System and method for capturing carbon dioxide in smelter flue gas to treat high-calcium and high-salt wastewater

Abstract

The present invention provides a system and method for capturing carbon dioxide in smelter flue gas to treat high-calcium and high-salt wastewater. The system includes: a pH value adjustment unit, having a high-calcium and high-salt wastewater inlet and an alkaline wastewater outlet, the pH value adjustment unit is used to adjust the pH value of the high-calcium and high-salt wastewater to obtain alkaline wastewater; a carbon dioxide capture unit, having a smelter flue gas inlet and a carbon dioxide outlet, the carbon dioxide capture unit is used to capture carbon dioxide in the smelter flue gas to form carbon dioxide; a decalcification reaction unit, having a carbon dioxide inlet and an alkaline wastewater inlet, the carbon dioxide inlet is connected to the carbon dioxide outlet, the alkaline wastewater inlet is connected to the alkaline wastewater outlet, the decalcification reaction unit is used to decalcify the alkaline wastewater to obtain a reaction slurry; a solid-liquid separation unit, connected to the decalcification reaction unit, is used to perform solid-liquid separation on the reaction slurry. The present invention solves the problem that the decalcification pretreatment process of high-calcium and high-salt wastewater in smelters is not energy-saving.

Description

Technical Field

[0001] The present invention relates to the technical field of carbon emission reduction and industrial wastewater treatment, and in particular to a system and method for capturing carbon dioxide in smelter flue gas to treat high-calcium and high-salt wastewater. Background Art

[0002] In current smelters, coal or coke is used as a reducing agent for the smelting of metal oxides and metal sulfides in large quantities during the smelting process of non-ferrous metals, so that the flue gas emitted contains a large amount of carbon dioxide. At the same time, multiple process sections such as smelting, flue gas washing, chemical water treatment station, sulfuric acid preparation and slag flushing in the process of non-ferrous metal smelting will also produce a large amount of high-calcium and high-salt wastewater. These high-calcium and high-salt wastewaters are rich in calcium ions, which are rich in calcium, magnesium, sodium, chlorine, fluorine, sulfate ions and other ions. In order to prevent calcium scaling from affecting the wastewater treatment section equipment, a decalcification pretreatment section needs to be set up in the wastewater treatment process. The commonly used decalcification process route is generally a softening filtration with a dosing reaction, and the reagents are lime, sodium hydroxide, sodium carbonate, etc. Due to the large amount of reagents used and insufficient reaction, the current decalcification pretreatment process mostly adopts a process route of directly passing carbon dioxide gas into the wastewater for softening reaction. The carbon dioxide gas comes from purchased liquid carbon dioxide, which is dissolved into the wastewater after being vaporized by a gasifier.

[0003] Conventional decalcification pretreatment processes use electricity or steam to heat water to vaporize liquid carbon dioxide, and then the carbon dioxide gas is introduced into a softening reaction tank for reaction. The process is simple. However, this conventional method requires the purchase of liquid carbon dioxide, which consumes a large amount of electricity or steam during the vaporization process, and wastes the cooling capacity of the liquid carbon dioxide during the vaporization process. Obviously, the conventional method is not energy-saving and greatly increases the operating cost of the wastewater treatment system.

[0004] In view of this, the present invention is proposed. Summary of the invention

[0005] The main purpose of the present invention is to provide a system and method for capturing carbon dioxide in smelter flue gas to treat high-calcium and high-salt wastewater, so as to solve the problems of low energy consumption and the need to purchase liquid carbon dioxide in the prior art decalcification pretreatment process for high-calcium and high-salt wastewater from smelters.

[0006] In order to achieve the above-mentioned purpose, according to one aspect of the present invention, there is provided a system for capturing carbon dioxide in smelter flue gas to treat high-calcium and high-salt wastewater, which comprises: a pH value adjustment unit having a high-calcium and high-salt wastewater inlet and an alkaline wastewater outlet, the pH value adjustment unit being used to adjust the pH value of the high-calcium and high-salt wastewater to obtain alkaline wastewater; a carbon dioxide capture unit having a smelter flue gas inlet and a carbon dioxide outlet, the carbon dioxide capture unit being used to capture carbon dioxide in the smelter flue gas to form carbon dioxide; a decalcification reaction unit having a carbon dioxide inlet and an alkaline wastewater inlet, the carbon dioxide inlet being connected to the carbon dioxide outlet, the alkaline wastewater inlet being connected to the alkaline wastewater outlet, the decalcification reaction unit being used to cause the alkaline wastewater to undergo a decalcification reaction under the action of carbon dioxide to obtain a reaction slurry; and a solid-liquid separation unit being connected to the decalcification reaction unit and being used to perform solid-liquid separation on the reaction slurry.

[0007] Furthermore, the pH value adjusting unit comprises: an alkali solution storage tank for supplying alkali solution; an alkali solution dilution tank connected to the alkali solution storage tank for diluting the alkali solution to obtain alkali solution dilution liquid; and a pH value adjusting pool having a high-calcium and high-salt wastewater inlet and an alkaline wastewater outlet.

[0008] Furthermore, the carbon dioxide capture unit is a carbon dioxide chemical absorption unit, a carbon dioxide physical absorption unit, an adsorption separation unit or a carbon dioxide membrane separation unit.

[0009] Furthermore, the system also includes a carbon dioxide storage tank, which is arranged on the flow path between the carbon dioxide inlet and the carbon dioxide outlet.

[0010] Furthermore, the solid-liquid separation unit includes: a sedimentation tank having a reaction slurry inlet, a supernatant outlet and a sludge outlet, the reaction slurry inlet being connected to the decalcification reaction unit; a liquid storage tank being connected to the supernatant outlet; a sludge tank being connected to the sludge outlet; a dehydration unit being connected to the outlet of the sludge tank and used for dehydrating the sludge discharged from the sludge tank; the dehydration unit having a filtrate outlet, which is connected to the pH adjustment tank.

[0011] According to another aspect of the present invention, a method for capturing carbon dioxide in smelter flue gas to treat high-calcium and high-salt wastewater is provided, which adopts the above-mentioned system and includes the following steps: S1, adjusting the pH value of the high-calcium and high-salt wastewater to alkaline through a pH adjustment unit to obtain alkaline wastewater; S2, capturing carbon dioxide in the smelter flue gas through a carbon dioxide capture unit; S3, allowing the alkaline wastewater and carbon dioxide to undergo a decalcification reaction in a decalcification reaction unit to obtain a reaction slurry; S4, performing solid-liquid separation on the reaction slurry through a solid-liquid separation unit.

[0012] Furthermore, the above step S1 includes: diluting the alkali solution to obtain an alkali solution dilution liquid; using the alkali solution dilution liquid to adjust the pH value of the high-calcium and high-salt wastewater to above 9.5; preferably, the alkali solution is one or more of a sodium hydroxide aqueous solution, a potassium hydroxide aqueous solution, and an ammonia aqueous solution; preferably, the mass concentration of the alkali solution dilution liquid is 10 to 30%.

[0013] Furthermore, in step S3, the reaction time during the decalcification reaction is 2 to 4 hours, the pH value of the reaction slurry is controlled at 10 to 11, and the reaction temperature is 20 to 30°C.

[0014] Furthermore, in step S4, the solid-liquid separation process includes: sending the reaction slurry into a sedimentation tank for sedimentation treatment to obtain a supernatant and sludge; sending the supernatant into a liquid storage tank; first sending the sludge into a sludge tank, and then sending it into a dehydration unit for dehydration treatment to obtain a mud cake and a filtrate; and returning the filtrate to step S1 for a pH adjustment step.

[0015] Furthermore, the high-calcium and high-salt wastewater contains 660-1340 mg / L of calcium ions, 2300-50400 mg / L of sodium ions, 420-504 mg / L of magnesium ions, 11.5-20.5 mg / L of iron ions, 150-930 mg / L of chloride ions, 12.56-22.33 mg / L of fluoride ions, and 3250-101410 mg / L of sulfate ions.

[0016] The present invention provides a system for capturing carbon dioxide in smelter flue gas to treat high-calcium and high-salt wastewater. The system reduces carbon emissions of enterprises by effectively capturing carbon dioxide in smelter flue gas, and simultaneously utilizes the recovered carbon dioxide to couple with the wastewater treatment system to remove calcium ions in wastewater, replacing the conventional decalcification pretreatment process. It does not require the purchase of liquid carbon dioxide, reduces electricity and steam energy consumption, greatly reduces the operating cost of the wastewater treatment system, and realizes carbon circulation among the entire plant sections of the smelter, with good environmental and economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The drawings constituting a part of the present application are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0018] Figure 1 A structural block diagram of a system for capturing carbon dioxide in smelter flue gas to treat high-calcium and high-salt wastewater according to an embodiment of the present invention is shown.

[0019] The above drawings include the following reference numerals:

[0020] 10. pH value adjustment unit; 11. alkali solution storage tank; 12. alkali solution dilution tank; 13. pH value adjustment tank; 20. carbon dioxide capture unit; 30. decalcification reaction unit; 40. solid-liquid separation unit; 41. sedimentation tank; 42. liquid storage tank; 43. sludge tank; 44. dehydration unit; 50. carbon dioxide storage tank. DETAILED DESCRIPTION

[0021] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0022] As described in the background technology section, the prior art decalcification pretreatment process for high-calcium and high-salt wastewater from smelters has the problems of being energy-inefficient and requiring external purchase of liquid carbon dioxide.

[0023] In order to solve the above problems, the present invention provides a system for capturing carbon dioxide in smelter flue gas to treat high-calcium and high-salt wastewater, such as Figure 1 As shown, the system includes a pH value adjusting unit 10, a carbon dioxide capture unit 20, a decalcification reaction unit 30 and a solid-liquid separation unit 40. The pH value adjusting unit 10 has a high-calcium and high-salt wastewater inlet and an alkaline wastewater outlet. The pH value adjusting unit 10 is used to adjust the pH value of the high-calcium and high-salt wastewater to obtain alkaline wastewater; the carbon dioxide capture unit 20 has a smelter flue gas inlet and a carbon dioxide outlet. The carbon dioxide capture unit 20 is used to capture carbon dioxide in the smelter flue gas to form carbon dioxide; the decalcification reaction unit 30 has a carbon dioxide inlet and an alkaline wastewater inlet, the carbon dioxide inlet is connected to the carbon dioxide outlet, the alkaline wastewater inlet is connected to the alkaline wastewater outlet, the decalcification reaction unit 30 is used to make the alkaline wastewater undergo a decalcification reaction under the action of carbon dioxide to obtain a reaction slurry; the solid-liquid separation unit 40 is connected to the decalcification reaction unit 30, and is used to perform solid-liquid separation on the reaction slurry.

[0024] Smelter flue gas usually contains a high concentration of carbon dioxide, generally 3-50%, and the gas volume is large. The system provided by the present invention reduces the carbon emissions of enterprises by effectively capturing carbon dioxide in the smelter flue gas, and at the same time uses the recovered carbon dioxide to couple the wastewater treatment system to remove calcium ions in the wastewater, replacing the conventional decalcification pretreatment process, without the need to purchase liquid carbon dioxide, reducing electricity and steam energy consumption, greatly reducing the operating cost of the wastewater treatment system, and realizing the carbon cycle between the entire plant sections of the smelter, with good environmental and economic benefits.

[0025] In a preferred embodiment, the pH value adjusting unit 10 includes an alkali solution storage tank 11, an alkali solution dilution tank 12 and a pH value adjusting tank 13, wherein the alkali solution storage tank 11 is used to supply alkali solution; the alkali solution dilution tank 12 is connected to the alkali solution storage tank 11 and is used to dilute the alkali solution to obtain an alkali solution dilution solution; the pH value adjusting tank 13 has a high calcium and high salt wastewater inlet and an alkaline wastewater outlet. After the high concentration alkali solution provided by the alkali solution storage tank 11 enters the alkali solution dilution tank 12 for dilution, it can be passed into the pH value adjusting tank 13 to adjust the pH value of the high calcium and high salt wastewater. Dilution through the alkali solution dilution tank 12 is more conducive to maintaining stability and uniformity during the pH value adjustment process.

[0026] The carbon dioxide capture unit 20 may be a common device in the field of carbon capture, such as but not limited to a carbon dioxide chemical absorption unit, a carbon dioxide physical absorption unit, an adsorption separation unit or a carbon dioxide membrane separation unit, etc. The capture principles are as follows:

[0027] In the chemical absorption unit, the carbon dioxide in the smelting flue gas and the chemical solvent undergo a reversible chemical reaction in the absorption tower, and the solvent is converted into a rich liquid containing carbon dioxide. The rich liquid enters the desorption tower and is heated and decomposed to release carbon dioxide. The absorption and desorption operations are performed alternately, thereby realizing the separation and recovery of carbon dioxide and the regeneration and recycling of the absorption liquid. It is a method that is currently widely used. At present, the commonly used absorbents for chemical absorption include: ammonia water, ionic liquids, potassium carbonate solutions, alcohol amine solutions, etc. The chemical absorption method captures CO2 with a purity of 99%, has a wide adaptability to flue gas components, mature technology, and is suitable for low-concentration and large-scale CO2 capture in industrial processes.

[0028] The physical absorption unit uses the difference in solubility of carbon dioxide in organic solvents under different operating conditions to achieve separation. Typical physical absorption methods include sulfolane method, polyethylene glycol dimethyl ether method, methanol method, pressurized water washing method, N-2 methyl pyrrolidone method, propylene carbonate method, etc. The physical absorption method captures CO2 with a purity of 98%, which is suitable for the capture of high-concentration CO2 in flue gas, the solvent is non-corrosive, and the energy consumption is relatively low.

[0029] The adsorption separation unit is a process that uses solid adsorbents to selectively adsorb and desorb carbon dioxide in mixed gases to achieve separation. According to different operating processes, the adsorption method can be divided into pressure swing adsorption, vacuum regeneration adsorption and temperature swing adsorption. The adsorption method captures CO2 with a purity of 97%, with relatively low energy consumption, simple process flow and no secondary pollution.

[0030] The membrane separation unit is a method of separating and classifying substances by utilizing the different requirements of particle size and pressure difference for isolation dispersion. It is a relatively new technology. The membrane separation process depends on the permeability and selectivity of the membrane. The purity of CO2 captured by the membrane separation method reaches 97%, with low system energy consumption, small equipment size, simple operation and maintenance, and strong compatibility.

[0031] The carbon dioxide captured by the carbon dioxide capture unit 20 can directly enter the decalcification reaction unit 30 to participate in the decalcification reaction of the alkaline wastewater. Of course, in order to make the reaction more stable and facilitate the adjustment of the intake amount of carbon dioxide, in a preferred embodiment, the system further includes a carbon dioxide storage tank 50, which is arranged on the flow path between the carbon dioxide inlet and the carbon dioxide outlet.

[0032] In a preferred embodiment, the solid-liquid separation unit 40 includes a sedimentation tank 41, a liquid storage tank 42, a sludge tank 43 and a dehydration unit 44; the sedimentation tank 41 has a reaction slurry inlet, a supernatant outlet and a sludge outlet, and the reaction slurry inlet is connected to the decalcification reaction unit 30; the liquid storage tank 42 is connected to the supernatant outlet; the sludge tank 43 is connected to the sludge outlet; the dehydration unit 44 is connected to the outlet of the sludge tank 43, and is used to dehydrate the sludge discharged from the sludge tank 43; the dehydration unit 44 has a filtrate outlet, which is connected to the pH value adjustment tank 13. In this arrangement, the reaction slurry formed by the decalcification reaction first enters the sedimentation tank 41 for sedimentation treatment, and the supernatant enters the liquid storage tank 42, which can be pumped to the downstream section for further deep treatment. The sedimentation bottom flow enters the sludge tank 43 for temporary storage, and then is dehydrated by the dehydration unit 44. The obtained mud cake is transported out for disposal, and the filtrate is returned to the pH adjustment unit 10 for cyclic treatment to further improve the pre-decalcification effect, and at the same time acts as a partial pH adjuster.

[0033] According to another aspect of the present invention, a method for capturing carbon dioxide in smelter flue gas to treat high-calcium and high-salt wastewater is provided, which adopts the above-mentioned system, and the method comprises the following steps: S1, adjusting the pH value of the high-calcium and high-salt wastewater to alkaline through a pH adjustment unit 10 to obtain alkaline wastewater; S2, capturing carbon dioxide in the smelter flue gas through a carbon dioxide capture unit 20; S3, allowing the alkaline wastewater and carbon dioxide to undergo a decalcification reaction in a decalcification reaction unit 30 to obtain a reaction slurry; S4, performing solid-liquid separation on the reaction slurry through a solid-liquid separation unit 40.

[0034] Smelter flue gas usually contains a high concentration of carbon dioxide, generally 3-50%, and the gas volume is large. The method provided by the present invention reduces the carbon emissions of enterprises by effectively capturing carbon dioxide in the flue gas of the smelter, and at the same time uses the recovered carbon dioxide to couple the wastewater treatment system to remove calcium ions in the wastewater, replacing the conventional decalcification pretreatment process, and does not require the purchase of liquid carbon dioxide, reducing electricity and steam energy consumption, greatly reducing the operating cost of the wastewater treatment system, and realizing the carbon cycle between the whole plant sections of the smelter, with good environmental and economic benefits.

[0035] In order to improve the stability of the pH adjustment process, in a preferred embodiment, the above step S1 includes: diluting the alkali solution to obtain an alkali solution dilution liquid; using the alkali solution dilution liquid to adjust the pH value of the high-calcium and high-salt wastewater to above 9.5. Adjusting the pH value of the high-calcium and high-salt wastewater to the above range is more conducive to the full decalcification reaction. More preferably, the pH value of the high-calcium and high-salt wastewater is adjusted to 9.5-12.5. Preferably, the alkali solution is one or more of an aqueous sodium hydroxide solution, an aqueous potassium hydroxide solution, and an ammonia solution; preferably, the mass concentration of the alkali solution dilution liquid is 10-30%. In addition to being able to effectively adjust the pH value, the use of the above alkali solution will not introduce new impurity ions into the system and will not affect the subsequent decalcification reaction.

[0036] In a preferred embodiment, in the above step S3, the reaction time during the decalcification reaction is 2 to 4 hours, the pH value of the reaction slurry is controlled at 10 to 11, and the reaction temperature is 20 to 30° C. Under the above process conditions, the decalcification reaction is carried out with higher removal efficiency of calcium ions.

[0037] The reaction slurry obtained after the decalcification reaction can directly enter the solid-liquid separation process. In actual operation, the solid-liquid separation process includes: sending the reaction slurry into the sedimentation tank 41 for sedimentation treatment to obtain supernatant and sludge; sending the supernatant into the liquid storage tank 42; sending the sludge into the sludge tank 43 first, and then entering the dehydration unit 44 for dehydration treatment to obtain mud cake and filtrate; returning the filtrate to step S1 for pH adjustment step. The above supernatant can be pumped to the downstream section for further deep treatment. The obtained mud cake is transported out for disposal, and the filtrate is returned to the pH adjustment unit 10 for circulation treatment, so as to further improve the pre-decalcification effect, and at the same time act as a partial pH regulator.

[0038] The method of the present invention can effectively treat high-calcium and high-salt wastewater in a smelter, especially high-calcium and high-salt wastewater containing 420-1340 mg / L of calcium ions, 2300-50400 mg / L of sodium ions, 460-504 mg / L of magnesium ions, 11.5-20.5 mg / L of iron ions, 150-930 mg / L of chloride ions, 12.56-22.33 mg / L of fluoride ions, 3250-101410 mg / L of sulfate ions, etc., and the treatment effect is better.

[0039] The present application is further described in detail below in conjunction with specific embodiments. These embodiments should not be construed as limiting the scope of protection claimed in the present application.

[0040] Comparative Example 1

[0041] The high calcium and high salt wastewater of a nonferrous smelting plant comes from sintering thickener, flue gas washing water and smelting wastewater, with a wastewater volume of 500m 3 / d, the wastewater contains 420mg / L calcium ions, 5400mg / L sodium ions, 480mg / L magnesium ions, 16mg / L iron ions, 250mg / L chloride ions, 16mg / L fluoride ions, and 6800mg / L sulfate ions. The factory purchases liquid carbon dioxide to remove calcium ions from the wastewater. Specifically, low-pressure steam is used as the heat energy of the vaporizer to vaporize the liquid carbon dioxide, and then it is passed into the reaction tank for reaction. The pH value of the effluent is 10.54, the hardness is <150mg / L, and the unit wastewater consumption of carbon dioxide is 0.55kg / m 3 , the unit wastewater consumption of sodium hydroxide is 1.29kg / m 3 , low-pressure steam consumption per unit wastewater is 0.5kg / m 3 , annual operating costs are 13.31 million yuan.

[0042] Example 1

[0043] The high calcium and high salt wastewater of a nonferrous smelting plant comes from sintering thickener, flue gas washing water and smelting wastewater, with a wastewater volume of 500m 3 / d, the wastewater contains 420mg / L calcium ions, 5400mg / L sodium ions, 480mg / L magnesium ions, 16mg / L iron ions, 250mg / L chloride ions, 16mg / L fluoride ions, and 6800mg / L sulfate ions. Figure 1 The system shown in the figure captures carbon dioxide in the flue gas of the smelter to treat high-calcium and high-salt wastewater. The specific treatment method is as follows:

[0044] Using sodium hydroxide lye, diluting it with water in an lye dilution tank to form a lye dilution liquid with a mass concentration of 30%, and then using the lye dilution liquid to adjust the pH value of the high-calcium and high-salt wastewater to 11.4 to form alkaline wastewater;

[0045] A 0.5t / d carbon dioxide capture system is used to capture carbon dioxide (carbon dioxide content of 11-15%) in the flue gas discharged from the waste heat boiler of the smelter. The carbon dioxide capture system uses a chemical absorption unit. After dust removal, the flue gas from the waste heat boiler enters the chemical absorption tower through a preheating reboiler. The carbon dioxide component reacts chemically with the absorbent ammonia water to form a rich liquid. The rich liquid enters the packed desorption tower and is heated and decomposed by steam to obtain 95% pure carbon dioxide and absorbent. The absorbent is sent to the system for recycling, and the treated waste heat boiler purified tail gas is discharged into the atmosphere. The mass transfer and energy transfer of the entire capture process are synergistically enhanced;

[0046] The above carbon dioxide was introduced into alkaline wastewater for decalcification reaction. The reaction temperature was 25°C, the reaction time was 3 hours, the effluent pH value was 10.54, and the hardness was <150 mg / L.

[0047] The operating cost of the carbon dioxide capture device is 200 yuan / tCO2, and the carbon dioxide consumption per ton of wastewater treated is 0.55kg / m 3 Calculation shows that the annual operating cost is 33,000 yuan. The annual carbon dioxide emission reduction of the whole plant is 110 tons. After the enterprise switched to the process of the present invention, the annual operating cost was saved by 13.277 million yuan compared with that before the technical transformation, the annual carbon dioxide capture was 180 tons, and the annual carbon dioxide emission reduction was 110 tons, which greatly reduced the production and operation costs of the enterprise, and significantly improved the environmental protection and economic benefits.

[0048] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A system for capturing carbon dioxide in smelter flue gas to treat high-calcium and high-salt wastewater, characterized in that: include: A pH value adjusting unit (10) has a high-calcium and high-salt wastewater inlet and an alkaline wastewater outlet, and the pH value adjusting unit (10) is used to adjust the pH value of the high-calcium and high-salt wastewater to above 9.5 to obtain alkaline wastewater; the pH value adjusting unit (10) uses an alkali diluent to adjust the pH value of the high-calcium and high-salt wastewater, and the alkali solution is one or more of a sodium hydroxide aqueous solution, a potassium hydroxide aqueous solution, and an ammonia aqueous solution; A carbon dioxide capture unit (20) having a smelter flue gas inlet and a carbon dioxide outlet, wherein the carbon dioxide capture unit (20) is used to capture carbon dioxide in the smelter flue gas to form carbon dioxide; A decalcification reaction unit (30) having a carbon dioxide inlet and an alkaline wastewater inlet, wherein the carbon dioxide inlet is connected to the carbon dioxide outlet, and the alkaline wastewater inlet is connected to the alkaline wastewater outlet. The decalcification reaction unit (30) is used to cause the alkaline wastewater to undergo a decalcification reaction under the action of the carbon dioxide to obtain a reaction slurry; The solid-liquid separation unit (40) is connected to the decalcification reaction unit (30) and is used to perform solid-liquid separation on the reaction slurry.

2. The system according to claim 1, characterized in that The pH value adjustment unit (10) comprises: an alkali solution storage tank (11) for supplying alkali solution; An alkali solution dilution tank (12), connected to the alkali solution storage tank (11), used to dilute the alkali solution to obtain an alkali solution dilution liquid; The pH value adjustment tank (13) has the high-calcium and high-salt wastewater inlet and the alkaline wastewater outlet.

3. The system according to claim 1 or 2, characterized in that: The carbon dioxide capture unit (20) is a carbon dioxide chemical absorption unit, a carbon dioxide physical absorption unit, an adsorption separation unit or a carbon dioxide membrane separation unit.

4. The system according to claim 3, characterized in that The system further comprises a carbon dioxide storage tank (50) which is arranged on the flow path between the carbon dioxide inlet and the carbon dioxide outlet.

5. The system according to claim 2, characterized in that The solid-liquid separation unit (40) comprises: A sedimentation tank (41) having a reaction slurry inlet, a supernatant outlet and a sludge outlet, wherein the reaction slurry inlet is connected to the decalcification reaction unit (30); A liquid storage tank (42), connected to the supernatant outlet; A sludge tank (43), connected to the sludge outlet; A dehydration unit (44) is connected to the outlet of the sludge tank (43) and is used to dehydrate the sludge discharged from the sludge tank (43); the dehydration unit (44) has a filtrate outlet, which is connected to the pH value adjustment tank (13).

6. A method for capturing carbon dioxide in smelter flue gas to treat high-calcium and high-salt wastewater, characterized in that: The method adopts the system according to any one of claims 1 to 5, and the method comprises the following steps: S1, adjusting the pH value of the high-calcium and high-salt wastewater to alkaline through a pH adjustment unit (10) to obtain alkaline wastewater; S2, capturing carbon dioxide from smelter flue gas by a carbon dioxide capture unit (20); S3, allowing the alkaline wastewater and the carbon dioxide to undergo a decalcification reaction in a decalcification reaction unit (30) to obtain a reaction slurry; S4, performing solid-liquid separation on the reaction slurry through a solid-liquid separation unit (40); Wherein, the step S1 comprises: diluting the alkali solution to obtain a diluted alkali solution; The alkali diluent is used to adjust the pH value of the high-calcium and high-salt wastewater to above 9.5; The alkali solution is one or more of a sodium hydroxide aqueous solution, a potassium hydroxide aqueous solution, and an ammonia aqueous solution.

7. The method according to claim 6, characterized in that The mass concentration of the alkali solution dilution is 10-30%.

8. The method according to claim 6 or 7, characterized in that: In the step S3, the reaction time during the decalcification reaction is 2-4 hours, the pH value of the reaction slurry is controlled at 10-11, and the reaction temperature is 20-30°C.

9. The method according to claim 6 or 7, characterized in that: The solid-liquid separation unit (40) comprises: A sedimentation tank (41) having a reaction slurry inlet, a supernatant outlet and a sludge outlet, wherein the reaction slurry inlet is connected to the decalcification reaction unit (30); A liquid storage tank (42), connected to the supernatant outlet; A sludge tank (43), connected to the sludge outlet; A dehydration unit (44) connected to the outlet of the sludge tank (43); the dehydration unit (44) has a filtrate outlet connected to the pH adjustment tank of the pH adjustment unit (10); In step S4, the solid-liquid separation process includes: The reaction slurry is sent to the sedimentation tank (41) for sedimentation treatment to obtain a supernatant and sludge; Sending the supernatant into the liquid storage tank (42); The sludge is first sent to the sludge tank (43), and then sent to the dehydration unit (44) for dehydration treatment to obtain a sludge cake and a filtrate; the filtrate is returned to the step S1 to perform the pH value adjustment step.

10. The method according to claim 6 or 7, characterized in that: The high-calcium and high-salt wastewater contains 420-1340 mg / L of calcium ions, 2300-50400 mg / L of sodium ions, 460-504 mg / L of magnesium ions, 11.5-20.5 mg / L of iron ions, 150-930 mg / L of chloride ions, 12.56-22.33 mg / L of fluoride ions, and 3250-101410 mg / L of sulfate ions.

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