Carbon dioxide trapping system based on liquid-liquid two-phase absorbent

Abstract

The invention discloses a carbon dioxide trapping system based on a liquid-liquid two-phase absorbent. The carbon dioxide trapping system comprises an absorption tower, a phase splitting tank, a primary heat exchanger, a secondary heat exchanger, a barren liquor heat exchanger and a desorption tower, a liquid outlet of the absorption tower is connected with a phase-splitting tank, rich liquid subjected to phase splitting in the phase-splitting tank is preheated through a primary heat exchanger, one part of the preheated rich liquid flows into a secondary heat exchanger, and the other part of the preheated rich liquid flows into a desorption tower; after heat exchange of the second-stage heat exchanger, rich liquor with high-temperature water vapor enters a desorption tower; a hot gaseous product discharged from a gas outlet of the desorption tower exchanges heat with the phase-split barren liquor at a barren liquor heat exchanger, and carbon dioxide is separated out; and hot barren liquor discharged from a liquid outlet of the desorption tower is a heat source of the second-stage heat exchanger and the first-stage heat exchanger. According to the system, the energy consumption of the liquid-liquid two-phase absorbent in the regeneration process is effectively reduced, and meanwhile, the purity of carbon dioxide after desorption is effectively improved.

Description

Technical Field

[0001] The present invention relates to a carbon dioxide capture system based on a liquid-liquid two-phase absorbent. Background Art

[0002] Currently, carbon capture, utilization, and storage (CCUS) technology is considered a key supporting means to achieve the carbon neutrality goal. Among them, the chemical absorption technology based on organic amine absorbents is considered to have great commercial application potential due to its high absorption capacity and carbon capture efficiency. However, one of the main challenges faced by the carbon capture technology using organic amines is the high capture cost, and the energy consumption in the desorption process accounts for the largest proportion. Taking 30wt.% MEA absorbent as an example, its desorption energy consumption is about 3.5 - 4.0 GJ / t of carbon dioxide, accounting for about 70% of the total operating energy consumption, resulting in a carbon capture cost of 350 - 500 yuan per ton of carbon dioxide.

[0003] CN119034456A discloses a multi-energy complementary regeneration heating system and method for chemical carbon dioxide capture, including a pre-washing tower, a circulation device, an absorption tower, a lean liquid circulation device, a phase separator, a lean-rich-lean liquid heat exchanger, a desorption tower, a cooling reflux device, a circulation cooler, a lean liquid cooler, and heating tubes, etc. However, this technology mainly relies on external heat sources and is only applicable to homogeneous absorbents. CN219682132U discloses a desorption tower and system for catalytic desorption of carbon dioxide. Taking 30wt.% MEA absorbent as an example, this process can reduce the desorption temperature from 105 - 120 °C to 75 - 98 °C. However, relying on catalysts to reduce desorption energy consumption is not suitable for large-scale industrial applications, and it does not involve the treatment of carbon dioxide after desorption and the recovery of volatile components of the absorbent. Summary of the Invention

[0004] Object of the Invention: The object of the present invention is to provide a carbon dioxide capture system based on a liquid-liquid two-phase absorbent, which effectively reduces the energy consumption of the liquid-liquid two-phase absorbent during the regeneration process by reducing the supply amount of external heat sources and the dependence on catalysts, and at the same time effectively improves the purity of carbon dioxide after desorption.

[0005] Technical Solution: The carbon dioxide capture system based on a liquid-liquid two-phase absorbent described in the present invention includes an absorption tower, a phase separation tank, a primary heat exchanger, a secondary heat exchanger, a lean liquid heat exchanger, and a desorption tower; the liquid outlet of the absorption tower is connected to the phase separation tank, and the rich liquid after phase separation in the phase separation tank is preheated by the primary heat exchanger. A part of the preheated rich liquid flows into the secondary heat exchanger, and a part flows into the desorption tower; the rich liquid with high-temperature water vapor after heat exchange in the secondary heat exchanger enters the desorption tower; the hot gaseous product discharged from the gas outlet of the desorption tower exchanges heat with the lean liquid after phase separation at the lean liquid heat exchanger to separate carbon dioxide; the hot lean liquid discharged from the liquid outlet of the desorption tower serves as the heat source of the heat exchanger and flows through the secondary heat exchanger and the primary heat exchanger in sequence.

[0006] Among them, the external heat source of the desorption tower is the hot steam generated by the mechanical vapor recompression process.

[0007] Among them, the hot gaseous products include carbon dioxide, water vapor and volatile organic amines.

[0008] Among them, a pre-washing tower is further included. The flue gas enters the pre-washing tower from the inlet of the pre-washing tower and flows upward. Cooling water is sprayed at the top of the pre-washing tower to remove sulfur dioxide in the flue gas and cool the flue gas.

[0009] The flue gas after being washed and cooled by water enters the absorption tower. The flue gas enters from the inlet of the absorption tower and flows upward in the absorption tower. An absorbent is sprayed at the upper end of the absorption tower; the flue gas treated by the absorbent is discharged from the top outlet of the absorption tower, and the absorbent that has absorbed carbon dioxide flows into the bottom of the absorption tower.

[0010] Among them, a packing bed is provided in the absorption tower. The packing bed can increase the gas-liquid contact area and extend the residence time of the absorbent in the tower. The absorbent contacts the flue gas in the absorption tower, and the absorbent reacts with carbon dioxide in the flue gas, thereby removing carbon dioxide in the flue gas.

[0011] Among them, the liquid-liquid two-phase absorbent is composed of N,N-dimethyl-1,3-propanediamine (DMPDA) with a mass fraction of 30%, N,N-dimethylcyclohexylamine (DMCA) with a mass fraction of 40% and deionized water with a mass fraction of 30%.

[0012] Among them, phase separation of the absorbent starts after it enters the phase separation tank. The lean liquid enters the upper phase and the rich liquid enters the lower phase. That is, the absorbent that has absorbed carbon dioxide enters the phase separation tank and stably separates in the phase separation tank. Due to the difference in intermolecular polarity and density, the lean phase enters the upper phase and the rich phase enters the lower phase. The system of the present invention is only applicable to the case where the upper phase is the lean liquid and the lower phase is the rich liquid after phase separation (the two-phase absorbent used in the present invention is composed of an active amine, a phase separation agent and a solvent. The product formed after the active amine absorbs carbon dioxide has a large polarity difference from the phase separation agent, which causes the absorbent to be divided into upper and lower phases. The active amine, the product and the solvent are combined into one phase, and the phase separation agent becomes another phase. Since the density of the phase separation agent is relatively small, the upper phase is the phase separation agent (not reacted with carbon dioxide, also called the lean phase), and the reaction product becomes the lower phase (rich phase) due to its relatively large density). After the absorbent is stably phase-separated, the rich liquid is transported to the rich liquid tank for storage, while the lean liquid directly enters the lean liquid heat exchanger for heat exchange, and the lean liquid after heat exchange enters the lean liquid tank.

[0013] The present invention utilizes the lean phase (upper phase) of the absorbent that is completely separated after absorption to cool down the desorbed carbon dioxide, water vapor and volatilized absorbent, thereby realizing the separation of carbon dioxide, water vapor and volatile organic amines, and reducing the loss of absorbent while improving the purity of carbon dioxide; the rich phase (lower phase) of the absorbent that is completely separated after absorption is split after preheating (preheating by utilizing the hot lean liquid after desorption in the desorption tower), one part is heated (the heat source comes from the hot lean liquid after desorption in the desorption tower) into a rich liquid with water vapor, and the other part directly enters the desorption tower; the rich liquid with water vapor enters the desorption tower, which can reduce the addition of external heat source in the desorption process and realize the utilization of waste heat.

[0014] Beneficial effects: Compared with the prior art, the present invention has the following significant effects: In order to reduce the desorption energy consumption, the present invention, on the one hand, adopts a two-phase absorbent to capture the carbon dioxide in the flue gas, and then separates the lean phase from the rich phase, and finally only regenerates the rich phase. This method can effectively reduce the latent heat of evaporation and sensible heat loss in the regeneration process, thereby reducing the desorption energy consumption; on the other hand, the heat of the lean liquid after desorption is fully utilized to heat the rich liquid, and on the basis of realizing the utilization of waste heat, the addition of external heat source in the desorption process is effectively reduced; at the same time, the lean liquid formed after phase separation is used to cool the desorbed carbon dioxide, water vapor and volatile organic amines, so as to realize the separation of carbon dioxide, water vapor and volatile organic amines, thereby reducing the loss of absorbent while improving the purity of carbon dioxide; the present invention improves the energy recycling within the system, reduces the dependence on external heat sources, and thus significantly reduces energy consumption. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 is a system principle diagram of the system of the present invention;

[0016] Figure 2 It is a system principle diagram corresponding to the processing process of Comparative Example 1;

[0017] Figure 3 It is a system schematic diagram corresponding to the processing process of comparative example 2. DETAILED DESCRIPTION

[0018] like Figure 1As shown in the figure, the carbon dioxide capture system based on the liquid-liquid two-phase absorbent of the present invention includes: a pre-washing tower 1 for pre-treating flue gas to remove sulfur dioxide therein and cool it down; an absorption tower 2 for absorbing carbon dioxide in the flue gas by spraying the liquid-liquid two-phase absorbent; a phase separation tank 3 for separating the absorbed absorbent into a lean liquid upper phase and a rich liquid lower phase; a rich liquid tank 5 for storing the separated rich liquid; a lean liquid tank 10 for storing the separated lean liquid; heat exchangers, including a lean liquid heat exchanger 8, a primary heat exchanger 6 and a secondary heat exchanger 7, for realizing heat recovery of the absorbent; a desorption tower 9 for desorbing the rich liquid to release carbon dioxide; and a mixing tank 4 for remixing the separated lean liquid and the desorbed lean liquid to form a new two-phase absorbent.

[0019] The inlet of the pre-washing tower 1 is located at the lower end of the pre-washing tower, and the outlet of the pre-washing tower 1 is located at the upper end of the pre-washing tower. The flue gas enters the pre-washing tower 1 from the inlet of the pre-washing tower 1 and flows upward. Cooling water is sprayed at the top of the pre-washing tower 1 to remove sulfur dioxide in the flue gas and cool down the flue gas.

[0020] The outlet pipeline of the pre-washing tower 1 is connected to the inlet pipeline of the absorption tower 2, so that the flue gas after water washing and cooling enters the absorption tower 2. The flue gas flows upward from the lower end of the absorption tower 2, and the organic amine absorbent is sprayed at the upper end of the absorption tower 2; a packing bed is arranged in the absorption tower 2, and the packing bed can increase the gas-liquid contact area and extend the residence time of the absorbent in the absorption tower 2. The flue gas treated by the absorbent is discharged from the outlet at the top of the absorption tower 2, and the absorbent that has absorbed carbon dioxide flows into the bottom of the absorption tower 2.

[0021] The outlet pipeline at the bottom of the absorption tower 2 is connected to the inlet pipeline of the phase separation tank 3. After the absorbent that has absorbed carbon dioxide enters the phase separation tank 3, phase separation begins, and the lean liquid enters the upper phase and the rich liquid enters the lower phase.

[0022] The lower end outlet pipeline of the phase separation tank 3 is connected to the inlet pipeline of the rich liquid tank 5, and the phase-separated rich liquid enters the rich liquid tank 5 for storage; the rich liquid tank 5 is connected to the inlet of the primary heat exchanger 6. The upper end outlet pipeline of the primary heat exchanger 6 is connected to the inlet of the three-way valve, and the two outlets of the three-way valve are respectively connected to the upper end inlet of the secondary heat exchanger 7 and the middle inlet of the desorption tower 9; half of the rich liquid in the lower phase is pumped into the secondary heat exchanger 7 after being preheated by the primary heat exchanger 6, and the other half is pumped into the desorption tower 9. The upper end outlet of the secondary heat exchanger 7 is connected to the lower end inlet of the desorption tower 9, and the water in the rich liquid in the lower phase is heated to steam and enters the desorption tower 9 after being further heated by the secondary heat exchanger 7. The lower end outlet of the desorption tower 9 is connected to the lower end inlet of the secondary heat exchanger 7, and the hot lean liquid after desorption is pumped into the secondary heat exchanger 7 to exchange heat with the preheated rich liquid. The lower outlet of the secondary heat exchanger 7 is connected to the lower end inlet of the primary heat exchanger 6, and the hot lean liquid after heat exchange in the secondary heat exchanger 7 is pumped into the primary heat exchanger 6. The lower end outlet of the primary heat exchanger 6 is connected to the lower end inlet of the mixing tank 4, and the lean liquid after heat exchange in the primary heat exchanger 6 is pumped into the mixing tank 4. In the primary heat exchanger 6, the cold rich liquid is heated by the warm lean liquid desorbed from the desorption tower 9, so that the cold rich liquid after phase separation is preheated to warm rich liquid before entering the desorption tower, which reduces the heating efficiency of the desorption tower, realizes the recovery and utilization of waste heat, shortens the heating time of the rich liquid in the absorption tower, and improves the operation efficiency of the system. At the same time, half of the warm rich liquid in the primary heat exchanger 6 is transported to the desorption tower 9 for thermal desorption, and the other half of the warm rich liquid is transported to the secondary heat exchanger 7 for secondary heat exchange. At this time, the warm rich liquid in the secondary heat exchanger 7 is heated by the hot lean liquid just flowing out of the desorption tower 9, thereby generating hot steam (the secondary heat exchanger heats the water in the rich liquid to generate high-temperature steam, while the organic components continue to enter the desorption tower for thermal desorption). The steam sends heat to the desorption tower, on the one hand, effectively reducing the input of external heat sources, on the other hand, reducing heat loss and improving the waste heat utilization rate.

[0023] The upper outlet of the phase separation tank 3 is connected to the lower inlet of the lean liquid heat exchanger 8, and the upper-phase lean liquid is pumped into the lean liquid heat exchanger 8. The upper outlet of the desorption tower 9 is connected to the upper inlet of the lean liquid heat exchanger 8. The carbon dioxide gas released after desorption, together with the mixed and volatilized organic amine and water vapor, enters the lean liquid heat exchanger 8 through the upper outlet of the desorption tower 9. After the upper-phase lean liquid separated out exchanges heat with the high-temperature gas, the separated carbon dioxide enters the post-treatment equipment through the outlet at the top of the lean liquid heat exchanger 8. In the lean liquid heat exchanger 8, since the upper-phase lean liquid separated out has a lower temperature, its own lower temperature can be used to cool the gaseous products desorbed in the desorption tower 9 in the heat exchanger, which is beneficial to separating carbon dioxide, water vapor, and volatile organic amine in the gaseous products. After heat exchange, the temperature of the carbon dioxide is reduced and can be transported to the subsequent compression treatment equipment; while the volatile organic amine and water vapor are condensed and refluxed into the desorption tower after heat exchange, thus reducing the loss of absorbent. The cold lean liquid can recover the heat dissipated by the desorption tower and become warm lean liquid after heat exchange, recover the heat dissipated by the desorption tower, and enter the lean liquid tank 10 for storage.

[0024] The upper outlet of the lean liquid heat exchanger 8 is connected to the inlet of the lean liquid tank 10. The outlet of the lean liquid tank 10 is connected to the upper inlet of the mixing tank 4. The two-phase absorbent in the mixing tank 4 is pumped into the absorption tower 2 again through the top inlet.

[0025] In the desorption tower, the warm rich liquid and the hot rich liquid are heated by the water vapor generated by the secondary heat exchanger 7 and become hot lean liquid. The hot lean liquid is transported to the secondary heat exchanger 7 at the bottom outlet of the desorption tower 9. In the secondary heat exchanger 7, the hot lean liquid exchanges heat with the warm rich liquid. The warm lean liquid in the secondary heat exchanger 7 is transported to the primary heat exchanger 6, and the warm lean liquid exchanges heat with the cold rich liquid in the primary heat exchanger 6, making the cold rich liquid become warm rich liquid and the warm lean liquid become cold lean liquid.

[0026] Example 1

[0027] The liquid-liquid two-phase absorbent used in the system of the present invention is composed of N,N-dimethyl-1,3-propanediamine (DMPDA) with a mass fraction of 30%, N,N-dimethylcyclohexylamine (DMCA) with a mass fraction of 40%, and deionized water with a mass fraction of 30%. The process flow is as Figure 1 .

[0028] Flue gas enters from the inlet of the pre-washing tower (1) with a flow rate of 5000 m3 / h. Cooling water is sprayed at the top of the pre-washing tower with a flow rate of 1000 L / h. Through the spraying of cooling water, the temperature of the flue gas is reduced from the initial value to 50 °C, and then the flue gas enters the absorption tower (2). The specific surface area of the packing bed in the absorption tower is 150 m2 / m3, and the flow rate of the absorbent sprayed at the top is 800 L / h. In the absorption tower, carbon dioxide in the flue gas is effectively absorbed by the liquid-liquid two-phase absorbent. The temperature of the flue gas at the outlet of the absorption tower is reduced to 40 °C, and the temperature of the absorbent is also 40 °C. The absorbent after absorbing carbon dioxide flows into the phase separation tank (3) for phase separation. After phase separation, the temperatures of the lean liquid phase and the rich liquid phase are both 40 °C.

[0029] The rich liquid is preheated to 90 °C through a primary heat exchanger (6) and then undergoes a split treatment: half enters the desorption tower (9), and the other half enters the secondary heat exchanger (7). The secondary heat exchanger (7) generates hot steam at 118 °C, heating the rich liquid to 108 °C and then entering the desorption tower. The external heating source temperature of the desorption tower is 130 °C. Under this condition, carbon dioxide is efficiently desorbed from the rich liquid, and the purity of the desorbed carbon dioxide gas reaches 99%, with a flow rate of 100 m3 / h. The hot lean liquid (120 °C) after desorption enters the secondary heat exchanger (7). After heat exchange through the secondary heat exchanger and the primary heat exchanger in sequence, the temperature is reduced to 40 °C, forming cold lean liquid. The cold lean liquid is mixed with the warm lean liquid in the lean liquid tank (10) in the mixing tank (4). The temperature of the mixed absorbent is still 40 °C and is pumped back to the top of the absorption tower again to complete the cycle.

[0030] The desorption energy consumption of this system when treating carbon dioxide is about 2.4 GJ / tCO 2 , and the desorption purity of carbon dioxide reaches 99%.

[0031] Example 2:

[0032] The liquid-liquid two-phase absorbent used in the system of the present invention is composed of N,N-dimethyl-1,3-propanediamine (DMPDA) with a mass fraction of 30%, N,N-dimethylcyclohexylamine (DMCA) with a mass fraction of 40%, and deionized water with a mass fraction of 30%. The process flow is as Figure 1 .

[0033] Flue gas enters from the inlet of the pre-washing tower (1) with a flow rate of 4500 m3 / h. Cooling water is sprayed at the top of the pre-washing tower with a flow rate of 1000 L / h. Through the spraying of cooling water, the temperature of the flue gas is reduced from the initial value to 45 °C. Subsequently, the flue gas enters the absorption tower (2). The specific surface area of the packing bed in the absorption tower is 140 m2 / m3, and the flow rate of the absorbent sprayed at the top is 750 L / h. In the absorption tower, carbon dioxide in the flue gas is effectively absorbed by the absorbent. The temperature of the flue gas at the outlet of the absorption tower is reduced to 38 °C, and the temperature of the absorbent is also 38 °C.

[0034] The absorbent after absorbing carbon dioxide flows into the phase separation tank (3) for phase separation. After phase separation, the temperatures of both the lean liquid phase and the rich liquid phase are 38°C. In the lean liquid heat exchanger (8), the cold lean liquid (38°C) exchanges heat with the hot gaseous product (115°C) at the outlet of the desorption tower (9). The temperature of the lean liquid rises to 68°C and then enters the lean liquid tank (10). The warm lean liquid in the lean liquid tank is sent to the mixing tank (4) by a pump. After mixing with the cold lean liquid, the temperature of the mixed absorbent is 38°C and it is sent to the top of the absorption tower by a pump again to complete the cycle.

[0035] The rich liquid is preheated to 85°C in the primary heat exchanger (6) and then undergoes a split flow treatment: half enters the desorption tower (9) and the other half enters the secondary heat exchanger (7). The secondary heat exchanger (7) generates hot steam at 120°C, heating the rich liquid to 110°C and then entering the desorption tower. The external heating source temperature of the desorption tower is 125°C. Under this condition, carbon dioxide is efficiently desorbed from the rich liquid, and the purity of the desorbed carbon dioxide gas reaches 99%, with a flow rate of 95 m3 / h. The hot lean liquid (115°C) after desorption enters the secondary heat exchanger (7). After sequentially exchanging heat in the secondary heat exchanger and the primary heat exchanger, the temperature drops to 38°C to form cold lean liquid. The cold lean liquid is mixed with the warm lean liquid in the lean liquid tank in the mixing tank. The temperature of the mixed absorbent is 38°C and it is sent to the top of the absorption tower by a pump again to complete the cycle.

[0036] The desorption energy consumption of this system when treating carbon dioxide is about 2.3 GJ / tCO 2 , and the desorption purity of carbon dioxide reaches 99%.

[0037] Example 3

[0038] The liquid-liquid two-phase absorbent used in the system of the present invention is composed of N,N-dimethyl-1,3-propanediamine (DMPDA) with a mass fraction of 30%, N,N-dimethylcyclohexylamine (DMCA) with a mass fraction of 40%, and deionized water with a mass fraction of 30%. The process flow is as Figure 1 .

[0039] The flue gas enters from the inlet of the pre-washing tower (1), and the flue gas flow rate is 5500 m3 / h. Cooling water is sprayed at the top of the pre-washing tower with a flow rate of 1000 L / h. Through the spraying action of the cooling water, the temperature of the flue gas is reduced from the initial value to 45°C. Subsequently, the flue gas enters the absorption tower (2). The specific surface area of the packing bed in the absorption tower is 140 m2 / m3, and the absorbent spraying flow rate is 750 L / h. In the absorption tower, carbon dioxide in the flue gas is effectively absorbed by the absorbent. The temperature of the flue gas at the outlet of the absorption tower drops to 38°C, and the temperature of the absorbent rises to 38°C. The absorbent after absorbing carbon dioxide flows into the phase separation tank (3) for phase separation. After phase separation, the temperatures of both the lean liquid phase and the rich liquid phase are 38°C.

[0040] The flow rate of the cold rich liquid in the rich liquid tank (5) is 330 L / h. After being preheated to 92 °C in the primary heat exchanger (6), it is split: half of the warm rich liquid (165 L / h) directly enters the desorption tower (9), and the other half enters the secondary heat exchanger (7). The secondary heat exchanger (7) generates hot steam at 122 °C, heating the rich liquid to 110 °C before entering the desorption tower. The external heating source temperature of the desorption tower is 132 °C. Under this condition, carbon dioxide is efficiently desorbed from the rich liquid, and the purity of the desorbed carbon dioxide gas reaches 99%, with a flow rate of 110 m3 / h.

[0041] The hot lean liquid after desorption (112 °C) enters the secondary rich-lean liquid heat exchanger and the primary rich-lean liquid heat exchanger in sequence for heat exchange. After heat exchange, the temperature drops to 38 °C, forming cold lean liquid. The cold lean liquid then enters the mixing tank (4) to be mixed with other liquids in the system, further stabilizing the temperature and performance of the absorbent.

[0042] The desorption energy consumption of this system when treating carbon dioxide is about 2.4 GJ / tCO 2 , and the desorption purity of carbon dioxide reaches 99%.

[0043] Comparative Example 1

[0044] This comparative example uses a traditional single-phase absorbent, an aqueous solution of monoethanolamine (MEA) with a mass fraction of 30%, for carbon dioxide capture. The process flow is as Figure 2 .

[0045] The flue gas enters from the inlet of the pre-washing tower (1), and the flue gas flow rate is 5000 m3 / h. Cooling water is sprayed at the top of the pre-washing tower, with a flow rate of 1000 L / h. Through the spraying action of the cooling water, the temperature of the flue gas is reduced from the initial value to 40 °C. Subsequently, the flue gas enters the absorption tower (2). The specific surface area of the packing bed in the absorption tower is 150 m2 / m3, and the spraying flow rate of the MEA absorbent is 800 L / h. In the absorption tower, carbon dioxide in the flue gas undergoes a chemical reaction with the MEA absorbent and is effectively absorbed. The temperature of the flue gas at the outlet of the absorption tower drops to 35 °C, and the temperature of the absorbent rises to 35 °C.

[0046] The rich liquid after absorbing carbon dioxide flows into the regeneration tower (9) through the rich-lean liquid heat exchanger (8). The rich liquid temperature is 45 °C, and the flow rate is 800 L / h. The rich liquid is preheated to 80 °C through the rich-lean liquid heat exchanger (8) and then enters the regeneration tower. The external heating source temperature of the regeneration tower is 120 °C. Under this condition, carbon dioxide is desorbed from the rich liquid, and the purity of the desorbed carbon dioxide gas reaches 90%, with a flow rate of 100 m3 / h. The hot lean liquid after desorption (110 °C) enters the rich-lean liquid heat exchanger (8) to exchange heat with the rich liquid entering the regeneration tower, preheating the rich liquid to 80 °C while its own temperature drops to 50 °C. The cold lean liquid after heat exchange is sent back to the top of the absorption tower through a pump to complete the cycle.

[0047] This system uses a single-phase MEA absorbent. When treating carbon dioxide, the regeneration energy consumption is about 3.8 GJ / t CO 2 , which is much higher than that of the liquid-liquid two-phase absorbent system. Moreover, cooling water needs to be introduced at the top of the regeneration tower to condense and separate the desorbed carbon dioxide and volatile absorbent, which will further increase the process cost and cause heat loss.

[0048] Comparative Example 2

[0049] The liquid-liquid two-phase absorbent used in this comparative example is composed of N,N-dimethyl-1,3-propanediamine (DMPDA) with a mass fraction of 30%, N,N-dimethylcyclohexylamine (DMCA) with a mass fraction of 40%, and deionized water with a mass fraction of 30%. The process flow is as Figure 3 .

[0050] The flue gas enters from the inlet of the pre-washing tower (1) with a flow rate of 5000 m3 / h. Cooling water is sprayed at the top of the pre-washing tower with a flow rate of 1000 L / h. Through the spraying action of the cooling water, the temperature of the flue gas is reduced from the initial value to 40 °C. Subsequently, the flue gas enters the absorption tower (2). The specific surface area of the packing bed in the absorption tower is 150 m2 / m3, and the spraying flow rate of the two-phase absorbent is 800 L / h. In the absorption tower, carbon dioxide in the flue gas reacts chemically with the absorbent and is effectively absorbed. The temperature of the flue gas at the outlet of the absorption tower drops to 35 °C, and the temperature of the absorbent rises to 35 °C.

[0051] The rich liquid after absorbing carbon dioxide flows into the phase separation tank (3). After phase separation, the two phases are distributed to the rich phase tank (5) and the lean phase tank (10). The temperatures of the rich phase and the lean phase are both 35 °C. The flow rate of the rich phase is 400 L / h, and the flow rate of the lean phase is 400 L / h. The rich phase is preheated to 90 °C through the rich-lean liquid heat exchanger (6) and then enters the desorption tower (9). The external heating source temperature of the desorption tower is 120 °C. Under this condition, carbon dioxide is desorbed from the rich liquid, and the purity of the desorbed carbon dioxide gas reaches 95%, with a flow rate of 100 m3 / h. The hot lean liquid (110 °C) after desorption enters the rich-lean liquid heat exchanger (6) and exchanges heat with the rich liquid entering the desorption tower, preheating the rich liquid to 90 °C while its own temperature drops to 50 °C. The cooled lean liquid after heat exchange enters the mixing tank (4) and mixes with the lean liquid in the lean phase tank (10). The temperature of the mixed absorbent is 45 °C. The mixed absorbent is pumped to the top of the absorption tower again to complete the cycle.

[0052] The desorption energy consumption of this system when treating carbon dioxide is about 2.8 GJ / tCO 2 , and the desorption purity of carbon dioxide reaches 95%.

[0053] The system of the present invention recovers the heat dissipated by the desorption tower through the lean liquid heat exchanger, reduces the loss of absorbent while improving the purity of carbon dioxide; realizes the preheating of rich liquid and the recovery of energy through the primary heat exchanger and the secondary heat exchanger, reduces the demand for external heat sources, and lowers the system energy consumption.

Claims

1. A carbon dioxide capture system based on a liquid-liquid two-phase absorbent, characterized in that: The invention comprises an absorption tower (2), a phase separation tank (3), a primary heat exchanger (6), a secondary heat exchanger (7), a lean liquid heat exchanger (8) and a desorption tower (9); the liquid outlet of the absorption tower (2) is connected to the phase separation tank (3); the rich liquid after phase separation in the phase separation tank (3) is preheated by the primary heat exchanger (6); part of the preheated rich liquid flows into the secondary heat exchanger (7) and part flows into the desorption tower (9); the rich liquid with high-temperature water vapor after heat exchange in the secondary heat exchanger (7) enters the desorption tower (9); the hot gaseous product discharged from the gas outlet of the desorption tower (9) exchanges heat with the lean liquid after phase separation at the lean liquid heat exchanger (8) to separate carbon dioxide; the hot lean liquid discharged from the liquid outlet of the desorption tower (9) is the heat source for the secondary heat exchanger (7) and the primary heat exchanger (6).

2. The carbon dioxide capture system based on a liquid-liquid two-phase absorbent according to claim 1, characterized in that: The external heat source of the desorption tower (9) is hot steam generated by a mechanical steam recompression process.

3. The carbon dioxide capture system based on liquid-liquid two-phase absorbent according to claim 1, characterized in that: The hot gaseous products include carbon dioxide, water vapor and volatile organic amines.

4. The carbon dioxide capture system based on liquid-liquid two-phase absorbent according to claim 1, characterized in that: It also includes a pre-washing tower (1) for washing and cooling the flue gas, and the flue gas after washing and cooling enters the absorption tower (2).

5. The carbon dioxide capture system based on liquid-liquid two-phase absorbent according to claim 4, characterized in that: A packing bed is provided in the absorption tower (2).

6. The carbon dioxide capture system based on liquid-liquid two-phase absorbent according to claim 1, characterized in that: The liquid-liquid two-phase absorbent consists of 30% by mass of N,N-dimethyl-1,3-propylenediamine, 40% by mass of N,N-dimethylcyclohexylamine and 30% by mass of water.

7. The carbon dioxide capture system based on liquid-liquid two-phase absorbent according to claim 6, characterized in that: After the absorbent enters the phase separation tank (3), phase separation begins, with the lean liquid entering the upper phase and the rich liquid entering the lower phase.

8. The carbon dioxide capture system based on liquid-liquid two-phase absorbent according to claim 7, characterized in that: The carbon dioxide gas released after desorption and the mixed volatilized organic amine and water vapor enter the lean liquid heat exchanger (8) through the upper outlet of the desorption tower (9), and the upper phase lean liquid after phase separation exchanges heat with the high-temperature gas, and the separated carbon dioxide enters the post-processing equipment through the top outlet of the lean liquid heat exchanger (8). The lean liquid after phase separation exchanges heat and flows back to the mixing tank to be remixed with the lean liquid after desorption.

9. The carbon dioxide capture system based on liquid-liquid two-phase absorbent according to claim 3, characterized in that: The hot gaseous product discharged from the gas outlet of the desorption tower (9) exchanges heat with the separated lean liquid at the lean liquid heat exchanger (8) to separate the carbon dioxide, while the volatile organic amines and water vapor are condensed after the heat exchange and flow back into the desorption tower.

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