Fly ash resource treatment method and system

Abstract

The present application relates to the technical field of waste incineration fly ash treatment, and particularly relates to a fly ash resource treatment method and system. The fly ash resource treatment method comprises the following steps: after fly ash is slurried, the fly ash is sent into an integrated water washing and extruding device, multi-stage countercurrent water washing and mechanical extruding dewatering are realized in the device, and dechlorinated fly ash and water washing clear liquid are output; the water washing clear liquid is sequentially subjected to heavy metal and hardness removal, ultrafiltration pretreatment, multi-stage countercurrent membrane concentration and evaporation crystallization treatment, and crystalline salt and distilled water are obtained. Through integrated device design, the present application integrates traditional multi-stage water washing, stirring and dewatering processes into one, simplifies the process flow, and reduces system complexity and maintenance difficulty; by introducing flue gas reuse to provide carbonation reagent, the amount of hardness removal reagent added is reduced; by multi-stage countercurrent membrane concentration, the clear liquid is efficiently pre-reduced, the energy consumption and cost of subsequent evaporation crystallization are reduced, and efficient and low-consumption resource utilization of fly ash is realized.

Description

Technical Field

[0001] This invention relates to the field of fly ash treatment technology for waste incineration, and in particular to a method and system for the resource utilization of fly ash. Background Technology

[0002] The incineration of municipal solid waste generates a large amount of fly ash, which is classified as hazardous waste due to its high content of chloride salts, heavy metals, and dioxins. To achieve the harmlessness and resource utilization of fly ash, one of the mainstream technical approaches is to dechlorinate the fly ash by washing it with water, and then evaporate and crystallize the washing liquid to recover chloride salts. The dechlorinated fly ash can then be used in building materials or disposed of safely.

[0003] Currently, the industry commonly uses a multi-stage countercurrent water washing + evaporation crystallization process for fly ash. Although this process achieves dechlorination and salt recovery of fly ash to a certain extent, the following shortcomings still exist in actual engineering applications and operations: Traditional processes typically employ multiple independent washing tanks or stirred tanks connected in series with solid-liquid separation equipment, forming a three-stage or even more-stage countercurrent washing system, as disclosed in patent documents such as CN117680479A and CN118751650A. This multi-equipment series arrangement results in a long washing process flow and a large footprint. Furthermore, the material transport, liquid level balancing, and countercurrent distribution of washing liquid between different stages require complex piping, pumps, valves, and automatic control systems, leading to complex control logic. This directly results in high initial investment costs, difficult operation and maintenance, increased potential failure points, and higher requirements for the professional skills of operators.

[0004] Fly ash washing solutions typically contain high concentrations of calcium and magnesium ions, as well as some heavy metals. To prevent scaling in subsequent evaporation and crystallization equipment and ensure the quality of the crystallized salt, the washing solution must undergo deep pretreatment before evaporation to remove hardness (calcium and magnesium) and heavy metals. Existing technologies (such as the patent with publication number CN117680479A) mostly rely on adding chemical agents such as lime, soda ash, sodium carbonate, and sodium sulfide to induce precipitation reactions. The large consumption of these chemicals not only directly increases treatment costs but also generates a large amount of chemical sludge, increasing the burden and cost of subsequent sludge disposal, resulting in poor overall process economics.

[0005] Traditional processes directly feed the low-concentration saline solution generated after water washing into the evaporation and crystallization system. Due to the high total water-to-ash ratio of the water washing process, the total volume of saline solution produced is enormous. The evaporation and crystallization process vaporizes a large amount of water; the larger the volume of water processed, the higher the steam and electricity consumption required. Although some improved solutions (such as the patent with publication number CN215089715U) have introduced nanofiltration for salt separation, they have not fundamentally reduced the volume and concentrated the saline solution before it enters the energy-intensive evaporation unit. Therefore, the large scale of the evaporation and crystallization unit, high investment costs, and persistently high operating energy consumption have become a key economic bottleneck restricting the promotion of fly ash resource utilization technology.

[0006] In summary, existing fly ash washing and resource recovery technologies have significant shortcomings in terms of system integration, operational economy, and energy efficiency. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to provide a method for the resource-based treatment of fly ash, in order to solve the problems of long multi-stage water washing process of fly ash, complicated equipment, difficult system logic control, high investment cost and high energy consumption of water washing liquid evaporation and salt separation equipment in the prior art mentioned above.

[0008] The technical solution adopted by this invention to solve its technical problem is: a method for the resource utilization of fly ash, comprising the following steps: S1. Fly ash and water are fed into the pulping unit for pulping to obtain fly ash slurry; S2. The fly ash slurry is fed into an integrated water washing and extrusion equipment for multi-stage countercurrent water washing and extrusion dewatering to obtain dechlorinated fly ash and water washing liquid; the multi-stage countercurrent water washing is an inter-stage countercurrent achieved inside the integrated water washing and extrusion equipment, that is, the leachate generated by the next stage water washing section is used as the washing water of the previous stage water washing section. S3. The water washing liquid is subjected to gravity and hardness removal treatment, membrane filtration treatment and evaporation crystallization and salt separation treatment in sequence to obtain crystalline salt and distilled water respectively. The distilled water is reused in step S1 and / or step S2.

[0009] By introducing an integrated washing and extrusion equipment, the traditionally dispersed multi-stage washing, agitation, and dewatering steps are completed within a single device. This solves the problems of long washing processes, numerous devices, complex automatic control logic, and high difficulty in system operation and maintenance, significantly shortening the process flow and greatly reducing the number of devices. The equipment achieves inter-stage counter-flow, reducing the need for complex external piping, pumps, valves, and control systems, simplifying the structure, and lowering investment and maintenance complexity. Simultaneously, it explicitly enables distilled water reuse, embodying the closed-loop water resource recycling concept and reducing fresh water consumption and wastewater discharge.

[0010] Further, in step S2, the integrated water washing and extrusion equipment includes a shell and a rotating shaft disposed in the shell. The shell is divided into multiple water washing and extrusion sections along the material forward direction. The rotating shaft is correspondingly provided with multiple sections, and its diameter increases progressively along the material forward direction. Each stage of the rotating shaft is provided with a spiral ribbon-shaped primary blade and a secondary blade disposed on the primary blade; The inner wall of the housing is a sealed wall at the beginning of each rotating shaft, and filter holes are provided in the middle and end sections. Driven by the rotating shaft, the fly ash slurry passes through each stage of water washing and extrusion sections in sequence. It is washed by the agitation of the secondary blades and dewatered by the extrusion action generated by the increased diameter of the rotating shaft and the filter holes.

[0011] By gradually increasing the diameter of the rotating shaft and using filter holes on the shell, mechanical extrusion dewatering of fly ash slurry is achieved. Compared with traditional centrifugal or pressure filtration dewatering that relies on added chemicals, this method has high dewatering efficiency and avoids the addition of additional chemicals, which helps to reduce operating costs. The spiral ribbon-shaped primary blades are responsible for conveying materials, while the secondary blades enhance the stirring effect. This design ensures that thorough washing can be completed during the conveying process, realizing continuous and synchronous washing and dewatering, and improving the processing efficiency of a single unit. The functions of multiple traditional tanks and dewatering machines are integrated into one shell, achieving system simplification and equipment integration.

[0012] Furthermore, in step S2, flue gas containing carbon dioxide is introduced into the integrated water washing and extrusion equipment; the flue gas is used to promote water washing agitation and / or form carbonate precipitates in the water washing liquid.

[0013] By introducing CO2 from the flue gas of a waste incineration plant as a carbonation agent into the water washing system, the CO2 reacts with calcium ions in the water to form calcium carbonate precipitate. This partially or completely replaces the expensive reagents such as soda ash and sodium carbonate used in traditional processes for hardening removal, significantly reducing reagent dosage and operating costs. The bubbles generated by the flue gas agitate the slurry, promoting contact between fly ash particles and water and improving chloride removal efficiency. Simultaneously, the weak acidity of the flue gas helps adjust the pH, promoting the dissolution of certain sparingly soluble salts.

[0014] Further, in step S3, the membrane filtration treatment specifically refers to a multi-stage countercurrent membrane concentration treatment, including: The water wash solution after degravity and hardness removal is first passed into the first-stage reverse osmosis membrane unit for concentration to obtain the first-stage permeate and the first-stage concentrate. The first-stage concentrate is passed into the second-stage reverse osmosis membrane unit for further concentration to obtain the second-stage permeate and the second-stage concentrate. The second-stage permeate is then returned to the feed water side of the first-stage reverse osmosis membrane unit. This process continues until the concentrate produced by the last stage of the reverse osmosis membrane unit reaches the predetermined concentration, at which point it is sent to the evaporation, crystallization, and salt separation treatment unit. The permeate produced by the first-stage reverse osmosis membrane unit is purified by at least another stage of reverse osmosis membrane unit and then output as recycled water.

[0015] Furthermore, the recycled water is reused in the final washing section and / or pulping unit of the integrated washing and extrusion equipment.

[0016] Using multi-stage reverse osmosis membranes for countercurrent concentration can significantly reduce the volume of the washing liquid with lower energy consumption, thereby reducing the amount of water that the subsequent evaporation and crystallization unit needs to process. The scale and processing capacity of the evaporation and crystallization system are determined by the amount of water evaporated. After pre-concentration by the membrane system, the required size of the evaporator and the power of the matching steam boiler or MVR compressor can be reduced accordingly, thus significantly reducing the equipment investment cost and operating energy consumption of the evaporation and crystallization unit. The membrane system produces high-quality water that can be directly reused as process makeup water, realizing the recycling of water resources within the system and further reducing fresh water consumption and wastewater discharge.

[0017] A fly ash resource recovery system for implementing the fly ash resource recovery method described above is also provided, characterized in that it comprises: (the following components are connected in sequence) The pulping unit is used to mix fly ash and water to prepare fly ash slurry; An integrated water washing and extrusion unit is used to perform multi-stage countercurrent water washing and extrusion dewatering on fly ash slurry, and output dechlorinated fly ash and water washing liquid. The water washing liquid treatment unit includes a gravity and hardness removal module, a membrane concentration module, and an evaporation and crystallization module connected in sequence, which are used to treat the water washing liquid and produce crystalline salt and recycled water.

[0018] Furthermore, the integrated water washing and extrusion unit includes an integrated water washing and extrusion device, which includes: The shell is divided into multiple chambers along the material's direction of travel, forming a multi-stage water washing and extrusion section. A rotating shaft is inserted into the housing and is provided in multiple stages corresponding to the multi-stage washing and extrusion section, with its diameter increasing progressively along the material's forward direction. A drive device is used to drive the rotating shaft to rotate; Each stage of the rotating shaft is provided with a spiral ribbon-shaped primary blade and a secondary blade provided on the primary blade; The inner wall of the housing is sealed at the beginning of each rotating shaft, and filter holes for dehydration are provided in the middle and end of each rotating shaft. The shell has an inlet at the beginning of each stage of the washing and extrusion section and a water inlet at the end of the last stage of the washing and extrusion section. The shell has an outlet at the end and a collection chamber at the bottom for collecting leachate from each stage. The collection chamber is connected to the inlet of the next stage of the washing and extrusion section through a pipeline to achieve interstage countercurrent.

[0019] Furthermore, the distribution of the secondary blades on the primary blades is irregular.

[0020] Furthermore, it also includes a flue gas reuse unit, which comprises: Flue gas source, used to provide flue gas containing carbon dioxide; The air supply duct connects the flue gas source to the housing of the integrated water washing and extrusion equipment and / or the reaction tank of the de-weighting and de-hardening module.

[0021] Furthermore, the membrane concentration module is a multi-stage countercurrent membrane concentration system, comprising at least two reverse osmosis membrane units connected in series; In this process, the product water outlet of each reverse osmosis membrane unit, except for the first stage, is connected to the inlet side of the previous stage reverse osmosis membrane unit through a return pipeline. The product water outlet of the first-stage reverse osmosis membrane unit is connected to a product water treatment unit, and the output end of the product water treatment unit serves as the reclaimed water output port of the system. The concentrate outlet of the final reverse osmosis membrane unit is connected to the evaporation and crystallization module.

[0022] The beneficial effects of this invention are: This invention integrates traditional multi-stage independent washing and dewatering equipment into one integrated washing and extrusion device, realizing continuous fly ash washing and dewatering processes and high equipment integration. This not only shortens the process flow and reduces the footprint and number of equipment, but also simplifies pipeline connections and automatic control logic, effectively solving the technical problems of redundant equipment and complex operation and maintenance in existing technologies, and reducing system investment and long-term operation and maintenance costs. By introducing a flue gas reuse unit, CO2-rich incineration flue gas is reused as a carbonation reagent in the washing and hardening process. It reacts with calcium ions to generate calcium carbonate precipitate, which can significantly reduce or even replace the chemical agents such as soda ash and sodium carbonate added in traditional processes for hardening removal. This reduces the cost of reagent procurement and subsequent chemical sludge treatment from the source, and enhances the economic competitiveness of the entire process. A multi-stage countercurrent membrane concentration system is set up before evaporation and crystallization. The reverse osmosis membrane technology is used to efficiently pre-concentrate the water washing liquid. This system can significantly reduce the volume of the liquid with low energy consumption, thereby proportionally reducing the processing scale, equipment investment and operating energy consumption of the subsequent high-energy-consuming evaporation and crystallization unit. This is a key technological breakthrough that solves the problem of high cost of traditional evaporation and crystallization processes and realizes energy consumption optimization of the entire resource utilization process.

[0023] The entire process achieves a closed-loop water resource cycle, with membrane-generated water, distilled water reuse, and flue gas CO2 utilization, making it green and environmentally friendly. Attached Figure Description

[0024] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0025] Figure 1 This is a schematic diagram of the fly ash resource utilization system of the present invention.

[0026] Figure 2 This is a schematic diagram of the integrated water washing and extrusion equipment in the fly ash resource utilization system of the present invention.

[0027] Figure 3 yes Figure 2 A partial schematic diagram.

[0028] Figure 4 This is a schematic diagram of the membrane concentration module in the fly ash resource utilization system of the present invention.

[0029] Figure 5 This is a flowchart of the fly ash resource utilization method of the present invention.

[0030] In the diagram: 100, pulping tank; 200, integrated water washing and extrusion equipment; 201, shell; 202, rotating shaft; 2021, primary impeller; 2022, secondary impeller; 203, drive unit; 210, chamber; 211, fly ash storage hopper; 300, degravity and hardness removal module; 301, first reaction tank; 302, second reaction tank; 400, tubular ultrafiltration membrane; 500, multi-stage countercurrent membrane concentration system; 501, first-stage reverse osmosis membrane unit; 502, second-stage reverse osmosis membrane unit; 503, third-stage reverse osmosis membrane unit; 600, evaporation and crystallization module; 700, flue gas source; P1, slurry pump; P2, chemical pump; P3, centrifugal pump; RF1, fan. Detailed Implementation

[0031] The present invention will now be described in further detail with reference to the accompanying drawings. These drawings are simplified schematic diagrams, illustrating only the basic structure of the invention, and therefore only show the components relevant to the invention.

[0032] Example 1 like Figure 1As shown, this embodiment provides a fly ash resource utilization system. The system includes a pulping unit, an integrated water washing and extrusion unit, and a water washing liquid treatment unit connected in sequence, as well as a flue gas recycling unit. The pulping unit is used to mix fly ash and water to prepare fly ash slurry. It includes a pulping tank 100, which is equipped with a stirrer. The fly ash is fly ash that has undergone low-temperature thermal decomposition treatment and is conveyed to the pulping tank 100 by a belt conveyor. The integrated water washing and extrusion unit is used to perform multi-stage countercurrent water washing and extrusion dewatering on the fly ash slurry, outputting dechlorinated fly ash and water washing liquid. The integrated water washing and extrusion unit includes an integrated water washing and extrusion device 200. A slurry pump P1 is installed on the connecting pipeline between the integrated water washing and extrusion device 200 and the pulping tank 100, used to transport the raw fly ash slurry in the pulping tank 100 to the integrated water washing and extrusion device 200. The water washing liquid treatment unit includes a gravity and hardness removal module 300, a membrane concentration module, and an evaporation and crystallization module 600 connected in sequence, which are used to treat the water washing liquid and produce crystalline salt and recycled water.

[0033] The heavy metal and hardness removal module 300 includes a first reaction tank 301 and a second reaction tank 302, both equipped with stirring devices. The heavy metal and hardness removal module 300 is used to remove heavy metal ions and calcium and magnesium hardness ions from the washing solution. Specifically, sodium sulfate is added to the first reaction tank 301 to generate heavy metal sulfate precipitates, and sodium carbonate is simultaneously added to the first reaction tank 301 and the second reaction tank 302, or CO2 from the flue gas is introduced to react with Ca²⁺. + Mg² + The reaction produces carbonate precipitate. The sludge settled at the bottom of the heavy metal removal and hard metal removal module 300 is filtered by plate and frame filter press to form a sludge cake with low water content, which is then transported off-site for incineration. The filtrate produced by plate and frame filter press contains residual reactants and incompletely precipitated heavy metal ions, and is returned to the first reaction tank 301 to continue participating in the reaction, thereby improving the utilization rate of the reagents and reducing wastewater discharge.

[0034] The membrane concentration module is a multi-stage countercurrent membrane concentration system 500, which includes at least two stages of reverse osmosis membrane units connected in series. The permeate outlet of each stage of reverse osmosis membrane unit, except for the first stage, is connected to the feed water side of the previous stage reverse osmosis membrane unit through a return pipeline. The permeate outlet of the first stage reverse osmosis membrane unit is connected to a permeate treatment unit, and the output end of the permeate treatment unit serves as the system's recycled water output port. The concentrate outlet of the last stage reverse osmosis membrane unit is connected to an evaporation and crystallization module.

[0035] like Figure 4As shown, a tubular ultrafiltration membrane 400 is installed between the multi-stage countercurrent membrane concentration system 500 and the gravimetric and hardening removal module 300. The tubular ultrafiltration membrane 400 is used for pretreatment of the fly ash washing liquid after gravimetric and hardening removal to remove suspended solids (SS) from the washing liquid, thus preventing suspended solids from entering the subsequent membrane system and causing membrane fouling. A chemical pump P2 is installed on the connecting pipeline between the tubular ultrafiltration membrane 400 and the gravimetric and hardening removal module 300, and a centrifugal pump P3 is installed between the tubular ultrafiltration membrane 400 and the countercurrent membrane concentration system 500. The concentrated water produced by the tubular ultrafiltration membrane 400 is returned to the first reaction tank 301 of the gravimetric and hardening removal module 300 for treatment together with the settled sludge, realizing the integration and reduction of solid waste within the system.

[0036] In this embodiment, the countercurrent membrane concentration system 500 is configured as a three-stage system: a first-stage reverse osmosis membrane unit 501, a second-stage reverse osmosis membrane unit 502, and a third-stage reverse osmosis membrane unit 503. The pore size of the third-stage reverse osmosis membrane unit 503 is larger than that of the second-stage reverse osmosis membrane unit 502. The first-stage reverse osmosis membrane unit 501 is a standard seawater desalination membrane. The wash water first enters the second-stage reverse osmosis membrane unit 502 with its larger pore size for treatment. The concentrate then enters the third-stage reverse osmosis membrane unit 503 for further concentration. The permeate is then returned to the second-stage reverse osmosis membrane unit 502 for further treatment. The system performs concentration sequentially until the concentration endpoint is reached. The permeate from the second-stage reverse osmosis membrane unit 502 enters the first-stage reverse osmosis membrane unit 501 for further filtration. The membrane concentrate is then returned to the second-stage reverse osmosis membrane unit 502 for further concentration. The permeate is then output as recycled water. Through this multi-stage countercurrent design, high-concentration of the wash water is achieved at a relatively low operating pressure, while simultaneously obtaining high-quality permeate. After being processed by this system, the amount of water entering the evaporation and crystallization module can be reduced by more than 50%, significantly reducing the evaporation load and energy consumption.

[0037] The flue gas reuse unit includes a flue gas source 700 and an air supply duct. The flue gas source 700 is the chimney of a waste incineration plant, used to provide flue gas containing carbon dioxide. A fan RF1 is installed on the air supply duct, connecting the flue gas source 700 to the housing of the integrated water washing and extrusion equipment 200 and the reaction tank of the degravity and hardness removal module 300. In the integrated water washing and extrusion equipment 200, the flue gas provides gas agitation to the slurry, promoting mixing; furthermore, the carbon dioxide in the flue gas reacts with the Ca²⁺ in the slurry. + The reaction produces a slightly soluble CaCO3 precipitate, which is discharged with the solid phase during the extrusion dehydration process, achieving preliminary hardening removal. In the heavy and hardening removal module 300, especially in the second reaction tank 302, the flue gas, as an inexpensive carbonation reagent, can partially or completely replace the large amount of sodium carbonate required in traditional processes for the precipitation and removal of Ca²⁺. + This significantly reduces the cost of the reagents, and the acidic gases in the flue gas also help regulate the pH of the system and promote the dissolution of certain salts.

[0038] like Figure 2 As shown, the integrated washing and extrusion equipment 200 includes a housing 201, a rotating shaft 202, and a drive unit 203. The interior of the housing 201 is divided into multiple chambers 210 along the material feeding direction, forming a multi-stage washing and extrusion section. The rotating shaft 202 passes through the housing 201 and is configured with multiple stages corresponding to the multi-stage washing and extrusion section, with its diameter increasing progressively along the material feeding direction. The drive unit 203 is used to drive the rotating shaft 202 to rotate. Figure 3 As shown, each stage of the rotating shaft 202 is equipped with a spiral ribbon-shaped primary blade 2021 and a secondary blade 2022 mounted on the primary blade. The secondary blades 2022 are randomly distributed on the primary blades 2021, achieving agitation and washing of the initial fly ash slurry during the rotational dewatering process. This random secondary blade design breaks the conventional laminar flow, forming more intense turbulence, thereby significantly improving the mass transfer efficiency between fly ash particles and the washing liquid, and accelerating the dissolution and elution of soluble substances such as chloride salts.

[0039] The inner wall of the housing 201 is sealed at the beginning of each stage of the rotating shaft 202. Fine filter holes for dewatering are provided in the middle and end sections of each stage of the rotating shaft 202. An inlet is provided at the beginning of each stage of the washing and extrusion section on the housing 201, and a water inlet is provided at the end of the final stage of the washing and extrusion section. An outlet is provided at the end of the housing 201. A collection chamber for collecting leachate from each stage is provided at the bottom of the housing 201, and the collection chamber is connected to the inlet of the previous stage of the washing and extrusion section via a pipeline to achieve countercurrent flow between stages. At the end of the integrated washing and extrusion equipment 200 near the drive device 203, corresponding to the final stage of the washing and extrusion section, a fly ash storage hopper 211 is provided. The fly ash storage hopper 211 is used to temporarily store the dechlorinated fly ash after multi-stage washing and extrusion, facilitating subsequent centralized discharge or transfer, and enabling continuous discharge and process connection of the equipment. Specifically, the leachate generated in the next stage of the washing and extrusion section is pumped to the previous stage as the washing water for that stage. This design enables the backflow reuse of the washing liquid, allowing the lower concentration of fresh water or permeate to be used for the final rinsing, while the higher concentration of leachate is used for the initial washing. This minimizes the consumption of fresh water and the amount of wastewater generated while ensuring the washing effect, and maximizes the salt concentration of the final discharged washing liquid, which is beneficial for subsequent resource recovery.

[0040] In this embodiment, the housing 201 has three chambers 210, forming a three-stage washing and extrusion section. The rotating shaft 202 is correspondingly arranged in three stages, each stage being frustoconical with the smallest diameter at the water inlet. The raw ash slurry in the slurry tank 100 is transported to the inlet of the first-stage washing and extrusion section via the slurry pump P1, entering the integrated washing and extrusion equipment and maintaining a high liquid level. As the rotating shaft rotates, the raw ash slurry is fully agitated under the action of gravity and the secondary blades, and is gradually and slowly conveyed to the discharge side. As the rotating shaft gradually thickens, the water in the slurry gradually seeps through the filter holes into the collection chamber under the extrusion action. After the water in the raw ash slurry is fully extruded, it enters the second-stage rotating extrusion area, and then undergoes washing, agitation, and extrusion dewatering before entering the third-stage rotating extrusion area. During this process, the water leachate from the next stage enters the previous stage as fly ash washing water, and water is only replenished at the water inlet of the last stage rotating extrusion area throughout the entire system. For example, the effluent from the tertiary washing and extrusion section is pumped by centrifugal pump P3 to the secondary washing and extrusion section as the washing water for that stage. The effluent from the secondary washing and extrusion section is then pumped by centrifugal pump P3 to the primary washing and extrusion section as the washing water for that stage. Ultimately, the chlorine content of the dechlorinated fly ash discharged from the end of the equipment can be stably kept below 1%, meeting the requirements for its utilization in building materials.

[0041] The evaporation and crystallization module 600 evaporates and crystallizes the concentrate produced by the multi-stage countercurrent membrane concentration system 500. A mechanical vapor recompression evaporator is preferably used, which introduces a small amount of start-up steam through a steam input pipe. The secondary steam generated by evaporation is compressed and pressurized by a fan RF2 on the input pipe, increasing its enthalpy before being recycled as the main heat source, resulting in extremely high energy efficiency. After evaporation and crystallization, crystalline salt products such as sodium chloride and potassium chloride are obtained, which are then centrifuged, dried, and transported for high-value utilization. The distilled water produced by evaporation has extremely high purity and is recycled back to the pulping tank 100 as pulping water via a reuse pipe and reflux pump P4, or used as supplementary water for the integrated water washing and extrusion equipment 200, achieving a closed-loop water resource circulation within the system with near-zero discharge.

[0042] Example 2 like Figure 5 As shown, a fly ash resource utilization method, using the fly ash resource utilization system of Example 1, includes the following steps: Step 1: The fly ash after low-temperature thermal decomposition treatment is transported to the slurry tank 100. The appropriate water-ash ratio is configured according to the properties of the fly ash, and washing water is added. The mixture is stirred evenly by a mixer to obtain fly ash slurry.

[0043] Step 2: The fly ash slurry in the slurry tank 100 is transported to the integrated water washing and extrusion equipment 200 by the slurry pump P1 for multi-stage countercurrent water washing and extrusion dewatering. The integrated water washing and extrusion equipment 200 achieves inter-stage countercurrent, that is, the leachate produced by the next stage of water washing is used as the washing water for the previous stage of water washing. At the same time, carbon dioxide-containing flue gas provided by the flue gas source 700 is introduced into the integrated water washing and extrusion equipment 200 through the air supply pipeline. The flue gas flow rate is adjusted according to the slurry processing volume and the required stirring and carbonation intensity. The fly ash after extrusion dewatering is discharged from the outlet of the integrated water washing and extrusion equipment 200. Its chlorine content is detected to be less than 1%, which meets the subsequent resource utilization standards and can be transported for the preparation of non-fired bricks, cement admixtures and other building materials. The collected primary water washing raw liquid is transported to the heavy and hard removal module 300 by the water pump.

[0044] Step 3: In the heavy metal removal and hardness removal module 300, the primary washing solution is treated to remove hardness and heavy metal ions; simultaneously, carbon dioxide-containing flue gas supplied by the flue gas source 700 is introduced into the reaction tank of the heavy metal removal and hardness removal module 300 through the air supply pipeline, utilizing the CO3²⁻ provided by the carbon dioxide in the flue gas. - Precipitation removal of Ca² + To reduce the amount of reagents added, the treated fly ash cleaning solution is transported to the tubular ultrafiltration membrane 400 via chemical pump P2.

[0045] Step 4: The tubular ultrafiltration membrane 400 pre-treats the fly ash cleaning solution to remove suspended solids from the washing solution. The product water is transported to the multi-stage countercurrent membrane concentration system 500 by centrifugal pump P3, and the concentrated water is returned to the first reaction tank 301 of the heavy and hard removal module 300.

[0046] Step 5: In the multi-stage countercurrent membrane concentration system 500, the pretreated washing liquid is concentrated using a multi-stage countercurrent membrane system. Specifically, the washing liquid first enters the second-stage reverse osmosis membrane unit 502 with a larger membrane pore size for treatment. The concentrate then enters the third-stage reverse osmosis membrane unit 503 for further concentration. The permeate is returned to the second-stage reverse osmosis membrane unit 502 for further treatment. The system concentrates the liquid sequentially until it reaches a predetermined concentration, after which it is sent to the evaporation and crystallization module 600. The permeate from the second-stage reverse osmosis membrane unit 502 enters the first-stage reverse osmosis membrane unit 501 for further filtration. The permeate from the first-stage reverse osmosis membrane unit 501 is output as recycled water and returned to the final washing section of the integrated washing and extrusion equipment 200 and / or the pulping tank 100 as fly ash washing water.

[0047] Step Six: In the evaporation and crystallization module 600, the concentrate produced by the multi-stage countercurrent membrane concentration system 500 is evaporated and crystallized. Steam (or starting energy) is introduced through the steam input pipe, and the MVR system is driven by the fan RF2 (compressor) for efficient operation, yielding crystalline salt products such as sodium chloride and potassium chloride, as well as distilled water. The crystalline salt products are dried, packaged, and transported for high-value utilization. The distilled water is recycled to the pulping tank 100 through the reuse pipe and reflux pump P4 for pulping, completing the water resource cycle of the entire process.

[0048] Specific examples Based on the processing of 1 ton of raw fly ash (chlorine content approximately 15%), using the above system and method, after processing by an integrated water washing and extrusion equipment, approximately 0.65 tons of dechlorinated fly ash (chlorine content <1%) and approximately 3.5 tons of raw water washing solution are obtained. The raw water washing solution, after gravity and hardness removal and ultrafiltration, enters a multi-stage countercurrent membrane concentration system 500, producing approximately 1.5 tons of concentrate and approximately 2 tons of high-quality reclaimed water. The 1.5 tons of concentrate enters the evaporation and crystallization module, ultimately yielding approximately 0.3 tons of industrial-grade mixed salt and approximately 1.2 tons of distilled water. The entire system requires very little fresh water replenishment, relying mainly on membrane-generated water and distilled water reuse, achieving near-zero wastewater discharge. Compared to the traditional three-stage water washing + direct evaporation process, the evaporation system's energy consumption is reduced by approximately 50%, and the cost of hardness removal agents is reduced by approximately 40%.

[0049] Based on the above-described preferred embodiments of the present invention, and through the foregoing description, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A method for the resource utilization of fly ash, characterized in that, Includes the following steps: S1. Fly ash and water are fed into the pulping unit for pulping to obtain fly ash slurry; S2. The fly ash slurry is fed into an integrated water washing and extrusion equipment (200) for multi-stage countercurrent water washing and extrusion dewatering to obtain dechlorinated fly ash and water washing liquid; the multi-stage countercurrent water washing is the inter-stage countercurrent realized inside the integrated water washing and extrusion equipment (200), that is, the leachate generated by the next stage water washing section is used as the washing water of the previous stage water washing section. The integrated water washing and extrusion equipment (200) includes a housing (201) and a rotating shaft (202) disposed in the housing (201). The housing (201) is divided into multiple water washing and extrusion sections along the material forward direction. The rotating shaft (202) is correspondingly provided with multiple sections, and its diameter increases step by step along the material forward direction. Each stage of the rotating shaft (202) is provided with a spiral ribbon-shaped primary blade (2021) and a secondary blade (2022) provided on the primary blade (2021). The inner wall of the housing (201) is a sealed wall at the beginning of each rotating shaft (202), and filter holes are provided in the middle and end sections; Driven by the rotating shaft (202), the fly ash slurry passes through each stage of water washing and extrusion sections in sequence. It is washed by stirring with the secondary blades (2022) and dewatered by the extrusion action generated by the increased diameter of the rotating shaft (202) and the filter holes. Flue gas containing carbon dioxide is introduced into the integrated water washing extrusion device (200); the flue gas is used to promote water washing agitation and / or form carbonate precipitates in the water washing liquid; S3. The water washing liquid is subjected to gravity and hardness removal treatment, membrane filtration treatment and evaporation crystallization and salt separation treatment in sequence to obtain crystalline salt and distilled water respectively. The distilled water is reused in step S1 and / or step S2.

2. The fly ash resource utilization method according to claim 1, characterized in that, In step S3, the membrane filtration process specifically refers to a multi-stage countercurrent membrane concentration process, including: The water wash solution after degravity and hardness removal treatment is first passed into the first-stage reverse osmosis membrane unit (501) for concentration to obtain the first-stage permeate and the first-stage concentrate. The first-stage concentrate is passed into the second-stage reverse osmosis membrane unit (502) for further concentration to obtain the second-stage permeate and the second-stage concentrate. The second-stage permeate is returned to the inlet side of the first-stage reverse osmosis membrane unit (501). This process continues until the concentrate produced by the last stage of the reverse osmosis membrane unit reaches the predetermined concentration, at which point it is sent to the evaporation, crystallization, and salt separation treatment unit. The permeate produced by the first-stage reverse osmosis membrane unit (501) is purified by at least another stage of reverse osmosis membrane unit and then output as recycled water.

3. The fly ash resource utilization method according to claim 2, characterized in that, The recycled water is reused in the final washing section and / or pulping unit of the integrated washing and extrusion equipment (200).

4. A fly ash resource recovery system for implementing the fly ash resource recovery method according to any one of claims 1 to 3, characterized in that, Including those connected sequentially: The pulping unit is used to mix fly ash and water to prepare fly ash slurry; An integrated water washing and extrusion unit is used to perform multi-stage countercurrent water washing and extrusion dewatering on fly ash slurry, and output dechlorinated fly ash and water washing liquid. The water washing liquid treatment unit includes a gravity and hardness removal module (300), a membrane concentration module, and an evaporation and crystallization module (600) connected in sequence, for treating the water washing liquid and producing crystalline salt and recycled water; The integrated water washing and extrusion unit includes an integrated water washing and extrusion device (200), which includes: The shell (201) is divided into multiple chambers (210) along the material advance direction to form a multi-stage water washing and extrusion section; A rotating shaft (202) is inserted into the housing (201) and is provided with multiple stages corresponding to the multi-stage water washing and extrusion section, and its diameter increases step by step along the material forward direction; A drive device (203) is used to drive the rotating shaft (202) to rotate; Each stage of the rotating shaft (202) is provided with a spiral ribbon-shaped primary blade (2021) and a secondary blade (2022) provided on the primary blade (2021). The inner wall of the housing (201) is sealed at the beginning of each rotating shaft (202), and filter holes for dehydration are provided in the middle and end of each rotating shaft (202). The shell (201) has an inlet at the beginning of each stage of the washing and extrusion section and a water inlet at the end of the last stage of the washing and extrusion section. The shell (201) has an outlet at the end and a collection chamber at the bottom for collecting leachate from each stage. The collection chamber is connected to the inlet of the next stage of the washing and extrusion section through a pipeline to achieve interstage countercurrent.

5. The fly ash resource utilization system according to claim 4, characterized in that, The distribution of the second-stage blade (2022) on the first-stage blade (2021) is irregular.

6. The fly ash resource utilization system according to claim 4, characterized in that, It also includes a flue gas reuse unit, which comprises: Flue gas source (700) is used to provide flue gas containing carbon dioxide; The air supply duct connects the flue gas source (700) to the housing (201) of the integrated water washing and extrusion equipment (200) and / or the reaction tank of the de-weighting and de-hardening module (300).

7. The fly ash resource utilization system according to claim 4, characterized in that, The membrane concentration module is a multi-stage countercurrent membrane concentration system (500), which includes at least two reverse osmosis membrane units connected in series; In this process, the product water outlet of each reverse osmosis membrane unit, except for the first stage, is connected to the inlet side of the previous stage reverse osmosis membrane unit through a return pipeline. The product water outlet of the first-stage reverse osmosis membrane unit (501) is connected to a product water treatment unit, and the output end of the product water treatment unit serves as the reclaimed water output port of the system. The concentrate outlet of the final stage reverse osmosis membrane unit is connected to the evaporation and crystallization module (600).

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