Process for removing flocculants remaining in water-washed municipal solid waste incineration fly ash

Abstract

The application discloses a kind of life garbage incineration fly ash water washing residual flocculant removal process, comprising: using multistage water washing process to life garbage incineration fly ash, cationic PAM is added to water washing system and is flocculated, after forming flocculation, countercurrent rinsing is carried out;Wastewater produced by water washing is sequentially treated as follows: adding negative charge particles to coagulation sedimentation, followed by ultraviolet catalytic oxidation.The application can significantly reduce the flocculant content in garbage incineration fly ash water washing liquid by adding charged particle coagulation sedimentation and ultraviolet catalytic oxidation process.After being treated by the process, the residual flocculant in fly ash water washing wastewater does not affect the normal operation of subsequent membrane module, improves the salt quality, the residual amount of monomer acrylamide is reduced by more than 90% (GB / T31246-2014 Water Treatment Agent Cationic Polyacrylamide Technical Conditions and Test Methods), ensures the stable operation of the whole water washing system production line, and the process runs stably.

Description

Technical Field

[0001] This invention belongs to the field of solid waste resource utilization, and relates to a process for removing residual flocculants from municipal solid waste fly ash after washing. Specifically, it involves a process innovation that utilizes physical and chemical mechanisms to remove residual flocculants from municipal solid waste fly ash washing wastewater, thereby achieving efficient reduction of flocculant residues in the washing liquid while ensuring economic efficiency and stability. Background Technology

[0002] As the mainstream of municipal solid waste treatment gradually shifts from sanitary landfill to incineration, fly ash from municipal solid waste incineration has become a significant pollutant. Municipal solid waste incineration fly ash refers to the residue collected in the flue gas purification system of municipal solid waste incineration power plants, containing organic pollutants such as benzene compounds and dioxins, as well as trace amounts of heavy metals such as Pb and Cr. According to the "Standard for Pollution Control of Municipal Solid Waste Incineration" (GB18485-2014), "Municipal solid waste incineration fly ash should be managed as hazardous waste." Therefore, fly ash must be collected separately and must not be mixed with municipal solid waste, incineration residue, or other hazardous waste.

[0003] According to the "Technical Specification for Pollution Control of Fly Ash from Municipal Solid Waste Incineration (Trial)" (HJ 1134-2020), environmental pollution should be prevented during the collection, storage, transportation, treatment, and disposal of fly ash from municipal solid waste incineration. Fly ash treatment processes include water washing, solidification / stabilization, molding, low-temperature pyrolysis, high-temperature sintering, and high-temperature melting. Pollution prevention and control during the utilization of fly ash and its treatment products should comply with the requirements of the "Technical Guidelines for Pollution Prevention and Control of Solid Waste Recycling" (HJ 1091-2020) and the "Integrated Wastewater Discharge Standard" (GB8978-2002).

[0004] The components present in high concentrations in fly ash include calcium chloride, calcium hydroxide, and calcium sulfate. Traditional water washing processes typically involve washing out soluble chloride ions, followed by the addition of heavy metal precipitants to remove heavy metal ions, and the use of calcium ion precipitants to precipitate calcium ions. The decalcified solution then enters an evaporator for evaporation and crystallization to obtain industrial-grade sodium chloride and potassium chloride. This process is relatively mature. The washed fly ash then proceeds to the next stage of resource utilization.

[0005] Currently, most traditional wastewater treatment processes for washing water do not use PAM (Polymerase Injection), relying solely on traditional plate and frame filtration. This necessitates the selection of filter cloths with low particle sizes to ensure solid-liquid separation, leading to higher filter cloth costs. Meanwhile, the application of new washing processes has reduced the operational intensity of traditional plate and frame filtration systems, freeing workers from tedious labor. Therefore, the application of PAM in washing water can solve some of the problems currently existing in the process. However, with the application of membrane systems and the instability of influent fly ash properties, large-scale PAM use results in high PAM residue levels, causing varying degrees of impact on membrane, filtration, and piping systems. Therefore, the use of PAM in the process is unavoidable, and minimizing its impact on the entire fly ash resource recovery production line is crucial.

[0006] Chinese invention patent CN201911142714.5 discloses a system and method for dechlorinating fly ash from municipal solid waste incineration by water washing. This system achieves solid-liquid separation by adding a high concentration of PAM during the water washing process and employing a multi-stage cyclone reactor. With three or more stages, the chlorine content of the washed fly ash can be reduced to approximately 0.5%, significantly lowering the chlorine content of fly ash in current three-stage countercurrent rinsing processes. However, the extensive use of PAM in this process has not been significantly assessed regarding its impact on subsequent systems.

[0007] Chinese invention patent CN202011526571.0 introduces a high-efficiency filter press process for municipal solid waste incineration fly ash washed sludge, which solves the problem of plate and frame clogging during the filter press process. Solving the clogging problem of the filter press plates and frames can also improve the complete operation of the system. The above solution is based on the case without the addition of PAM. If PAM is added, the impact of PAM residue on the plates and frames is not fully introduced in this project and lacks sufficient research.

[0008] Chinese Invention Patent CN201811549232.7 discloses an energy-saving treatment process for waste incineration fly ash. This invention discloses an energy-saving treatment process for waste fly ash, including fly ash washing, heavy metal removal, decolorization, calcium removal, and evaporation crystallization steps, or including fly ash washing, heavy metal removal, decolorization, and evaporation crystallization steps. The fly ash washing is a multi-stage countercurrent washing process. The washing liquid from the last stage of the multi-stage countercurrent washing is subjected to reverse osmosis membrane desalination treatment. The purified water produced by the reverse osmosis membrane desalination treatment is reused as the water source for the last stage washing, and the concentrated water produced by the reverse osmosis membrane desalination treatment is used as the water source for the next stage washing. The mass ratio of fly ash to water in the first stage washing is controlled to be 1:1 to 1.1. After the first stage washing, solid-liquid separation is performed. The solid is pulverized and enters the next stage washing, while the liquid enters the heavy metal removal step. This invention can significantly reduce energy consumption during evaporation crystallization and reduce production costs without increasing the number of washing stages. The applicability of the reverse osmosis membrane in the system, especially when the system uses PAM, requires reconsidering the system's tolerance performance.

[0009] With PAM's ability to reduce labor intensity and operational complexity of plate and frame filter presses, and especially with the rise of new water washing systems, it has become an unavoidable water treatment chemical. Based on these applications, it is necessary to minimize PAM residue in the washing wastewater to ensure the proper operation of other sections of the washing production line. Summary of the Invention

[0010] In view of this, the present invention provides a process for removing residual flocculants from fly ash of municipal solid waste incineration by water washing, in order to solve the problems in the background art.

[0011] This invention provides a process for removing residual flocculants from fly ash of municipal solid waste incineration through water washing, comprising the following steps:

[0012] A multi-stage water washing process is used for fly ash from municipal solid waste incineration. Cationic PAM is added to the water washing system for flocculation. After flocs are formed, they are rinsed in a countercurrent manner to remove calcium ions, chloride ions, sodium ions, potassium ions and sulfate ions from the fly ash.

[0013] The waste liquid generated from water washing is treated in the following manner: negatively charged particles are added for coagulation and sedimentation, followed by ultraviolet catalytic oxidation to reduce the residual amount of cationic PAM in the waste liquid.

[0014] In one optional embodiment, in the multi-stage washing process, the chlorine content of the fly ash after countercurrent rinsing is less than 1%.

[0015] In one alternative embodiment, the negatively charged particles are selected from one or more of kaolin, diatomaceous earth, washed sand, and reservoir sediment.

[0016] In one optional embodiment, the concentration of the negatively charged particles is 10–1000 mg / L.

[0017] In one optional embodiment, the particle size of the negatively charged particles is 15–40 μm.

[0018] In one optional embodiment, the ultraviolet light energy intensity of the ultraviolet catalytic oxidation is 0.8 kW to 1.2 kW / m². 3 .

[0019] In one optional embodiment, the residence time of the ultraviolet catalytic oxidation is 0.5 to 2 hours.

[0020] In one optional embodiment, before or during the ultraviolet catalytic oxidation, ferrous chloride and hydrogen peroxide are added to the waste liquid to construct an advanced oxidation system; wherein the concentration of ferrous chloride is 10-100 mg / L and the concentration of hydrogen peroxide is 20-200 mg / L.

[0021] In one optional embodiment, the treatment process further includes a calcium removal step: adding a calcium removal agent to the waste liquid after ultraviolet catalytic oxidation to control the calcium ion content in the effluent to be less than 20 mg / L; the calcium removal agent is selected from one or more of sodium sulfate and sodium carbonate.

[0022] In one optional embodiment, the treatment process further includes a membrane separation step: nanofiltration of the treated waste liquid, wherein the water production rate of the nanofiltration membrane is controlled to be above 85%.

[0023] The beneficial effects of the above technical solution are as follows:

[0024] The method of this invention utilizes the widely available and stable wastewater from the fly ash washing process of municipal solid waste incineration for process development and research, and has broad applicability.

[0025] The method of this invention, while pursuing high processing efficiency, also meets the high-efficiency and stable processing requirements of the production line.

[0026] The process employed in this invention not only offers significant economic benefits, reducing the cost of the washing section by more than 50%, but also ensures the sustainable operation of the production line.

[0027] This invention provides continuous feeding and discharging management throughout the entire process, ensuring the stable operation of the entire system.

[0028] The method of this invention is simple to operate, highly adaptable, and suitable for the treatment needs of fly ash washing wastewater of different scales and different PAM residues. It also has a large number of practical applications to support it.

[0029] This invention identifies the problem of PAM residue treatment in the early stage of diversified resource utilization of fly ash from waste incineration, and systematically proposes a solution to this problem, providing a solution for fly ash resource utilization.

[0030] This invention, based on a simple processing method that does not affect the existing process flow, not only solves the problem of PAM residue but also improves the salt quality during the crystallization process, providing a new solution for the stable operation of the water washing production line. Attached Figure Description

[0031] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0032] Figure 1 This is a schematic diagram of a high-efficiency fly ash washing and dechlorination process for municipal solid waste according to the present invention. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0034] Combination Figure 1 As shown in the embodiment of the present invention, a process for removing residual flocculant from fly ash incinerated from municipal solid waste is disclosed. The fly ash washing process employs a multi-stage washing process, using cationic PAM to achieve fly ash flocculation, forming flocs with low moisture content, which are then subjected to countercurrent rinsing. The addition of cationic PAM achieves efficient agglomeration of fly ash particles, ensuring washing efficiency within a relatively small number of stages. The multi-stage washing process removes calcium ions, chloride ions, sodium ions, potassium ions, sulfate ions, etc., from the fly ash, ensuring that the chloride content of the washed fly ash is less than 1%. Although the "Technical Specification for Pollution Control of Fly Ash from Municipal Solid Waste Incineration (Trial)" (HJ 1134-2020) requires the chloride content of pretreated fly ash to be less than 2%, the addition of high-concentration PAM inevitably leads to residual organic matter in the system. In particular, residual cationic PAM can cause enrichment of anionicly charged membrane surfaces, making it difficult for the membrane system to operate stably. Simultaneously, the residue of cationic PAM also leads to an increase in the organic matter content in the salts during the crystallization process. The main innovative value of this technology lies in how to ensure the stability of the multi-stage washing process while using cationic PAM. This invention solves the problem of flocculant residue through the following technological innovations.

[0035] This system employs a flocculant addition process in the fly ash washing or water treatment process to reduce flocculant residue and ensure the stable operation of the fly ash washing resource utilization production line.

[0036] The negatively charged particles added to the primary filtrate are mainly one or more of kaolin, diatomaceous earth, washed sand mud, and reservoir bottom sediment, with a concentration of 10–1000 mg / L (on an oven-dry basis).

[0037] The intensity of ultraviolet light energy needs to be ensured to be 0.8kW~1.2kW / m3.

[0038] Ferrous chloride and hydrogen peroxide are used to construct an advanced oxidation catalytic system under alkaline conditions, which can ensure the efficient decomposition of PAM residual organic matter. The concentration of ferrous chloride added is 10-100 mg / L, and the concentration of hydrogen peroxide added is 20-200 mg / L (based on 30% hydrogen peroxide).

[0039] The main calcium removal agents are sodium sulfate and sodium carbonate, with the control index being less than 20 mg / L of calcium ions in the effluent.

[0040] The residence time of the ultraviolet catalytic oxidation device is 0.5 to 2 hours.

[0041] The water production rate of nanofiltration membranes is controlled at over 85%.

[0042] The particle size of the negatively charged particles is between 15 and 40 μm.

[0043] This invention significantly reduces PAM residue in waste liquid through the synergistic effect of negatively charged particle adsorption and ultraviolet catalytic oxidation, reducing the residual amount of monomeric acrylamide by more than 90% (GB / T 31246-2014 Technical conditions and test methods for cationic polyacrylamide in water treatment agents), solving the membrane fouling problem, reducing the backwash water volume of the membrane system by more than 25%, and reducing the offline cleaning frequency by more than 50%.

[0044] This invention reduces the organic content in crystalline salts; for example, the total organic carbon (TOC) in sodium chloride can be reduced by 20% to 30%, thus expanding the application scenarios of salts.

[0045] This invention reduces operating costs by decreasing the frequency of filter cloth replacement (which can be extended by more than 2 times) and reducing the frequency of evaporator cleaning (from once a day to once every 3 days), resulting in a reduction of more than 50% in the overall cost of the water washing section.

[0046] This invention is adaptable to production lines of different sizes and wastewater with different PAM residue levels. It is easy to operate and can run continuously throughout the entire process with high stability.

[0047] In existing technologies, cationic PAM is a non-degradable long-chain molecule, making it difficult to handle after residue formation. This invention, through molecular design, introduces ester groups (such as polyethylene glycol diacrylate crosslinking agents) into the PAM molecular chain to prepare hydrolyzable cationic PAM. In the alkaline environment (pH = 11-13) of fly ash washing, the ester bonds can be slowly hydrolyzed and broken, reducing the PAM molecular weight from 15 million to below 5 million, making it easier for subsequent processes to decompose. This invention breaks through the traditional approach of "passively treating residues after adding non-degradable PAM," endowing PAM with environmental degradability from the source. Combined with multi-stage gradient washing (high shear to enhance initial flocculation, low shear to reduce later PAM dissolution), the PAM dosage is reduced by 30%-40%, and the initial residue value is reduced from 2.5 mg / L to 1.0 mg / L. The degradable PAM of this invention achieves a 50% degradation rate after 3 days in the washing system, reducing the load of subsequent oxidation processes by 40%.

[0048] To address the problems of traditional negatively charged particles being difficult to recover and prone to causing secondary pollution, this invention utilizes a co-precipitation method to load Fe3O4 magnetic particles onto the surface of kaolin, preparing composite particles that combine negative charge adsorption and magnetic separation functions. The surface negative charge density reaches -30 to -40 mV (compared to -15 to -20 mV for the original kaolin), increasing the adsorption capacity for cationic PAM from 80 mg / g to 150 mg / g. Simultaneously, rapid particle separation (separation time < 5 min) can be achieved using an external magnetic field (0.1–0.3 T), with a recovery rate > 90%, and the particles can be reused more than 5 times. This invention combines charge adsorption and magnetic separation, solving the linear "addition-discharge" treatment mode of traditional particles and achieving solid waste reduction and reagent recycling. After the magnetic particles are recycled 3 times, the PAM removal rate remains above 85%, and solid waste generation is reduced by 60%.

[0049] To address the issues of high energy consumption and poor salt quality in traditional nanofiltration-evaporation processes, this improvement employs bipolar membrane electrodialysis for desalination: the bipolar membrane generates H₂... + The pH of the wastewater can be adjusted to neutral by OH-, preventing the precipitation of calcium and magnesium ions. A homogeneous ion exchange membrane selectively retains organic matter, ensuring that the TOC of the desalinated water is <5 mg / L. The concentrated water is then evaporated and crystallized at low temperature (60–70°C) to obtain industrial salt with a NaCl purity >99.5%. This invention integrates pH adjustment and desalination, solving the multi-step operation problem of "calcium removal-pH adjustment-evaporation" in traditional processes, while simultaneously reducing energy consumption through low-temperature evaporation. Performance verification: Electrodialysis desalination rate >90%, TOC of the crystallized salt reduced from 36 mg / kg to below 10 mg / kg, meeting the industrial grade 1 salt standard, and evaporation energy consumption reduced by 30%.

[0050] In the original process, negatively charged particles (such as kaolin and diatomaceous earth) mainly remove PAM through physical adsorption. This embodiment uses acid / alkali modification treatment (e.g., stirring with 5% hydrochloric acid at 60°C for 1.5 hours) to increase the hydroxyl groups and negative charge density on the particle surface. After modification, the adsorption capacity of the particles for cationic PAM can be increased by 20%–50%, and the dosage can be reduced from 200 mg / L to 100–150 mg / L, reducing reagent costs while maintaining removal efficiency. For example, the adsorption rate of PAM by modified kaolin increases from 65% to 85%, reducing the load on subsequent oxidation processes.

[0051] As a further improved embodiment, ozone (dosage 20-30 mg / L) was introduced into the original UV + Fenton (ferrous chloride + hydrogen peroxide) system. The hydroxyl radicals (·OH) generated by ozone decomposition under UV light synergistically accelerate the breakage of PAM molecular chains with the Fenton system. Comparative experiments showed that the synergistic system could increase the PAM decomposition efficiency from 70% to 90%, and the UV light intensity from 1.0 kW / m². 3 Reduced to 0.8kW / m 3The dwell time is shortened from 1 hour to 0.6 hours, reducing energy consumption by 15% to 20%.

[0052] Adding nano-TiO2 (particle size 20-50 nm) to an ultraviolet catalytic oxidation device, after modification with a silane coupling agent, allows it to be uniformly dispersed in the waste liquid, enhancing the absorption and conversion efficiency of ultraviolet light. TiO2, as a photocatalyst, is recyclable (lifespan ≥ 3 months), further improving PAM decomposition efficiency and reducing the residual PAM concentration in the waste liquid from 1.2 mg / L to below 0.5 mg / L, thus reducing the risk of membrane fouling.

[0053] By optimizing the solid-liquid ratio (1:1.2–1.5) and stirring rate (300–500 r / min) during the primary water washing process, the contact efficiency between fly ash particles and water is enhanced, reducing the PAM dosage (from 0.6% to 0.3%–0.5%). For example, when the stirring rate during the primary water washing process is increased to 400 r / min, the fly ash agglomeration speed is accelerated, and the PAM dosage is reduced by 20% for the same flocculation effect, thus reducing residual PAM at the source.

[0054] The original process, which involved adding the calcium removal agent all at once, easily led to localized supersaturation, resulting in small calcium salt particles and a large amount of sludge. The stepwise addition of the agent first removes 80%–90% of the calcium ions (forming large calcium carbonate particles) with sodium carbonate, followed by deep calcium removal with sodium sulfate. This increases the particle size of the precipitated particles from 5–10 μm to 20–30 μm, reduces the moisture content of the filter cake from 65% to 55%, reduces sludge volume by 20%, and improves filter press efficiency by 30%.

[0055] An activated carbon-resin composite packing column is added before the nanofiltration membrane. The activated carbon adsorbs large-molecule PAM, while the resin (such as a weakly basic anion exchange resin) adsorbs small-molecule PAM degradation products. The synergistic effect ensures that the residual PAM entering the nanofiltration membrane is ≤0.1 mg / L. In actual operation, the backwashing cycle of the nanofiltration membrane is extended from 7 days to 10 days, and the offline cleaning cycle is extended from once per month to once every 2 months.

[0056] An online PAM concentration detector (based on the principle of turbidity-fluorescence coupling) and a Zeta potential meter are introduced to provide real-time feedback on PAM residue and particle charge status in the waste liquid. When the PAM concentration > 5 mg / L, the dosage of negatively charged particles is automatically increased; when the Zeta potential deviates from the range of -15 to -20 mV, the ozone concentration is adjusted. This system can reduce the fluctuation range of reagent consumption from ±20% to ±5%, ensuring the stability of treatment effect while avoiding waste.

[0057] Low molecular weight (8-10 million) cationic PAM was screened because its shorter molecular chain makes it easier to be oxidized and decomposed. Comparative experiments showed that, under the same treatment process, the residual amount of low molecular weight PAM was 40% lower than that of high molecular weight PAM (above 15 million), and the TOC in the crystalline salt was reduced by 10-15 mg / kg, further improving the salt quality.

[0058] The beneficial effects of the above technical solution are as follows:

[0059] Improved processing efficiency: The total PAM removal rate has increased from 80% in the original process to over 95%, and the membrane system operating cycle has been extended by 50% to 80%.

[0060] Cost reduction: consumption of reagents (negatively charged particles, oxidants) is reduced by 20% to 30%, energy consumption is reduced by 15% to 25%, and overall operating costs are reduced by another 10% to 15%;

[0061] Enhanced stability: Through online control and pretreatment optimization, the system's ability to withstand load fluctuations is improved, making it adaptable to wastewater with PAM residue levels of 0.5–10 mg / L;

[0062] Solid waste reduction: The amount of calcium-removing sludge and waste membrane residue generated is reduced by 20% to 30%, which is more in line with the planning requirements of "zero-waste city".

[0063] Example 1

[0064] The fly ash washing process for waste incineration employs a multi-stage washing technique, adding cationic PAM at a dosage of 0.5–0.8% of the fly ash's dry weight. The washing solution contains 200 mg / L of 18μm kaolin, 50 mg / L of ferrous chloride in the calcium removal reaction stage, and 100 mg / L of hydrogen peroxide. The ultraviolet light intensity is 1.0 kW / m³, and the residence time is 1 hour. The average molecular weight of the washing solution, originally 2356 Daltons, was reduced to 1688 Daltons after the above treatment, significantly reducing flocculant residue. Simultaneously, the backwash water volume of the supporting ultrafiltration + nanofiltration membrane system, previously reaching 80 tons / day, has been reduced to 60 tons / day, improving the membrane system's operating efficiency. The TOC in crystalline sodium chloride has decreased from 50 mg / kg to 36 mg / kg, improving salt quality and expanding its market reach.

[0065] Example 2

[0066] The fly ash washing process for waste incineration employs a multi-stage washing technique, with cationic PAM added at a concentration of 0.6% of the dry weight of the fly ash. The washing solution contains 100 mg / L of 20 μm diatomaceous earth, 25 mg / L of ferrous chloride in the calcium removal reaction stage, 100 mg / L of hydrogen peroxide, an ultraviolet light intensity of 1.0 kW / m³, and a residence time of 0.5 h. The proportion of particles smaller than 0.5 μm in the washing solution increased from 10.18% to 22.32%, indicating that the significant reduction in flocculant residue led to a re-matching of particle size distribution.

[0067] Example 3

[0068] After adopting this invention, a company in a certain city reduced the amount of mother liquor outsourced for processing from 2% to 0.8%, a reduction of 60%. The cleaning frequency of the evaporator was also greatly reduced from once a day to once every three days.

[0069] Example 4

[0070] After adopting this invention, the offline cleaning of the "ultrafiltration + nanofiltration" system in a company's water washing production line in a certain city was reduced from twice a month to once a month.

[0071] Example 5

[0072] After adopting this invention, a fly ash disposal unit in a certain province changed the filter cloth replacement frequency of the plate and frame filter press in the calcium removal reaction section from once a month to once every two months, which greatly reduced the filtration cost of the plate and frame filter press.

[0073] Example 6

[0074] After adopting this invention, a fly ash disposal unit in a certain province added cationic PAM at a dosage of 0.6% of the dry weight of the fly ash. The concentration of 20μm diatomaceous earth added to the washing solution was 100 mg / L, the concentration of ferrous chloride added to the calcium removal reaction section was 10 mg / L, the concentration of hydrogen peroxide added was 50 mg / L, the ultraviolet light energy intensity was 1.2 kW / m³, and the residence time was 0.6 h. The TOC in the crystalline sodium chloride decreased from 38 mg / kg to 30 mg / kg, improving salt quality and expanding its market. Simultaneously, pipeline cleaning was reduced from once a month to once every six months, improving the stable operating efficiency of the production line.

[0075] Although embodiments of the invention have been described in conjunction with the accompanying drawings, those skilled in the art can make various modifications and variations without departing from the spirit and scope of the invention, and such modifications and variations all fall within the scope defined by the appended claims.

Claims

1. A process for removing residual flocculants from fly ash of municipal solid waste incineration by water washing, characterized in that, Includes the following steps: A multi-stage water washing process is used for fly ash from municipal solid waste incineration. Cationic PAM is added to the water washing system for flocculation. After flocs are formed, they are rinsed in a countercurrent manner to remove calcium ions, chloride ions, sodium ions, potassium ions and sulfate ions from the fly ash. The waste liquid generated from water washing is treated as follows: negatively charged particles are added for coagulation and sedimentation, followed by ultraviolet catalytic oxidation to reduce the residual amount of cationic PAM in the waste liquid; The negatively charged particles are selected from one or more of kaolin, diatomaceous earth, washed sand mud, and reservoir bottom sediment; The ultraviolet light energy intensity of the ultraviolet catalytic oxidation is 0.8~1.2 kW / m². 3 ; Before or during the ultraviolet catalytic oxidation, ferrous chloride and hydrogen peroxide are added to the waste liquid to construct an advanced oxidation system; wherein the concentration of ferrous chloride is 10~100mg / L and the concentration of hydrogen peroxide is 20~200mg / L.

2. The removal process according to claim 1, characterized in that, In the multi-stage water washing process, the chlorine content of the fly ash after countercurrent rinsing is less than 1%.

3. The removal process according to claim 1 or 2, characterized in that, The concentration of the negatively charged particles is 10~1000 mg / L.

4. The removal process according to claim 1 or 2, characterized in that, The particle size of the negatively charged particles is 15~40μm.

5. The removal process according to claim 1, characterized in that, The residence time for the ultraviolet catalytic oxidation is 0.5~2h.

6. The removal process according to claim 1, characterized in that, The removal process also includes a calcium removal step: adding a calcium removal agent to the waste liquid after ultraviolet catalytic oxidation to control the calcium ion content in the effluent to be less than 20 mg / L; the calcium removal agent is selected from one or more of sodium sulfate and sodium carbonate.

7. The removal process according to claim 1, characterized in that, The removal process also includes a membrane separation step: the treated waste liquid is subjected to nanofiltration, and the water production rate of the nanofiltration membrane is controlled at above 85%.

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