A carbon dioxide capture system based on liquid-solid phase separation

Abstract

A carbon dioxide capture system based on liquid-solid phase separation includes a pretreatment tower, an absorption tower, a clear liquid mixing pool, a slurry mixing pool and a desorption tower, wherein a plurality of absorption towers are connected in series, and an interstage heat exchanger and a liquid-solid separation pool are provided at the liquid outlet of each level of the absorption tower, and the clear liquid separated by the first-level liquid-solid separation pool is sent to the clear liquid mixing pool, and the clear liquid separated by the remaining liquid-solid separation pools is sent to the upper-level absorption tower; the slurry outlets of the liquid-solid separation pools at each level are connected to the inlet of the slurry mixing pool, the slurry mixing pool is connected to the slurry preheater, the slurry preheater is connected to the lean-rich liquid heat exchanger, the lean-rich liquid heat exchanger is connected to the slurry inlet of the steam desorption tower, the steam desorption tower is connected to the air desorption tower, the air desorption tower liquid outlet is connected to the clear liquid mixing pool, and the clear liquid mixing pool liquid outlet is connected to the liquid inlet of the final absorption tower. The present invention can not only reduce the overall size and carbon footprint, but also reduce the energy consumption of the system, thereby achieving the purpose of saving the cost of carbon dioxide capture.

Description

Technical Field

[0001] The present invention relates to the field of carbon dioxide capture in gas purification, in particular to a carbon dioxide capture system based on liquid-solid phase separation. Background Art

[0002] Currently, climate change and carbon neutrality are hot issues around the world. Carbon capture, utilization and storage (CCUS) is an indispensable technical means to achieve carbon neutrality and alleviate global warming.

[0003] Among the technical routes for carbon capture, post-combustion capture does not require the construction of new projects. Instead, it only requires the installation of carbon capture devices on traditional carbon emission sources. It requires little process modification and is a more feasible option.

[0004] Among the technical means of post-combustion capture, the chemical solvent absorption method has good operability and scalability and is most likely to achieve large-scale commercial application. The chemical solvent absorption method uses an absorption solvent (CO 2 The lean liquid) reacts with CO in the mixed gas under low temperature and normal pressure conditions. 2 A selective chemical reaction occurs and it is absorbed, and the resulting CO 2 The rich liquid undergoes a reverse reaction under high temperature and pressure conditions to desorb relatively pure CO 2 , thereby achieving CO 2 Separation from other components of the mixed gas and simultaneous regeneration of the absorption solvent (CO 2 Lean solution) recovers CO 2 ability, and so on.

[0005] Application in post-combustion CO 2 The chemical absorption solvents for capture have undergone many developments. Currently, common absorption solvents include organic amines (including composite organic amines), cooling ammonia, ionic liquids, amino acid salt solutions, activated carbonate solutions, etc. 2 The focus of chemical absorption solvent development is to find a new chemical absorption solvent that takes into account the absorption rate, absorption capacity, stability, volatility, viscosity and corrosion of the absorbent to the capture equipment, so as to achieve low energy consumption of the capture process as a whole (mainly including the external heat required for thermal regeneration of the absorbent, such as steam to provide the sensible heat, reaction heat and latent heat required for regeneration, and the relatively pure CO 2 Compression work required for gas compression) and cost optimization.

[0006] In addition, different absorption solvents use different capture processes and equipment, and the operating conditions used are also different. The improvement of the process flow is also of great significance to reducing the capture energy consumption and cost. 2 The energy consumption and cost of capture remain high, becoming a key issue that needs to be urgently addressed for the large-scale promotion and application of this technology. Summary of the invention

[0007] The technical problem to be solved by the present invention is to provide a carbon dioxide capture system based on liquid-solid phase separation of absorption solvent, which can not only reduce the size of the corresponding equipment and reduce the carbon footprint, but also save the energy consumption required for the entire system, thereby achieving the purpose of reducing the cost of carbon dioxide capture.

[0008] The technical solution of the present invention is to provide a carbon dioxide capture system based on liquid-solid phase separation with the following structure, including a pretreatment tower, an absorption tower, a clear liquid mixing tank, a slurry mixing tank and a desorption tower, wherein there are several absorption towers, which are connected in series with each other; the desorption tower includes a steam desorption tower and an air desorption tower, which are connected in series with each other; the air inlet of the pretreatment tower is for external flue gas to be treated to enter, and the air outlet is connected with the air inlet of the first-stage absorption tower among the several absorption towers; the air outlet of the last-stage absorption tower among the several absorption towers is connected with the air inlet of the flue gas condenser, and the air outlet of the flue gas condenser is connected with the outside; an interstage heat exchanger and a liquid-solid separation tank are provided at the liquid outlet of each stage of the absorption tower in the several absorption towers, and the interstage heat exchanger is used to heat the CO flowing out of the liquid outlet. 2 The rich solution is cooled and the cooled CO 2 The rich solution is transported to the corresponding liquid-solid separation tank; the clear liquid separated by the first-stage liquid-solid separation tank is heated by the first-stage interstage heat exchanger and then transported to the clear liquid mixing tank, and the remaining interstage heat exchangers heat the clear liquid separated by the corresponding liquid-solid separation tank and transport it to the liquid inlet of the upper-stage absorption tower in sequence; the slurry outlets of each stage of the liquid-solid separation tank are connected to the inlet of the slurry mixing tank, and a slurry preheater and a lean-rich liquid heat exchanger are provided at the outlet of the slurry mixing tank. The slurry inlet of the slurry preheater is connected to the outlet of the slurry mixing tank, and the slurry preheater The slurry outlet of the reactor is connected with the slurry inlet of the lean-rich liquid heat exchanger, the slurry outlet of the lean-rich liquid heat exchanger is connected with the slurry inlet of the steam desorption tower, the liquid outlet of the steam desorption tower is connected with the liquid inlet of the air desorption tower; the air outlet of the air desorption tower is connected with the air inlet of the boiler air preheater, the liquid outlet of the air desorption tower is connected with the lean liquid inlet of the slurry preheater, the lean liquid outlet of the slurry preheater is connected with the inlet of the clear liquid mixing tank, the liquid outlet of the clear liquid mixing tank is connected with the liquid inlet of the flue gas condenser, and the liquid outlet of the flue gas condenser is connected with the liquid inlet of the final absorption tower.

[0009] The carbon dioxide capture system based on liquid-solid phase separation described in the present invention further includes a water evaporator, a pressurized fan II, a gas heat exchanger, a by-product gas condenser and a product gas condenser; the flue gas inlet of the gas heat exchanger is for external flue gas to be treated to enter, and the flue gas outlet of the gas heat exchanger is connected to the air inlet of the pretreatment tower; the air inlet of the water evaporator is connected to the air outlet of the gas heat exchanger, the air inlet of the gas heat exchanger is connected to the air outlet of the pressurized fan II, and the air inlet of the pressurized fan II is connected to the outside world; the air outlet of the water evaporator is connected to the The air inlet of the air desorption tower is connected; the water outlet of the water evaporator is connected to the water inlet of the by-product gas condenser, the water outlet of the by-product gas condenser is connected to the water inlet of the product gas condenser, and the water outlet of the product gas condenser is connected to the water inlet of the water evaporator; the air inlet of the by-product gas condenser is connected to the air outlet of the air desorption tower, and the air outlet of the by-product gas condenser is connected to the air inlet of the boiler air preheater; the air inlet of the product gas condenser is connected to the air outlet at the top of the steam desorption tower, and the air outlet of the product gas condenser is connected to the air inlet of the carbon dioxide compressor.

[0010] The carbon dioxide capture system based on liquid-solid phase separation described in the present invention further includes a reboiler, wherein the liquid inlet of the reboiler is connected to the outlet of the incompletely desorbed lean liquid of the steam desorption tower, the air outlet of the reboiler is connected to the air inlet of the lower part of the steam desorption tower, the liquid outlet of the reboiler is connected to the lean liquid inlet of the lean-rich liquid heat exchanger, and the lean liquid outlet of the lean-rich liquid heat exchanger is connected to the liquid inlet of the air desorption tower; the reboiler is provided with a saturated steam inlet and a condensate outlet.

[0011] The present invention discloses a carbon dioxide capture system based on liquid-solid phase separation, wherein a hydrocyclone is provided between each liquid-solid separation tank and the slurry mixing tank, the slurry inlet of the hydrocyclone is connected to the slurry outlet of the corresponding liquid-solid separation tank, the slurry outlets of the hydrocyclones are connected to the inlet of the slurry mixing tank, and the clear liquid outlet of each hydrocyclone is connected to the clear liquid outlet of the corresponding liquid-solid separation tank.

[0012] The present invention discloses a carbon dioxide capture system based on liquid-solid phase separation, wherein a slurry pump is installed between the slurry outlet of each hydrocyclone and the inlet of the slurry mixing tank, and between the outlet of the slurry mixing tank and the slurry inlet of the slurry preheater.

[0013] The present invention discloses a carbon dioxide capture system based on liquid-solid phase separation, wherein a clear liquid pump is installed at the confluence of the clear liquid outlet of the liquid-solid separation tank and the hydrocyclone, and at the liquid outlet of the clear liquid mixing tank.

[0014] The present invention relates to a carbon dioxide capture system based on liquid-solid phase separation, wherein a pressurized fan I is installed between the air outlet of the pretreatment tower and the air inlet of the first-stage absorption tower.

[0015] In the carbon dioxide capture system based on liquid-solid phase separation described in the present invention, a circulating water pump is installed between the water outlet of the by-product gas condenser and the water inlet of the product gas condenser.

[0016] After adopting the above structure, compared with the prior art, the carbon dioxide capture system based on liquid-solid phase separation of the present invention has the following advantages:

[0017] 1. Use an absorption solvent that can separate liquid from solid phases, and arrange the absorption tower in multiple stages in series, so that during operation, the absorption solvent (CO 2 The lean liquid) is mixed with CO in the upper absorption tower cavity. 2 The absorption reaction occurs upon contact, and the CO produced 2 The rich liquid then undergoes liquid-solid phase separation, and the slurry containing the solid phase directly enters the steam desorption tower for regeneration, that is, a portion of the absorption solvent is stripped from the absorption system and does not enter the next-stage absorption tower, which reduces the size of the next-stage absorption tower, making the entire device more compact and substantially reducing the cost of the carbon capture system;

[0018] 2. Since the absorption solvent entering the next absorption tower recovers CO 2 Lean liquid state, so it can always maintain good gas-liquid mass transfer driving force and CO 2 Compared with the original method without multi-stage absorption, CO 2 The absorption capacity is higher and the size of the absorption tower is smaller, which can further reduce the cost of the carbon capture system;

[0019] 3. Since only part of the solvent is absorbed, i.e., CO-rich 2 The slurry needs to enter the desorption tower to regenerate the lean CO 2 The absorption solvent is used to reduce the amount of solvent to be processed during desorption, so the size of the desorption tower can be reduced, making the whole more compact and saving the cost of the carbon capture system;

[0020] 4. Rich in CO 2 The slurry contains only a small amount of solution, so the stripping heat and sensible heat required for desorption are small, the amount of steam required is reduced, and the capture energy consumption is reduced; and because CO 2 The concentration is greatly enriched in the rich slurry to be regenerated, so that the stripping pressure can be very high, reducing the capture energy consumption and subsequent CO 2 Compression work requirement;

[0021] 5. The air desorption tower driven by water-saturated air can deeply desorb CO in the lean liquid 2, using the waste heat integrated in the system (which is usually released directly into the environment) without consuming additional steam, improving the overall energy utilization rate and saving costs; this waste heat also includes but is not limited to using the condensate heat exchanger to recover the heat of the saturated steam condensate in the reboiler, using the compression interstage cooler to recover CO 2 Interstage heat in the multi-stage compression process of the compressor, as well as utilizing other low-grade waste heat from the capture system;

[0022] 6. The byproduct gas obtained from the outlet of the air desorption tower contains a small amount of CO 2 , enters the boiler air preheater, and the CO in the flue gas after combustion 2 The content increases, and due to the deep desorption of CO in the lean liquid 2 The loading capacity is further reduced, which increases the gas-liquid mass transfer driving force and CO 2 The absorption rate increases the CO 2 The absorption capacity can reduce the amount of solvent required, which can further reduce the size of the absorption tower and the capture cost;

[0023] 7. Rich in CO 2 The slurry is heat exchanged with the deep desorption lean liquid discharged from the bottom of the air desorption tower and the initial regeneration lean liquid discharged from the bottom of the steam desorption tower, which can increase the CO2-rich 2 The temperature of the slurry before entering the lean-rich liquid heat exchanger indirectly increases the operating temperature of the air desorption tower and improves the degree of deep desorption. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a structural block diagram of a carbon dioxide capture system based on liquid-solid phase separation of the present invention. DETAILED DESCRIPTION

[0025] The following is a further detailed description of a carbon dioxide capture system based on liquid-solid phase separation of the present invention in conjunction with the accompanying drawings and specific embodiments:

[0026] like Figure 1As shown, in a specific embodiment, a carbon dioxide capture system based on liquid-solid phase separation of the present invention includes a pretreatment tower PTC, an absorption tower A, a clear liquid mixing tank LM, a slurry mixing tank SM and a desorption tower D. There are several absorption towers A, which are connected in series with each other. The desorption tower D includes a steam desorption tower DS and an air desorption tower DA, which are connected in series with each other. For the convenience of description, the absorption tower A is set in two stages in this embodiment, namely the first-stage absorption tower A1 and the final-stage absorption tower A2, and the steam desorption tower DS and the air desorption tower DA are each set in one stage. Correspondingly, the interstage heat exchanger HE32 includes a first-stage interstage heat exchanger HE3 and a final-stage interstage heat exchanger HE2; the liquid-solid separation tank C includes a first-stage liquid-solid separation tank C1 and a final-stage liquid-solid separation tank C2; the hydrocyclone HC includes a first-stage hydrocyclone HC1 and a final-stage hydrocyclone HC2; there are three slurry pumps SP, namely, a first slurry pump SP1, a second slurry pump SP2 and a third slurry pump SP3; there are three clear liquid pumps LP, namely, a first clear liquid pump LP1, a second clear liquid pump LP2 and a third clear liquid pump LP3.

[0027] Taking two stages as an example, the specific structure of the capture system of the present invention is as follows:

[0028] The CO captured by the present invention 2 It can be low CO2-containing gas discharged into the atmosphere from concentrated emission sources in industries such as power generation, steel, building materials, nonferrous metals, petrochemicals, chemicals, and papermaking. 2 Concentration of smoke or exhaust gas.

[0029] After being cooled by air, the external flue gas to be treated enters the pretreatment tower PTC from the air inlet. The air outlet of the pretreatment tower PTC is connected to the lower air inlet of the first-stage absorption tower A1, and a pressurized fan IB1 is installed on this pipeline to ensure the smooth supply of flue gas. The top air outlet of the first-stage absorption tower A1 is connected to the lower air inlet of the final absorption tower A2, thereby forming a series connection. In order to recover water vapor in the flue gas, a flue gas condenser HE1 is provided at the top air outlet of the final absorption tower A2. The air inlet of the flue gas condenser HE1 is connected to the air outlet of the final absorption tower A2, and the air outlet of the flue gas condenser HE1 is connected to the outside world. Therefore, during operation, after the water vapor in the flue gas is recovered, it is discharged into the external environment atmosphere through the chimney. In this process, the condensed water flows back to the final absorption tower A2 to maintain the water balance of the system.

[0030] The first stage interstage heat exchanger HE3 and the first stage liquid-solid separation tank C1 are arranged at the liquid outlet of the first stage absorption tower A1. The bottom liquid outlet of the first stage absorption tower A1 is connected to the CO2 of the first stage interstage heat exchanger HE3. 2 The rich liquid inlet is connected to the first stage interstage heat exchanger HE3 CO 2 The rich liquid outlet and the CO at the top of the first-stage liquid-solid separation tank C1 2The first stage interstage heat exchanger HE3 is used to heat the CO flowing out of the liquid outlet. 2 The rich solution is cooled and the cooled CO 2 The rich solution is transported to the first-stage liquid-solid separation tank C1.

[0031] The upper clear liquid outlet of the first-stage liquid-solid separation tank C1 is connected to the clear liquid inlet of the first-stage interstage heat exchanger HE3. To ensure the smooth flow of the clear liquid, a first clear liquid pump LP1 is installed on this pipeline. The clear liquid outlet of the first-stage interstage heat exchanger HE3 is connected to the top inlet of the clear liquid mixing tank LM. In other words, the clear liquid separated by the first-stage liquid-solid separation tank C1 is heated by the first-stage interstage heat exchanger HE3 and then transported to the clear liquid mixing tank LM.

[0032] A first-stage hydrocyclone HC1 is provided at the slurry outlet of the first-stage liquid-solid separation tank C1. The top slurry inlet of the first-stage hydrocyclone HC1 is connected to the bottom slurry outlet of the first-stage liquid-solid separation tank C1. The upper clear liquid outlet of the first-stage hydrocyclone HC1 is connected to the upper clear liquid outlet of the first-stage liquid-solid separation tank C1, that is, the clear liquids discharged from the two are collected here. The bottom slurry outlet of the first-stage hydrocyclone HC1 is connected to the inlet of the slurry mixing tank SM. To ensure the smooth flow of the slurry, a first slurry pump SP1 is installed on the pipeline between the first-stage hydrocyclone HC1 and the slurry mixing tank SM.

[0033] The liquid outlet of the final absorption tower A2 is provided with a final interstage heat exchanger HE2 and a final liquid-solid separation tank C2. The bottom liquid outlet of the final absorption tower A2 is connected to the CO2 of the final interstage heat exchanger HE2. 2 The rich liquid inlet is connected to the final interstage heat exchanger HE2. 2 The rich liquid outlet is connected to the top rich liquid inlet of the final liquid-solid separation tank C2. The final interstage heat exchanger HE2 is used to heat the CO flowing out of the liquid outlet. 2 The rich solution is cooled and the cooled CO 2 The rich solution is transported to the final liquid-solid separation tank C2.

[0034] The upper clear liquid outlet of the final liquid-solid separation tank C2 is connected to the clear liquid inlet of the final interstage heat exchanger HE2. To ensure the smooth flow of the clear liquid, a second clear liquid pump LP2 is installed on this pipeline. The clear liquid outlet of the final interstage heat exchanger HE2 is connected to the liquid inlet at the top of the first-stage absorption tower A1, that is, the clear liquid separated by the final liquid-solid separation tank C2 is heated by the final interstage heat exchanger HE2 and then transported to the liquid inlet of the upper absorption tower as CO 2 Lean solution.

[0035] A final hydrocyclone HC2 is provided at the slurry outlet of the final liquid-solid separation tank C2, the top slurry inlet of the final hydrocyclone HC2 is connected to the bottom slurry outlet of the final liquid-solid separation tank C2, and the upper clear liquid outlet of the final hydrocyclone HC2 is connected to the upper clear liquid outlet of the final liquid-solid separation tank C2, that is, the clear liquids discharged from the two are collected here. The bottom slurry outlet of the final hydrocyclone HC2 is connected to the inlet of the slurry mixing tank SM. To ensure the smooth flow of the slurry, a second slurry pump SP2 is installed on the pipeline between the final hydrocyclone HC2 and the slurry mixing tank SM.

[0036] A slurry preheater HE4 and a lean-rich liquid heat exchanger HE5 are provided at the outlet of the slurry mixing tank SM. The slurry inlet of the slurry preheater HE4 is connected to the outlet of the slurry mixing tank SM, and a third slurry pump SP3 is installed on this pipeline; the slurry outlet of the slurry preheater HE4 is connected to the slurry inlet of the lean-rich liquid heat exchanger HE5, and the slurry outlet of the lean-rich liquid heat exchanger HE5 is connected to the upper slurry inlet of the steam desorption tower DS; the liquid outlet of the steam desorption tower DS is connected to the liquid inlet of the air desorption tower DA, thereby forming a series connection between the two.

[0037] In order to make CO 2 The slurry is fully heated and decomposed to produce CO 2 The present invention also includes a reboiler RB, which is provided with a saturated steam inlet and a condensate outlet. The liquid inlet of the reboiler RB is connected to the outlet of the incompletely desorbed lean liquid of the steam desorption tower DS, the gas outlet of the reboiler RB is connected to the gas inlet at the bottom of the steam desorption tower DS, the liquid outlet of the reboiler RB is connected to the lean liquid inlet of the lean-rich liquid heat exchanger HE5, the lean liquid outlet of the lean-rich liquid heat exchanger HE5 is connected to the upper liquid inlet of the air desorption tower DA, the gas outlet of the air desorption tower DA is connected to the gas inlet of the boiler air preheater, the liquid outlet of the air desorption tower DA is connected to the lean liquid inlet of the slurry preheater HE4, the lean liquid outlet of the slurry preheater HE4 is connected to the inlet of the clear liquid mixing tank LM, and the third clear liquid pump LP3 is installed at the liquid outlet of the clear liquid mixing tank LM to allow the clear liquid to flow smoothly into the liquid inlet of the flue gas condenser HE1, and the liquid outlet of the flue gas condenser HE1 is connected to the liquid inlet at the top of the final absorption tower A2.

[0038] To assist CO 2The lean liquid is deeply desorbed. The present invention also includes a water evaporator WE, a pressurized fan IIB2, a gas heat exchanger HE0, a by-product gas condenser HE6 and a product gas condenser HE7. The flue gas inlet of the gas heat exchanger HE0 is for the external flue gas to be treated to enter, and the flue gas outlet of the gas heat exchanger HE0 is connected to the air inlet of the pretreatment tower PTC; the air inlet of the water evaporator WE is connected to the air outlet of the gas heat exchanger HE0, the air inlet of the gas heat exchanger HE0 is connected to the air outlet of the pressurized fan IIB2, and the air inlet of the pressurized fan IIB2 is connected to the outside world; the top air outlet of the water evaporator WE is connected to the air inlet of the lower part of the air desorption tower DA; the water outlet at the bottom of the water evaporator WE is connected to the water inlet of the by-product gas condenser HE6; the water outlet of the by-product gas condenser HE6 is connected to the water inlet of the product gas condenser HE7, and a circulating water pump WP is installed on this pipeline; the product gas condenser The water outlet of HE7 is connected with the upper water inlet of the water evaporator WE; the air inlet of the by-product gas condenser HE6 is connected with the top air outlet of the air desorption tower DA, and the air outlet of the by-product gas condenser HE6 is connected with the air inlet of the boiler air preheater. During the operation, the condensed water generated from the outlet gas at the top of the air desorption tower DA flows back to the air desorption tower DA to maintain the water balance of the system; the air inlet of the product gas condenser HE7 is connected with the air outlet at the top of the steam desorption tower DS, and the air outlet of the product gas condenser HE7 is connected with the air inlet of the carbon dioxide compressor CC. During the operation, the condensed water generated from the outlet gas at the top of the steam desorption tower DS flows back to the steam desorption tower DS to maintain the water balance of the system.

[0039] The carbon dioxide absorption solvent used in the present invention is a mixed solution of carbonates and bicarbonates of alkali metal ions, such as a mixed solution of potassium carbonate and potassium bicarbonate, or a mixed solution of sodium carbonate and sodium bicarbonate, or a mixed solution of multiple alkali metal ions. Such absorption solvents can be prepared by those skilled in the art according to actual needs.

[0040] Solvent absorption of CO 2 Liquid-solid phase separation can occur after that. The solvent absorbs CO at 60-80℃ 2 (Because the absorption solvent reacts with CO at low temperature 2 The reaction rate is low), so that the carbonate in the absorption solvent is partially converted into bicarbonate, absorbing CO 2 The solvents before and after are kept in liquid state, but because the solubility of bicarbonate is much lower than that of carbonate of the same alkali metal ion, crystallization (precipitation) may occur when saturation is reached, and when cooled (such as at 35-55°C), a large amount of precipitation may occur rapidly, and most of the absorbed CO 2 It is concentrated and distributed in the solid phase in the form of bicarbonate.

[0041] The absorption solvent used in the present invention is widely available, cheap, easy to obtain, environmentally friendly, non-volatile, does not undergo thermal or oxidative degradation, has little corrosion to the capture device, has low viscosity in liquid state, and is resistant to SO in flue gas. 2 , NOx and other acidic gas impurities. But carbonate and CO 2 The kinetic rate of the reaction to generate bicarbonate is slow. In practical applications, in order to speed up the solvent to CO 2 In order to reduce the absorption rate, a small amount of activator (catalyst) can be used as an additive to the absorption solvent. The activators (catalysts) used are organic amines and their derivatives, amino acids (such as proline, glycine, sarcosine, taurine), inorganic salts (such as borates), etc. However, compared with organic amines and their derivatives, activators (catalysts) of amino acids and inorganic salts generally have the advantages of no volatility and good stability.

[0042] The working principle of the present invention is as follows:

[0043] CO generated from boiler combustion 2 The external flue gas, after selective catalytic reduction denitrification, bag dust removal, and flue gas desulfurization device, has a temperature of about 55-60°C. After heat exchange with the external cold air ready to enter the boiler air preheater through the gas heat exchanger HE0, it enters the flue gas pretreatment tower PTC, where it is countercurrently washed with circulating water (or dilute alkali solution) to remove particulate matter and water-soluble impurities in the flue gas;

[0044] The pre-treated flue gas enters from the air inlet at the bottom of the first-stage absorption tower A1 under the action of the pressure fan IB1, and flows from bottom to top, mixing with the CO sprayed down from the liquid inlet at the top of the first-stage absorption tower A1. 2 The lean solution contacts and reacts in countercurrent. The reaction temperature of the absorption tower is 60-80°C. The lean solution absorbs the carbon dioxide in the flue gas and converts it into CO 2 The rich solution is discharged from the liquid outlet at the bottom of the first-stage absorption tower A1, and the flue gas with some carbon dioxide removed is discharged through the gas outlet at the top of the first-stage absorption tower A1;

[0045] The flue gas discharged from the top outlet of the first-stage absorption tower A1 enters from the air inlet at the bottom of the final absorption tower A2 and flows from bottom to top, mixing with the CO sprayed down through the liquid inlet at the top of the final absorption tower A2. 2 The lean solution contacts and reacts in countercurrent. The reaction temperature of the absorption tower is 60-80°C. The lean solution absorbs the carbon dioxide in the flue gas and converts it into CO 2 The rich solution is discharged from the liquid outlet at the bottom of the final absorption tower A2, while the flue gas without carbon dioxide is discharged through the gas outlet at the top of the final absorption tower A2. After being cooled and the water vapor in the flue gas is recovered by the flue gas condenser HE1, it is discharged into the external environment atmosphere through the chimney;

[0046] CO discharged from the bottom outlet of the final absorption tower A2 2 The rich solution is cooled to 35-55°C by the final interstage heat exchanger HE2. Since the temperature difference between cooling and absorption reaction is small, the cooling load of the required cooling water is not high. 2 The rich solution then enters an inverted cone-shaped final liquid-solid separation tank C2, where the rich solution is circulated and stirred, a liquid-solid phase change occurs, crystals (precipitates) are precipitated, and the absorption solvent is separated into a clear liquid and a slurry; due to the difference in density between the two, the clear liquid overflows out of the separation tank from the upper clear liquid outlet, and the slurry flows out from the bottom slurry outlet of the separation tank under the action of gravity; the final liquid-solid separation tank C2 is a continuous operation, the liquid-solid phase separation occurs quickly, and the residence time is short, so the size of the separation tank is small;

[0047] The slurry material flowing out from the slurry outlet at the bottom of the final liquid-solid separation tank C2 enters the final hydrocyclone HC2 to further improve the liquid-solid separation efficiency; the clear liquid separated by the final hydrocyclone HC2 is mixed with the clear liquid overflowing from the final liquid-solid separation tank C2, and is injected into the final interstage heat exchanger HE2 through the second clear liquid pump LP2, and flows into the liquid inlet at the top of the first absorption tower A1 after being heated; the slurry separated by the final hydrocyclone HC2 enters the slurry mixing tank SM through the second slurry pump SP2. Since the slurry needs to maintain a certain fluidity, the liquid-solid separation efficiency of the final hydrocyclone HC2 does not need to be very high;

[0048] The CO sprayed from the upper liquid inlet of the first-stage absorption tower A1 2 Lean solution, and CO in the flue gas moving upward 2 A countercurrent contact reaction occurs (temperature is 60-80°C), and the generated CO 2 The rich solution is discharged from the liquid outlet at the bottom of the first-stage absorption tower A1; the discharged CO 2 The rich solution is cooled to 35-55°C by the first interstage heat exchanger HE3, and then enters an inverted cone-shaped first-stage liquid-solid separation tank C1 for circulation and stirring, and a liquid-solid phase change (crystallization or precipitation) occurs, and the solution is divided into a clear liquid and a slurry. Due to the difference in density between the two, the clear liquid overflows the separation tank from the upper clear liquid outlet, and the slurry flows out from the bottom slurry outlet of the separation tank under the action of gravity and enters the first-stage hydrocyclone HC1 to further improve the liquid-solid separation efficiency. The clear liquid separated by the first-stage hydrocyclone HC1 is mixed with the clear liquid overflowing from the first-stage liquid-solid separation tank C1, and is injected into the first interstage heat exchanger HE3 through the first-stage clear liquid pump LP1, and flows into the clear liquid mixing tank LM after being heated. The slurry separated by the first-stage hydrocyclone HC1 enters the slurry mixing tank SM through the first slurry pump SP1. Similarly, since the slurry needs to maintain fluidity, the separation efficiency of the first-stage hydrocyclone HC1 does not need to be very high.

[0049] The slurry delivered by the first slurry pump SP1 and the second slurry pump SP2 is mixed in the slurry mixing tank SM and delivered to the slurry preheater HE4 through the third slurry pump SP3, where the CO2 discharged from the bottom outlet of the air desorption tower DA and deeply desorbed is 2 The lean solution is heated and the preheated slurry is sent to the lean-rich solution heat exchanger HE5; the CO 2 The lean solution is cooled in the slurry preheater HE4 and returned to the clear liquid mixing tank LM to be mixed with the clear liquid from the first interstage heat exchanger HE3; the mixed liquid flows through the liquid outlet of the clear liquid mixing tank LM and the third clear liquid pump LP3 into the flue gas condenser HE1, where it is heated and then enters the upper liquid inlet of the final absorption tower A2 to be recycled as an absorption solvent;

[0050] The fully regenerated CO2 flows out of the reboiler RB outlet after passing through the lean-rich liquid heat exchanger HE5. 2 The slurry further heated by the lean liquid enters the steam desorption tower DS through the slurry inlet located at the upper part of the steam desorption tower DS; the CO rich 2 The slurry flows down along the steam desorption tower DS and is thermally decomposed to produce CO 2 , and initially regenerate CO 2 The lean solution flows out from the bottom of the steam desorption tower DS and enters the reboiler RB to exchange heat with low-pressure or medium-pressure saturated steam, and is further heated and decomposed in large quantities to obtain fully regenerated CO 2 Lean solution and CO rich solution 2 The product gas is rich in CO 2 The product gas returns to the steam desorption tower DS from the lower gas inlet, moves upward and heats the CO2-rich 2 The slurry flows out from the top of the steam desorption tower DS; the saturated steam is initially regenerated by CO 2 The lean solution is cooled, and the resulting condensate flows out of the reboiler RB; the fully regenerated CO 2 The lean solution is cooled by the lean-rich solution heat exchanger HE5, and enters the air desorption tower DA through the liquid inlet at the top of the air desorption tower DA to be further regenerated;

[0051] The air desorption tower DA is a stripping tower operated at atmospheric pressure, with air as carrier gas; the fully regenerated CO entering the air desorption tower DA 2 The lean solution is countercurrently contacted with the air flow containing saturated water vapor entering from the lower part of the air desorption tower DA, and the fully regenerated CO 2 The lean solution is deeply desorbed here, and the deeply desorbed CO 2 The lean solution flows out from the liquid outlet at the bottom of the air desorption tower DA, is cooled by the slurry preheater HE4, and flows back to the clear liquid mixing tank LM; the CO generated by deep desorption2 The gas is mixed with the air flow containing saturated water vapor, flows out through the top outlet of the air desorption tower DA, and enters the by-product gas condenser HE6, where it undergoes heat exchange with the water flow from the bottom of the water evaporator WE. The mixed gas is cooled, part of the water vapor is recovered, and the condensate is returned to the air desorption tower DA to maintain the water balance of the system. The cooled mixed air contains a small amount (3-4%) of CO generated by deep desorption. 2 , returns to the boiler to participate in combustion, making the CO in the flue gas of the coal-fired boiler 2 The content of CO increases from 13-14% to 15-16%, which in turn strengthens the 2 The driving force of absorption increases both the absorption rate and capacity;

[0052] The water heated by the by-product gas condenser HE6 flows through the circulating water pump WP into the product gas condenser HE7 and mixes with the CO2-rich gas flowing out from the top outlet of the steam desorption tower DS. 2 The product gas undergoes heat exchange, the product gas is cooled, the water vapor is recovered, and the condensed water returns to the steam desorption tower DS to maintain the water balance of the system; the cooled product gas enters the carbon dioxide compressor CC, where it undergoes multi-stage compression (including interstage cooling), dehydration, purification and liquefaction to obtain liquid CO 2 , and is temporarily stored in a storage tank for downstream use. The water flow heated by the product gas condenser HE7 returns to the water evaporator WE, enters the water evaporator WE through the upper water inlet, and countercurrently contacts with the air flow entering from the lower part of the water evaporator WE. Part of the water evaporates and becomes water vapor, taking away part of the heat. The cooling water flow flowing out of the bottom of the water evaporator WE enters the by-product gas condenser HE6 to be heated and recycled; the air flow sent in by the booster fan IIB2 is heated by the external hot flue gas in the gas heat exchanger HE0, and then enters the water evaporator WE. The air flow containing saturated water vapor obtained by the water evaporator WE enters the air inlet at the lower part of the air desorption tower DA.

[0053] The beneficial effects of the present invention are as follows:

[0054] 1. Use an absorption solvent that can produce liquid-solid phase separation, and one side of the absorption tower is arranged in multiple stages in series. The absorption solvent (CO 2 The lean solution) is mixed with CO in the upper absorption tower cavity. 2 The absorption reaction occurs upon contact, and the CO produced 2 The rich solution undergoes liquid-solid phase separation, and the slurry containing the solid phase directly enters the steam desorption tower for regeneration, that is, a portion of the absorption solvent is stripped from the absorption system and does not enter the next-stage absorption tower, thus reducing the required size of the next-stage absorption tower, making the device more compact and reducing the cost of the capture system;

[0055] 2. Since the absorption solvent entering the next absorption tower recovers CO2 Lean solution state, so it can always maintain good gas-liquid mass transfer driving force and CO 2 The absorption rate is compared with the arrangement without multi-stage absorption. 2 The absorption capacity is increased, the size of the absorption tower is further reduced, and the cost of the capture system is reduced;

[0056] 3. The reaction temperature of the absorption tower is maintained at 60-80°C, which is higher than the reaction temperature of the amine-based absorption solvent (40°C), which can increase the solvent's CO 2 absorption rate; at the same time, the CO returned from the clear liquid mixing tank to the final absorption tower 2 Lean liquid does not need further cooling, saving the energy consumption caused by cooling water cooling load;

[0057] 4. CO after absorption 2 The bicarbonate crystals (precipitates) produced by cooling the rich liquid are easy to separate, and the hydrocyclone does not require a very high liquid-solid separation efficiency, because the solid precipitate needs to be combined with a small amount of solution to form a slurry, which is then pumped into the desorption system through a slurry pump;

[0058] 5. The carbonate / bicarbonate absorption solvent used has lower reaction heat than traditional organic amine solvents; and due to its stable properties, desorption can occur at a higher temperature (140-160°C), making the desorption pressure higher, so the regeneration energy consumption is low;

[0059] 6. Absorption solvent tolerance to SO 2 The ability to absorb acidic gases such as sulfur is strong, and the flue gas does not need to be deeply desulfurized in the pretreatment tower; and the absorption solvent can tolerate O in the air. 2 , no oxidative degradation occurs, and it can be used in air desorption towers containing O 2 On the contrary, most of the organic amines and their derivatives are not suitable for this process due to their high oxidative degradation.

[0060] 7. Since only part of the solvent is absorbed, i.e., CO-rich 2 The slurry needs to enter the desorption tower to regenerate the lean CO 2 The absorption solvent is reduced, and the amount of solvent to be processed during desorption is reduced, so the size of the desorption tower can be reduced, making it more compact and reducing system costs;

[0061] 8. Rich in CO 2 The slurry contains only a small amount of solution to maintain fluidity, so the stripping heat and sensible heat required for desorption are small, the amount of steam required is also reduced, and the capture energy consumption is reduced; and because CO 2 The concentration is in the rich CO 2 The slurry is greatly enriched, the stripping pressure is increased, and the capture energy consumption and subsequent CO 2 Compression work requirement;

[0062] 9. The air desorption tower driven by water-saturated air can deeply desorb CO in the lean liquid 2 , using the waste heat integrated in the system (which is usually released directly to the environment) without consuming additional steam, improving energy utilization and saving costs; this waste heat includes but is not limited to using the condensate heat exchanger to recover the heat of the saturated steam condensate in the reboiler, using the compression interstage cooler to recover CO 2 Interstage heat in the multi-stage compression process of the compressor, as well as utilizing other low-grade waste heat from the capture system;

[0063] 10. Since the byproduct gas introduced into the air desorption tower contains 3-4% CO 2 (Depending on CO 2 Lean liquid temperature) enters the boiler air preheater and is used as combustion air to remove CO from the flue gas at the outlet of the coal-fired boiler. 2 The content increased from 13-14% to 15-16%; and the CO in the lean solution after deep desorption 2 The loading capacity is further reduced, which can enhance the gas-liquid mass transfer driving force and CO 2 The absorption rate increases the CO 2 The circulating load capacity reduces the required amount of absorption solvent, which can further reduce the size of the absorption tower and the capture cost;

[0064] 11. Rich in CO 2 The slurry is heat exchanged with the deep desorption lean liquid discharged from the bottom of the air desorption tower and the fully regenerated lean liquid discharged from the reboiler, which can increase the CO2-rich 2 The temperature of the slurry before and after entering the lean-rich liquid heat exchanger indirectly increases the operating temperature of the air desorption tower and improves the degree of deep desorption.

[0065] The embodiments described above are merely descriptions of preferred implementations of the present invention and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope of the present invention.

Claims

1. A carbon dioxide capture system based on liquid-solid phase separation, comprising a pretreatment tower (PTC), an absorption tower (A), a clear liquid mixing tank (LM), a slurry mixing tank (SM) and a desorption tower (D), characterized in that: The absorption towers (A) are in plurality and are connected in series with each other; the desorption towers (D) include a steam desorption tower (DS) and an air desorption tower (DA), which are connected in series with each other; The air inlet of the pretreatment tower (PTC) is for the external flue gas to be treated to enter, and the air outlet is connected to the air inlet of the first-stage absorption tower (A1) among the plurality of absorption towers (A); The gas outlet of the final absorption tower in the plurality of absorption towers (A) is connected to the gas inlet of the flue gas condenser (HE1), and the gas outlet of the flue gas condenser (HE1) is connected to the outside; An interstage heat exchanger (HE32) and a liquid-solid separation tank (C) are provided at the liquid outlet of each stage of the absorption towers (A), wherein the interstage heat exchanger (HE32) is used to cool the CO2-rich solution flowing out of the liquid outlet and transport the cooled CO2-rich solution to the corresponding liquid-solid separation tank (C); The clear liquid separated by the first-stage liquid-solid separation tank (C1) is heated by the first-stage interstage heat exchanger (HE3) and then transported to the clear liquid mixing tank (LM). The remaining interstage heat exchangers heat the clear liquid separated by the corresponding liquid-solid separation tank (C) and then transport it to the liquid inlet of the upper-stage absorption tower in sequence. The slurry outlets of each level of the liquid-solid separation tank (C) are connected to the inlet of the slurry mixing tank (SM); a slurry preheater (HE4) and a lean-rich liquid heat exchanger (HE5) are provided at the outlet of the slurry mixing tank (SM); the slurry inlet of the slurry preheater (HE4) is connected to the outlet of the slurry mixing tank (SM); the slurry outlet of the slurry preheater (HE4) is connected to the slurry inlet of the lean-rich liquid heat exchanger (HE5); the slurry outlet of the lean-rich liquid heat exchanger (HE5) is connected to the slurry inlet of the steam desorption tower (DS); and the liquid outlet of the steam desorption tower (DS) is connected to the liquid inlet of the air desorption tower (DA); The air outlet of the air desorption tower (DA) is connected to the air inlet of the boiler air preheater, the liquid outlet of the air desorption tower (DA) is connected to the lean liquid inlet of the slurry preheater (HE4), the lean liquid outlet of the slurry preheater (HE4) is connected to the inlet of the clear liquid mixing tank (LM), the liquid outlet of the clear liquid mixing tank (LM) is connected to the liquid inlet of the flue gas condenser (HE1), and the liquid outlet of the flue gas condenser (HE1) is connected to the liquid inlet of the final absorption tower.

2. A carbon dioxide capture system based on liquid-solid phase separation according to claim 1, characterized in that: It also includes a water evaporator (WE), a pressure blower II (B2), a gas heat exchanger (HE0), a by-product gas condenser (HE6) and a product gas condenser (HE7); The flue gas inlet of the gas heat exchanger (HE0) is for the external flue gas to be treated to enter, and the flue gas outlet of the gas heat exchanger (HE0) is connected to the air inlet of the pretreatment tower (PTC); The air inlet of the water evaporator (WE) is connected to the air outlet of the gas heat exchanger (HE0), the air inlet of the gas heat exchanger (HE0) is connected to the air outlet of the pressurizing fan II (B2), and the air inlet of the pressurizing fan II (B2) is connected to the outside; The air outlet of the water evaporator (WE) is communicated with the air inlet of the air desorption tower (DA); The water outlet of the water evaporator (WE) is communicated with the water inlet of the by-product gas condenser (HE6), the water outlet of the by-product gas condenser (HE6) is communicated with the water inlet of the product gas condenser (HE7), and the water outlet of the product gas condenser (HE7) is communicated with the water inlet of the water evaporator (WE); The air inlet of the by-product gas condenser (HE6) is communicated with the air outlet of the air desorption tower (DA), and the air outlet of the by-product gas condenser (HE6) is communicated with the air inlet of the boiler air preheater; The air inlet of the product gas condenser (HE7) is communicated with the air outlet at the top of the steam desorption tower (DS), and the air outlet of the product gas condenser (HE7) is communicated with the air inlet of the carbon dioxide compressor (CC).

3. A carbon dioxide capture system based on liquid-solid phase separation according to claim 1 or 2, characterized in that: It also includes a reboiler (RB), the liquid inlet of the reboiler (RB) is connected to the outlet of the incompletely desorbed lean liquid of the steam desorption tower (DS), the air outlet of the reboiler (RB) is connected to the air inlet of the lower part of the steam desorption tower (DS), the liquid outlet of the reboiler (RB) is connected to the lean liquid inlet of the lean-rich liquid heat exchanger (HE5), and the lean liquid outlet of the lean-rich liquid heat exchanger (HE5) is connected to the liquid inlet of the air desorption tower (DA); the reboiler (RB) is provided with a saturated steam inlet and a condensate outlet.

4. A carbon dioxide capture system based on liquid-solid phase separation according to claim 3, characterized in that: A hydrocyclone (HC) is provided between each liquid-solid separation tank (C) and the slurry mixing tank (SM), the slurry inlet of the hydrocyclone (HC) is connected to the slurry outlet of the corresponding liquid-solid separation tank (C), the slurry outlets of the hydrocyclone (HC) are connected to the inlet of the slurry mixing tank (SM), and the clear liquid outlet of each hydrocyclone (HC) is connected to the clear liquid outlet of the corresponding liquid-solid separation tank (C).

5. A carbon dioxide capture system based on liquid-solid phase separation according to claim 4, characterized in that: A slurry pump (SP) is installed between the slurry outlet of each hydrocyclone (HC) and the inlet of the slurry mixing tank (SM), and between the outlet of the slurry mixing tank (SM) and the slurry inlet of the slurry preheater (HE4).

6. A carbon dioxide capture system based on liquid-solid phase separation according to claim 5, characterized in that: A clear liquid pump (LP) is installed at the confluence of the clear liquid outlets of the liquid-solid separation tank (C) and the hydrocyclone (HC), as well as at the liquid outlet of the clear liquid mixing tank (LM).

7. A carbon dioxide capture system based on liquid-solid phase separation according to claim 6, characterized in that: A pressurizing fan I (B1) is installed between the air outlet of the pretreatment tower (PTC) and the air inlet of the first-stage absorption tower (A1).

8. A carbon dioxide capture system based on liquid-solid phase separation according to claim 2, characterized in that: A circulating water pump (WP) is installed between the water outlet of the by-product gas condenser (HE6) and the water inlet of the product gas condenser (HE7).

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