System and method for separating salt by coupling leachate membrane concentrate with fly ash water washing

Abstract

The invention relates to a system and a method for separating salt by coupling leachate membrane concentrate with fly ash washing, and belongs to the technical field of synergistic treatment of leachate and household garbage incineration fly ash. The system comprises a fly ash washing salt separation system and a leachate membrane concentrated solution treatment system, the percolate membrane concentrated solution is dried, granulated and screened and then fed into a rotary kiln to be incinerated to remove organic matter, high-temperature flue gas generated by the rotary kiln is mixed with air and fed into a drying tower to serve as a drying heat source, then dust removal is conducted through a dust remover, the mixture is divided into two paths, one path enters a heat exchanger to exchange heat with air, and the heated air serves as combustion-supporting air of the rotary kiln; and the other path is introduced into the pulping tank and the fly ash washing system to adjust the pH and solidify the heavy metal. Through deep coupling of leachate membrane concentrated solution treatment and fly ash washing salt separation, treatment of waste with waste is realized, and the investment cost and the operation cost are reduced.

Description

Technical Field

[0001] This invention belongs to the field of co-treatment technology of leachate and fly ash from municipal solid waste incineration, and relates to a system and method for coupling leachate membrane concentrate with fly ash water washing and salt separation. Background Technology

[0002] With the continuous growth in demand for municipal solid waste treatment, waste-to-energy incineration has become the mainstream disposal method. However, the treatment and disposal of its associated wastes, including leachate membrane concentrate and fly ash from municipal solid waste incineration, are becoming increasingly prominent issues.

[0003] Landfill leachate membrane concentrate is the concentrated liquid retained after the raw landfill leachate has undergone biodegradation in a membrane bioreactor (MBR) and then passed through a nanofiltration (NF) or reverse osmosis (RO) membrane. Its volume typically accounts for 20%–30% of the raw leachate, but its pollutant concentration is extremely high. Unlike the raw leachate, the pollutants remaining in the membrane concentrate are mostly humic substances that are difficult to biodegrade. It also features high salt content, complex metal ions, and extremely low biodegradability, making direct biochemical treatment difficult. Methods such as reinjection, advanced oxidation, and drying incineration are commonly used to remove organic matter. Drying incineration can reduce the volume of the concentrate to 2%–10% of the raw liquid, but it generates a large amount of high-temperature flue gas. Direct emission of this gas not only wastes thermal energy, but the resulting mixture of salts contains heavy metals and is usually classified as hazardous waste for landfill disposal, resulting in high disposal costs and environmental risks.

[0004] Meanwhile, fly ash from municipal solid waste incineration, as an inevitable byproduct of the incineration process, is subject to strict control over its resource utilization. According to the "Technical Specification for Pollution Control of Municipal Solid Waste Incineration Fly Ash (Trial) HJ1134-2020," the soluble chlorine content should not exceed 2%, preferably not higher than 1%; the leaching concentration of heavy metals in the fly ash treatment product should be prepared according to HJ557, and the leaching concentration of heavy metals should not exceed the maximum allowable emission concentration limit specified in GB 8978; the total amount of dioxin residues should not exceed 50 ng-TEQ / kg (based on the dry weight of fly ash), etc. Currently, a three-stage countercurrent water washing system meets the above requirements, and sodium chloride and potassium chloride in the fly ash are separated through evaporation crystallization desalination technology for resource utilization. However, the fly ash washing system requires a large amount of water replenishment and generates a large amount of concentrated brine that needs further treatment. It also requires the addition of acid or the introduction of acidic gas (usually CO2) to adjust the pH value to promote heavy metal precipitation and decalcification reactions. Overall, the technology is complex and has high operating costs.

[0005] Given that the drying and incineration process of landfill leachate membrane concentrate generates a large amount of flue gas and mixed salts, while the water washing treatment of municipal solid waste incineration fly ash requires acidic gases such as CO2, and is also suitable for treating the mixed salts from the drying and incineration of landfill leachate membrane concentrate, the two can be organically combined. On the one hand, the acidic flue gas (mainly CO2) generated during the drying and incineration process of the membrane concentrate is introduced to adjust the pH of the fly ash water washing system, promoting heavy metal precipitation and decalcification reactions, and reducing the use of reagents. On the other hand, the fly ash water washing system is used to separate salts from the products of membrane concentrate drying and incineration, ultimately achieving synergistic recovery of salts and stable disposal of ash residue.

[0006] Therefore, developing an integrated system and method that can achieve the co-treatment of leachate concentrate and fly ash, the cascade utilization of energy and the efficient recovery of materials, and realize material complementarity and energy synergy to form an integrated process of waste treatment and resource recycling has become a key direction that urgently needs to be broken through in the field of environmental protection technology. It has important practical significance and broad application prospects. Summary of the Invention

[0007] In view of this, the purpose of the present invention is to provide a system and method for desalination by coupling leachate membrane concentrate with fly ash water washing, so as to achieve waste treatment and reduce investment and operating costs.

[0008] To achieve the above objectives, the present invention provides the following technical solution: A system for coupling leachate membrane concentrate with fly ash washing and salt separation includes a fly ash washing and salt separation system and a leachate membrane concentrate treatment system. The fly ash washing and salt separation system includes a fly ash washing system, a reaction tank, an ultrafiltration system, a nanofiltration system, and an MVR evaporation system connected in sequence. The leachate membrane concentrate treatment system includes a drying tower, a dust collector, a granulation device, a screening machine, and a rotary kiln connected in sequence. The dust collector has a first flue gas outlet and a second flue gas outlet. The first flue gas outlet is connected to the heat exchanger; the air inlet of the heat exchanger is connected to a blower, and the air outlet of the heat exchanger is connected to the combustion air supply port of the rotary kiln through a pipeline; the flue gas outlet of the heat exchanger is connected to a condensation system. The second flue gas outlet is divided into two paths: one path connects to the fly ash washing system, and the other path connects to a pulping tank. The inlet of the pulping tank receives incinerated ash from the rotary kiln outlet, and the outlet of the pulping tank is connected to the reaction tank.

[0009] Optionally, the outlet of the condensation system is connected to the pulping tank and the fly ash washing system.

[0010] Optionally, the sediment discharge ports of the reaction tank, ultrafiltration system, and nanofiltration system are all connected to the fly ash washing system.

[0011] Optionally, the outlet of the first wash filtrate of the fly ash washing system is connected to the reaction tank.

[0012] Optionally, the granulation device is a roller press granulation device, and the fly ash washing system is a three-stage countercurrent fly ash washing system.

[0013] A method for desalination using leachate membrane concentrate coupled with fly ash washing, based on the aforementioned system for desalination using leachate membrane concentrate coupled with fly ash washing, includes the following steps: S1. The leachate membrane concentrate is atomized and sprayed into the drying tower, where it comes into direct contact with the high-temperature flue gas mixed with air from the rotary kiln, and is dried into dried ash. S2. The flue gas carrying the dried ash enters the dust collector for gas-solid separation. The collected dried ash is sent to the granulation device for granulation, and then screened by the screening machine. The qualified particles are sent to the rotary kiln. S3. Granular dried ash is incinerated in a rotary kiln under the high temperature provided by biogas combustion to remove the organic matter contained therein; S4. The incinerated ash from the rotary kiln enters the pulping tank for pulping. The flue gas from the dust collector outlet is divided into two paths: the first path enters the heat exchanger to exchange heat with the air, and the flue gas after heat exchange is discharged after passing through the condensation system. The heated air is used as the combustion air for the rotary kiln; the second path of flue gas is fed into the pulping tank and the fly ash washing system to adjust the pH and solidify heavy metals; the solution in the pulping tank is sent into the reaction tank. S5. The fly ash from municipal solid waste incineration enters the fly ash washing system for countercurrent washing. The resulting first wash filtrate is sent to the reaction tank, mixed with the solution from the pulping tank, and a decalcification agent is added to carry out the decalcification reaction. S6. The effluent from the reaction tank passes through an ultrafiltration system and a nanofiltration system in sequence to remove suspended solids and divalent salt impurities before the solution enters the product water tank. S7. The solution from the product water tank enters the MVR evaporation system for evaporation, crystallization, and salt separation to obtain sodium chloride and potassium chloride products; The precipitates generated by the reaction tank, ultrafiltration system, and nanofiltration system are all returned to the fly ash washing system.

[0014] Optionally, the flue gas cooled by the heat exchanger is further cooled by the condensation system to produce condensate; the makeup water sources for the fly ash washing system and the pulping tank include condensate produced by the condensation system and the MVR evaporation system, as well as industrial water; excess condensate from the condensation system is discharged to the leachate clear liquid tank.

[0015] Optionally, the rotary kiln can be fueled by biogas produced from the anaerobic treatment of landfill leachate, or by natural gas or liquefied petroleum gas when biogas is unavailable.

[0016] Optionally, the flue gas temperature at the dust collector outlet is 100~110℃, the flue gas temperature after heat exchange is 50~60℃, and the heated air temperature is 30~60℃.

[0017] Optionally, the temperature of the flue gas introduced into the drying tower is 300~400℃, and the flow rate is 15000~25000 m³ / h.

[0018] The beneficial effects of this invention are as follows: 1. Achieves deep synergy between the treatment of two wastes and the treatment of waste with waste: This invention deeply couples the treatment of leachate membrane concentrate with the salt separation of fly ash water washing, achieving a perfect combination of "treating waste with waste"; by utilizing the flue gas generated from the incineration of membrane concentrate, it provides free pH adjuster and heat energy for the fly ash water washing system, which not only saves the cost of purchasing acidic agents, but also avoids the risks brought about by the introduction of complex flue gas, significantly reducing the investment and operating costs of the system.

[0019] 2. Achieves efficient tiered utilization of energy: This invention fully utilizes the sensible heat of the high-temperature flue gas from the rotary kiln, including for air preheating, material drying, and solution conditioning, achieving multi-stage tiered utilization of thermal energy, greatly improving energy utilization efficiency, and significantly reducing the overall energy consumption of the system.

[0020] 3. Achieved material recycling and near-zero emissions: By coupling the leachate membrane concentrate treatment system with the fly ash washing and desalination system, this invention constructs a material recycling system. The system realizes multi-stage water recycling (such as the reuse of MVR condensate and flue gas condensate), achieving zero wastewater discharge. All precipitates (including those generated from membrane concentrate treatment) are returned to the fly ash washing system, where they form the final ash residue together with the insoluble matter of fly ash. There is no new solid waste discharge from the system, which not only reduces the investment and operating costs of leachate membrane concentrate resource utilization, but also reduces the water replenishment requirements of the fly ash washing and desalination system, truly achieving zero wastewater and solid waste generation.

[0021] 4. High-value recovery of salt resources: This invention removes organic matter from the leachate membrane concentrate ash residue using only a rotary kiln. Since the rotary kiln only incinerates the dried ash residue, the removal of organic matter in the dried ash residue is more thorough, creating conditions for the efficient separation of sodium chloride and potassium chloride. Because only the organic matter in the leachate membrane concentrate ash residue is removed using a rotary kiln, the system is simpler, making salt separation more efficient. In addition, the incinerated ash residue can be collected separately, further facilitating efficient salt separation. Therefore, this invention achieves high-value recovery of salt substances.

[0022] 5. Economical operation and strong adaptability: This invention is particularly suitable for waste incineration plants that have already built fly ash washing and desalination systems. It can directly use biogas produced by anaerobic fermentation of leachate in the plant as fuel, without the need for additional energy, with low operating costs, and has strong economic efficiency and wide applicability.

[0023] Other advantages, objectives, and features of the invention will be set forth in part in the description which follows, and in part will be apparent to those skilled in the art from the following examination, or may be learned from practice of the invention. The objectives and other advantages of the invention can be realized and obtained through the following description. Attached Figure Description

[0024] To make the objectives, technical solutions, and advantages of the present invention clearer, the preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings, wherein: Figure 1 This is a schematic diagram of the system for desalination of the percolate membrane concentrate coupled with fly ash washing. Detailed Implementation

[0025] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of the present invention. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0026] The accompanying drawings are for illustrative purposes only and are schematic diagrams, not actual pictures. They should not be construed as limiting the invention. To better illustrate the embodiments of the invention, some parts in the drawings may be omitted, enlarged, or reduced, and do not represent the actual product dimensions. It is understandable to those skilled in the art that some well-known structures and their descriptions may be omitted in the drawings.

[0027] In the accompanying drawings of the embodiments of the present invention, the same or similar reference numerals correspond to the same or similar components. In the description of the present invention, it should be understood that if terms such as "upper," "lower," "left," "right," "front," and "rear" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, they are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, the terms used to describe positional relationships in the drawings are only for illustrative purposes and should not be construed as limiting the present invention. For those skilled in the art, the specific meaning of the above terms can be understood according to the specific circumstances.

[0028] Example 1 Please see Figure 1A leachate membrane concentrate coupled with fly ash washing and salt separation system includes a fly ash washing and salt separation system and a leachate membrane concentrate system. The fly ash washing and salt separation system mainly includes a fly ash washing system 10, a reaction tank 11, an ultrafiltration system 12, a nanofiltration system 13, and an MVR evaporation system 15. The leachate membrane concentrate treatment system mainly includes a drying tower 1, a dust collector 2, a granulation device 3, a screening machine 4, a rotary kiln 5, a heat exchanger 6, a condensation system 7, and a pulping tank 8.

[0029] The leachate membrane concentrate is pumped into the atomizer of the drying tower 1 and mixed with the high-temperature flue gas generated by the rotary kiln 5 through swirl spraying. The dried ash is collected with the flue gas to the dust collector 2. The collected dried ash enters the granulation device 3 for granulation. The granulation device 3 can be a roller press granulation device. The flue gas after dust removal enters the heat exchanger 6 to exchange heat with the air.

[0030] The dried ash residue from the outlet of granulation unit 3 enters screening machine 4 for screening, the powder returns to granulation unit 3 for granulation, and the granules enter rotary kiln 5 for incineration to remove organic matter.

[0031] Rotary kiln 5 uses biogas as its energy source. The air heated by heat exchanger 6 is used as the combustion air for biogas. As the rotary kiln moves forward, the organic matter in the granular dried ash is burned in the biogas environment. The dried ash after combustion enters the pulping tank 8 from the outlet of rotary kiln 5. The high-temperature flue gas from rotary kiln 5 mixes with ambient air and then enters drying tower 1 to dry the leachate membrane concentrate. The flue gas from dust collector 2 has two outlets. The flue gas from one outlet enters the fly ash washing system 10 and the pulping tank 8. The fly ash washing system 10 can be a three-stage countercurrent fly ash washing system. The flue gas from the other outlet exchanges heat with heat exchanger 6 and is then condensed by condensation system 7 before being discharged.

[0032] The air inlet of heat exchanger 6 is connected to blower 9, and the air outlet of heat exchanger 6 is connected to rotary kiln 5; the flue gas inlet of heat exchanger 6 is connected to dust collector 2, and the flue gas outlet is connected to condensing system 7; the condensate pipe of condensing system 7 is connected to pulping tank 8 and fly ash washing system 10, and excess condensate can also be discharged to leachate clear liquid tank.

[0033] The pulping tank 8 receives the dried ash residue from the outlet of the rotary kiln 5. The flue gas from the rotary kiln 5 enters the pulping tank 8 and reacts with the solution to adjust the pH and form some salt precipitate. The precipitate and solution are discharged together into the reaction tank 11.

[0034] Fly ash enters the fly ash washing system 10 for treatment. The makeup water for this system is industrial water, which can be replaced by the condensate from the MVR evaporation system 15 and the condensate from the condensation system 7. The precipitates from the pulping tank 8, reaction tank 11, ultrafiltration system 12, and nanofiltration system 13 are all returned to the fly ash washing system 10. After the reaction, they form ash residue together with the insoluble matter of the fly ash. The first washing filtrate enters the reaction tank 11 and is mixed with the solution from the pulping of the dried ash residue. A decalcification reaction is then carried out using a decalcification agent.

[0035] The solution from the outlet of reaction tank 11 enters the ultrafiltration system 12 and nanofiltration system 13 in sequence to remove divalent salts and suspended solids. The remaining solution enters the product water tank 14 and then enters the MVR evaporation system 15 for salt separation to obtain sodium chloride and potassium chloride solutions.

[0036] This invention is the optimal solution for the resource utilization of leachate membrane concentrate in the case of an existing municipal solid waste fly ash washing and salt separation system in a waste incineration plant.

[0037] Example 2 A method for desalination by coupling leachate membrane concentrate with fly ash water washing, based on the above-mentioned system for desalination by coupling leachate membrane concentrate with fly ash water washing.

[0038] Taking the standalone operation of a membrane concentrate processing 50 tons / day of leachate as an example: The solids content of the leachate membrane concentrate is assumed to be 10%. Regarding water balance, condensation system 7 produces approximately 25 t / d of condensate, with approximately 0.5 t / d of condensate flowing from condensation system 7 into the pulping tank 8, and approximately 24.5 t / d of condensate flowing from condensation system 7 into the leachate clearing tank. As for flue gas, approximately 20,000 m³ of 350°C flue gas is required to enter drying tower 1. 3 / h, requires approximately 225m³ of biogas. 3 / h, the flue gas fed into the pulping tank 8 by dust collector 2 is approximately 250m³. 3 / h. Regarding solid products: Dust collector 2 produces approximately 5t / d of dried ash, which requires landfill disposal or co-processing at a municipal solid waste incineration plant.

[0039] Taking a municipal solid waste fly ash washing and desalination system with a processing capacity of 100t / d operating independently as an example: The water-to-ash ratio for the washing process is 2:1. Regarding water balance, approximately 150 t / d of condensate flows from the MVR evaporation system 15 into the fly ash washing system 10, with an additional 50 t / d of supplementary water required. Regarding flue gas, approximately 5000 m³ of flue gas needs to be treated by the flue gas treatment system of the municipal solid waste incineration plant. 3 / h or the effect of using chemical agents instead of flue gas treatment. In terms of solid products: about 100t / d of ash and slag, about 15t / d of sodium chloride, and about 5t / d of potassium chloride are produced.

[0040] Taking the coupled operation of the two as an example: Regarding water balance, the flue gas condensation generates approximately 25 t / d of condensate. Approximately 0.3 t / d of condensate enters the pulping tank 8 from the flue gas, approximately 0.2 t / d of condensate enters the pulping tank 8 from the condensation system 7, approximately 6.2 t / d of condensate enters the fly ash washing system 10 from the flue gas, approximately 18.3 t / d of condensate enters the fly ash washing system 10 from the condensation system 7, and approximately 150 t / d of condensate enters the fly ash washing system 10 from the MVR evaporation system 15. The system requires an additional 25.5 t / d of water replenishment, resulting in a reduction of 24.5 t / d.

[0041] Regarding the flue gas, approximately 20,000 m³ of 350°C flue gas needs to enter drying tower 1. 3 / h, approximately 250m³ of flue gas is fed from dust collector 2 into pulping tank 8. 3 The amount of flue gas fed from dust collector 2 into fly ash washing system 10 is approximately 5000 m³ / h. 3 / h. Approximately 300m³ of biogas is required. 3 / h, approximately 12500m³ of air enters the rotary kiln 5 from the heat exchanger 6. 3 / h, the air volume from the passage between rotary kiln 5 and drying tower 1 is approximately 7000m³ / h. 3 / h. The system does not require the introduction of a flue gas treatment system from a municipal solid waste incineration plant to treat approximately 5000 m³ of flue gas. 3 / h or the effect of using chemical agents instead of flue gas treatment.

[0042] Regarding solid byproducts: Approximately 101 tons of ash and slag, 18 tons of sodium chloride, and 6.5 tons of potassium chloride are generated per day. No solid waste requires landfill disposal or co-processing at a waste incineration plant.

[0043] The biogas produced by the anaerobic fermentation of leachate from the municipal solid waste incineration plant eliminates the need for additional energy purchases. Natural gas or liquefied petroleum gas can be used as a substitute when biogas is unavailable.

[0044] This invention removes organic matter from the dried ash residue of leachate membrane concentrate obtained through rotary kiln incineration; removes divalent salts, suspended solids, and other impurities through pulping, decalcification, ultrafiltration, and nanofiltration processes; the separated precipitate is mixed with or treated separately with the ash residue from the fly ash washing process of municipal solid waste incineration; the purified solution enters an MVR (Medium-Vacuum Resinerary Vaporizer) to obtain sodium chloride and potassium chloride products. By coupling leachate membrane concentrate treatment with the fly ash washing and salt separation process of waste incineration, this invention reduces the investment and operating costs of leachate membrane concentrate resource utilization, reduces the need for makeup water in the fly ash washing and salt separation system, and simultaneously achieves zero wastewater and solid waste generation.

[0045] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A system for desalination of leachate membrane concentrate coupled with fly ash washing, comprising a fly ash washing system, the fly ash washing system comprising a fly ash washing system (10), a reaction tank (11), an ultrafiltration system (12), a nanofiltration system (13), and an MVR evaporation system (15) connected in sequence, characterized in that: It also includes a leachate membrane concentrate treatment system, which includes a drying tower (1), a dust collector (2), a granulation device (3), a screening machine (4), and a rotary kiln (5) connected in sequence; the dust collector (2) is provided with a first flue gas outlet and a second flue gas outlet; The first flue gas outlet is connected to the heat exchanger (6); the air inlet of the heat exchanger (6) is connected to a blower (9), and the air outlet of the heat exchanger (6) is connected to the combustion air supply port of the rotary kiln (5) through a pipeline; the flue gas outlet of the heat exchanger (6) is connected to a condensation system (7). The second flue gas outlet is divided into two paths. One path is connected to the fly ash washing system (10), and the other path is connected to the pulping tank (8). The feed inlet of the pulping tank (8) receives the incineration ash from the rotary kiln outlet, and the outlet of the pulping tank (8) is connected to the reaction tank (11).

2. The system for leachate membrane concentrate coupled with fly ash washing and salt separation according to claim 1, characterized in that: The outlet of the condensation system (7) is connected to the pulping tank (8) and the fly ash washing system (10).

3. The system for leachate membrane concentrate coupled with fly ash washing and salt separation according to claim 1, characterized in that: The sediment discharge ports of the reaction tank (11), ultrafiltration system (12), and nanofiltration system (13) are all connected to the fly ash washing system (10).

4. The system for leachate membrane concentrate coupled with fly ash washing and salt separation according to claim 1, characterized in that: The first wash filtrate outlet of the fly ash washing system (10) is connected to the reaction tank (11).

5. The system for leachate membrane concentrate coupled with fly ash washing and salt separation according to claim 1, characterized in that: The granulation device (3) is a roller press granulation device, and the fly ash washing system (10) is a three-stage countercurrent fly ash washing system.

6. A method for desalination of leachate membrane concentrate coupled with fly ash washing, characterized in that: The system based on the leachate membrane concentrate coupled with fly ash washing and salt separation according to any one of claims 1 to 5 includes the following steps: S1. The leachate membrane concentrate is atomized and sprayed into the drying tower (1), where it comes into direct contact with the high-temperature flue gas mixed with air from the rotary kiln (5) and dried into dried ash. S2. The flue gas carrying the dried ash enters the dust collector (2) for gas-solid separation. The collected dried ash is sent to the granulation device (3) for granulation, and then screened by the screening machine (4). The qualified particles are sent to the rotary kiln (5). S3. The granular dried ash residue is incinerated in a rotary kiln (5) under the high temperature environment provided by biogas combustion to remove the organic matter contained therein; S4. The incinerated ash from the rotary kiln (5) enters the pulping tank (8) for pulping. The flue gas from the dust collector (2) outlet is divided into two paths: the first path enters the heat exchanger (6) to exchange heat with the air, and the flue gas after heat exchange is discharged after passing through the condensation system (7). The heated air is used as the combustion air for the rotary kiln (5); the second path of flue gas is introduced into the pulping tank (8) and the fly ash washing system (10) to adjust the pH and solidify heavy metals; the solution in the pulping tank (8) is sent into the reaction tank (11). S5. The fly ash from municipal solid waste incineration enters the fly ash washing system (10) for countercurrent washing. The resulting first washing filtrate is sent to the reaction tank (11) and mixed with the solution from the pulping tank (8). Decalcification agent is added to carry out the decalcification reaction. S6. The effluent from the reaction tank (11) passes through the ultrafiltration system (12) and the nanofiltration system (13) in sequence to remove suspended solids and divalent salt impurities, and then the solution enters the product water tank (14). S7. The solution in the product water tank (14) enters the MVR evaporation system (15) for evaporation, crystallization and salt separation to obtain sodium chloride and potassium chloride products; The precipitates generated by the reaction tank (11), ultrafiltration system (12) and nanofiltration system (13) are all returned to the fly ash washing system (10).

7. The method for desalination of leachate membrane concentrate coupled with fly ash washing according to claim 6, characterized in that: After being cooled by the heat exchanger (6), the flue gas is deeply cooled by the condensation system (7) to produce condensate. The makeup water sources for the fly ash washing system (10) and the pulping tank (8) include the condensate produced by the condensation system (7) and the MVR evaporation system (19), as well as industrial water. Excess condensate from the condensation system (7) is discharged to the leachate clearing tank.

8. The method for desalination of leachate membrane concentrate coupled with fly ash washing according to claim 6, characterized in that: The rotary kiln (5) is fueled by biogas produced by anaerobic treatment of landfill leachate. When biogas is unavailable, it can be replaced by natural gas or liquefied petroleum gas.

9. The method for desalination of leachate membrane concentrate coupled with fly ash washing according to claim 6, characterized in that: The flue gas temperature at the outlet of the dust collector (2) is 100~110℃, the flue gas temperature after heat exchange is 50~60℃, and the air temperature after heating is 30~60℃.

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