dioxide capture system and a capture process to solve the problems that the existing capture process cannot effectively utilize the absorption heat and desorption waste heat of the CO2 capture system, the desorption rate is too high resulting in high desorption energy consumption, and the desorption temperature is too high resulting in too large a temperature difference between the hot and cold ends of the heat pump, resulting in too low a coefficient of performance of the heat pump for heating and poor energy-saving effect.

[0005] The technical solution of the present invention to solve the above technical problems is as follows: Provide a low-energy-consumption heat pump-assisted carbon dioxide capture system, including a flue gas pretreatment system, a carbon dioxide absorption system, a carbon dioxide desorption system, and a heat pump system;

[0006] The heat pump system includes a heat pump pre-evaporator 11, a heat pump evaporator 15, a heat pump medium gas-liquid separation tank 33, a heat pump compressor 51, a heat pump condenser 14, and a throttle valve 61;

[0007] The flue gas pretreatment system includes a flue gas reboiler 10, a scrubbing tower 21, a scrubbing liquid circulation tank 31, and a scrubbing liquid circulation pump 71; The hot fluid outlet of the flue gas reboiler 10 is connected to the bottom gas inlet of the scrubbing tower 21; The bottom scrubbing liquid outlet of the scrubbing tower 21 is connected to the scrubbing liquid return port of the scrubbing liquid circulation tank 31; The bottom scrubbing liquid outlet of the scrubbing liquid circulation tank 31 is connected to the liquid inlet of the scrubbing liquid circulation pump 71; The outlet of the scrubbing liquid circulation pump 71 is connected to the hot fluid inlet of the heat pump pre-evaporator 11; The hot fluid outlet of the heat pump pre-evaporator 11 is connected to the top scrubbing liquid inlet of the scrubbing tower 21;

[0008] The carbon dioxide absorption system includes an absorption tower 22; the gas outlet at the top of the scrubbing tower 21 is connected to the flue gas inlet at the bottom of the absorption tower 22; the absorbent inlet in the upper middle part of the absorption tower 22 is connected to the hot fluid outlet of the heat pump evaporator 15; the absorbent inlet at the top of the absorption tower 22 is connected to the hot fluid outlet of the cooler 16; a purified gas outlet is arranged at the top of the absorption tower 22; the rich liquid outlet at the bottom of the absorption tower 22 is connected to the liquid inlet of the rich liquid transfer pump 72;

[0009] The carbon dioxide desorption system includes a rich liquid transfer pump 72, a phase separation tank 32, a lean phase transfer pump 73, a rich phase transfer pump 74, a rich and lean liquid heat exchanger 12, a lean liquid transfer pump 75, a desorption tower 23, a first forced circulation pump 76, a second forced circulation pump 70, a mixing tank 36, a desorbed gas cooler 17, a vacuum pump 81, an enriched gas condenser 18, a first condensate collection tank 34, a second condensate collection tank 35, and a condensate transfer pump 77; the outlet pipeline of the rich liquid transfer pump 72 is divided into two branches, one branch is connected to the phase separation tank 32, and the other branch is merged with the outlet pipeline of the eighth valve 48 through the fifth valve 45; the heavy phase outlet pipeline of the phase separation tank 32 is divided into two branches, which are respectively connected to the inlets of the sixth valve 46 and the fourth valve 44, and the light phase outlet pipeline of the phase separation tank 32 is divided into two branches, which are respectively connected to the inlets of the second valve 42 and the third valve 43; the outlet pipelines of the second valve 42 and the sixth valve 46 are merged and then connected to the inlet pipeline of the rich phase transfer pump 74, and the outlet pipeline of the rich phase transfer pump 74 is connected to the eighth valve 48; the outlet pipelines of the third valve 43 and the fourth valve 44 are merged and then connected to the inlet pipeline of the lean phase transfer pump 73, the outlet pipeline of the lean phase transfer pump 73 is connected to the seventh valve 47, and the seventh valve 47 is connected to the hot fluid inlet of the heat pump evaporator 15; the merged outlet pipelines of the fifth valve 45 and the eighth valve 48 are divided into two branches, one is connected to the cold fluid inlet of the rich and lean liquid heat exchanger 12, and the other is connected to the hot fluid inlet of the heat pump evaporator 15; the cold fluid outlet pipeline of the rich and lean liquid heat exchanger 12 is connected to the rich liquid inlet at the top of the desorption tower 23; the bottom of the desorption tower 23 is divided into three liquid outlet pipelines, one of which is connected to the inlet of the first forced circulation pump 76, the outlet of the first forced circulation pump 76 is connected to the cold fluid inlet of the heat pump condenser 14, and the outlet of the heat pump condenser 14 is connected to the gas-liquid mixture inlet at the bottom of the desorption tower 23; one of the liquid outlet pipelines at the bottom of the desorption tower 23 is connected to the inlet of the second forced circulation pump 70, the outlet of the second forced circulation pump 70 is connected to the cold fluid inlet of the flue gas reboiler 10, and the cold fluid outlet pipeline of the flue gas reboiler 10 is merged with the cold fluid outlet pipeline of the heat pump condenser 14 and then enters the gas-liquid mixture inlet at the bottom of the desorption tower 23; the other liquid pipeline at the bottom of the desorption tower 23 is connected to the mixing tank 36, and the gas pipeline at the top of the mixing tank 36 is connected to the gas inlet above the liquid level of the bottom of the desorption tower 23; the mixing tank 36 is provided with a heater 13; the liquid pipeline at the bottom of the mixing tank 36 is connected to the inlet of the lean liquid transfer pump 75, and the outlet pipeline of the lean liquid transfer pump 75 is connected to the hot fluid inlet of the rich and lean liquid heat exchanger 12; the hot fluid outlet pipeline of the rich and lean liquid heat exchanger 12 is merged with one of the outlet pipelines of the eighth valve 48 and then connected to the hot fluid inlet of the heat pump evaporator 15; the outlet pipeline of the heat pump evaporator 15 is divided into two branches, one branch is connected to the absorbent inlet in the middle and upper part of the absorption tower 22, and the other branch is connected to the hot fluid inlet of the absorbent cooler 16; the gas pipeline at the top of the desorption tower 23 is connected to the desorbed gas cooler 17, the condensate pipeline of the desorbed gas cooler 17 is connected to the first condensate collection tank 34, and the non-condensable gas pipeline of the desorbed gas cooler 17 is connected to the inlet of the vacuum pump 81;The outlet of the vacuum pump 81 is connected to the inlet of the enriched gas condenser 18; the condensate outlet of the enriched gas condenser 18 is connected to the second condensate collection tank 35; the liquid outlet pipelines of the first condensate collection tank 34 and the second condensate collection tank 35 are connected to the inlet pipeline of the condensate transfer pump 77; the outlet pipeline of the condensate transfer pump 77 is divided into two branches, one is the sewage pipeline, and the other is connected to the cold fluid inlet of the absorbent cooler 16.

[0010] The outlet pipeline of the throttle valve 61 is connected to the cold fluid inlet of the heat pump pre-evaporator 11; the cold fluid outlet pipeline of the heat pump pre-evaporator 11 is connected to the cold fluid inlet of the heat pump evaporator 15; the cold fluid outlet of the heat pump evaporator 15 is connected to the inlet of the gas-liquid mixture in the middle of the heat pump medium gas-liquid separation tank 33; the gas-phase pipeline at the top of the heat pump medium gas-liquid separation tank 33 is connected to the air inlet of the heat pump compressor 51; the outlet of the heat pump compressor 51 is connected to the heat fluid inlet of the heat pump condenser 14; the heat fluid outlet of the heat pump condenser 14 is connected to the inlet of the throttle valve 61.

[0011] The beneficial effects of the present invention are as follows:

[0012] The present invention uses flue gas to directly heat the reboiler of the desorption tower, reducing the external energy demand during the regeneration process of the absorbent rich liquid in the desorption tower. The flue gas is directly contacted and heat-exchanged with the washing liquid in the washing tower, improving the heat exchange efficiency during the flue gas cooling process. The heat pump pre-evaporator supplies the heat of the flue gas absorbed by the washing tower to the heat pump, converting the heat exchange method of the flue gas heat from gas-liquid heat exchange to liquid-liquid heat exchange, improving the heat exchange efficiency of the heat pump pre-evaporator, increasing the cold end temperature of the heat pump, improving the coefficient of performance of the heat pump for heating, and reducing energy consumption. A large amount of absorbent is used at the top of the absorption tower for absorption at a lower temperature, which can significantly reduce the temperature of the absorption tail gas at the top of the absorption tower, reduce the water vapor content, and reduce the heat loss of absorption in the absorption tower. The absorbent rich liquid with a large flow rate and high CO2 load can meet the requirements of CO2 capture volume at a lower desorption rate, reducing the desorption energy consumption. Part of the rich liquid directly enters the absorption tower to absorb CO2 again after being cooled by taking heat from the heat pump, which can further increase the CO2 load in the absorbent. The decompression desorption operation is adopted to reduce the CO2 partial pressure in the desorption tower, which can reduce the desorption temperature of the reboiler, reduce the temperature difference between the hot and cold ends of the heat pump, improve the coefficient of performance of the heat pump for heating, enhance the energy-saving effect, and also reduce the thermal degradation of the organic amine absorbent and extend the service life of the absorbent. The heat pump evaporator is arranged behind the rich and lean liquid heat exchanger to utilize the waste heat of the lean liquid, reducing the electric power consumption of the heat pump compressor and achieving energy saving. After the regenerated absorbent takes heat from the heat pump evaporator, a part of it directly returns to the middle of the absorption tower without being cooled by the absorbent cooler, which can increase the temperature of the rich liquid to a certain extent, reduce the temperature difference between the hot and cold ends of the heat pump, and improve the coefficient of performance of the heat pump for heating.

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

[0014] Furthermore, the washing tower 21 is a plate tower, a packed tower or a spray tower.

[0015] Furthermore, the absorption tower 22 is at least one of a plate tower, a packed tower and a rotating packed bed.

[0016] Furthermore, the filler of the absorption tower 22 is a surface-modified filler.

[0017] The beneficial effects of adopting the above technical solution are: improving the absorption efficiency of the absorption tower and reducing the height of the tower.

[0018] The present invention also provides a carbon dioxide capture process using the above capture system, comprising the following steps:

[0019] S1: The flue gas containing carbon dioxide is transported to the flue gas reboiler 10 for heat exchange to obtain cooling flue gas. The cooling flue gas and the washing liquid after heat exchange in the heat pump pre-evaporator 11 are respectively introduced into the washing tower 21 from the bottom and the top of the washing tower 21. The washing liquid washes and exchanges heat with the cooling flue gas to obtain washing flue gas.

[0020] S2: The scrubbing flue gas and the absorbent are introduced into the absorbent tower 22 from the bottom and the top of the absorbent tower 22 respectively, and the absorbent adsorbs CO2 in the scrubbing flue gas to obtain an absorbent-rich liquid;

[0021] S3: 50% to 100% of the absorbent rich liquid is transported to the lean-rich liquid heat exchanger 12, and then enters the desorption tower 23 from the top of the desorption tower 23 after preheating, flows downward from the top of the desorption tower 23 and countercurrently contacts and exchanges heat with the desorption gas phase from the bottom of the desorption tower 23 to desorb CO2, and the absorbent rich liquid finally flows into the bottom of the desorption tower 23, and is transported to the heat pump condenser 14 by the first forced circulation pump 76, and returns to the bottom of the desorption tower 23 for gas-liquid separation after heat exchange with the gaseous high-temperature and high-pressure heat pump medium in the heat pump condenser 14, to obtain the desorption gas phase and the desorption gas phase. Liquid phase; the desorbed liquid phase enters the mixing tank 36 for stirring to obtain desorbed CO2 and regenerated absorbent, the desorbed CO2 returns to the bottom of the desorber 23 through the upper pipeline of the mixing tank 36, and mixes with the desorbed gas at the bottom of the desorber 23 to obtain a mixed desorbed gas, which flows to the top of the desorber 23; the regenerated absorbent is transported from the bottom of the mixing tank 36 to the lean-rich liquid heat exchanger 12 through the lean liquid delivery pump 75 to preheat the rich liquid; the remaining absorbent rich liquid is mixed with the regenerated absorbent from the lean-rich liquid heat exchanger 12 and enters the heat pump evaporator 15 to recover heat;

[0022] Alternatively, the lean absorbent solution is transported to the phase separator 32 for phase separation to obtain a CO2-lean phase and a CO2-rich phase; 50% to 100% of the CO2-rich phase is transported to the lean-rich solution heat exchanger 12, preheated, and then enters the desorption tower 23 from the top of the desorption tower 23. It flows downward from the top of the desorption tower 23 and countercurrently contacts and exchanges heat with the desorbed gas phase from the bottom of the desorption tower 23 to desorb CO2. The CO2-rich phase finally flows into the bottom of the desorption tower 23 and is transported to the heat pump condenser 14 by the first forced circulation pump 76. After exchanging heat with the gaseous high-temperature and high-pressure heat pump medium in the heat pump condenser 14, it returns to the bottom of the desorption tower 23 for gas-liquid separation to obtain a desorbed gas phase and a desorbed liquid phase; the desorbed liquid phase enters the mixing tank 36 for stirring to obtain desorbed CO2 and regenerated absorbent. The desorbed CO2 returns to the bottom of the desorption tower 23 through the upper pipeline of the mixing tank 36 and is mixed with the desorbed gas phase at the bottom of the desorption tower 23 to obtain a mixed desorbed gas. The mixed desorbed gas flows towards the top of the desorption tower 23; the regenerated absorbent is transported from the bottom of the mixing tank 36 to the lean-rich solution heat exchanger 12 by the lean solution transfer pump 75 to preheat the rich solution; the remaining CO2-rich phase is mixed with the regenerated absorbent from the lean-rich solution heat exchanger 12 and then mixed with the CO2-lean phase to enter the heat pump evaporator 15 to recover waste heat;

[0023] S4: After the regenerated absorbent recovers waste heat through the heat pump evaporator 15, a part of it directly returns to the middle absorbent return port of the absorption tower 22, and the remaining part is combined with the fresh absorbent supply pipeline, enters the absorbent cooler 16, and then returns to the top absorbent return port of the absorption tower 22;

[0024] S5: The mixed desorbed gas enters the desorbed gas cooler 17 for cooling. The condensed water generated by the cooling enters the first condensed water collection tank 34. The non-condensable gas enters the vacuum pump 81. The tail gas of the vacuum pump 81 enters the enrichment gas condenser 18 for cooling. The condensed water generated by the cooling enters the second condensed water collection tank 35 and is mixed with the condensed water in the first condensed water collection tank 34 and then transported to the condenser 16 by the condensed water transfer pump 77. The trapped CO2 is obtained at the outlet of the enrichment gas condenser 18.

[0025] Based on the above technical solutions, the present invention can be further improved as follows:

[0026] Further, the volume concentration of CO2 in the flue gas containing carbon dioxide is higher than 1%.

[0027] Further, the washing liquid is a Ca(OH)2 solution or a NaOH solution, and the pH value of the solution is 8 to 10.

[0028] Further, the absorbent is a homogeneous absorbent or a phase-changing absorbent.

[0029] Further, the homogeneous absorbent is ethanolamine.

[0030] Further, the gaseous high-temperature and high-pressure heat pump medium is pentafluoropropane; after the gaseous high-temperature and high-pressure heat pump medium exchanges heat with the rich absorbent liquid, it is condensed into a liquid state, partially vaporized after passing through the throttle valve 61, and enters the heat pump pre-evaporator 11 in the form of a gas-liquid mixture to absorb the heat of the washing liquid, then enters the heat pump evaporator 15 to recover the waste heat of the absorbent, continues to vaporize, and then enters the gas-liquid separation tank 33 for gas-liquid separation. The gas phase enters the heat pump compressor 51 to be pressurized and heated, and then enters the heat pump condenser 14 to heat the desorbed liquid.

[0031] The present invention has the following beneficial effects:

[0032] 1. Using the flue gas to directly supply heat to the reboiler of the desorption tower, reducing the flue gas temperature to 80°C - 90°C, while reducing the flue gas temperature, reducing the external energy demand during the regeneration process of the rich absorbent liquid in the desorption tower.

[0033] 2. Using the flue gas to directly contact and exchange heat with the washing liquid in the washing tower to improve the heat exchange efficiency during the flue gas cooling process, heating the washing liquid to 45°C - 80°C, serving as the heat source of the heat pump pre-evaporator, supplying the heat of the flue gas absorbed by the washing tower to the heat pump, changing the heat exchange mode of the flue gas heat from gas-liquid heat exchange to liquid-liquid heat exchange, improving the heat exchange efficiency of the heat pump pre-evaporator, raising the cold end temperature of the heat pump pre-evaporator to 40°C - 55°C, improving the coefficient of performance of the heat pump for heating, and reducing energy consumption.

[0034] 3. The molar ratio of the total amount of organic amine in the circulating absorbent to the captured CO2 is 5 - 20:1. A large amount of absorbent is used at the top of the absorption tower for absorption at a relatively low temperature of 35°C - 40°C, which can significantly reduce the temperature of the absorption tail gas at the top of the absorption tower, reduce the water vapor content, and reduce the heat loss of absorption in the absorption tower.

[0035] 4. Using 0 - 50% of the rich liquid to directly take heat through the heat pump and then enter the absorption tower to absorb CO2 again can further increase the CO2 loading in the absorbent.

[0036] 5. After the lean liquid takes heat from the heat pump evaporator, 10% - 90% of the lean liquid directly returns to the middle of the absorption tower without being cooled by the absorbent cooler, which can increase the temperature of the rich liquid to a certain extent, thereby reducing the temperature difference between the hot and cold ends of the heat pump and improving the coefficient of performance of the heat pump for heating.

[0037] 6. The desorption tower is depressurized and desorbed at an operating pressure of 20 kPa (absolute pressure) - 80 kPa (absolute pressure), which can reduce the CO2 partial pressure in the desorption tower, lower the desorption temperature of the reboiler, reduce the temperature difference between the hot and cold ends of the heat pump, improve the coefficient of performance of the heat pump for heating, enhance the energy-saving effect, and also reduce the thermal degradation of the organic amine absorbent and extend the service life of the absorbent.

[0038] 7. The heat pump evaporator is arranged after the rich-lean liquid heat exchanger to utilize the waste heat of the lean liquid, which can reduce the power consumption of the heat pump compressor and achieve energy saving. Description of the Drawings

[0039] Figure 1 Structural schematic diagram of Embodiment 1 of the carbon dioxide capture system of the present invention;

[0040] Figure 2 Structural schematic diagram of Application Example 1 of the carbon dioxide capture system of the present invention;

[0041] Among them, 10, flue gas reboiler; 11, heat pump pre-evaporator; 12, rich and lean liquid heat exchanger; 13, heater; 14, heat pump condenser; 15, heat pump evaporator; 16, absorbent cooler; 17, desorbed gas cooler; 18, enriched gas condenser; 21, scrubbing tower; 22, absorption tower; 23, desorption tower; 31, scrubbing liquid circulation tank; 32, phase separation tank; 33, heat pump medium gas-liquid separation tank; 34, first condensate collection tank; 35, second condensate collection tank; 36, mixing 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; 51, heat pump compressor; 61, throttle valve; 70, second forced circulation pump; 71, scrubbing liquid circulation pump; 72, rich liquid transfer pump; 73, lean phase transfer pump; 74, rich phase transfer pump; 75, lean liquid transfer pump; 76, first forced circulation pump; 77, condensate transfer pump; 81, vacuum pump; 91, blower. Detailed implementation manners

[0042] The principles and features of the present invention will be described below in conjunction with the accompanying drawings. The examples given are only used to explain the present invention and are not intended to limit the scope of the present invention.

[0043] Embodiment 1:

[0044] A low-energy-consumption heat pump-assisted carbon dioxide capture system, as Figure 1 shown, the system includes a flue gas pretreatment system, a carbon dioxide absorption system, a carbon dioxide desorption system, and a heat pump system.

[0045] The flue gas pretreatment system includes a flue gas reboiler 10, a scrubbing tower 21, a scrubbing liquid circulation tank 31 and a scrubbing liquid circulation pump 71. The high-temperature flue gas is connected to the hot fluid inlet of the flue gas reboiler 10, and the hot fluid outlet of the flue gas reboiler 10 is connected to the bottom gas inlet of the scrubbing tower 21; fresh scrubbing liquid is connected to the top scrubbing liquid replenishment port of the scrubbing liquid circulation tank 31, and the bottom scrubbing liquid extraction port of the scrubbing liquid circulation tank 31 is connected to the liquid inlet of the scrubbing liquid circulation pump 71; the outlet of the scrubbing liquid circulation pump 71 is connected to the hot fluid inlet of the heat pump pre-evaporator 11; the hot fluid outlet of the heat pump pre-evaporator 11 is connected to the top scrubbing liquid inlet of the scrubbing tower 21, and at the same time, the hot fluid outlet branch pipeline of the heat pump pre-evaporator 11 is the scrubbing liquid sewage pipeline; the bottom scrubbing liquid outlet of the scrubbing tower 21 is connected to the scrubbing liquid return port of the scrubbing liquid circulation tank 31 to recycle the scrubbing liquid. The scrubbing tower 21 can be a plate tower, a packed tower, or an empty tower spray. The flue gas pretreatment system is used to remove SO x and dust from the flue gas, and at the same time cool the flue gas, which is beneficial to improving the rich liquid CO2 load of the carbon dioxide absorption system.

[0046] The carbon dioxide absorption system is an absorption tower 22, which can be a plate tower, a packed tower, a rotating packed bed with better mass transfer enhancement effect connected in series and parallel with each other, or a combination between a tower device and a rotating packed bed. The packing of the absorption tower 22 can be ordinary commercial packing or surface-modified packing. To improve the efficiency of the absorption tower, the packing is surface-treated so that the absorbent presents 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 gas outlet at the top of the scrubbing tower 21 is connected to the bottom flue gas inlet of the absorption tower 22; the absorbent inlet in the middle and upper part of the absorption tower 22 is connected to the hot fluid outlet of the heat pump evaporator 15; the absorbent inlet at the top of the absorption tower 22 is connected to the hot fluid outlet of the cooler 16; a purified gas outlet is provided at the top of the absorption tower 22; the rich liquid outlet at the bottom of the absorption tower 22 is connected to the liquid inlet of the rich liquid transfer pump 72.

[0047] The carbon dioxide desorption system includes a rich liquid transfer pump 72, a phase separation tank 32, a lean phase transfer pump 73, a rich phase transfer pump 74, a rich and lean liquid heat exchanger 12, a lean liquid transfer pump 75, a desorption tower 23, a second forced circulation pump 70, a first forced circulation pump 76, a mixing tank 36, a desorbed gas cooler 17, a vacuum pump 81, an enriched gas condenser 18, a first condensate collection tank 34, a second condensate collection tank 35, and a condensate transfer pump 77. The outlet pipeline of the rich liquid transfer pump 72 is divided into two branches. One branch is connected to the phase separation tank 32 through a first valve 41, and the other branch is merged with the outlet pipeline of an eighth valve 48 through a fifth valve 45; the heavy phase outlet pipeline of the phase separation tank 32 is divided into two branches, which are respectively connected to the inlets of a sixth valve 46 and a fourth valve 44. The light phase outlet pipeline of the phase separation tank 32 is divided into two branches, which are respectively connected to the inlets of a second valve 42 and a third valve 43; the outlet pipelines of the second valve 42 and the sixth valve 46 are merged and then connected to the inlet pipeline of the rich phase transfer pump 74. The outlet pipeline of the rich phase transfer pump 74 is connected to the eighth valve 48; the outlet pipelines of the third valve 43 and the fourth valve 44 are merged and then connected to the inlet pipeline of the lean phase transfer pump 73. The outlet pipeline of the lean phase transfer pump 73 is connected to a seventh valve 47, and the seventh valve 47 is connected to the hot fluid inlet of a heat pump evaporator 15; the outlet pipelines of the fifth valve 45 and the eighth valve 48 are merged and then divided into two branches. One branch is connected to the cold fluid inlet of the rich and lean liquid heat exchanger 12, and the other branch is connected to the hot fluid inlet of the heat pump evaporator 15; the cold fluid outlet pipeline of the rich and lean liquid heat exchanger 12 is connected to the rich liquid inlet at the top of the desorption tower 23; one liquid outlet pipeline at the bottom of the desorption tower 23 is connected to the inlet of the second forced circulation pump 70; the outlet of the second forced circulation pump 70 is connected to the cold fluid inlet of a flue gas reboiler 10; the cold fluid outlet pipeline of the flue gas reboiler 10 is merged with the outlet pipeline of a heat pump condenser 14 and then enters the gas-liquid mixture inlet pipeline at the bottom of the desorption tower 23; another liquid pipeline at the bottom of the desorption tower 23 is connected to the inlet of the first forced circulation pump 76. The outlet of the first forced circulation pump 76 is connected to the cold fluid inlet of the heat pump condenser 14; another liquid pipeline at the bottom of the desorption tower 23 is communicated with a mixing tank 36 with stirring. The gas pipeline at the top of the mixing tank 36 is communicated with the gas inlet above the liquid level at the bottom of the desorption tower 23; the mixing tank 36 is equipped with a heater 13, and the heater 13 can adopt electric heating or other heating methods; the liquid pipeline at the bottom of the mixing tank 36 is connected to the inlet of the lean liquid transfer pump 75. The outlet pipeline of the lean liquid transfer pump 75 is connected to the hot fluid inlet of the rich and lean liquid heat exchanger 12; the hot fluid outlet pipeline of the rich and lean liquid heat exchanger 12 is merged with one outlet pipeline of the eighth valve 48 and then connected to the hot fluid inlet of the heat pump evaporator 15; the outlet pipeline of the heat pump evaporator 15 is divided into two branches. One branch is connected to the absorbent inlet in the upper middle part of an absorption tower 22, and the other branch is merged with a fresh MEA supply pipeline and then connected to the hot fluid inlet of an absorbent cooler 16;The gas pipeline at the top of the desorption tower 23 is connected to the desorbed gas cooler 17. The condensate pipeline of the desorbed gas cooler 17 is connected to the first condensate collection tank 34. The non-condensable gas pipeline of the desorbed gas cooler 17 is connected to the inlet of the vacuum pump 81. The outlet of the vacuum pump 81 is connected to the inlet of the enriched gas condenser 18. The condensate outlet of the enriched gas condenser 18 is connected to the second condensate collection tank 35. The outlet of the enriched gas condenser 18 is the trapped CO2 product. The liquid outlet pipelines of the first condensate collection tank 34 and the second condensate collection tank 35 are connected to the inlet pipeline of the condensate transfer pump 77. The outlet pipeline of the condensate transfer pump 77 is divided into two branches. One is the sewage pipeline, and the other is connected to the cold fluid inlet of the absorbent cooler 16.

[0048] The heat pump system includes a heat pump pre-evaporator 11, a heat pump evaporator 15, a heat pump medium gas-liquid separation tank 33, a heat pump compressor 51, a heat pump condenser 14, and a throttle valve 61. The outlet pipeline of the throttle valve 61 is connected to the cold fluid inlet of the heat pump pre-evaporator 11. The cold fluid outlet pipeline of the heat pump pre-evaporator 11 is connected to the cold fluid inlet of the heat pump evaporator 15. The cold fluid outlet of the heat pump evaporator 15 is connected to the inlet of the gas-liquid mixture in the middle of the heat pump medium gas-liquid separation tank 33. The gas pipeline at the top of the heat pump medium gas-liquid separation tank 33 is connected to the intake port of the heat pump compressor 51. The outlet of the heat pump compressor 51 is connected to the hot fluid inlet of the heat pump condenser 14. The hot fluid outlet of the heat pump condenser 14 is connected to the inlet of the throttle valve 61.

[0049] Example 2

[0050] A process for low-energy consumption carbon dioxide capture, using the low-energy consumption heat pump assisted carbon dioxide capture system in Example 1, includes the following steps:

[0051] S1: High-temperature flue gas above 100°C enters the hot fluid inlet of the flue gas reboiler 10, and part of the rich liquid is regenerated using the waste heat of the high-temperature flue gas. The temperature of the flue gas at the hot fluid outlet of the flue gas reboiler 10 drops to 85°C - 90°C, and then it enters the bottom gas inlet of the scrubbing tower 21. If the temperature of the flue gas is relatively low and its heat cannot be directly used for desorbing CO2, the flue gas reboiler 10 is cancelled, and the flue gas directly enters the bottom gas inlet of the scrubbing tower 21.

[0052] Fresh alkaline washing liquid is added from the top washing liquid replenishment port of the washing liquid circulation tank 31. The washing liquid uses a Ca(OH)2 solution or a NaOH solution, and the pH value of the solution is controlled between 8 and 10. The washing liquid is transported from the bottom washing liquid extraction port of the washing liquid circulation tank 31 through the washing liquid circulation pump 71 and enters the hot fluid inlet of the heat pump pre-evaporator 11. After the heat is recovered by the heat pump pre-evaporator 11, the washing liquid at 40°C to 60°C enters the top washing liquid inlet of the washing tower 21 from the hot fluid outlet of the heat pump pre-evaporator 11. At the same time, the branch pipeline of the hot fluid outlet of the heat pump pre-evaporator 11 is the washing liquid sewage pipeline, and part of the washing liquid is discharged to prevent the accumulation of sulfates, sulfites and dust in the flue gas pretreatment system. The alkaline washing liquid can remove the dust in the flue gas when it is in full contact with the flue gas in the washing tower 21. The SO x in the flue gas reacts with the alkali to form salts and is removed from the flue gas. At the same time, the direct contact between the alkali liquid and the flue gas can quickly exchange heat. The washing liquid is heated by the flue gas to 50°C to 80°C and returns to the washing liquid circulation tank 31 from the bottom washing liquid outlet of the washing tower 21 for recycling, while the temperature of the flue gas is reduced to 35°C to 50°C.

[0053] S2: The flue gas enters the absorption tower 22 from the top gas outlet of the washing tower 21 and flows upward from the bottom of the absorption tower 22, and is in full contact with the absorbent at a temperature of 40°C to 55°C from the hot fluid outlet of the heat pump evaporator 15 in the upper middle part of the absorption tower 22. Part of the CO2 in the flue gas can be absorbed. After the absorbent is regenerated and takes heat from the heat pump evaporator 15, a part of it directly returns to the middle part of the absorption tower without being cooled by the absorbent cooler 16, which can reduce the heat loss of the system, can increase the rich liquid temperature to a certain extent, reduce the temperature difference between the hot and cold ends of the heat pump, and improve the coefficient of performance of the heat pump. The flue gas continues to flow to the top of the absorption tower and is in full contact with the absorbent at a temperature of 35°C to 40°C from the hot fluid outlet of the cooler 16 at the top of the absorption tower 22, further absorbing the CO2 in the flue gas. The low-temperature absorption at 35°C to 40°C can significantly reduce the temperature of the absorption tail gas at the top of the absorption tower 22, reduce the water vapor content, and reduce the absorption heat loss of the absorption tower. The mass flow rate of the absorbent returned to the middle part of the absorption tower 22 accounts for 10% to 90% of the mass flow rate of the circulating absorbent, and the mass flow rate of the absorbent returned to the top of the absorption tower 22 accounts for 90% to 10% of the mass flow rate of the circulating absorbent. The molar ratio of the total amount of organic amine in the circulating absorbent to the trapped CO2 is 5 mol to 20 mol amine / mol CO2. The exhaust temperature of the purified gas at the top of the absorption tower 22 is 35°C to 50°C, and the temperature of the absorbent rich liquid at the bottom of the absorption tower 22 is 35°C to 65°C.

[0054] The absorbent can be a homogeneous absorbent or a phase change absorbent.

[0055] If the absorbent is a homogeneous absorbent, there is no need to use the phase separation tank 32. Close 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 at the inlet and outlet of 32, and open the fifth valve 45. The rich liquid transfer pump 72 transports 50% - 100% of the absorbent rich liquid through the pipeline where the fifth valve 45 is located, preheats it in the rich and lean liquid heat exchanger 12, and then enters the top rich liquid inlet of the desorption tower 23. 0 - 50% of the absorbent rich liquid is transported to the heat pump evaporator 15 to recover heat.

[0056] If the absorbent is a phase change absorbent, then close the fifth valve 45 and open the seventh valve 47 and the eighth valve 48; if the density of the CO2 rich phase is greater than that of the lean phase, then close the second valve 42 and the fourth valve 44 and open the third valve 43 and the sixth valve 46; if the density of the CO2 rich phase is less than that of the lean phase, then open the second valve 42 and the fourth valve 44 and close the third valve 43 and the sixth valve 46; the CO2 lean phase is transported to the heat pump evaporator 15 by the lean phase transfer pump 73 through the seventh valve 47 to recover waste heat, and 50% - 100% of the CO2 rich phase is transported by the rich phase transfer pump 74 to the rich and lean liquid heat exchanger 12 for preheating and then enters the top liquid phase inlet of the desorption tower 23, and 0 - 50% of the CO2 rich phase is transported to the heat pump evaporator 15 to recover heat.

[0057] S3: Part of the liquid at the bottom of the desorption tower 23 is transported by the second forced circulation pump 70 to the cold fluid inlet of the flue gas reboiler 10, and the heat of the high-temperature flue gas is used to desorb CO2 (if the flue gas temperature is too low and the heat available for directly desorbing CO2 is too little, then cancel the flue gas reboiler 10). This part of the liquid is heated to 65°C - 100°C in the flue gas reboiler 10 and then returns to the bottom of the desorption tower;

[0058] The throttle valve 61 throttles, depressurizes, and cools the liquid heat pump medium from the heat pump condenser 14 and partially vaporizes it. This heat pump medium is pentafluoropropane. Control the outlet pressure of the throttle valve 61 to reduce the temperature of the heat pump medium to 2°C - 10°C lower than the lower temperature of the heat fluid outlet of the heat pump pre-evaporator 11 and the heat fluid outlet of the heat pump evaporator 15 to ensure sufficient heat transfer driving force; the gas-liquid mixture of the heat pump medium throttled by the throttle valve 61 enters the heat pump pre-evaporator 11 under the action of the pressure difference, absorbs the heat of the washing liquid and partially vaporizes, and then enters the heat pump evaporator 15 to recover the waste heat of the absorbent; after the heat pump medium vaporizes, it enters the gas-liquid separation tank 33 from the cold fluid outlet of the heat pump evaporator 15 for gas-liquid separation, and the gas phase enters the heat pump compressor 51 to be pressurized and heated to 80°C - 140°C; the high-temperature and high-pressure heat pump medium steam at the outlet of the heat pump compressor 51 enters the heat pump condenser 14 to condense and release heat to heat the absorbent that needs to be regenerated;

[0059] Part of the liquid at the bottom of the desorption tower 23 is transported by the first forced circulation pump 76 to the cold fluid inlet of the heat pump condenser 14, and after being heated to 65°C to 100°C by absorbing the heat recovered by the heat pump, it returns to the bottom of the desorption tower; the stirring of the mixing tank 36 can promote the overflow of the desorbed CO2 from the liquid phase, which is beneficial to reducing the desorption temperature. The mixing tank 36 and the bottom of the desorption tower 23 form a communicating vessel and can automatically maintain the same liquid level; the heater 13 is used to provide sufficient heat for the desorption tower to regenerate the absorbent during the start-up stage of the device, and can also supplement heat during the stable operation stage.

[0060] The regenerated absorbent is transported from the bottom of the desorption tower 23 to the lean-rich liquid heat exchanger 12 by the lean liquid transfer pump 75 to preheat the rich liquid (for phase change absorbents, it is to preheat the rich phase); the lean-rich liquid heat exchanger 12 maintains the temperature difference between the inlet and outlet of the hot and cold fluids at 2°C to 10°C to recover as much waste heat of the lean liquid as possible; after the lean liquid recovers heat through the lean-rich liquid heat exchanger 12, it enters the hot fluid inlet of the heat pump evaporator 15 to further recover heat, and its temperature is reduced to 40°C to 60°C; the outlet pipeline of the heat pump evaporator 15 is divided into two branches. One branch is connected to the absorbent return port in the middle of the absorption tower 22, and the other branch is merged with the fresh MEA supply pipeline and then enters the absorbent cooler 16 to be cooled to 35°C to 40°C.

[0061] S4: The desorption tower 23 operates under negative pressure, and the operating pressure is 20 kPa (absolute pressure) to 80 kPa (absolute pressure), which can effectively reduce the desorption temperature; to reduce the operating load of the vacuum pump 81, the desorbed gas at the top of the desorption tower 23 enters the desorbed gas cooler 17 and is cooled to 15°C to 40°C. The condensed water of the desorbed gas cooler 17 enters the first condensate collection tank 34; the non-condensable gas of the desorbed gas cooler 17 enters the inlet of the vacuum pump 81, and the tail gas of the vacuum pump 81 enters the enriched gas condenser 18 and is condensed to 15°C to 40°C to reduce the moisture in the enriched CO2; the condensed water of the enriched gas condenser 18 enters the second condensate collection tank 35, and the outlet of the enriched gas condenser 18 is the captured CO2 product.

[0062] It should be noted that the order of the above steps is not limited, as long as the application of the present invention can be realized.

[0063] Application Example 1

[0064] The temperature of the flue gas at the first-stage reformer of a new synthesis system in a natural gas chemical plant is 150°C, and the pressure is 0.5 kPa (gauge pressure). The composition is shown in Table 1 below. Based on this flue gas source, the process flow of a heat pump-assisted carbon dioxide capture system with a capture capacity of 1000 tons / year is as Figure 2 shown.

[0065] Table 1 Composition of the flue gas at the outlet of the first-stage reformer of a new synthesis system in a natural gas chemical project

[0066]

[0067] The high-temperature flue gas at 150°C enters the hot fluid inlet of the flue gas reboiler 10 to regenerate part of the rich liquid by utilizing the waste heat of the high-temperature flue gas. The temperature of the flue gas at the hot fluid outlet of the flue gas reboiler 10 drops to 76.9°C and is then transported by the blower 90 into the bottom gas inlet of the scrubber 21; Fresh alkaline scrubbing liquid is added from the top scrubbing liquid replenishment port of the scrubbing liquid circulation tank 31. The scrubbing liquid uses a Ca(OH)2 solution or a NaOH solution, and the pH value of the solution is 9; The scrubbing liquid is transported from the bottom scrubbing liquid extraction port of the scrubbing liquid circulation tank 31 to the hot fluid inlet of the heat pump pre-evaporator 11 by the scrubbing liquid circulation pump 71. After recovering heat through the heat pump pre-evaporator 11, the scrubbing liquid at 46.1°C enters the top scrubbing liquid inlet of the scrubber 21 from the hot fluid outlet of the heat pump pre-evaporator 11. At the same time, the branch pipeline at the hot fluid outlet of the heat pump pre-evaporator 11 is the scrubbing liquid sewage pipeline to discharge part of the scrubbing liquid to prevent the accumulation of sulfates, sulfites, and dust in the flue gas pretreatment system; The alkaline scrubbing liquid fully contacts the flue gas in the scrubber 21 to remove the dust in the flue gas. The SO x in the flue gas reacts with the alkali to form salts and is removed from the flue gas. At the same time, the direct contact between the alkali liquid and the flue gas can quickly exchange heat; The scrubbing liquid is heated to 59.6°C by the flue gas and returns to the scrubbing liquid circulation tank 31 from the bottom scrubbing liquid outlet of the scrubber 21 for recycling. The temperature of the flue gas drops to 51.8°C and enters the absorber 22 from the top gas outlet of the scrubber 21.

[0068] The absorber 22 uses a packed absorber. The flue gas flows upward from the bottom of the absorber 22 and fully contacts the absorbent at 46.1°C from the hot fluid outlet of the heat pump evaporator 15 in the upper-middle part of the absorber 22, and part of the CO2 in the flue gas can be absorbed; The flue gas continues to flow upward to the top of the absorber and fully contacts the absorbent at 40°C from the hot fluid outlet of the absorbent cooler 16 at the top of the absorber 22 to further absorb the CO2 in the flue gas; The mass flow rate of the absorbent returned from the middle of the absorber 22 accounts for 10% of the mass flow rate of the circulating absorbent, and the mass flow rate of the absorbent returned from the top of the absorber 22 accounts for 90% of the mass flow rate of the circulating absorbent.

[0069] In this example, an industrial MEA absorbent is used. The molar ratio of the total amount of organic amine in the circulating absorbent to the captured CO2 is 14.24 mol amine / mol CO2; The exhaust temperature of the purified gas at the top of the absorber 22 is 41.9°C, and the temperature of the rich absorbent at the bottom of the absorber 22 is 48.9°C.

[0070] 100% of the rich absorbent solution is transported to the rich-lean solution heat exchanger 12 and preheated to 67.1 °C before entering the top rich liquid inlet of the desorption tower 23; a part of the liquid at the bottom of the desorption tower 23 is transported to the cold fluid inlet of the flue gas reboiler 10 by the second forced circulation pump 70, and CO2 is desorbed by using the heat of the high-temperature flue gas. This part of the liquid is heated to 71.8 °C in the flue gas reboiler 10 and then returned to the bottom of the desorption tower; a part of the liquid at the bottom of the desorption tower 23 is transported to the cold fluid inlet of the heat pump condenser 14 by the first forced circulation pump 76, and is heated to 71.8 °C after absorbing the heat recovered by the heat pump and then returned to the bottom of the desorption tower 23; the liquid pipeline at the bottom of the desorption tower 23 is connected to the mixing tank 36 with stirring, and the gas pipeline at the top of the mixing tank 36 is connected to the gas inlet above the liquid level of the bottom of the desorption tower 23; the stirring of the mixing tank 36 can promote the overflow of the desorbed CO2 from the liquid phase, which is beneficial to reducing the desorption temperature; the mixing tank 36 is equipped with a heater 13, which is used to provide sufficient heat for the desorption tower to regenerate the absorbent during the start-up stage of the device.

[0071] The regenerated absorbent is transported from the bottom of the desorption tower 23 to the rich-lean solution heat exchanger 12 by the lean solution transfer pump 75 to preheat the rich solution. The rich-lean solution heat exchanger 12 maintains a temperature difference of 5 °C between the inlet and outlet of the cold and hot fluids; the lean solution enters the hot fluid inlet of the heat pump evaporator 15 after recovering heat in the rich-lean solution heat exchanger 12 to further recover heat and reduce its temperature to 46.1 °C; the outlet pipeline of the heat pump evaporator 15 is divided into two branches. One branch is connected to the absorbent return port in the middle of the absorption tower 22, and the other branch is merged with the fresh MEA supply pipeline and then enters the absorbent cooler 16 to be cooled to 40 °C.

[0072] The desorption tower 23 operates under negative pressure, and the operating pressure is 40 kPa (absolute pressure), which can effectively reduce the desorption temperature; to reduce the operating load of the vacuum pump 81, the desorbed gas at the top of the desorption tower 23 enters the desorbed gas cooler 17 and is cooled to 30 °C. The condensed water of the desorbed gas cooler 17 enters the first condensate collection tank 34, and the non-condensable gas of the desorbed gas cooler 17 enters the inlet of the vacuum pump 81; the tail gas of the vacuum pump 81 enters the enriched gas condenser 18 and is condensed to 30 °C to reduce the moisture in the enriched CO2; the condensed water of the enriched gas condenser 18 enters the second condensate collection tank 35, and the outlet of the enriched gas condenser 18 is the captured CO2 product with a purity of 93.7% and a CO2 capture rate of 90%; the liquid outlet pipelines of the first condensate collection tank 34 and the second condensate collection tank 35 are connected to the inlet pipeline of the condensate transfer pump 77. The outlet pipeline of the condensate transfer pump 77 is divided into two branches, one is the sewage pipeline, and the other is connected to the cold fluid inlet of the absorbent cooler.

[0073] The heat pump system in this application example consists of a heat pump pre-evaporator 11, a heat pump evaporator 15, a heat pump medium gas-liquid separation tank 33, a heat pump compressor 51, a heat pump condenser 14, and a throttle valve 61. The throttle valve 61 throttles, reduces the pressure, and cools the liquid heat pump medium from the heat pump condenser 14 to partially vaporize it. The heat pump medium is pentafluoropropane. The outlet pressure of the throttle valve 61 is controlled so that the temperature of the heat pump medium is 5°C lower than the lower temperature of the hot fluid outlet temperature of the heat pump pre-evaporator 11 and the hot fluid outlet temperature of the heat pump evaporator 15 to ensure sufficient heat transfer driving force. The gas-liquid mixture of the heat pump medium throttled by the throttle valve 61 enters the heat pump pre-evaporator 11 under the action of the pressure difference to absorb the heat of the washing liquid and partially vaporize, and then enters the heat pump evaporator 15 to recover the waste heat of the absorbent. After vaporization, the heat pump medium enters the gas-liquid separation tank 33 from the cold fluid outlet of the heat pump evaporator 15 for gas-liquid separation. The gas phase enters the heat pump compressor 51 to be pressurized and heated to 83.1°C. The high-temperature and high-pressure heat pump medium steam at the outlet of the heat pump compressor 51 enters the heat pump condenser 14 to condense and release heat to heat the absorbent that needs to be regenerated.

[0074] The total theoretical energy consumption for the absorption and regeneration process of CO2 capture in this application example is 2.4 GJ / t CO2, which is 33.3% lower than the energy consumption of 3.6 GJ / t CO2 in the conventional MEA capture process.

[0075] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A low-energy consumption heat pump-assisted carbon dioxide capture system, characterized in that, It includes flue gas pretreatment system, carbon dioxide absorption system, carbon dioxide desorption system and heat pump system; The heat pump system comprises a heat pump pre-evaporator (11), a heat pump evaporator (15), a heat pump medium gas-liquid separation tank (33), a heat pump compressor (51), a heat pump condenser (14) and a throttle valve (61); The flue gas pretreatment system comprises a flue gas reboiler (10), a scrubbing tower (21), a scrubbing liquid circulation tank (31) and a scrubbing liquid circulation pump (71); the hot fluid outlet of the flue gas reboiler (10) is connected to the gas inlet at the bottom of the scrubbing tower (21); the scrubbing liquid outlet at the bottom of the scrubbing tower (21) is connected to the scrubbing liquid return port of the scrubbing liquid circulation tank (31); the scrubbing liquid outlet at the bottom of the scrubbing liquid circulation tank (31) is connected to the liquid inlet of the scrubbing liquid circulation pump (71); the outlet of the scrubbing liquid circulation pump (71) is connected to the hot fluid inlet of the heat pump pre-evaporator (11); the hot fluid outlet of the heat pump pre-evaporator (11) is connected to the scrubbing liquid inlet at the top of the scrubbing tower (21); The carbon dioxide absorption system comprises an absorption tower (22); the gas outlet at the top of the scrubbing tower (21) is connected to the flue gas inlet at the bottom of the absorption tower (22); the absorbent inlet at the middle and upper part of the absorption tower (22) is connected to the hot fluid outlet of the heat pump evaporator (15); the absorbent inlet at the top of the absorption tower (22) is connected to the hot fluid outlet of the cooler (16); the top of the absorption tower (22) is provided with a purified gas outlet; the rich liquid outlet at the bottom of the absorption tower (22) is connected to the liquid inlet of a rich liquid delivery pump (72); the absorption tower (22) is at least one of a plate tower, a packed tower and a rotating packed bed; the filler of the absorption tower (22) is a surface modified filler; The carbon dioxide desorption system includes a rich liquid transfer pump (72), a phase separation tank (32), a lean phase transfer pump (73), a rich phase transfer pump (74), a rich and lean liquid heat exchanger (12), a lean liquid transfer pump (75), a desorption tower (23), a first forced circulation pump (76), a second forced circulation pump (70), a mixing tank (36), a desorbed gas cooler (17), a vacuum pump (81), an enriched gas condenser (18), a first condensate collection tank (34), a second condensate collection tank (35), and a condensate transfer pump (77); the outlet pipeline of the rich liquid transfer pump (72) is divided into two branches, one branch is connected to the phase separation tank (32), and the other branch is merged with the outlet pipeline of the eighth valve (48) through the fifth valve (45); the heavy phase outlet pipeline of the phase separation tank (32) is divided into two branches, which are respectively connected to the inlets of the sixth valve (46) and the fourth valve (44), and the light phase outlet pipeline of the phase separation tank (32) is divided into two branches, which are respectively connected to the inlets of the second valve (42) and the third valve (43); the outlet pipelines of the second valve (42) and the sixth valve (46) are merged and then connected to the inlet pipeline of the rich phase transfer pump (74), and the outlet pipeline of the rich phase transfer pump (74) is connected to the eighth valve (48); the outlet pipelines of the third valve (43) and the fourth valve (44) are merged and then connected to the inlet pipeline of the lean phase transfer pump (73), the outlet pipeline of the lean phase transfer pump (73) is connected to the seventh valve (47), and the seventh valve (47) is connected to the hot fluid inlet of the heat pump evaporator (15); the outlet pipelines of the fifth valve (45) and the eighth valve (48) are merged and then divided into two branches, one is connected to the cold fluid inlet of the rich and lean liquid heat exchanger (12), and the other is connected to the hot fluid inlet of the heat pump evaporator (15); the cold fluid outlet pipeline of the rich and lean liquid heat exchanger (12) is connected to the rich liquid inlet at the top of the desorption tower (23); the bottom of the desorption tower (23) is divided into three liquid outlet pipelines, one of which is connected to the inlet of the first forced circulation pump (76), the outlet of the first forced circulation pump (76) is connected to the cold fluid inlet of the heat pump condenser (14), and the outlet of the heat pump condenser (14) is connected to the gas-liquid mixture inlet at the bottom of the desorption tower (23); another liquid outlet pipeline at the bottom of the desorption tower (23) is connected to the inlet of the second forced circulation pump (70), the outlet of the second forced circulation pump (70) is connected to the cold fluid inlet of the flue gas reboiler (10), and the cold fluid outlet pipeline of the flue gas reboiler (10) is merged with the cold fluid outlet pipeline of the heat pump condenser (14) and then enters the gas-liquid mixture inlet at the bottom of the desorption tower (23); another liquid pipeline at the bottom of the desorption tower (23) is connected to the mixing tank (36), and the gas phase pipeline at the top of the mixing tank (36) is connected to the gas inlet above the liquid level of the bottom of the desorption tower (23); the mixing tank (36) is provided with a heater (13).The liquid pipeline at the bottom of the mixing tank (36) is connected to the inlet of the lean liquid transfer pump (75), and the outlet pipeline of the lean liquid transfer pump (75) is connected to the hot fluid inlet of the rich / lean liquid heat exchanger (12); the hot fluid outlet pipeline of the rich / lean liquid heat exchanger (12) is merged with one outlet pipeline of the eighth valve (48) and then connected to the hot fluid inlet of the heat pump evaporator (15); the outlet pipeline of the heat pump evaporator (15) is divided into two branches, one branch is connected to the absorbent inlet in the middle and upper part of the absorption tower (22), and the other branch is connected to the hot fluid inlet of the absorbent cooler (16); the gas pipeline at the top of the desorption tower (23) is connected to the desorbed gas cooler (17), the condensate pipeline of the desorbed gas cooler (17) is connected to the first condensate collection tank (34), and the non-condensable gas pipeline of the desorbed gas cooler (17) is connected to the inlet of the vacuum pump (81); the outlet of the vacuum pump (81) is connected to the inlet of the enriched gas condenser (18); the condensate outlet of the enriched gas condenser (18) is connected to the second condensate collection tank (35); the liquid outlet pipelines of the first condensate collection tank (34) and the second condensate collection tank (35) are connected to the inlet pipeline of the condensate transfer pump (77); the outlet pipeline of the condensate transfer pump (77) is divided into two branches, one is the sewage discharge pipeline, and the other is connected to the cold fluid inlet of the absorbent cooler (16). The outlet pipeline of the throttle valve (61) is connected to the cold fluid inlet of the heat pump pre-evaporator (11); the cold fluid outlet pipeline of the heat pump pre-evaporator (11) is connected to the cold fluid inlet of the heat pump evaporator (15); the cold fluid outlet of the heat pump evaporator (15) is connected to the gas-liquid mixture inlet in the middle of the heat pump medium gas-liquid separation tank (33); the gas phase pipeline at the top of the heat pump medium gas-liquid separation tank (33) is connected to the air inlet of the heat pump compressor (51); the outlet of the heat pump compressor (51) is connected to the hot fluid inlet of the heat pump condenser (14); and the hot fluid outlet of the heat pump condenser (14) is connected to the inlet of the throttle valve (61).

2. The low-energy-consumption heat pump-assisted carbon dioxide capture system according to claim 1, characterized in that, The washing tower (21) is a plate tower, a packed tower or a spray tower.

3. A carbon dioxide capture process using the low-energy consumption heat pump-assisted carbon dioxide capture system according to any one of claims 1 to 2, characterized in that, The following steps are involved: S1: conveying the flue gas containing carbon dioxide to the flue gas reboiler (10) for heat exchange to obtain cooling flue gas, the cooling flue gas and the washing liquid after heat exchange in the heat pump pre-evaporator (11) are respectively introduced into the washing tower (21) from the bottom and top of the washing tower (21), and the washing liquid washes and exchanges heat with the cooling flue gas to obtain washed flue gas; S2: introducing the scrubbing flue gas and the absorbent into the absorbent tower (22) from the bottom and the top of the absorbent tower (22) respectively, and the absorbent adsorbs CO2 in the scrubbing flue gas to obtain an absorbent-rich liquid; S3: Deliver 50% - 100% of the absorbent rich solution to the lean-rich solution heat exchanger (12). After preheating, it enters the desorption tower (23) from the top of the desorption tower (23), and flows downward from the top of the desorption tower (23) to countercurrently contact and exchange heat with the desorbed gas phase from the bottom of the desorption tower (23) to desorb CO2. The absorbent rich solution finally flows into the bottom of the desorption tower (23), and is transported by the first forced circulation pump (76) to the heat pump condenser (14). After exchanging heat with the gaseous high-temperature and high-pressure heat pump medium in the heat pump condenser (14), it returns to the bottom of the desorption tower (23) for gas-liquid separation to obtain the desorbed gas phase and the desorbed liquid phase. The desorbed liquid phase enters the mixing tank (36) for stirring to obtain desorbed CO2 and the regenerated absorbent. The desorbed CO2 returns to the bottom of the desorption tower (23) through the upper pipeline of the mixing tank (36) and is mixed with the desorbed gas phase at the bottom of the desorption tower (23) to obtain the mixed desorbed gas, and the mixed desorbed gas flows towards the top of the desorption tower (23). The regenerated absorbent is transported from the bottom of the mixing tank (36) to the lean-rich solution heat exchanger (12) by the lean solution delivery pump (75) to preheat the rich solution. The remaining absorbent rich solution is mixed with the regenerated absorbent from the lean-rich solution heat exchanger (12) and then enters the heat pump evaporator (15) to recover heat; Alternatively, deliver the absorbent rich solution to the phase separation tank (32) for phase separation to obtain the CO2 lean phase and the CO2 rich phase. Deliver 50% - 100% of the CO2 rich phase to the lean-rich solution heat exchanger (12). After preheating, it enters the desorption tower (23) from the top of the desorption tower (23), and flows downward from the top of the desorption tower (23) to countercurrently contact and exchange heat with the desorbed gas phase from the bottom of the desorption tower (23) to desorb CO2. The CO2 rich phase finally flows into the bottom of the desorption tower (23) and is transported by the first forced circulation pump (76) to the heat pump condenser (14). After exchanging heat with the gaseous high-temperature and high-pressure heat pump medium in the heat pump condenser (14), it returns to the bottom of the desorption tower (23) for gas-liquid separation to obtain the desorbed gas phase and the desorbed liquid phase. The desorbed liquid phase enters the mixing tank (36) for stirring to obtain desorbed CO2 and the regenerated absorbent. The desorbed CO2 returns to the bottom of the desorption tower (23) through the upper pipeline of the mixing tank (36) and is mixed with the desorbed gas phase at the bottom of the desorption tower (23) to obtain the mixed desorbed gas, and the mixed desorbed gas flows towards the top of the desorption tower (23). The regenerated absorbent is transported from the bottom of the mixing tank (36) to the lean-rich solution heat exchanger (12) by the lean solution delivery pump (75) to preheat the rich solution. The remaining CO2 rich phase is mixed with the regenerated absorbent from the lean-rich solution heat exchanger (12), and then mixed with the CO2 lean phase and enters the heat pump evaporator (15) to recover the waste heat; S4: After the regenerated absorbent recovers waste heat through the heat pump evaporator (15), a part of it directly returns to the middle absorbent return port of the absorption tower (22), and the remaining part is merged with the fresh absorbent supply pipeline, then enters the absorbent cooler (16) and returns to the top absorbent return port of the absorption tower (22). S5: The mixed desorbed gas enters the desorbed gas cooler (17) for cooling. The condensed water generated by the cooling enters the first condensed water collection tank (34), and the non-condensable gas enters the vacuum pump (81). The tail gas of the vacuum pump (81) enters the enriched gas condenser (18) for cooling. The condensed water generated by the cooling enters the second condensed water collection tank (35). The condensed water in the second condensed water collection tank (35) is mixed with the condensed water in the first condensed water collection tank (34) and then is transported to the absorbent cooler (16) through the condensed water transfer pump (77). The trapped CO2 is obtained at the outlet of the enriched gas condenser (18).

4. The carbon dioxide capture process according to claim 3, wherein The volume concentration of CO2 in the flue gas containing carbon dioxide is higher than 1%.

5. The carbon dioxide capture process according to claim 3, characterized in that, The washing liquid is a Ca(OH)2 solution or a NaOH solution, and the pH value of the solution is 8 - 10.

6. The carbon dioxide capture process according to claim 3, characterized in that, The absorbent is a homogeneous absorbent or a phase-changing absorbent.

7. The carbon dioxide capture process according to claim 6, wherein, The homogeneous absorbent is ethanolamine.

8. The carbon dioxide capture process according to claim 3, wherein The gaseous high-temperature and high-pressure heat pump medium is pentafluoropropane. After the gaseous high-temperature and high-pressure heat pump medium exchanges heat with the rich absorbent liquid, it is condensed into a liquid state. After passing through the throttle valve (61), it is partially vaporized and enters the heat pump pre-evaporator (11) in the form of a gas-liquid mixture to absorb the heat of the washing liquid, then enters the heat pump evaporator (15) to recover the waste heat of the absorbent, continues to vaporize, and then enters the gas-liquid separation tank (33). After gas-liquid separation, the gas phase enters the heat pump compressor (51) to be pressurized and heated, and then enters the heat pump condenser (14) to heat the desorbed liquid.

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