System and method for extracting liquid calcium chloride, sodium chloride and potassium chloride from fly ash

Abstract

The invention relates to a system and a method for extracting liquid calcium chloride, sodium chloride and potassium chloride from fly ash, and belongs to the technical field of resource utilization of household garbage incineration fly ash. The system comprises a washing unit, a filtrate treatment unit and a salt separation and purification unit. The method comprises the following steps: carrying out four-stage countercurrent washing of water washing, acid pickling, water washing and water washing on the fly ash, and carrying out deep dechlorination to produce qualified ash residues; performing impurity removal and nanofiltration on high-salt filtrate discharged by primary water washing, and reusing concentrated liquor for acid washing; carrying out impurity removal and nanofiltration on high-calcium filtrate discharged by secondary pickling, and carrying out high-pressure reverse osmosis concentration on concentrated liquor to obtain a liquid calcium chloride product; and evaporating the nanofiltration produced water to produce sodium chloride and potassium chloride. According to the method, evaporation-free production of the calcium chloride liquid is realized through coupling of circulating pickling and membrane separation concentration technologies, sodium chloride and potassium chloride are synchronously produced, and the method has the advantages of high resource product value, low energy consumption and remarkable ash residue reduction effect.

Description

Technical Field

[0001] This invention belongs to the field of resource utilization technology of fly ash from municipal solid waste incineration, and relates to a system and method for extracting liquid calcium chloride, sodium chloride and potassium chloride from fly ash. Background Technology

[0002] Currently, municipal solid waste incineration for power generation has become the mainstream method of waste treatment. However, the fly ash produced during the incineration process is classified as hazardous waste because it is rich in chloride salts (such as sodium chloride NaCl, potassium chloride KCl, and calcium chloride CaCl2), heavy metals, and toxic and harmful substances such as dioxins. How to achieve the harmless disposal and high-value resource utilization of fly ash has become a key bottleneck restricting the green development of the waste incineration industry.

[0003] Currently, one of the mainstream technical approaches for fly ash resource utilization is water washing and dechlorination pretreatment. This technology aims to reduce the chlorine content in fly ash slag by dissolving soluble chloride salts through water washing, making it suitable for subsequent production as a raw material for cement kiln co-processing or as aggregate in building materials. However, existing water washing processes generally face the following technical challenges: 1. Limited chloride removal efficiency and ash reduction effect. Although conventional water washing processes can remove most of the soluble chlorides in fly ash, the removal efficiency is often difficult to achieve the ideal level, and the ash reduction effect is usually only 15-35%.

[0004] 2. High-salinity wastewater treatment is costly and has a low resource utilization rate. The large amount of high-salinity wastewater generated during the washing process contains high concentrations of sodium. + K + Ca² + Cl - And heavy metal ions. Current technologies for treating this type of wastewater typically require the addition of large amounts of calcium removal agents (such as sodium carbonate) to remove calcium ions in order to achieve subsequent evaporation and crystallization or meet discharge standards. This process not only consumes a large amount of reagents, significantly increasing operating costs, but also generates a large number of byproducts, resulting in a final fly ash reduction of less than 15%, greatly diminishing its economic viability.

[0005] 3. Evaporation crystallization is energy-intensive, and the resource recovery of calcium chloride is difficult. For the sodium chloride and potassium chloride abundant in washing solutions, existing technologies mostly use evaporation crystallization to recover mixed salts or separate them. However, for high-boiling-point salts like calcium chloride, direct evaporation to produce solid products or high-concentration liquids is particularly costly.

[0006] Therefore, developing an integrated process system and method that can efficiently remove chloride salts from fly ash, simultaneously achieve efficient separation and resource conversion of calcium chloride, sodium chloride, and potassium chloride, and significantly reduce processing energy consumption and operating costs is of great practical significance and broad application prospects for improving the technical and economic efficiency of waste incineration fly ash resource utilization and promoting the development of a circular economy. Summary of the Invention

[0007] In view of this, the purpose of the present invention is to provide a system and method for extracting liquid calcium chloride, sodium chloride and potassium chloride from fly ash, so as to achieve deep dechlorination and volume reduction of fly ash.

[0008] To achieve the above objectives, the present invention provides the following technical solution: A system for extracting liquid calcium chloride, sodium chloride, and potassium chloride from fly ash includes a washing unit, a filtrate treatment unit, and a salt separation and purification unit. The washing unit is used to perform multi-stage countercurrent washing of fly ash, including a first-stage water washing system, a second-stage acid washing system, a third-stage water washing system, and a fourth-stage water washing system arranged in sequence; The primary washing system includes a primary pulping tank, a primary washing tank, a primary slurry pump, a primary dewatering machine, and a primary filtrate tank arranged in sequence, with the primary filtrate tank connected to the primary pulping tank; The secondary pickling system includes a secondary pickling tank, a secondary slurry pump, a secondary dewatering machine, and a secondary filtrate tank arranged in sequence. The secondary filtrate tank is connected to the secondary pickling tank, and the secondary pickling tank is connected to the wet slag outlet of the primary dewatering machine. The three-stage washing system includes a three-stage washing tank, a three-stage slurry pump, a three-stage dewatering machine, and a three-stage filtrate tank arranged in sequence. The three-stage filtrate tank is connected to the three-stage acid washing tank, and the three-stage washing tank is connected to the wet sludge outlet of the two-stage dewatering machine. The four-stage washing system includes a four-stage washing tank, a four-stage slurry pump, a four-stage dewatering machine, and a four-stage filtrate tank arranged in sequence. The four-stage filtrate tank is connected to the four-stage acid washing tank, and the four-stage washing tank is connected to the wet sludge outlet of the three-stage dewatering machine. The filtrate treatment unit includes a primary filtrate treatment system and a secondary filtrate treatment system; The primary filtrate treatment system includes a concentrate tank, a pressure filtration device, an ultrafiltration system, and a first nanofiltration system arranged in sequence; the concentrate tank is connected to the primary filtrate pool; the concentrate end of the ultrafiltration system is connected to the concentrate tank, and the concentrate end of the first nanofiltration system is connected to the secondary acid washing tank. The two-stage filtrate treatment system includes a gravity removal tank, a filtration device, and a second nanofiltration system arranged in sequence; the gravity removal tank is connected to the two-stage filtrate tank. The salt separation and purification unit includes an evaporation and crystallization system connected to the product water end of the first nanofiltration system and the product water end of the second nanofiltration system, and a high-pressure reverse osmosis system connected to the concentrate end of the second nanofiltration unit.

[0009] Optionally, the product water end of the high-pressure reverse osmosis system is connected to the tertiary filtrate tank.

[0010] Optionally, the condensate pipe of the evaporation crystallization system is connected to the four-stage filtrate tank.

[0011] Optionally, the fourth-stage filtrate tank is connected to an industrial water pipe to supply industrial water to the fourth-stage filtrate tank.

[0012] Optionally, the fourth-stage filtrate tank is connected to a fourth-stage drain pipe, which is connected to the third-stage filtrate tank to supply water to the third-stage filtrate tank.

[0013] Optionally, the tertiary filtrate tank is connected to a tertiary drain pipe, which is connected to the secondary and primary filtrate tanks to supply water to them.

[0014] Optionally, the concentrate tank is connected to a barium chloride addition device, the degravation tank is connected to a sodium sulfide addition device, and the secondary pickling tank is connected to a hydrochloric acid addition device.

[0015] A method for extracting liquid calcium chloride, sodium chloride, and potassium chloride from fly ash, based on the aforementioned system for extracting liquid calcium chloride, sodium chloride, and potassium chloride from fly ash, includes the following steps: S1. Primary washing: Fly ash is mixed with primary washing filtrate, washed, and then dehydrated to obtain primary wet sludge and primary washing filtrate; the primary washing filtrate is recycled, and when the chloride ion concentration in it exceeds the first threshold, primary concentrated water is discharged. S2. Secondary pickling: The primary wet residue and the secondary pickling filtrate are mixed and hydrochloric acid is added for pickling, followed by dehydration to obtain secondary wet residue and secondary pickling filtrate; the secondary pickling filtrate is recycled, and when the chloride ion concentration exceeds the second threshold, the secondary concentrate is discharged; S3. Tertiary washing: The secondary wet residue is subjected to tertiary washing, and after washing, it is dehydrated to obtain tertiary wet residue and tertiary filtrate. The tertiary filtrate is recycled. S4. Fourth-stage water washing: The third-stage wet slag is washed with fourth-stage water, and then dewatered to obtain the final ash and fourth-stage filtrate. The fourth-stage filtrate is recycled. S5. Primary Concentrate Treatment: The primary concentrate is purified by sulfate removal and ultrafiltration, and then enters the first nanofiltration system for separation; the permeate from the first nanofiltration system enters the evaporation and crystallization system, and the concentrate from the first nanofiltration system is returned to the secondary acid washing system; S6. Secondary concentrate treatment and calcium chloride purification: After heavy metal removal treatment, the secondary concentrate enters the second nanofiltration system for separation; the permeate from the second nanofiltration system enters the evaporation crystallization system, and the concentrate from the second nanofiltration system enters the high-pressure reverse osmosis system for concentration to obtain liquid calcium chloride product; S7. Evaporation and Crystallization: The permeate water from the first nanofiltration system and the permeate water from the second nanofiltration system are evaporated and crystallized to obtain sodium chloride and potassium chloride products.

[0016] Optionally, in step S1, the fly ash is fly ash that has undergone low-temperature pyrolysis treatment; the liquid-to-solid ratio of the washing is 3:1 to 5:1.

[0017] Optionally, in step S2, the amount of hydrochloric acid added is 0.6~0.9 mg / L. 3 / t dry ash.

[0018] Optionally, in step S5, sulfate ions are removed by adding barium chloride.

[0019] Optionally, in step S6, heavy metals are removed by adding sodium sulfide; the concentration of the liquid calcium chloride product is 25%~30%.

[0020] Optionally, the first threshold is 100,000 mg / L.

[0021] Optionally, the second threshold is 150,000 mg / L.

[0022] Optionally, the circulation rate of the secondary pickling is 2~4m³. 3 / t dry ash, the circulation rate for both the third-stage and fourth-stage water washing is 3~5m³. 3 / t dry ash.

[0023] The beneficial effects of this invention are as follows: 1. This invention achieves deep dechlorination and efficient ash reduction: Through a four-stage countercurrent washing process of "first-stage water washing + first-stage acid washing + two-stage water washing," chloride salts (including insoluble calcium salts) in fly ash can be deeply removed, resulting in a final ash ash chloride content of less than 1%, meeting the requirements of HJ1134-2020 standard, and achieving a significant reduction in ash volume. This invention increases fly ash volume reduction from 20-25% to 60-70%. Conventional fly ash washing processes typically reduce ash volume by 15-35%, and the introduction of calcium precipitation during subsequent high-salinity wastewater treatment often results in a final ash ash reduction of less than 15%. This invention significantly improves fly ash volume reduction.

[0024] 2. The pickling system in this invention adopts a circulating pickling method, which can significantly increase the calcium chloride concentration in the pickling solution to 20%~25%.

[0025] 3. In this invention, the water washing filtrate and acid washing filtrate are separated by membrane separation technology to separate monovalent salts (sodium chloride, potassium chloride) and divalent salts (calcium chloride). The concentration of the separated calcium chloride liquid can be increased to more than 30% after membrane concentration, realizing the production of liquid calcium chloride industrial products without evaporation.

[0026] 4. This invention not only produces conventional sodium chloride and potassium chloride, but also, through innovative cyclic acid washing and membrane integration processes including nanofiltration and high-pressure reverse osmosis, directly produces industrial-grade liquid calcium chloride with a concentration of up to 30%, conforming to the GB / T 26520-2011 standard for "Industrial Calcium Chloride," greatly enhancing the economic value of fly ash resource utilization. The by-product calcium chloride of this invention can generate an additional 100-150 RMB / ton of raw fly ash revenue.

[0027] 5. This invention employs nanofiltration to achieve efficient separation of monovalent salts (sodium chloride, potassium chloride) and divalent salts (calcium chloride), and utilizes high-pressure reverse osmosis to concentrate the calcium chloride solution at room temperature, avoiding the high energy consumption problem of traditional evaporation to produce liquid calcium chloride. Simultaneously, the acid washing system adopts a circulation mode, improving the utilization rate of hydrochloric acid and the concentration of calcium chloride in the acid washing solution, reducing the consumption of fresh hydrochloric acid and the load on subsequent wastewater treatment.

[0028] 6. This invention reuses the high-calcium concentrate separated from the primary washing water via nanofiltration in the pickling stage, replenishing the pickling solution and achieving the recycling of materials within the system. The entire process system has a high degree of integration, reducing the addition of chemicals such as calcium removal agents, lowering operating costs, and ensuring that all final products are utilized as resources, which aligns with green environmental protection principles. Traditional high-salinity wastewater treatment processes typically introduce large amounts of calcium removal agents, leading to increased operating costs and the additional generation of sodium chloride with very low added value.

[0029] 7. This invention achieves efficient separation and full-component resource utilization of chloride salts (NaCl, KCl, CaCl2) in fly ash. In particular, it innovatively obtains high-concentration liquid calcium chloride through a non-evaporation path of "circulating acid washing + nanofiltration purification + reverse osmosis concentration", which has the advantages of low energy consumption, high product added value and good environmental benefits.

[0030] 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

[0031] 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 extracting liquid calcium chloride, sodium chloride, and potassium chloride from fly ash according to the present invention.

[0032] Figure labels: 1. Ultrafiltration system; 2. First nanofiltration system; 3. Evaporation and crystallization system; 4. Second nanofiltration system; 5. High-pressure reverse osmosis system. Detailed Implementation

[0033] 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.

[0034] 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.

[0035] 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.

[0036] Example 1 Please see Figure 1 This is a system for extracting liquid calcium chloride, sodium chloride, and potassium chloride from fly ash, comprising a washing unit, a filtrate treatment unit, and a salt separation and purification unit.

[0037] Washing Unit: Used for multi-stage countercurrent washing of fly ash, including a sequentially arranged primary water washing system, a secondary acid washing system, a tertiary water washing system, and a quaternary water washing system; the primary water washing system includes a sequentially arranged primary pulping tank, a primary water washing tank, a primary slurry pump, a primary dewatering machine, and a primary filtrate tank, with the primary filtrate tank connected to the primary pulping tank; the secondary acid washing system includes a sequentially arranged secondary acid washing tank, a secondary slurry pump, a secondary dewatering machine, and a secondary filtrate tank, with the secondary filtrate tank connected to the secondary acid washing tank. The secondary pickling tank is connected to the wet sludge outlet of the primary dewatering machine; the tertiary washing system includes a tertiary washing tank, a tertiary slurry pump, a tertiary dewatering machine, and a tertiary filtrate tank arranged in sequence, with the tertiary filtrate tank connected to the tertiary pickling tank and the tertiary washing tank connected to the wet sludge outlet of the secondary dewatering machine; the quaternary washing system includes a quaternary washing tank, a quaternary slurry pump, a quaternary dewatering machine, and a quaternary filtrate tank arranged in sequence, with the quaternary filtrate tank connected to the quaternary pickling tank and the quaternary washing tank connected to the wet sludge outlet of the tertiary dewatering machine.

[0038] Filtrate treatment unit: Used to treat primary concentrate discharged from the primary water washing system and secondary concentrate discharged from the secondary acid washing system, including a primary filtrate treatment system and a secondary filtrate treatment system; the primary filtrate treatment system includes a concentrate tank, a pressure filtration device, an ultrafiltration system 1, and a first nanofiltration system 2 arranged in sequence; the concentrate tank is connected to the primary filtrate tank; the concentrate end of the ultrafiltration system 1 is connected to the concentrate tank, and the concentrate end of the first nanofiltration system 2 is connected to the secondary acid washing tank; the secondary filtrate treatment system includes a weight removal tank, a filtration device, and a second nanofiltration system 4 arranged in sequence; the weight removal tank is connected to the secondary filtrate tank.

[0039] Salt separation and purification unit: used to separate and purify target salt products from filtrate, including evaporation crystallization system 3 connected to the water production end of the first nanofiltration system 2 and the water production end of the second nanofiltration system 4, and high-pressure reverse osmosis system 5 connected to the concentrate end of the second nanofiltration unit; the water production end of the high-pressure reverse osmosis system 5 is connected to the tertiary filtrate tank; the condensate pipe of the evaporation crystallization system 3 is connected to the quaternary filtrate tank.

[0040] Water supply to the filtrate tank: The fourth-stage filtrate tank is connected to the industrial water pipe to supply industrial water to the fourth-stage filtrate tank; the fourth-stage filtrate tank is connected to the fourth-stage drainage pipe, which is connected to the third-stage filtrate tank to supply water to the third-stage filtrate tank; the third-stage filtrate tank is connected to the third-stage drainage pipe, which is connected to the second-stage and first-stage filtrate tanks to supply water to the second-stage and first-stage filtrate tanks.

[0041] Material addition method: The concentrated water tank is connected to a barium chloride addition device, the degravation tank is connected to a sodium sulfide addition device, and the secondary pickling tank is connected to a hydrochloric acid addition device.

[0042] Example 2 A method for extracting liquid calcium chloride, sodium chloride, and potassium chloride from fly ash includes the following steps: (1) After low-temperature pyrolysis, the fly ash is pulped in the primary pulping tank and then pumped to the primary washing tank. Primary filtrate is circulated into the primary pulping tank at a liquid-to-solid ratio of 3:1 to 5:1. The fly ash and primary filtrate are thoroughly stirred and mixed evenly, and the soluble salts are dissolved in the primary filtrate. The soluble salt dissolution rate of fly ash after primary washing is about 90%. The primary slurry is pumped to the primary dewatering machine. After dewatering, the wet slag enters the secondary pickling tank. The moisture content of the wet slag is about 30% to 40%. The filtrate from the dewatering machine flows by gravity into the primary filtrate tank.

[0043] (2) After the wet sludge from the primary dewatering stage enters the secondary pickling tank, the pickling filtrate from the secondary filtrate tank is circulated into the secondary pickling tank at a rate of 2-4 m³ / h. 3 / t dry ash, then slowly add industrial hydrochloric acid to the secondary pickling tank, the amount of hydrochloric acid added is 0.6~0.9m 3 / t dry ash. After the primary wet slag and the secondary pickling solution have fully reacted, the secondary slurry is pumped to the secondary dewatering machine. After dewatering, the wet slag enters the tertiary washing tank. The moisture content of the wet slag is about 30%~40%. The filtrate from the secondary dewatering machine is returned to the secondary filtrate tank.

[0044] (3) After the wet sludge from the secondary dewatering stage enters the tertiary washing tank, the filtrate from the tertiary filtrate tank is circulated into the tertiary washing tank at a circulation rate of 3-5 m³. 3 / t dry ash. After the secondary wet slag and tertiary filtrate have fully reacted, the tertiary slurry is pumped to the tertiary dewatering machine. After dewatering, the wet slag enters the tertiary washing tank. The moisture content of the wet slag is approximately 30%~40%. The filtrate from the tertiary dewatering machine is returned to the tertiary filtrate tank.

[0045] (4) After the wet sludge from the third-stage dewatering enters the fourth-stage washing tank, the filtrate from the fourth-stage filtrate tank is circulated into the fourth-stage washing tank at a circulation rate of 3-5 m³. 3 / t dry ash. After the tertiary wet slag and tertiary filtrate have fully reacted, the tertiary slurry is pumped to a tertiary dewatering machine. The wet slag after dewatering is the final product, with a moisture content of approximately ≤30%, a chlorine content of <1%, and heavy metal and dioxin levels meeting the requirements of the "Technical Specification for Pollution Control of Municipal Solid Waste Incineration Fly Ash" HJ1134-2020, and can be utilized as a resource.

[0046] (5) When the chloride ion concentration of the primary filtrate exceeds 100,000 mg / L, it is discharged from the primary water washing system and enters the concentrated water pretreatment section.

[0047] (6) Add barium chloride to the concentrated water in step (5) to generate barium sulfate precipitate, and remove sulfate ions from the water by pressure filtration.

[0048] (7) The filtrate from the pressure filter is further treated by an ultrafiltration (UF) system to remove suspended solids from the water.

[0049] (8) The ultrafiltration water enters the nanofiltration system (NF) to achieve the separation of monovalent and divalent salts. After separation, the monovalent salt water enters the MVR system and is evaporated, crystallized, and cooled to produce sodium chloride and potassium chloride respectively.

[0050] (9) The concentrated water produced in step (8), namely CaCl2 liquid, enters the secondary acid washing system for circulating acid washing.

[0051] (10) When the chloride ion concentration of the secondary pickling filtrate exceeds 150,000 mg / L, the secondary pickling filtrate shall be discharged from the secondary pickling system.

[0052] (11) Add sodium sulfide to the high-calcium brine in step (10) to form sulfide precipitate and separate it to remove heavy metals.

[0053] (12) The filtrate from step (11) enters a nanofiltration (NF) system to separate Ca. 2+ and Na + K + Ions are used to purify calcium chloride liquid. NF permeate is fed to the MVR system (evaporation control system). NF concentrate enters the high-pressure reverse osmosis system.

[0054] (13) The high-pressure reverse osmosis system (high-pressure STRO) further concentrates the NF concentrate to obtain a liquid calcium chloride product with a concentration of about 25~30%.

[0055] This invention significantly reduces the volume of raw fly ash through a fly ash washing and acid washing process. The resulting ash residue can be detoxified by low-temperature pyrolysis or co-processed in a cement kiln, greatly reducing the amount of ash residue and its chloride content. This invention avoids the use of evaporation to produce calcium chloride, achieving a liquid calcium chloride concentration of 25-30% through a circulating acid washing, nanofiltration purification, and reverse osmosis concentration mode. The use of a nanofiltration membrane system for purification and a reverse osmosis membrane for concentration reduces the energy consumption of the evaporation crystallization system, decreases the dosage of calcium removal agents, and lowers investment and operating costs. By coupling circulating acid washing with membrane separation and concentration technologies, this invention achieves the evaporation-free production of liquid calcium chloride, simultaneously producing sodium chloride and potassium chloride, offering advantages such as high-value resource utilization, low energy consumption, and significant ash residue reduction.

[0056] This invention employs a four-stage washing process for fly ash: a primary water wash, a primary acid wash, and a secondary water wash. This ensures that the final ash meets the requirements of the "Technical Specification for Pollution Control of Fly Ash from Municipal Solid Waste Incineration" (HJ1134-2020) and can be utilized as a resource. Furthermore, the final ash complies with the relevant provisions of GB 5085.1-2007 "Identification Standard for Hazardous Waste: Corrosivity Identification" and GB 5085.3-2007 "Identification Standard for Hazardous Waste: Leaching Toxicity Identification," making it safer and more environmentally friendly.

[0057] 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 extracting liquid calcium chloride, sodium chloride, and potassium chloride from fly ash, characterized in that: It includes a washing unit, a filtrate treatment unit, and a salt separation and purification unit; The washing unit is used to perform multi-stage countercurrent washing of fly ash, including a first-stage water washing system, a second-stage acid washing system, a third-stage water washing system, and a fourth-stage water washing system arranged in sequence; The primary washing system includes a primary pulping tank, a primary washing tank, a primary slurry pump, a primary dewatering machine, and a primary filtrate tank arranged in sequence, with the primary filtrate tank connected to the primary pulping tank; The secondary pickling system includes a secondary pickling tank, a secondary slurry pump, a secondary dewatering machine, and a secondary filtrate tank arranged in sequence. The secondary filtrate tank is connected to the secondary pickling tank, and the secondary pickling tank is connected to the wet slag outlet of the primary dewatering machine. The three-stage washing system includes a three-stage washing tank, a three-stage slurry pump, a three-stage dewatering machine, and a three-stage filtrate tank arranged in sequence. The three-stage filtrate tank is connected to the three-stage acid washing tank, and the three-stage washing tank is connected to the wet sludge outlet of the two-stage dewatering machine. The four-stage washing system includes a four-stage washing tank, a four-stage slurry pump, a four-stage dewatering machine, and a four-stage filtrate tank arranged in sequence. The four-stage filtrate tank is connected to the four-stage acid washing tank, and the four-stage washing tank is connected to the wet sludge outlet of the three-stage dewatering machine. The filtrate treatment unit includes a primary filtrate treatment system and a secondary filtrate treatment system; The primary filtrate treatment system includes a concentrate tank, a pressure filtration device, an ultrafiltration system, and a first nanofiltration system arranged in sequence; the concentrate tank is connected to the primary filtrate tank; the concentrate end of the ultrafiltration system is connected to the concentrate tank; and the concentrate end of the first nanofiltration system is connected to the secondary acid washing tank. The two-stage filtrate treatment system includes a gravity removal tank, a filtration device, and a second nanofiltration system arranged in sequence; the gravity removal tank is connected to the two-stage filtrate tank. The salt separation and purification unit includes an evaporation and crystallization system connected to the product water end of the first nanofiltration system and the product water end of the second nanofiltration system, and a high-pressure reverse osmosis system connected to the concentrate end of the second nanofiltration unit.

2. The system for extracting liquid calcium chloride, sodium chloride, and potassium chloride from fly ash according to claim 1, characterized in that: The product water end of the high-pressure reverse osmosis system is connected to the three-stage filtration tank.

3. The system for extracting liquid calcium chloride, sodium chloride, and potassium chloride from fly ash according to claim 1, characterized in that: The condensate pipe of the evaporation crystallization system is connected to the four-stage filtrate tank.

4. The system for extracting liquid calcium chloride, sodium chloride, and potassium chloride from fly ash according to claim 1, characterized in that: The fourth-stage filtrate tank is connected to a fourth-stage drainage pipe, which is connected to the third-stage filtrate tank to supply water to the third-stage filtrate tank.

5. The system for extracting liquid calcium chloride, sodium chloride, and potassium chloride from fly ash according to claim 1, characterized in that: The tertiary filtrate tank is connected to a tertiary drainage pipe, which is connected to the secondary and primary filtrate tanks to supply water to them.

6. The system for extracting liquid calcium chloride, sodium chloride, and potassium chloride from fly ash according to claim 1, characterized in that: The concentrate tank is connected to a barium chloride addition device, the degravation tank is connected to a sodium sulfide addition device, and the secondary pickling tank is connected to a hydrochloric acid addition device.

7. A method for extracting liquid calcium chloride, sodium chloride, and potassium chloride from fly ash, based on the system for extracting liquid calcium chloride, sodium chloride, and potassium chloride from fly ash according to any one of claims 1 to 6, characterized in that, Includes the following steps: S1. Primary washing: Fly ash is mixed with primary water filtrate, washed, and then dehydrated to obtain primary wet sludge and primary filtrate; the primary filtrate is recycled, and when the chloride ion concentration in it exceeds the first threshold, primary concentrated water is discharged; S2. Secondary pickling: The primary wet residue and the secondary pickling filtrate are mixed and hydrochloric acid is added for pickling, followed by dehydration to obtain secondary wet residue and secondary pickling filtrate; the secondary pickling filtrate is recycled, and when the chloride ion concentration exceeds the second threshold, the secondary concentrate is discharged; S3. Tertiary washing: The secondary wet residue is subjected to tertiary washing, and after washing, it is dehydrated to obtain tertiary wet residue and tertiary filtrate. The tertiary filtrate is recycled. S4. Fourth-stage water washing: The third-stage wet slag is washed with fourth-stage water, and then dewatered to obtain the final ash and fourth-stage filtrate. The fourth-stage filtrate is recycled. S5. Primary Concentrate Treatment: The primary concentrate is purified by sulfate removal and ultrafiltration, and then enters the first nanofiltration system for separation; the permeate from the first nanofiltration system enters the evaporation and crystallization system, and the concentrate from the first nanofiltration system is returned to the secondary acid washing system; S6. Secondary concentrate treatment and calcium chloride purification: After heavy metal removal treatment, the secondary concentrate enters the second nanofiltration system for separation; the permeate from the second nanofiltration system enters the evaporation crystallization system, and the concentrate from the second nanofiltration system enters the high-pressure reverse osmosis system for concentration to obtain liquid calcium chloride product; S7. Evaporation and Crystallization: The permeate water from the first nanofiltration system and the permeate water from the second nanofiltration system are evaporated and crystallized to obtain sodium chloride and potassium chloride products.

8. The method for extracting liquid calcium chloride, sodium chloride, and potassium chloride from fly ash according to claim 7, characterized in that: In step S1, the fly ash is fly ash that has undergone low-temperature pyrolysis treatment; the liquid-solid ratio of the washing process is 3:1 to 5:

1.

9. The method for extracting liquid calcium chloride, sodium chloride, and potassium chloride from fly ash according to claim 7, characterized in that: In step S2, the amount of hydrochloric acid added is 0.6~0.9 mg. 3 / t dry ash.

10. The method for extracting liquid calcium chloride, sodium chloride, and potassium chloride from fly ash according to claim 7, characterized in that: In step S5, barium chloride is added to remove sulfate ions.

11. The method for extracting liquid calcium chloride, sodium chloride, and potassium chloride from fly ash according to claim 7, characterized in that: In step S6, heavy metals are removed by adding sodium sulfide; the concentration of the liquid calcium chloride product is 25%~30%.

12. The method for extracting liquid calcium chloride, sodium chloride, and potassium chloride from fly ash according to claim 7, characterized in that: The first threshold is 100,000 mg / L.

13. The method for extracting liquid calcium chloride, sodium chloride, and potassium chloride from fly ash according to claim 7, characterized in that: The second threshold is 150,000 mg / L.

14. The method for extracting liquid calcium chloride, sodium chloride, and potassium chloride from fly ash according to claim 7, characterized in that: The circulation rate for secondary pickling is 2-4 m³ / h. 3 / t dry ash, the circulation rate for both the third-stage and fourth-stage water washing is 3~5m³. 3 / t dry ash.

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