CN114291958A

CN114291958A - Wastewater containing salt and CO2Exhaust gas treatment system and method

Info

Publication number: CN114291958A
Application number: CN202210095957.3A
Authority: CN
Inventors: 胡惊雷; 方忠海
Original assignee: MEIJING (BEIJING) ENVIRONMENTAL PROTECTION TECHNOLOGY CO LTD
Current assignee: MEIJING (BEIJING) ENVIRONMENTAL PROTECTION TECHNOLOGY CO LTD
Priority date: 2022-01-26
Filing date: 2022-01-26
Publication date: 2022-04-08

Abstract

The invention provides a treatment system for salt-containing wastewater and a system containing CO₂Treatment system and method for waste gas for treating salt-containing waste water and CO-containing waste water₂The waste gas is treated by a multi-stage absorption unit and a multi-stage crystallization unit, so that salt-containing waste water and CO-containing waste water can be treated₂And simultaneously treating the waste gas. The system and the method provided by the invention can treat high-concentration brine, and specifically recover sulfate, chloride and nitrate in wastewater without specific treatmentProduces the mixed salt which can not be utilized, obtains the high-quality additional product, realizes the resource treatment of the salt-containing wastewater, and has no secondary pollution. Can be simultaneously reacted with CO₂Organically combined emission reduction for absorbing CO from exhaust gas₂Reduce CO₂The sodium bicarbonate with wide application is produced, and the method has obvious environmental benefit and economic benefit.

Description

Wastewater containing salt and CO2Exhaust gas treatment system and method

Technical Field

The invention relates to the field of waste gas and wastewater treatment, in particular to waste water containing inorganic salts such as sulfate and the like and CO₂The exhaust gas treatment system and the exhaust gas treatment method.

Background

Along with the shortage of water resources and the further improvement of environmental protection standards, the reuse rate of water in industrial projects is gradually improved, zero discharge or near zero discharge is gradually required in recent years, advanced treatment and recycling of effluent water or circulating water and sewage of sewage treatment plants are generally carried out in the industries of petrifaction, coal chemical industry, fine chemical industry, power plants and the like at present, the subsequent treatment problem of high-concentration brine after wastewater recycling is increasingly severe, some enterprises build evaporation pond temporary storage and natural evaporation, some enterprises build evaporation crystallization devices to carry out evaporation crystallization on the high-concentration brine, most of the high-concentration brine obtains mixed salt, individual enterprises separate sodium chloride, sodium sulfate and part of miscellaneous salt, the mixed salt does not go out, miscellaneous salt needs to be treated as hazardous waste, the sodium sulfate market is limited, the price is low, the market price of the sodium chloride is also low, and the application and popularization of zero discharge devices are severely restricted due to the problems, the high investment of the zero discharge devices and the like, the zero-emission treatment technology of the high-concentration brine with large product market capacity and good economic benefit is urgently needed.

Recently to CO at home and abroad₂The requirements and policies for emission reduction are continuously released and upgraded, the survival and development of enterprises generally face huge pressure and demand for carbon reduction, and how to reduce CO is realized in addition to energy conservation and consumption reduction₂Is also a real problem facing the enterprise.

Disclosure of Invention

In view of the above-mentioned drawbacks and CO present in the treatment of high-strength brine₂The invention aims to provide the waste water containing inorganic salts such as sulfate and the like and CO₂A system and method for treating exhaust gas.

The invention provides a treatment system for salt-containing wastewater, which comprises: the wastewater pretreatment unit is used for pretreating the salt-containing wastewater to remove organic matters, suspended matters and impurities in the salt-containing wastewater and reduce the hardness of the salt-containing wastewater; the first nanofiltration unit is connected with the wastewater pretreatment unit and is used for performing nanofiltration treatment on the effluent of the wastewater pretreatment unit; the second freezing and crystallizing unit is respectively connected with the first nanofiltration unit, the second nanofiltration unit, the ammonium sulfate evaporation and crystallization unit and the ammonium chloride evaporation and crystallization unit and is used for carrying out freezing and crystallizing treatment on nanofiltration trapped fluid of the first sodium filtration unit, nanofiltration trapped fluid of the second nanofiltration unit, crystallization mother liquor of the ammonium sulfate evaporation and crystallization unit and crystallization mother liquor of the ammonium chloride evaporation and crystallization unit, recovering sodium sulfate crystals and simultaneously discharging outlet water to the second nanofiltration unit; the second nanofiltration unit is connected with the second freezing crystallization unit and is used for performing nanofiltration treatment on the effluent of the second freezing crystallization unit; the nanofiltration retentate is returned to the second freeze crystallization unit and/or the wastewater pretreatment unit; the ammonium chloride evaporation crystallization unit is connected with the second nanofiltration unit and is used for carrying out evaporation crystallization treatment on the effluent of the second nanofiltration unit, recovering ammonium chloride crystals and discharging mother liquor; and the ammonium nitrate freezing and crystallizing unit is connected with the ammonium chloride evaporating and crystallizing unit and is used for adding desalted water into the evaporating and crystallizing mother liquor of the ammonium chloride evaporating and crystallizing unit for dilution, carrying out freezing and crystallizing treatment, recovering ammonium nitrate crystals and returning effluent to the ammonium chloride evaporating and crystallizing unit.

According to an embodiment of the invention, the processing system further comprises: a first absorption unit for absorbing CO₂CO of exhaust gas₂Absorption treatment; the second absorption unit is connected with the first absorption unit and used for carrying out CO treatment on the tail gas of the first absorption unit again by adopting ammonia water₂Absorbing treatment, and conveying part of absorption circulating solution to the first absorption unit; the first tail gas washing unit is connected with the second absorption unit and is used for washing the tail gas of the second absorption unit and discharging a washing solution; the second tail gas washing unit is connected with the first tail gas washing unit and is used for washing the tail gas of the first tail gas washing unit by adopting desalted water and washing the tail gasConveying the washing circulating solution to the first tail gas washing unit; the sodium bicarbonate centrifugal separation unit is connected with the first absorption unit g' unit and is used for carrying out centrifugal separation treatment on the sodium bicarbonate slurry in the first absorption unit, recovering sodium bicarbonate crystals and discharging mother liquor; the first freezing and crystallizing unit is connected with the sodium bicarbonate centrifugal separation unit and is used for freezing and crystallizing mother liquor of a centrifugal machine of the sodium bicarbonate centrifugal separation unit, recovering mixed crystals of sodium bicarbonate and ammonium bicarbonate and discharging the mother liquor; the ammonium sulfate evaporative crystallization unit is connected with the first freezing crystallization unit and is used for carrying out evaporative crystallization treatment on the freezing crystallization mother liquor of the first freezing crystallization unit, recovering ammonium sulfate crystals and discharging the mother liquor; and the sodium sulfate solution preparation unit is respectively connected with the first absorption unit, the first freezing and crystallizing unit and the first tail gas washing unit, is used for receiving the mixed crystals of the sodium bicarbonate and the ammonium bicarbonate of the first freezing and crystallizing unit and the discharged washing solution of the first tail gas washing unit, and is prepared into a solution with the sodium sulfate crystals to be sent to an absorption tower of the first absorption unit.

According to another embodiment of the present invention, the sodium sulfate solution preparation unit is connected to the second freezing and crystallizing unit to receive the sodium sulfate crystals of the second freezing and crystallizing unit.

According to another embodiment of the invention, the absorption towers of the first absorption unit and the second absorption unit are bubble towers, the absorption tower of the first absorption unit is internally provided with an absorption area and a precipitation area, sodium bicarbonate crystals formed in the reaction process are precipitated to the bottom of a cone of the bubble tower, and the bottom of the cone is provided with an air loosening and purging device.

According to another embodiment of the present invention, the absorption column employs separate absorption solution circulation and sodium bicarbonate slurry circulation.

According to another embodiment of the present invention, the depth of the liquid level in the absorption column of the first absorption unit is 10 to 20 m, and the height of the liquid level in the absorption column of the second absorption unit is 5 to 10 m.

According to another embodiment of the invention, the system further comprises a reverse osmosis concentration unit, wherein the reverse osmosis concentration unit is connected with the first nanofiltration unit and the second freezing and crystallizing unit and is used for performing reverse osmosis desalination treatment on the nanofiltration membrane permeate of the first nanofiltration unit and conveying reverse osmosis concentrated water to the second freezing and crystallizing unit for treatment.

In another aspect, the present invention provides a method for treating salt-containing wastewater, comprising: a wastewater pretreatment step, namely pretreating the salt-containing wastewater to remove organic matters, suspended matters and impurities in the salt-containing wastewater and reduce the hardness of the salt-containing wastewater; a first nanofiltration step, wherein the effluent of the wastewater pretreatment step is subjected to nanofiltration treatment; a second freezing and crystallizing step, namely freezing and crystallizing the nanofiltration trapped fluid of the first nanofiltration step, the crystallization mother liquor of the ammonium sulfate evaporation and crystallization step, the nanofiltration trapped fluid of the second nanofiltration step and the crystallization mother liquor of the ammonium chloride evaporation and crystallization step, recovering sodium sulfate crystals, and simultaneously discharging the effluent to the second nanofiltration step; a second nanofiltration step, wherein nanofiltration treatment is carried out on the effluent of the second freezing crystallization step; the nanofiltration retentate is returned to the second freeze crystallization step and/or pretreatment step; an ammonium chloride evaporation crystallization step, wherein the effluent of the second nanofiltration step is subjected to evaporation crystallization treatment, ammonium chloride crystals are recovered, and meanwhile, mother liquor is discharged; and a step of ammonium nitrate freezing crystallization, in which desalted water is added into the evaporation crystallization mother liquor of the step of ammonium chloride evaporation crystallization, freezing crystallization treatment is carried out, ammonium nitrate crystals are recovered, and effluent is returned to the step of ammonium chloride evaporation crystallization.

According to an embodiment of the present invention, the processing method further includes: a first absorption step of introducing CO₂CO of exhaust gas₂Absorption treatment while ensuring CO₂Excess; a second absorption step of carrying out CO again on the tail gas of the first absorption step by adopting ammonia water₂An absorption treatment while conveying a part of the absorption circulation solution to the first absorption step; a first tail gas washing step, wherein the tail gas in the second absorption step is washed, and meanwhile, a washing solution is discharged; a second off-gas washing step of washing an off-gas from the first off-gas washing stepWashing the gas with demineralized water, and conveying the washing circulating solution to the first tail gas washing step; a sodium bicarbonate centrifugal separation step, wherein the sodium bicarbonate slurry formed in the first absorption step is subjected to centrifugal separation treatment, sodium bicarbonate crystals are recovered, and meanwhile, mother liquor is discharged; a first freezing and crystallizing step, namely freezing and crystallizing the centrifugal mother liquor of the sodium bicarbonate centrifugal separation step, recovering mixed crystals of sodium bicarbonate and ammonium bicarbonate, and discharging the mother liquor; an ammonium sulfate evaporation crystallization step, wherein the freezing crystallization mother liquor of the first freezing crystallization step is subjected to evaporation crystallization treatment, ammonium sulfate crystals are recovered, and the mother liquor is discharged; and a sodium sulfate solution preparation step, namely preparing a mixed crystal of sodium bicarbonate and ammonium bicarbonate in the first freezing and crystallizing step, an discharged washing solution in the first tail gas washing step and a sodium sulfate crystal into a solution and sending the solution to the first absorption step.

According to another embodiment of the present invention, the temperatures of the first absorption step and the second absorption step are both 30 to 40 ℃.

According to another embodiment of the present invention, the temperature of the first freezing and crystallizing step is 5 to 10 ℃.

According to another embodiment of the present invention, the hardness of the effluent of the wastewater pretreatment step is less than 1mg/L (as CaCO)₃Meter), SDI is less than 3.

According to another embodiment of the invention, the method further comprises a reverse osmosis concentration step, wherein reverse osmosis desalination treatment is carried out on the nanofiltration membrane permeate of the first nanofiltration step, and freeze crystallization treatment is carried out on reverse osmosis concentrated water in a second freeze crystallization step.

According to another embodiment of the present invention, the temperature of the second freezing and crystallizing step is-5 to 5 ℃.

According to another embodiment of the invention, the temperature of the ammonium nitrate freeze crystallization step is 10-20 ℃.

According to another embodiment of the invention, the concentration of ammonium nitrate in the discharged mother liquor of the ammonium chloride evaporative crystallization step is 1400-6000 g/L, and preferably 4000-5000 g/L.

According to another embodiment of the present invention, in the ammonium nitrate freeze crystallization step, the addition amount of the demineralized water is 40 to 120% of the flow rate of the evaporation mother liquor, and more preferably 100 to 120%.

The invention also provides a CO-containing material₂A system for treating exhaust gas comprising: a first absorption unit for absorbing CO₂CO of exhaust gas₂Absorption treatment; the second absorption unit is connected with the first absorption unit and used for carrying out CO treatment on the tail gas of the first absorption unit again by adopting ammonia water₂Absorbing treatment, and conveying part of absorption circulating solution to the first absorption unit; the first tail gas washing unit is connected with the second absorption unit and is used for washing the tail gas of the second absorption unit and discharging a washing solution; the second tail gas washing unit is connected with the first tail gas washing unit and used for washing the tail gas of the first tail gas washing unit by adopting desalted water and conveying a washing circulating solution to the first tail gas washing unit; the sodium bicarbonate centrifugal separation unit is connected with the first absorption unit and is used for carrying out centrifugal separation treatment on the sodium bicarbonate slurry in the first absorption unit, recovering sodium bicarbonate crystals and discharging the mother liquor; the first freezing and crystallizing unit is connected with the sodium bicarbonate centrifugal separation unit and is used for freezing and crystallizing mother liquor of a centrifugal machine of the sodium bicarbonate centrifugal separation unit, recovering mixed crystals of sodium bicarbonate and ammonium bicarbonate and discharging the mother liquor; the ammonium sulfate evaporative crystallization unit is connected with the first freezing crystallization unit and is used for carrying out evaporative crystallization treatment on the freezing crystallization mother liquor of the first freezing crystallization unit, recovering ammonium sulfate crystals and discharging the mother liquor; and the sodium sulfate solution preparation unit is respectively connected with the first absorption unit, the first freezing and crystallizing unit and the first tail gas washing unit, is used for receiving the mixed crystals of the sodium bicarbonate and the ammonium bicarbonate of the first freezing and crystallizing unit and the discharged washing solution of the first tail gas washing unit, and is prepared into a solution with the sodium sulfate crystals to be sent to an absorption tower of the first absorption unit.

According to an embodiment of the present invention, the absorption towers of the first absorption unit and the second absorption unit are bubble towers, an absorption zone and a precipitation zone are arranged in the absorption tower of the first absorption unit, sodium bicarbonate crystals formed during the reaction are precipitated at the bottom of a cone of the bubble tower, and an air loosening and purging device is arranged at the bottom of the cone.

In another aspect of the present invention, there is provided a composition comprising CO₂A method of treating exhaust gas comprising: a first absorption step of introducing CO₂CO of exhaust gas₂Absorption treatment while ensuring CO₂Excess; a second absorption step of carrying out CO again on the tail gas of the first absorption step by adopting ammonia water₂An absorption treatment while conveying a part of the absorption circulation solution to the first absorption step; a first tail gas washing step, wherein the tail gas in the second absorption step is washed, and meanwhile, a washing solution is discharged; a second tail gas washing step, wherein the tail gas of the first tail gas washing step is washed by desalted water, and a washing circulating solution is conveyed to the first tail gas washing step; a sodium bicarbonate centrifugal separation step, wherein the sodium bicarbonate slurry formed in the first absorption step is subjected to centrifugal separation treatment, sodium bicarbonate crystals are recovered, and meanwhile, mother liquor is discharged; a first freezing and crystallizing step, namely freezing and crystallizing the centrifugal mother liquor of the sodium bicarbonate centrifugal separation step, recovering mixed crystals of sodium bicarbonate and ammonium bicarbonate, and discharging the mother liquor; an ammonium sulfate evaporation crystallization step, wherein the freezing crystallization mother liquor of the first freezing crystallization step is subjected to evaporation crystallization treatment, ammonium sulfate crystals are recovered, and the mother liquor is discharged; a step of preparing a sodium sulfate solution, in which the mixed crystals of the sodium bicarbonate and the ammonium bicarbonate in the first freezing and crystallizing step, the discharged washing solution in the first tail gas washing step and the sodium sulfate crystals are prepared into a solution and sent to the first absorption step。

According to an embodiment of the present invention, the temperatures of the first absorption step and the second absorption step are both 30 to 40 ℃.

The system and method provided by the invention can treat high-concentration brine with CO₂Organically combined emission reduction for CO in waste gas₂And sulfate, chloride and nitrate in the wastewater are recovered in a targeted manner, the phenomenon of unavailable mixed salt is avoided, high-quality additional products are obtained, the resource treatment of the salt-containing wastewater is realized, no secondary pollution is caused, and CO is absorbed from the waste gas₂Reduce CO₂The sodium bicarbonate with wide application is produced, and the method has obvious environmental benefit and economic benefit.

Drawings

FIG. 1 shows a CO-containing composition according to the present invention₂The waste gas and the saline wastewater are comprehensively utilized and treated.

Wherein the reference numerals are as follows:

1. containing CO₂An exhaust gas; 2. a first absorption tower; 3. a slurry circulating pump; 4. a first absorption tower circulating pump; 5. a first absorption tower solution heat exchanger; 6. partition plates; 7. tail gas of a first absorption tower; 8. a second absorption tower; 9. a second absorption tower circulating pump; 10. circulating the solution by the second absorption tower; 11. the second absorption tower delivers the solution; 12. second absorption tower tail gas; 13. a first tail gas scrubbing tower; 14. a first tail gas scrubbing tower circulating pump; 15. circulating solution in a first tail gas washing tower; 16. discharging solution from a first tail gas washing tower; 17. washing tower tail gas with first tail gas; 18. a second tail gas scrubbing tower; 19. a second tail gas washing tower circulating pump; 20. circulating solution in a second tail gas washing tower; 21. the second tail gas washing tower delivers the solution; 22. discharging tail gas; 23. desalting water; 24. a sodium bicarbonate centrifugal separation unit; 25. sodium bicarbonate centrifuge mother liquor; 26. a first freeze crystallization unit; 27. a first frozen crystallization mother liquor; 28. an ammonium sulfate evaporation crystallization unit; 29. evaporating and crystallizing mother liquor by using ammonia sulfate; 30. pretreatment of wastewaterA unit; 31. a first nanofiltration unit; 32. a first nanofiltration retentate; 33. a first nanofiltration permeate; 34. a reverse osmosis concentration unit; 35. reverse osmosis concentrated water; 36. a second freeze crystallization unit; 37. a second frozen crystallization mother liquor; 38. a second nanofiltration unit; 39. a second nanofiltration permeate; 40. second nanofiltration trapped fluid; 41. ammonia water; 42. a sodium sulfate solution; 43. an ammonium chloride evaporative crystallization unit; 44. 45, evaporating and crystallizing mother liquor by ammonium chloride; 46. a ammonium nitrate freeze crystallization unit; 47. freezing and crystallizing mother liquor of ammonium nitrate; 48. a sodium sulfate solution preparation unit;

A. sodium bicarbonate; B. mixing the crystals; C. ammonium sulfate; D. salt-containing wastewater to be treated; E. mirabilite; F. ammonium chloride; G. desalting water; H. ammonium nitrate; I. and (5) producing water by reverse osmosis.

Detailed Description

To make the objects, technical solutions and advantages of the present invention clearer, example embodiments will now be described more fully with reference to the accompanying drawings. Example embodiments may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the concept of example embodiments to those skilled in the art. The same reference numerals in the drawings denote the same or similar structures, and thus their detailed description will be omitted.

The first aspect of the present invention provides a system for treating salt-containing wastewater, which can perform salt recovery on salt-containing wastewater containing sodium chloride, sodium sulfate and sodium nitrate, comprising: the device comprises a wastewater pretreatment unit, a first nanofiltration unit, a second freezing and crystallizing unit, a second nanofiltration unit, an ammonium chloride evaporation and crystallization unit and an ammonium nitrate freezing and crystallizing unit. The invention also provides a catalyst containing CO₂Treatment system for waste gas, which can be used for treating CO-containing waste gas₂An exhaust gas, comprising: the device comprises a first absorption unit, a second absorption unit, a first tail gas washing unit, a second tail gas washing unit, a sodium bicarbonate centrifugal separation unit, a first freezing crystallization unit, an ammonium sulfate evaporation crystallization unit and a sodium sulfate solution preparation unit. Treatment system for salt-containing wastewater and CO-containing wastewater₂The waste gas treatment system can be used independentlyOr can be combined, when the two treatment systems are combined, the salt-containing wastewater and the CO-containing wastewater can be treated simultaneously₂And (4) exhaust gas. Treating high-concentration brine with CO₂Organically combined emission reduction for CO in waste gas₂And sulfate, chloride and nitrate in the wastewater are recovered in a targeted manner, the phenomenon of unavailable mixed salt is avoided, high-quality additional products are obtained, the resource treatment of the salt-containing wastewater is realized, no secondary pollution is caused, and CO is absorbed from the waste gas₂Reduce CO₂The sodium bicarbonate with wide application is produced, and the method has obvious environmental benefit and economic benefit. The connection between the units and the connection between them when such a system is used in combination is explained in detail below. As will be understood by those skilled in the art from the following description, according to the inventive concept of the present invention, when two systems exist separately, the treatment of the salt-containing wastewater and the CO-containing wastewater can be separately performed₂The treatment of the exhaust gas will not be repeated.

A first absorption unit for absorbing CO₂CO of exhaust gas₂And (5) absorption treatment.

The second absorption unit is connected with the first absorption unit and used for carrying out CO treatment on the tail gas of the first absorption unit again by adopting ammonia water₂Absorbing and treating, and conveying part of the absorption circulating solution to the first absorption unit.

The absorption towers of the first absorption unit and the second absorption unit can adopt a bubble tower, an absorption area and a precipitation area are arranged in the absorption tower of the first absorption unit, sodium bicarbonate crystals formed in the reaction process are precipitated to the bottom of a cone of the bubble tower, and an air loosening and blowing device is arranged at the bottom of the cone. The absorption tower can adopt independent absorption solution circulation and sodium bicarbonate slurry circulation. The depth of the liquid level in the absorption tower of the first absorption unit is preferably 10-20 m, and the height of the liquid level in the absorption tower of the second absorption unit is preferably 5-10 m.

And the first tail gas washing unit is connected with the second absorption unit and is used for washing the tail gas of the second absorption unit and discharging a washing solution.

And the second tail gas washing unit is connected with the first tail gas washing unit and used for washing the tail gas of the first tail gas washing unit by adopting desalted water and conveying the washing circulating solution to the first tail gas washing unit.

And the sodium bicarbonate centrifugal separation unit is connected with the first absorption unit and is used for carrying out centrifugal separation treatment on the sodium bicarbonate slurry in the first absorption unit, recovering sodium bicarbonate crystals and discharging the mother liquor.

The first freezing and crystallizing unit is connected with the sodium bicarbonate centrifugal separation unit and is used for freezing and crystallizing mother liquor of the centrifugal machine of the sodium bicarbonate centrifugal separation unit, recovering mixed crystals of sodium bicarbonate and ammonium bicarbonate, and discharging the mother liquor.

And the ammonium sulfate evaporative crystallization unit is connected with the first freezing crystallization unit and is used for carrying out evaporative crystallization treatment on the freezing crystallization mother liquor of the first freezing crystallization unit, recovering ammonium sulfate crystals and discharging the mother liquor outwards.

And the sodium sulfate solution preparation unit is respectively connected with the first absorption unit, the first freezing and crystallizing unit and the first tail gas washing unit, is used for receiving the mixed crystals of the sodium bicarbonate and the ammonium bicarbonate of the first freezing and crystallizing unit and the discharged washing solution of the first tail gas washing unit, and is prepared into a solution with the sodium sulfate crystals to be sent to an absorption tower of the first absorption unit. The sodium sulfate solution preparation unit can also be connected with the second freezing and crystallizing unit and used for receiving the sodium sulfate crystals of the second freezing and crystallizing unit.

And the wastewater pretreatment unit is used for pretreating the salt-containing wastewater to remove organic matters, suspended matters and impurities in the salt-containing wastewater and reduce the hardness of the salt-containing wastewater.

And the first nanofiltration unit is connected with the wastewater pretreatment unit and is used for performing nanofiltration treatment on the effluent of the wastewater pretreatment unit.

And the second freezing and crystallizing unit is respectively connected with the first nanofiltration unit, the second nanofiltration unit, the ammonium sulfate evaporating and crystallizing unit and the ammonium chloride evaporating and crystallizing unit and is used for carrying out freezing and crystallizing treatment on the nanofiltration trapped fluid of the first sodium filtration unit, the nanofiltration trapped fluid of the second nanofiltration unit, the crystallization mother liquor of the ammonium sulfate evaporating and crystallizing unit and the crystallization mother liquor of the ammonium chloride evaporating and crystallizing unit, recovering sodium sulfate crystals and simultaneously discharging outlet water to the second nanofiltration unit.

The second nanofiltration unit is connected with the second freezing crystallization unit and is used for performing nanofiltration treatment on the effluent of the second freezing crystallization unit; the nanofiltration retentate is returned to the second freeze crystallization unit and/or the wastewater pretreatment unit.

And the ammonium chloride evaporation crystallization unit is connected with the second nanofiltration unit and is used for carrying out evaporation crystallization treatment on the effluent of the second nanofiltration unit, recovering ammonium chloride crystals and discharging mother liquor.

And the ammonium nitrate freezing and crystallizing unit is connected with the ammonium chloride evaporating and crystallizing unit and is used for adding desalted water into the evaporating and crystallizing mother liquor of the ammonium chloride evaporating and crystallizing unit for dilution, carrying out freezing and crystallizing treatment, recovering ammonium nitrate crystals and returning effluent to the ammonium chloride evaporating and crystallizing unit.

The treatment system also comprises a reverse osmosis concentration unit, wherein the reverse osmosis concentration unit is connected with the first nanofiltration unit and the second freezing and crystallizing unit and is used for performing reverse osmosis desalination treatment on the nanofiltration membrane permeate of the first nanofiltration unit, the obtained reverse osmosis concentrated water is salt-containing concentrated water mainly containing sodium chloride and sodium nitrate, and the reverse osmosis concentrated water is conveyed to the second freezing and crystallizing unit for treatment.

The processing system of the present invention is explained in detail below in conjunction with fig. 1.

The first absorption unit comprises a first absorption tower 2, a slurry circulating pump 3, a first absorption tower circulating pump 4 and a first absorption tower solution heat exchanger 5 and is used for absorbing CO₂CO of exhaust gas₂And (5) absorption treatment. Containing CO₂Waste gas 1 firstly enters a first absorption unit, and the first absorption unit comprises a first absorption tower 2, a slurry circulating pump 3, a first absorption tower circulating pump 4 and a first absorption tower solution heat exchanger 5. Containing CO₂The waste gas 1 enters the first absorption tower 2 from a bottom distributor of the first absorption tower 2, and CO in the waste gas₂Absorbed by the solution in the tower and reacts with (NH) in the solution₄)₂CO₃Reaction to form NH₄HCO₃At the same time, Na from the sodium sulfate solution preparation unit₂SO₄The solution is also conveyed by a pump to the first absorption tower 2 as the reaction proceedsNa in solution⁺、NH₄ ⁺、HCO₃ ^-、SO₄ ^2-The ion concentration gradually increases due to NaHCO₃Is less soluble when NaHCO is present in solution₃After the concentration is saturated, the ions are separated out in a crystalline form, and other ionic compounds exist in a solution form.

The first absorption column is not particularly limited in the present invention, and any absorption column commonly used in the art may be used. In a preferred embodiment, a bubble column may be used. In a preferred embodiment, a partition 6 is provided in the column to divide the absorption column into an absorption zone and a settling zone, a gas distributor is arranged at the bottom of the absorption zone, while the bottom of the settling zone is in communication with the cone of the absorption column, and the sodium bicarbonate crystals settle gradually in the settling zone to the cone of the absorption column. The slurry circulating pump 3 sucks the slurry from the bottom of the cone of the absorption tower, one part of the slurry is circulated back to the cone of the absorption tower, and the other part of the slurry is conveyed to the sodium bicarbonate centrifugal separation unit 24 for recovering the sodium bicarbonate. Meanwhile, the first absorption tower circulating pump 4 sucks absorption solution from the bottom of the sedimentation zone of the absorption tower cylinder to circulate to the top of the absorption tower so as to ensure the uniformity of gas absorption and reaction in the absorption tower and improve CO₂The efficiency of absorption. And a first absorption tower solution heat exchanger 5 is arranged on the absorption solution circulating loop, and the temperature of the solution in the tower is adjusted by using a heat exchange medium.

The tail gas 7 of the first absorption unit flows out from the top of the first absorption tower 2 and enters the second absorption unit. The second absorption unit is connected with the first absorption unit, comprises a second absorption tower 8 and a second absorption tower circulating pump 9, and is used for carrying out CO again on the tail gas of the first absorption unit by adopting ammonia water₂Absorbing and treating, and conveying part of the absorption circulating solution to the first absorption unit. The ammonia 41 is fed to the lower part of the second absorption tower, the tail gas 7 of the first absorption tower enters the second absorption tower from the bottom distributor of the second absorption tower, and the residual CO in the tail gas 7₂Absorbed by the solution in the tower and reacts with ammonia in the solution to generate (NH)₄)₂CO₃. The second absorption tower circulating pump 9 extracts absorption circulating solution 10 from the bottom of the absorption tower and circulates the absorption circulating solution to the top of the absorption tower so as to ensure that gas in the absorption tower is absorbed and reactedHomogenizing and improving CO₂The efficiency of absorption. At the same time, part of the circulating solution 11 is fed to the first absorption column 2, to supply the first absorption column with the required (NH)₄)₂CO₃And NH₃。

The second absorption column is not particularly limited in the present invention, and any absorption column commonly used in the art may be used. In a preferred embodiment, a bubble column may be used.

The tail gas 12 of the second absorption unit flows out from the top of the second absorption tower 8 and enters the first tail gas washing unit. The first tail gas washing unit is connected with the second absorption unit, comprises a first tail gas washing tower 13 and a first tail gas washing tower circulating pump 14, and is used for washing the tail gas of the second absorption unit and discharging a washing solution outside. The tail gas 12 enters the first tail gas washing tower 13 from the bottom of the first tail gas washing tower 13 and is in countercurrent contact with the circulating solution flowing down from the top in the tower, and the residual CO in the tail gas 12₂And NH₃Is absorbed by the circulating solution. The circulating pump 14 of the first tail gas washing tower extracts the circulating solution 15 from the liquid tank at the bottom of the first tail gas washing tower and circulates the circulating solution to the top of the first tail gas absorption tower, and meanwhile, the discharged solution 16 of the first tail gas washing tower is conveyed to the sodium sulfate solution preparation unit 48.

The first tail gas scrubbing tower is not particularly limited, and a scrubbing tower which is common in the art can be used. In a preferred embodiment, a packed column may be used. The invention has no special limitation on the form of the filler, and the number of layers and the height of the filler in the first tail gas washing tower are also not limited, and one or more layers can be adopted as long as the same washing effect is achieved.

The tail gas 17 of the first tail gas washing unit flows out from the top of the first tail gas washing tower 13 and enters the second tail gas washing unit. The second tail gas washing unit is connected with the first tail gas washing unit, comprises a second tail gas washing tower 18 and a second tail gas washing tower circulating pump 19, is used for washing the tail gas of the first tail gas washing unit by adopting demineralized water, and conveys a washing circulating solution to the first tail gas washing unit. The tail gas 17 enters the second tail gas washing tower 18 from the bottom of the second tail gas washing tower 18 and flows counter to the circulating solution flowing down from the top in the towerStream contact, residual NH in tail gas 17₃Is absorbed by water washing. And a circulating pump 19 of the second tail gas washing tower extracts a circulating solution 20 from a liquid tank at the bottom of the second tail gas washing tower to circulate to the top of the first tail gas absorption tower, and simultaneously conveys an effluent solution 21 of the second tail gas washing tower to the first tail gas washing tower 13. The desalted water 23 required for scrubbing is directly supplemented into the second tail gas scrubbing tower. The exhaust gas 22 from the second off-gas scrubber is discharged directly after reaching the specified emission standard.

The second tail gas scrubbing tower is not particularly limited, and a scrubbing tower which is common in the art can be used. In a preferred embodiment, a packed column may be used. The invention has no special limitation on the form of the filler, and the number of layers and the height of the filler in the second tail gas washing tower are also not limited, and one or more layers can be adopted as long as the same washing effect is achieved.

The sodium bicarbonate slurry from slurry circulation pump 3 enters sodium bicarbonate centrifuge unit 24. The sodium bicarbonate centrifugal separation unit 24 is connected with the first absorption unit and is used for carrying out centrifugal separation treatment on the sodium bicarbonate slurry in the first absorption unit, recovering sodium bicarbonate crystals and discharging the mother liquor. The sodium bicarbonate centrifugal separation unit 24 comprises a centrifugal separation device, and the centrifugal separation device is used for carrying out centrifugal separation on the slurry to obtain a sodium bicarbonate product A and a centrifuge mother liquor 25.

The centrifugal separation device used in the centrifugal separation unit is not particularly limited, and a centrifuge and accessory equipment commonly used in the field can be selected, so long as the separation of the sodium bicarbonate crystals from the solution is achieved.

The centrifuge mother liquor 25 of the sodium bicarbonate centrifugation unit enters a first freeze crystallization unit 26. The first freezing and crystallizing unit 26 is connected with the sodium bicarbonate centrifugal separation unit 24, and is used for freezing and crystallizing mother liquor of the centrifugal separation unit of the sodium bicarbonate, recovering mixed crystals of the sodium bicarbonate and the ammonium bicarbonate, and discharging the mother liquor. The first freezing crystallization unit 26 comprises a freezing crystallization separation device, the centrifuge mother liquor 25 is frozen and cooled by external cooling medium, and NaHCO dissolved in water is cooled along with the temperature reduction₃And NH₄HCO₃Reaching supersaturation state, separating out in crystal form and separating out from solution. The sodium sulfate and the ammonium sulfate in the solution still exist in the form of solution and can not be separated out, thereby obtaining NaHCO₃And NH₄HCO₃The mixed crystal of (1). The freezing temperature is preferably 5-10 ℃, so as to reduce the concentration of bicarbonate ions in the freezing crystallization mother liquor 27 as much as possible, and prevent the release of ammonia and CO after the decomposition of sodium bicarbonate and ammonium bicarbonate in the solution in the subsequent ammonium sulfate evaporation crystallization process₂The treatment cost and the burden of the ammonium sulfate evaporation, crystallization, condensation and non-condensable gas treatment are increased. The mixed crystal B obtained in the first freezing and crystallizing unit 26 is sent to a sodium sulfate solution preparing unit 48. The effluent of the first freezing crystallization unit 26, i.e. the first freezing crystallization mother liquor 27, is sent to the ammonium sulfate evaporation crystallization unit 28 for further processing.

The first frozen crystallization mother liquor 27 of the first frozen crystallization unit 26 enters an ammonium sulfate evaporative crystallization unit 28. And the ammonium sulfate evaporation crystallization unit 28 is connected with the first freezing crystallization unit 26 and is used for carrying out evaporation crystallization treatment on the freezing crystallization mother liquor of the first freezing crystallization unit 26, recovering ammonium sulfate crystals and discharging the mother liquor. An evaporative crystallizer is arranged in the ammonium sulfate evaporative crystallization unit 28. The water in the first mother frozen crystal 27 is evaporated by heating with steam in the evaporator-crystallizer. At the evaporation temperature, the bicarbonate in the solution is completely decomposed, the concentration of ammonium sulfate in the solution is continuously increased along with the continuous evaporation until reaching a supersaturated state and being separated out in a crystallization mode, and a solid ammonium sulfate product C is obtained, wherein the purity of the obtained ammonium sulfate product C is high (can reach more than 99 percent), and can reach industrial-grade standards. The evaporated gas is condensed into evaporation condensate J for recycling.

As the evaporation proceeds, the concentration of sodium sulfate in the solution increases, and in order to prevent the sodium sulfate from crystallizing out, a part of the evaporative crystallization mother liquor is discharged, and the ammonium sulfate evaporative crystallization mother liquor 29 is sent to the second freezing and crystallizing unit 36. In addition to the requirement that sodium sulfate in the ammonium sulfate evaporative crystallization mother liquor does not crystallize out, the discharge amount of the ammonium sulfate evaporative crystallization mother liquor needs to be sufficient to provide enough sulfate ions to ensure that all sodium ions and potassium ions in the salt-containing wastewater D are crystallized out of the second freezing and crystallizing unit 36 in the form of sulfate.

The ammonium sulfate evaporator crystallizer of the present invention is not particularly limited, and for example, multi-effect evaporation or MVR evaporation crystallization known in the art can be used.

The salt-containing wastewater D to be treated enters the wastewater pretreatment unit 30. The wastewater pretreatment unit 30 is used for pretreating the salt-containing wastewater D to remove organic matters, suspended matters, amphoteric oxides, colloids, calcium, magnesium, hardness, most of organic matters and other impurities, so that the hardness in the wastewater is less than 1mg/L (as CaCO)₃Meter), SDI is less than 3, so that the existing concentration of the impurities does not influence the operation of subsequent units such as nanofiltration treatment, reverse osmosis concentration, freezing crystallization, evaporative crystallization and the like and the quality of products.

The wastewater pretreatment unit is not particularly limited, and equipment for removing impurities such as hardness, organic matters and the like, which is common in the field, can be adopted, for example, agents such as lime, soda ash, flocculating agents and the like can be adopted for clarification and softening treatment, medium filtration or ultrafiltration membrane filtration is adopted for removing suspended matters in the wastewater, chelating resin is adopted for adsorption for deep removal of hardness, and ozone oxidation or activated carbon, resin adsorption and the like are adopted for removal of the organic matters, so long as the equipment achieves the same treatment effect.

The effluent of the wastewater pretreatment unit enters a first nanofiltration unit 31. The first nanofiltration unit 31 is connected to the wastewater pretreatment unit 30, and is configured to perform nanofiltration on the effluent of the wastewater pretreatment unit. The first nanofiltration unit 31 is provided with a nanofiltration membrane assembly through which most of monovalent ions such as sodium chloride, sodium nitrate and water can permeate and most of organic matters and SO₄ ^2-Is impermeable to the nanofiltration membrane, and therefore the nanofiltration membrane module separates the salt-containing wastewater into two streams, i.e. rich in organic matter and SO₄ ^2-And a first nanofiltration permeate 33 rich in sodium chloride and sodium nitrate. The first nanofiltration retentate 32 enters a second freeze crystallization unit 36 and the first nanofiltration permeate 33 enters a reverse osmosis concentration unit 34.

The invention relates to a nanofiltration membrane componentThere is no particular limitation, and a nanofiltration membrane module commonly used in the art may be used. In a preferred embodiment, the organic and SO are optionally treated₄ ^2-The nanofiltration membrane component has high removal rate. In a preferred embodiment, the inlet water temperature of the nanofiltration membrane can be 5-40 ℃, preferably 20-25 ℃, SO that SO in the first nanofiltration trapped fluid 32 can be removed₄ ^2-The concentration of the (C) is concentrated to an ideal value as far as possible without saturation, so that the water quantity of subsequent treatment is reduced, and the energy consumption is saved. The nanofiltration membrane module may be used in one or more stages, and in a preferred embodiment, two-stage nanofiltration is used to avoid too high a concentration factor in a single stage nanofiltration.

The first nanofiltration permeate 33 of the first nanofiltration unit 31 enters a reverse osmosis concentration unit 34. The reverse osmosis concentration unit 34 is connected to the first nanofiltration unit 31, and is configured to perform reverse osmosis desalination on a nanofiltration membrane permeate of the first nanofiltration unit 31, where the obtained reverse osmosis concentrated water is a salt-containing concentrated water mainly containing sodium chloride and sodium nitrate. The reverse osmosis concentration unit 34 is provided with a reverse osmosis membrane module, and performs reverse osmosis desalination treatment on the first nanofiltration permeate 33. Since most of the salt and all organic matters cannot permeate the reverse osmosis membrane module, the reverse osmosis membrane module divides the first nanofiltration permeate 33 into two streams, i.e., reverse osmosis product water I containing less salt and reverse osmosis concentrate 35 rich in salt and organic matters, the reverse osmosis product water I can be directly recycled, and the reverse osmosis concentrate 35 enters the second freezing and crystallizing unit 36. In a preferred embodiment, the reverse osmosis membrane modules of the reverse osmosis concentration unit 34 may be multi-staged, such as two-staged, using various reverse osmosis membrane modules of different types to form the final treatment unit to enhance desalination. In a preferred embodiment, the salt content in the reverse osmosis concentrated water 35 is 7-10%.

The reverse osmosis concentrated water 35 of the reverse osmosis concentration unit 34 enters a second freezing and crystallizing unit 36 together with the nanofiltration trapped fluid 32 from the first sodium filtration unit 31, the ammonium sulfate evaporative crystallization mother liquor 29 from the ammonium sulfate evaporative crystallization unit 28, the second nanofiltration trapped fluid 40 from the second nanofiltration unit 38 and the evaporative crystallization mother liquor 45 from the ammonium chloride evaporative crystallization unit, and the second freezing and crystallizing unit 36 comprises a freezing and crystallizing separation device, the solutions are frozen and cooled by an external cooling medium, and sodium sulfate dissolved in the water reaches an oversaturated state along with the reduction of the temperature, is separated out in a crystallization form and is separated from the solution. The ammonium chloride, ammonium sulfate and ammonium nitrate in the solution still exist in the form of solution, and can not be separated out, so that the sodium sulfate crystal E (mirabilite) with high purity can be obtained. The freezing temperature is preferably-5 to 5 ℃ in order to crystallize sodium sulfate out of the solution as much as possible.

The second frozen crystallization mother liquor 37 of the second frozen crystallization unit 36 enters a second nanofiltration unit 38. And the second freezing and crystallizing unit 36 is respectively connected with the first nanofiltration unit 31, the ammonium sulfate evaporation and crystallization unit 28, the reverse osmosis concentration unit 34, the second nanofiltration unit 38 and the ammonium chloride evaporation and crystallization unit 43, and is used for carrying out freezing and crystallizing treatment on the nanofiltration trapped liquid of the first nanofiltration unit 32, the crystallization mother liquid of the ammonium sulfate evaporation and crystallization unit 28, the reverse osmosis concentrated water of the reverse osmosis concentration unit 34, the nanofiltration trapped liquid of the second nanofiltration unit 38 and the evaporation and crystallization mother liquid of the ammonium chloride evaporation and crystallization unit 43, recovering sodium sulfate crystals, and simultaneously discharging the effluent to the second nanofiltration unit.

The second nanofiltration unit 38 is connected with the second freezing crystallization unit 36 and is used for performing nanofiltration treatment on the effluent of the second freezing crystallization unit 36; the nanofiltration retentate is returned to the second freeze crystallization unit 36 and/or the wastewater pretreatment unit 30. The second nanofiltration unit 38 is provided with a nanofiltration membrane module, most of the monovalent ions such as Cl^-、NO₃ ^-、NH₄ ⁺、Na⁺And water can permeate the nanofiltration membrane, and most of organic matters and SO₄ ^2-Is impermeable to the nanofiltration membrane, and therefore the nanofiltration membrane module separates the brine concentrate into two streams, i.e., rich in organic matter and SO₄ ^2-And a second nanofiltration permeate 39 enriched in monovalent ions and a second nanofiltration retentate 40 enriched in monovalent ions. The second nanofiltration retentate 40 is recycled to the second freezing and crystallizing unit 36 and/or the wastewater pretreatment unit 30, and the second nanofiltration permeate 39 enters the ammonium chloride evaporative crystallization unit 43.

The nanofiltration membrane component is not particularly limited, and the nanofiltration membrane component can adopt sodium which is common in the fieldAnd (3) a filter membrane component. In a preferred embodiment, the organic and SO are optionally treated₄ ^2-The nanofiltration membrane component has high removal rate. In a preferred embodiment, the inlet water temperature of the nanofiltration membrane can be 5-40 ℃, preferably 20-25 ℃, SO that SO in the second nanofiltration trapped fluid 40 can be removed₄ ^2-The concentration is concentrated as much as possible to the desired value without saturation.

The second nanofiltration permeate 39 of the second nanofiltration unit 38 enters an ammonium chloride evaporative crystallization unit 43. The ammonium chloride evaporation crystallization unit 43 is connected with the second nanofiltration unit 38, and is used for carrying out evaporation crystallization treatment on the effluent of the second nanofiltration unit 38, recovering ammonium chloride crystals, and discharging the mother liquor. An evaporative crystallizer is arranged in the ammonium chloride evaporative crystallization unit 43. And heating by adopting steam in the evaporative crystallizer to evaporate water in the second nanofiltration permeating liquid 39. With the continuous evaporation, the concentration of ammonium chloride in the solution is continuously increased until reaching a supersaturated state and being separated out in a crystallization form, and a solid ammonium chloride product F is obtained, wherein the purity of the obtained ammonium chloride is high (can reach more than 99 percent), and can reach industrial-grade standards. The evaporated gas is condensed into evaporation condensate for recycling.

With the evaporation, the concentration of other ions such as sodium chloride, sodium nitrate and ammonium nitrate in the solution is continuously increased, and in order to prevent the crystallization of the salts from influencing the product quality of ammonium chloride, a small amount of evaporation crystallization mother liquor needs to be discharged periodically and intermittently or continuously, a part of the evaporation crystallization mother liquor 44 of ammonium chloride is sent to an ammonium nitrate freezing crystallization unit 46, and the other part of the evaporation crystallization mother liquor 45 of ammonium chloride is sent to a second freezing crystallization unit 36, so that the concentration range of ammonium nitrate in the evaporation mother liquor is controlled to be 1400-6000 g/L, preferably 4000-5000 g/L.

The ammonium chloride evaporative crystallizer of the present invention is not particularly limited, and for example, multi-effect evaporation or MVR evaporative crystallization known in the art may be used.

The ammonium chloride evaporative crystallization mother liquor 44 discharged from the ammonium chloride evaporative crystallization unit 43 enters an ammonium nitrate freeze crystallization unit 46. And the ammonium nitrate freezing and crystallizing unit 46 is connected with the ammonium chloride evaporating and crystallizing unit 43 and is used for adding desalted water into the discharged evaporating and crystallizing mother liquor of the ammonium chloride evaporating and crystallizing unit 43, carrying out freezing and crystallizing treatment, recovering ammonium nitrate crystals and returning effluent to the ammonium chloride evaporating and crystallizing unit 43. While the ammonium chloride evaporative crystallization mother liquor 44 enters the ammonium nitrate freezing and crystallizing unit 46, the demineralized water G is added into the evaporative crystallization mother liquor 44 for dilution so as to prevent other salts except the ammonium nitrate from crystallizing out in the subsequent freezing and crystallizing process. The amount of the demineralized water to be added may be 10 to 400% by volume, preferably 40 to 120% by volume, and more preferably 100 to 120% by volume of the evaporation mother liquor 44. The ammonium nitrate freezing and crystallizing unit 46 comprises a freezing and crystallizing separation device, ammonium chloride evaporation and crystallization mother liquor 44 is frozen and cooled through an external cooling medium, and ammonium nitrate dissolved in water reaches a supersaturated state along with the reduction of the temperature, is separated out in a crystallization form, and is separated from the solution. The ammonium chloride in the solution still exists in the form of solution and cannot be separated out, so that ammonium nitrate crystals H are obtained. The freezing temperature is-5 to 60 ℃, preferably 0 to 20 ℃, and more preferably 10 to 20 ℃, so that the ammonium nitrate is crystallized from the solution as much as possible, and the energy consumption is lower. The ammonium nitrate frozen crystallization mother liquor 47 of the ammonium nitrate frozen crystallization unit returns to the ammonium chloride evaporative crystallization unit 43 for continuous processing.

And a sodium sulfate solution preparation unit 48, which is respectively connected to the first absorption unit, the first freezing and crystallizing unit 24, the second freezing and crystallizing unit 36 and the first tail gas washing unit, and is used for receiving the mixed crystals of sodium bicarbonate and ammonium bicarbonate of the first freezing and crystallizing unit 24, the sodium sulfate crystals of the second freezing and crystallizing unit 36 and the discharged washing solution of the first tail gas washing unit, and preparing a solution to be sent to the absorption tower 2 of the first absorption unit. The sodium sulfate solution preparation unit 48, which includes crystal transportation and dissolution equipment, prepares sodium sulfate solution from the mixed crystal B of sodium bicarbonate and ammonium bicarbonate in the first freezing and crystallizing unit 24, the sodium sulfate crystal E in the second freezing and crystallizing unit 36, and the discharged washing solution 16 in the first tail gas washing unit, and sends the prepared sodium sulfate solution to the absorption tower 2 of the first absorption unit.

The second aspect of the invention provides a method for treating salt-containing wastewater, which is used for treating the salt-containing wastewater and comprises the following steps: a wastewater pretreatment step,The method comprises a first nanofiltration step, a second freezing and crystallizing step, a second nanofiltration step, an ammonium chloride evaporation and crystallization step and an ammonium nitrate freezing and crystallizing step. The invention also provides a catalyst containing CO₂Method for treating exhaust gas containing CO₂The exhaust gas is treated, including: the method comprises a first absorption step, a second absorption step, a first tail gas washing step, a second tail gas washing step, a sodium bicarbonate centrifugal separation step, a first freezing crystallization step, an ammonium sulfate evaporation crystallization step and a sodium sulfate solution preparation step. Like the treatment system, these two treatment methods may be combined or may be performed separately. The steps of the two-certificate processing method and the relationship between the steps are explained in detail below with reference to fig. 1. For the two processes carried out separately, it will be understood by those skilled in the art that the processes carried out separately can achieve the treatment of the salt-containing wastewater and the CO-containing wastewater, respectively, as described below₂The waste gas treatment is not repeated.

A first absorption step of introducing CO₂CO of exhaust gas 1₂Absorption treatment while ensuring CO₂In excess.

A second absorption step of subjecting the tail gas 7 of the first absorption step to CO again using ammonia water 41₂The absorption treatment is carried out while a part of the absorption circulating solution 11 is sent to the first absorption step.

The temperature of the first absorption step and the temperature of the second absorption step are both preferably 30-40 ℃.

And a first tail gas washing step, wherein the tail gas 12 of the second absorption step is washed, and meanwhile, a washing solution 16 is discharged.

And a second tail gas washing step, wherein the tail gas 17 of the first tail gas washing step is washed by desalted water, and the washing circulating solution 21 is conveyed to the first tail gas washing step.

And a sodium bicarbonate centrifugal separation step of performing centrifugal separation treatment on the sodium bicarbonate slurry formed in the first absorption step, recovering sodium bicarbonate crystals A and discharging the mother liquor 25.

In the first freezing and crystallizing step, the centrifugal mother liquor 25 in the sodium bicarbonate centrifugal separation step is subjected to freezing and crystallizing treatment, the mixed crystal B of sodium bicarbonate and ammonium bicarbonate is recovered, and meanwhile, the mother liquor 27 is discharged outside. The temperature of the first freezing and crystallizing step is preferably 5 to 10 ℃.

And an ammonium sulfate evaporation crystallization step, wherein the freezing crystallization mother liquor 27 of the first freezing crystallization step is subjected to evaporation crystallization treatment, ammonium sulfate crystals C are recovered, and the mother liquor 29 is discharged.

And (3) a wastewater pretreatment step, namely pretreating the salt-containing wastewater D to remove organic matters, suspended matters, calcium, magnesium, hardness and other impurities.

And a first nanofiltration step, wherein nanofiltration treatment is carried out on the effluent of the wastewater pretreatment step.

And a reverse osmosis concentration step, namely performing reverse osmosis desalination treatment on the nanofiltration membrane permeate 33 obtained in the first nanofiltration step to obtain reverse osmosis concentrated water 35 which is salt-containing concentrated water mainly containing sodium chloride and sodium nitrate.

And a second freezing and crystallizing step, namely performing freezing and crystallizing treatment on the nanofiltration trapped fluid 32 of the first nanofiltration step, the crystallization mother liquor 29 of the ammonium sulfate evaporation and crystallization step, the reverse osmosis concentrated water 35 of the reverse osmosis concentration step, the nanofiltration trapped fluid 40 of the second nanofiltration step and the crystallization mother liquor 45 of the ammonium chloride evaporation and crystallization step, recovering sodium sulfate crystals E, and simultaneously discharging the effluent 37 to the second nanofiltration step. The temperature of the second freezing and crystallizing step is preferably-5 to 5 ℃.

A second nanofiltration step, wherein nanofiltration treatment is carried out on the effluent 37 of the second freezing and crystallizing step; nanofiltration retentate 40 is returned to the second freeze crystallization step.

And (3) an ammonium chloride evaporation and crystallization step, namely, carrying out evaporation and crystallization treatment on the nanofiltration permeating liquid 39 of the second nanofiltration step, recovering ammonium chloride crystals, and discharging mother liquor 44 and 45. The concentration of ammonium nitrate in the discharged mother liquor in the ammonium chloride evaporation crystallization step is 1400-6000 g/L, and is preferably 4000-5000 g/L.

And (4) a step of freezing and crystallizing ammonium nitrate, in which desalted water G is added into the evaporation and crystallization mother liquor 45 of the ammonium chloride evaporation and crystallization step for dilution, freezing and crystallization treatment is carried out, ammonium nitrate crystals I are recovered, and effluent 47 is returned to the ammonium chloride evaporation and crystallization step. The temperature of the ammonium nitrate freezing and crystallizing step is preferably 10-20 ℃. In the step of freezing and crystallizing ammonium nitrate, the addition amount of the desalted water is preferably 40-120% of the flow rate of the evaporation mother liquor, and more preferably 100-120%

And a sodium sulfate solution preparation step, namely receiving the mixed crystals B of the sodium bicarbonate and the ammonium bicarbonate in the first freezing and crystallizing step, the sodium sulfate crystals E in the second freezing and crystallizing step and the discharged washing solution 16 in the first tail gas washing step to prepare a solution 42, and sending the solution 42 to the absorption tower in the first absorption step.

The CO-containing of the invention₂The comprehensive utilization and treatment system and the comprehensive utilization and treatment method for the waste gas and the salt-containing waste water can be suitable for the waste gas and the waste water generated in the industries of common petrifaction, coal chemical industry, fine chemical industry, power plants and the like, and a large amount of high-concentration CO exists in the industries generally₂Waste gases and waste waters containing amounts of chlorides, nitrates and sulfates are well suited for use with the treatment system and method of the present invention.

The present invention will be described in further detail below with reference to examples.

Example 1

The CO-containing is carried out according to the following steps₂And (4) treating waste gas and salt-containing wastewater.

a. CO-containing gas to be treated₂CO in exhaust gas₂Content 45%, N₂Content 45% of O₂5% of water, 5% of SO₂Less than 50mg/m³The sodium sulfate solution is pressurized by a fan and sent into a first absorption tower, the first absorption tower is a bubble tower, absorption solution is filled in the tower, the liquid level is 20 meters, the absorption solution comes from a second absorption tower, and meanwhile, sodium sulfate solution is conveyed from sodium sulfate solution preparation equipment to the first absorption tower. The first absorption tower is provided with a solution circulating pump, and the absorption solution is extracted from the bottom of the first absorption tower cylinder and circulated to the tower top. After absorption reaction, CO in tail gas of the first absorption tower₂The content is 10%.

b. The tail gas of the first absorption tower enters the bottom of a second absorption tower, the second absorption tower is also a bubble tower, absorption solution is filled in the tower, the liquid level height is 10m, the second absorption tower is provided with a solution circulating pump, the absorption solution is extracted from the bottom of the second absorption tower and circulated to the top of the tower, and meanwhile, part of the circulating solution is conveyed to the first absorption tower. And simultaneously replenishing ammonia water to the second absorption tower. After absorption reaction, the second absorptionCO in tower tail gas₂Content of 1% NH₃The content is 30mg/m³。

c. And tail gas of the second absorption tower enters the bottom of the first tail gas washing tower, the first tail gas washing tower is a packed tower, two layers of packing are arranged in the tower, the height of each layer of packing is 4m, the first tail gas washing tower is provided with a solution circulating pump, circulating solution is extracted from a liquid tank at the bottom of the first tail gas washing tower and conveyed to the top of the tower, part of the circulating solution is discharged to sodium sulfate solution preparation equipment, and supplemented solution is from the circulating solution discharged from the second absorption tower. After being washed by the first tail gas washing tower, CO in the tail gas of the first tail gas washing tower₂The content is less than 0.2 percent.

d. The tail gas of the first tail gas washing tower enters the bottom of a second tail gas washing tower, the second tail gas washing tower is also a packed tower, two layers of packing are arranged in the tower, the height of each layer of packing is 4m, a solution circulating pump is arranged in the second tail gas washing tower, circulating solution is extracted from a liquid tank at the bottom of the second tail gas washing tower and is conveyed to the top of the tower, and part of the circulating solution is discharged to the first tail gas washing tower and is supplemented with demineralized water. After being washed by the second tail gas washing tower, the CO in the tail gas of the second tail gas washing tower₂The content is less than 0.2 percent, and the ammonia content is less than 0.2mg/m³And the standard emission is achieved.

e. And pumping the sodium bicarbonate slurry settled at the bottom of the cone of the first absorption tower by a slurry pump, feeding the slurry into a sodium bicarbonate centrifugal separation device, and performing centrifugal separation to obtain sodium bicarbonate crystals, wherein the total alkalinity of the sodium bicarbonate product can reach over 99.0 percent, and the sodium bicarbonate crystal meets the industrial application requirements.

f. The sodium bicarbonate centrifugal separation mother liquor is sent into a freezing crystallization separation device, in the freezing crystallization separation device, the water temperature is firstly cooled to 10 ℃, sodium bicarbonate is precipitated in a crystallization form after reaching a supersaturation state, and then sodium bicarbonate crystals are separated from the solution through centrifugal separation.

g. And f, enabling the frozen crystallization mother liquor generated in the step f to enter an ammonium sulfate evaporation crystallization device, wherein the ammonium sulfate evaporation crystallization device adopts two-effect reduced pressure evaporation, the evaporation temperature is 80 ℃, the purity of the recovered ammonium sulfate product can reach more than 99 percent, the ammonium sulfate product meets the industrial application requirement, and the evaporated mother liquor is discharged to a second frozen crystallization unit.

h. Salt-containing wastewater to be treated, Na⁺Concentration 35000mg/l, Ca²⁺At a concentration of 1368Mg/l, Mg²⁺Concentration 244mg/l, Cl^-Concentration 36100mg/l, SO₄ ^2-HCO with a concentration of 15600mg/l₃ ^-Concentration 216mg/l, NO₃ ^-The concentration is 1209mg/l, and the organic matter concentration is: CODcr600mg/L, TDS: 105600mg/L, hardness (as CaCO)₃Calculated) 300mg/L, and suspended substance 40 mg/L.

The salt-containing wastewater is pretreated by clarification and softening, ozone oxidation, multi-medium filtration, ultrafiltration and resin softening.

Adding sodium hydroxide, a coagulant PFS, a flocculant PAM and other medicaments into the wastewater, and allowing the wastewater to enter a clarification tank for clarification and softening treatment. Wherein, the adding amount of the sodium hydroxide is 8200mg/l, the adding amount of the coagulant PFS is 15mg/l, and the adding amount of the flocculating agent is 1.5 ppm. The clarification tank adopts a high-efficiency clarification tank. The suspension of the effluent of the clarification tank is less than 10mg/L, and the hardness is less than 100mg/L (as CaCO)₃Meter). And (3) carrying out ozone oxidation on the effluent of the clarification tank, wherein the ozone oxidation is 3-stage catalytic oxidation, and CODcr of the effluent of the ozone oxidation is 100 mg/l.

And the ozone oxidation effluent is lifted by a pump and is sent into a multi-medium filter, quartz sand and anthracite are filled in the multi-medium filter, wherein the filling height of the quartz sand is 800mm, the filling height of the anthracite is 400mm, and the filtering speed is 7.0 m/h. The suspended substance of the effluent of the multi-medium filter is less than 2mg/L, and the turbidity is less than 5 NTU.

And the effluent of the multi-media filter enters an ultrafiltration membrane treatment system, the water recovery rate is 94%, the effluent suspended substance is approximately equal to 0mg/L, the effluent turbidity is less than 0.1NTU, and the effluent SDI value is less than 3.

The water produced by ultrafiltration enters a weak acid cation bed, weak acid cation exchange resin is filled in the weak acid cation bed, and the hardness of the effluent of the weak acid cation bed is as CaCO₃Calculated) is less than 1 mg/L.

i. The pretreated effluent enters a membrane component system of a first nanofiltration unit, and a nanofiltration membrane component adopts a GE DK8040 nanofiltration membrane component. The nanofiltration adopts two stages, the arrangement and combination mode of NF membrane elements of the first stage NF adopts two-stage design, a pump is added between the stages, and the arrangement and combination mode of the NF membrane elements of the second stage NF device adoptsThe concentrated water reflux is designed and arranged by a section. SO in nanofiltration membrane trapped fluid₄ ^2-To a concentration of about 60g/L, into a second freeze crystallization unit;

j. the nanofiltration permeate enters a reverse osmosis concentration unit, the reverse osmosis concentration unit adopts two-stage reverse osmosis membrane concentration treatment, the first-stage reverse osmosis membrane adopts an ultrahigh pressure membrane element, the recovery rate is 38%, the produced water of the first-stage reverse osmosis enters the second-stage reverse osmosis, the recovery rate of the second-stage reverse osmosis is 83%, the concentrated water of the second-stage reverse osmosis returns to the water inlet end of the first-stage reverse osmosis, the TDS of the produced water of the second-stage reverse osmosis is less than 500mg/L, and the produced water is directly recycled. Na in first-stage reverse osmosis concentrated water⁺Concentration 40000mg/l, Cl^-Concentration 55000mg/l, NO₃ ^-The concentration is 4950mg/l, and the mixture is sent to a second freezing and crystallizing unit;

k. the first nanofiltration trapped fluid, the reverse osmosis concentrated water of the reverse osmosis concentration unit and the ammonium sulfate evaporative crystallization mother liquor enter a second freezing crystallization unit, in a freezing crystallization separation device of the second freezing crystallization unit, the water temperature is firstly cooled to 2 ℃, sodium sulfate is precipitated in a crystallization form when reaching a supersaturation state, and then sodium sulfate crystals are separated from the solution through centrifugal separation.

l, heating the solution centrifugally separated in the second freezing and crystallizing unit to 25 ℃, conveying the solution to the water inlet end of a nanofiltration membrane component of a second nanofiltration unit, and enabling the second nanofiltration unit to adopt a membrane element same as that of the first nanofiltration unit to carry out SO in the nanofiltration membrane trapped liquid again₄ ^2-Concentrating to 60g/L, and returning to the second freezing and crystallizing unit;

and (3) allowing the nanofiltration permeate generated in the step (m) and the step (l) to enter an ammonium chloride evaporation crystallization device, wherein the ammonium chloride evaporation crystallization device adopts double-effect reduced pressure evaporation, the evaporation temperature is 80 ℃, the purity of the recovered ammonium chloride product can reach more than 99.3 percent, the industrial application requirements are met, the external discharge capacity of the evaporation mother liquor is 12 percent, and most of the evaporation mother liquor returns to a second freezing crystallization unit.

And n, introducing the discharged evaporation mother liquor of the ammonium chloride evaporation crystallization device into an ammonium nitrate freezing crystallization device, adding 100% of demineralized water for dilution, reducing the temperature of the solution to 20 ℃, separating out ammonium nitrate in a supersaturated state in a crystallization form, and separating out ammonium nitrate crystals from the solution through centrifugal separation, wherein the purity of the ammonium nitrate product can reach 99.5%, and the ammonium nitrate product meets the requirements of industrial application.

And o, returning the solution centrifugally separated in the ammonium nitrate freezing crystallization separation device to the ammonium chloride evaporation crystallization device.

According to the embodiment, the CO is absorbed by the first absorption tower and the second absorption tower₂The sodium bicarbonate solid is obtained by absorption, the sodium bicarbonate solid is settled to the bottom of a first absorption tower, the sodium bicarbonate solid product is obtained by normal-temperature centrifugal separation through the washing of a first tail gas washing tower and a second tail gas washing tower, the content of ammonia and other substances in the discharged waste gas reaches the discharge standard, a part of bicarbonate is recovered by freezing crystallization separation, the concentration of the bicarbonate in the feed solution of an ammonia sulfate evaporation crystallization unit is reduced, the ammonium sulfate evaporation crystallization is used for obtaining an ammonium sulfate solid product, the accumulation of sodium sulfate in the ammonium sulfate evaporation crystallization unit is prevented through the discharge of ammonium sulfate evaporation crystallization mother liquor, enough ammonium ions are provided for obtaining ammonium chloride and ammonium nitrate products in waste water treatment, and most of hardness, suspended matters, organic matters and colloids in the salt-containing waste water are removed through clarification and softening, ozone oxidation, medium filtration and ultrafiltration membrane filtration, residual hardness (i.e., Ca) was removed by softening with a weak acid cation resin²⁺、Mg²⁺) The interception and concentration of sulfate and organic matters are realized after the treatment of the first nanofiltration unit, most of water is recycled after the reverse osmosis concentration, the salt-containing wastewater is concentrated to obtain high-concentration sodium-containing salt water, the first nanofiltration intercepted solution, the reverse osmosis concentrated water and the ammonium sulfate evaporative crystallization mother liquor are subjected to second freezing crystallization centrifugal separation to obtain sodium sulfate crystals and are prepared into a sodium sulfate solution, the interception and separation of the sulfate and the organic matters are realized again after the second freezing crystallization mother liquor passes through the second nanofiltration membrane, and the enrichment of the sulfate and the organic matters in the ammonium chloride evaporative crystallization device is avoided. The permeate liquid of the second nanofiltration membrane is evaporated and crystallized to obtain ammonium chloride solid, the discharged ammonium chloride evaporation mother liquor is separated by an ammonium nitrate freezing and crystallizing device to realize crystallization and separation of ammonium nitrate, and a part of the ammonium chloride evaporation crystallization mother liquor returns to the second freezing and crystallizing unit to avoid sodium chloride and nitrateSodium and organic matters are enriched in an ammonium chloride evaporation crystallization device.

By these treatment steps, the CO can be contained₂CO in exhaust gas₂Absorbing, and separating salt and water in the salt-containing wastewater to obtain high-quality solid sodium bicarbonate, ammonium chloride, ammonium sulfate and ammonium nitrate products. The method and the system can also ensure that the system can run stably, economically and reliably for a long time without secondary pollution, and have obvious economic benefit and environmental benefit.

While the present invention has been described with reference to exemplary embodiments, it is understood that the terminology used is intended to be in the nature of words of description and illustration, rather than of limitation. As the present invention may be embodied in several forms without departing from the spirit or essential characteristics thereof, it should also be understood that the above-described embodiments are not limited by any of the details of the foregoing description, but rather should be construed broadly within its spirit and scope as defined in the appended claims, and therefore all changes and modifications that fall within the meets and bounds of the claims, or equivalences of such meets and bounds are therefore intended to be embraced by the appended claims.

Claims

1. A system for treating salt-containing wastewater, comprising:

the wastewater pretreatment unit is used for pretreating the salt-containing wastewater to remove organic matters, suspended matters and impurities in the salt-containing wastewater and reduce the hardness of the salt-containing wastewater;

the first nanofiltration unit is connected with the wastewater pretreatment unit and is used for performing nanofiltration treatment on the effluent of the wastewater pretreatment unit;

the second freezing and crystallizing unit is respectively connected with the first nanofiltration unit, the second nanofiltration unit, the ammonium sulfate evaporation and crystallization unit and the ammonium chloride evaporation and crystallization unit and is used for carrying out freezing and crystallizing treatment on nanofiltration trapped fluid of the first sodium filtration unit, nanofiltration trapped fluid of the second nanofiltration unit, crystallization mother liquor of the ammonium sulfate evaporation and crystallization unit and crystallization mother liquor of the ammonium chloride evaporation and crystallization unit, recovering sodium sulfate crystals and simultaneously discharging outlet water to the second nanofiltration unit;

the second nanofiltration unit is connected with the second freezing crystallization unit and is used for performing nanofiltration treatment on the effluent of the second freezing crystallization unit; the nanofiltration retentate is returned to the second freeze crystallization unit and/or the wastewater pretreatment unit;

the ammonium chloride evaporation crystallization unit is connected with the second nanofiltration unit and is used for carrying out evaporation crystallization treatment on the effluent of the second nanofiltration unit, recovering ammonium chloride crystals and discharging mother liquor; and

2. The saline wastewater treatment system according to claim 1, further comprising:

a first absorption unit for absorbing CO₂CO of exhaust gas₂Absorption treatment;

the second absorption unit is connected with the first absorption unit and used for carrying out CO treatment on the tail gas of the first absorption unit again by adopting ammonia water₂Absorbing treatment, and conveying part of absorption circulating solution to the first absorption unit;

the first tail gas washing unit is connected with the second absorption unit and is used for washing the tail gas of the second absorption unit and discharging a washing solution;

the second tail gas washing unit is connected with the first tail gas washing unit and used for washing the tail gas of the first tail gas washing unit by adopting desalted water and conveying a washing circulating solution to the first tail gas washing unit;

the sodium bicarbonate centrifugal separation unit is connected with the first absorption unit and is used for carrying out centrifugal separation treatment on the sodium bicarbonate slurry in the first absorption unit, recovering sodium bicarbonate crystals and discharging the mother liquor;

the first freezing and crystallizing unit is connected with the sodium bicarbonate centrifugal separation unit and is used for freezing and crystallizing mother liquor of a centrifugal machine of the sodium bicarbonate centrifugal separation unit, recovering mixed crystals of sodium bicarbonate and ammonium bicarbonate and discharging the mother liquor;

the ammonium sulfate evaporative crystallization unit is connected with the first freezing crystallization unit and is used for carrying out evaporative crystallization treatment on the freezing crystallization mother liquor of the first freezing crystallization unit, recovering ammonium sulfate crystals and discharging the mother liquor;

and the sodium sulfate solution preparation unit is respectively connected with the first absorption unit, the first freezing and crystallizing unit and the first tail gas washing unit, is used for receiving the mixed crystals of the sodium bicarbonate and the ammonium bicarbonate of the first freezing and crystallizing unit and the discharged washing solution of the first tail gas washing unit, and is prepared into a solution with the sodium sulfate crystals to be sent to an absorption tower of the first absorption unit.

3. The brine wastewater treatment system according to claim 2, wherein said sodium sulfate solution preparation unit is connected to said second freezing and crystallization unit for receiving sodium sulfate crystals of said second freezing and crystallization unit.

4. The salt-containing wastewater treatment system according to claim 2, wherein the absorption towers of the first absorption unit and the second absorption unit are bubble towers, the absorption tower of the first absorption unit is internally provided with an absorption zone and a precipitation zone, sodium bicarbonate crystals formed in the reaction process are precipitated at the bottom of a cone of the bubble tower, and an air loosening and purging device is arranged at the bottom of the cone.

5. The saline waste water treatment system according to claim 4, wherein said absorption tower employs separate absorption solution circulation and sodium bicarbonate slurry circulation.

6. The saline wastewater treatment system according to claim 4, wherein the depth of the liquid level in the absorption tower of said first absorption unit is 10-20 m, and the height of the liquid level in the absorption tower of said second absorption unit is 5-10 m.

7. The saline wastewater treatment system according to claim 1, further comprising a reverse osmosis concentration unit connected to the first nanofiltration unit and the second freeze crystallization unit for performing reverse osmosis desalination on the nanofiltration membrane permeate of the first nanofiltration unit and delivering reverse osmosis concentrated water to the second freeze crystallization unit for treatment.

8. A method for treating salt-containing wastewater, which is characterized by comprising the following steps:

a wastewater pretreatment step, namely pretreating the salt-containing wastewater to remove organic matters, suspended matters and impurities in the salt-containing wastewater and reduce the hardness of the salt-containing wastewater;

a first nanofiltration step, wherein the effluent of the wastewater pretreatment step is subjected to nanofiltration treatment;

a second freezing and crystallizing step, namely freezing and crystallizing the nanofiltration trapped fluid of the first nanofiltration step, the crystallization mother liquor of the ammonium sulfate evaporation and crystallization step, the nanofiltration trapped fluid of the second nanofiltration step and the crystallization mother liquor of the ammonium chloride evaporation and crystallization step, recovering sodium sulfate crystals, and simultaneously discharging the effluent to the second nanofiltration step;

a second nanofiltration step, wherein nanofiltration treatment is carried out on the effluent of the second freezing crystallization step; the nanofiltration retentate is returned to the second freeze crystallization step and/or pretreatment step;

an ammonium chloride evaporation crystallization step, wherein the effluent of the second nanofiltration step is subjected to evaporation crystallization treatment, ammonium chloride crystals are recovered, and meanwhile, mother liquor is discharged; and

and (3) a step of freezing and crystallizing ammonium nitrate, namely adding desalted water into the evaporation and crystallization mother liquor of the ammonium chloride evaporation and crystallization step, carrying out freezing and crystallization treatment, recovering ammonium nitrate crystals, and returning effluent to the ammonium chloride evaporation and crystallization step.

9. The method for treating salt-containing wastewater according to claim 8, further comprising:

a first absorption step of introducing CO₂CO of exhaust gas₂Absorption treatment while ensuring CO₂Excess;

a second absorption step of carrying out CO again on the tail gas of the first absorption step by adopting ammonia water₂An absorption treatment while conveying a part of the absorption circulation solution to the first absorption step;

a first tail gas washing step, wherein the tail gas in the second absorption step is washed, and meanwhile, a washing solution is discharged;

a second tail gas washing step, wherein the tail gas of the first tail gas washing step is washed by desalted water, and a washing circulating solution is conveyed to the first tail gas washing step;

a sodium bicarbonate centrifugal separation step, wherein the sodium bicarbonate slurry formed in the first absorption step is subjected to centrifugal separation treatment, sodium bicarbonate crystals are recovered, and meanwhile, mother liquor is discharged;

a first freezing and crystallizing step, namely freezing and crystallizing the centrifugal mother liquor of the sodium bicarbonate centrifugal separation step, recovering mixed crystals of sodium bicarbonate and ammonium bicarbonate, and discharging the mother liquor;

an ammonium sulfate evaporation crystallization step, wherein the freezing crystallization mother liquor of the first freezing crystallization step is subjected to evaporation crystallization treatment, ammonium sulfate crystals are recovered, and the mother liquor is discharged;

and a sodium sulfate solution preparation step, namely preparing a mixed crystal of sodium bicarbonate and ammonium bicarbonate in the first freezing and crystallizing step, an discharged washing solution in the first tail gas washing step and a sodium sulfate crystal into a solution and sending the solution to the first absorption step.

10. The method for treating salt-containing wastewater according to claim 9, wherein the temperatures of the first absorption step and the second absorption step are both 30-40 ℃.

11. The method for treating salt-containing wastewater according to claim 9, wherein the temperature of the first freezing and crystallizing step is 5-10 ℃.

12. The method as claimed in claim 8, wherein the hardness of the effluent of the wastewater pretreatment step is less than 1mg/L (as CaCO)₃Meter), SDI is less than 3.

13. The method for treating salt-containing wastewater according to claim 8, further comprising a reverse osmosis concentration step of subjecting the nanofiltration membrane permeate of the first nanofiltration step to reverse osmosis desalination, and subjecting the reverse osmosis concentrated water to freeze crystallization in a second freeze crystallization step.

14. The method for treating salt-containing wastewater according to claim 13, wherein the temperature of the second freezing and crystallizing step is-5 to 5 ℃.

15. The method for treating salt-containing wastewater according to claim 8, wherein the temperature of the ammonium nitrate freezing and crystallizing step is 10-20 ℃.

16. The method for treating salt-containing wastewater according to claim 8, wherein in the ammonium nitrate freeze crystallization step, the addition amount of the desalted water is 40-120% of the flow rate of the evaporation mother liquor, and more preferably 100-120%.

17. The method for treating salt-containing wastewater according to claim 8, wherein the concentration of ammonium nitrate in the discharged mother liquor of the ammonium chloride evaporation crystallization step is 1400-6000 g/L, preferably 4000-5000 g/L.

18. Containing CO₂An exhaust gas treatment system, comprising:

a second absorption unit connected with the first absorption unit and used for absorbing ammonia waterThe tail gas of the first absorption unit is subjected to CO again₂Absorbing treatment, and conveying part of absorption circulating solution to the first absorption unit;

19. The CO-containing of claim 18₂The waste gas treatment system is characterized in that the absorption towers of the first absorption unit and the second absorption unit adopt bubble towers, an absorption area and a precipitation area are arranged in the absorption tower of the first absorption unit, and reaction is carried outSodium bicarbonate crystals formed in the process are precipitated to the bottom of a cone of the bubble column, and an air loosening and purging device is arranged at the bottom of the cone.

20. The CO-containing of claim 18₂The waste gas treatment system is characterized in that the absorption tower adopts independent absorption solution circulation and sodium bicarbonate slurry circulation.

21. The CO-containing of claim 18₂The waste gas treatment system is characterized in that the liquid level depth in the absorption tower of the first absorption unit is 10-20 m, and the liquid level height in the absorption tower of the second absorption unit is 5-10 m.

22. Containing CO₂A method for treating exhaust gas, comprising:

23. The CO-containing of claim 22₂The method for treating the waste gas is characterized in that the temperatures of the first absorption step and the second absorption step are both 30-40 ℃.

24. The CO-containing of claim 22₂The method for treating exhaust gas is characterized in that the temperature of the first freezing and crystallizing step is 5-10 ℃.