A method for regulating and directional conversion of waste incineration fly ash components

Abstract

The application provides a waste incineration fly ash component regulation and directional conversion treatment method, and belongs to the technical field of solid waste treatment. The method comprises the following steps: S1, the waste incineration fly ash is first subjected to primary water washing to remove most of soluble chlorides and heavy metals, and the obtained solid after solid-liquid separation is subjected to forced rinsing using regenerated water or clean water to obtain water-washed fly ash and water-washing waste liquid; S2, a core-shell structure Fe2O3 / Fe / C composite catalyst is prepared, mixed with the water-washed fly ash to form granules, and then subjected to catalytic pyrolysis in an inert or micro-oxygen environment to crack dioxin organic matter; and S3, the water-washing waste liquid is subjected to pretreatment and then subjected to staged evaporation-selective crystallization to recover inorganic salt components in a differentiated manner; and flue gas is introduced into an incinerator for synergistic heat treatment. The application can remove inorganic salts and easily soluble heavy metals in the fly ash, promote directional catalytic cracking of dioxins, and resourcefully utilize the inorganic salts, so that fly ash reduction, harmlessness and resource utilization are achieved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of solid waste treatment, in particular to a garbage incineration fly ash component regulation and directional conversion treatment method. BACKGROUND

[0002] With the acceleration of urbanization, the production of municipal solid waste increases. Garbage incineration for power generation has become the main way of garbage disposal in China due to its large processing capacity, significant volume and mass reduction effect, and possible source recycling. However, during the process of garbage incineration, hazardous waste fly ash is produced, mainly from the collection of flue gas purification system and the fine ash settled at the bottom of flue and chimney, containing inorganic salts and heavy metals such as Pb, Cd, Zn and Cu, as well as excess reagents added during flue gas purification.

[0003] At present, the fly ash treatment technologies at home and abroad mainly include cement solidification or chemical stabilization for landfill, high-temperature melting and wet extraction. The cement solidification technology is to mix fly ash with cement and water in a certain proportion, and use the cementation characteristics of cement to seal harmful substances such as heavy metals in the cement structure. This technology is simple to operate and has low cost, but it has problems such as increase in the volume of solidified body, influence of chloride salt in fly ash on the cement solidification effect, and long-term stability to be verified. At the same time, this technology is essentially still a pretreatment before landfill, and does not realize the reduction and resource utilization of fly ash. The chemical stabilization technology is to add chemical reagents (such as chelating agents, sodium sulfide, phosphates, etc.) to fly ash to form higher-stability compounds with heavy metals, thereby reducing the leaching toxicity of heavy metals. This technology has good stabilization effect on heavy metals, but the cost of reagents is high, and the treated solid still needs to be landfilled, which does not solve the fundamental problem.

[0004] Landfill treatment is the most popular fly ash disposal technology internationally and domestically. Fly ash usually needs to be pretreated (such as cement solidification, chemical stabilization, etc.) to meet the requirements of landfill sites, and then sent to special landfill sites for safe landfill or zoned landfill in sanitary landfill sites. This technology has the advantages of mature equipment, large processing capacity, and relatively low investment, but has problems such as occupation of a large amount of land resources, long-term environmental risk, and increasing treatment cost year by year.

[0005] High-temperature melting technology is to heat fly ash to 1400-1500℃ to make it melt, which destroys organic pollutants such as dioxins at high temperature, and seals heavy metals in glassy slag. This technology has complete treatment effect, but has high energy consumption, huge equipment investment and high operating cost.

[0006] Wet extraction technology is to use acidic or alkaline solution to selectively leach heavy metals in fly ash to realize the separation and recovery of heavy metals. This technology can realize the resource utilization of heavy metals, but has complex process, generates a large amount of heavy metal-containing wastewater, and has high risk of secondary pollution.

[0007] In recent years, with the improvement of environmental protection requirements and the popularization of the concept of circular economy, fly ash treatment technology is developing towards resource utilization. The water washing desalination technology takes advantage of the characteristics of chlorides in fly ash that are easily soluble in water, and separates chlorides from fly ash by water washing method, which not only reduces the risk of fly ash, but also recovers and produces industrial salt, and has good application prospect. Studies have shown that by optimizing the water washing process parameters, the dechlorination effect can be effectively improved, creating good conditions for subsequent treatment.

[0008] Catalytic pyrolysis technology promotes the decomposition of organic pollutants and the stabilization of heavy metals at relatively low temperatures by using catalysts, which has the advantages of low energy consumption and good treatment effect. Studies have shown that under the action of appropriate catalysts, the efficient decomposition of dioxins and the stabilization of heavy metals in fly ash can be achieved at temperatures of 300 to 450℃. However, catalytic pyrolysis technology usually needs to be carried out in an inert atmosphere such as nitrogen or argon, and the control of oxygen content is extremely high, usually below 0.1~0.3%. Although it is relatively easy to control the oxygen-free environment in the laboratory, it is very difficult in actual engineering, and has high requirements for equipment production, operation control, etc., which is costly and cumbersome, and is not conducive to engineering application. Therefore, it is urgent to develop a comprehensive treatment method integrating water washing desalination, catalytic pyrolysis and inorganic salt recovery technology to realize the efficient and harmless treatment and resource utilization of waste incineration fly ash. SUMMARY

[0009] In view of the above problems existing in the prior art, the present application provides a waste incineration fly ash component regulation and directional conversion treatment method. The present application strengthens the forced leaching by primary water washing, prepares oxygen-resistant Fe2O3 / Fe / C catalyst, integrates water washing desalination, micro-oxygen environment catalytic pyrolysis and three major technical units of staged crystallization and quality-based recovery of inorganic salt, removes inorganic salt and easily soluble heavy metals from fly ash, promotes the directional catalytic cracking of dioxins, and resources the inorganic salt, realizes the reduction, harmlessness and resource utilization of fly ash.

[0010] The technical scheme of the present application is as follows:

[0011] A waste incineration fly ash component regulation and directional conversion treatment method, the method comprising the following steps:

[0012] S1, the waste incineration fly ash is first subjected to primary water washing to remove soluble chlorides and heavy metals, and the obtained solid after solid-liquid separation is subjected to forced leaching using regenerated water or clean water, to obtain water-washed fly ash and water-washing waste liquid, and to deeply separate residual soluble chlorides and heavy metals, and to remove the chlorine source re-synthesized from dioxins;

[0013] S2, a core-shell structure Fe2O3 / Fe / C composite catalyst is prepared, mixed with water-washed fly ash to form a granule, and subjected to catalytic pyrolysis in an inert or micro-oxygen environment to crack dioxin organic matter;

[0014] S3, the waste water after pretreatment is evaporated and crystallized in sections to recover inorganic salt components; and the flue gas is sent into a incinerator for heat treatment.

[0015] Preferably, the specific steps of the first-stage water washing of the fly ash in step S1 include:

[0016] A1, the fly ash of waste incineration is mixed with the condensed water from the recovered inorganic salt components and additional clean water at a liquid-solid ratio of 2-5 L / kg, stirred at 200-500 r / min for 15-60 min at room temperature, and then solid-liquid separation is performed to obtain a solid and a first batch of waste water;

[0017] A2, the obtained solid is uniformly washed with clean water at a liquid-solid ratio of 0.5-1 L / kg, and then solid-liquid separation is performed again to obtain the washed fly ash and a second batch of waste water; the soluble chlorine content in the washed fly ash is less than 1%, reducing the chlorine source for dioxin resynthesis.

[0018] Further, the amount of clean water used in step A1 is determined by supplementing the liquid-solid ratio of 2-5 L / kg that has not been reached after using the condensed water.

[0019] Preferably, the preparation method of the Fe2O3 / Fe / C composite catalyst in step S2 includes the following steps:

[0020] N1, a suspension is prepared by ultrasonic dispersion of biochar as a carrier in deionized water; then iron salt solution is added dropwise under stirring;

[0021] N2, then sodium hydroxide or ammonia solution is slowly added dropwise, the dropwise addition speed is controlled at 1-3 ml / min, the pH of the reaction system is maintained at 8-10, and the reaction time is 2-4 hours;

[0022] N3, after the reaction is completed, the product is aged for 6-12 hours, then centrifugal separation is performed, and the product is washed with deionized water until the pH of the washing liquid approaches neutral;

[0023] N4, the obtained product is dried at 80-120℃ for 12-24 hours, Fe2O3 is loaded on the biochar carrier by the co-precipitation method described above, and the Fe loading amount is 10-20 wt%;

[0024] N5, the dried product is selectively reduced at 280-320℃ under H2 / N2 mixed atmosphere for 2-3 hours to form a Fe2O3 / Fe / C composite catalyst with core-shell structure; the particle size of the obtained Fe2O3 / Fe / C composite catalyst is 200-500 μm, and the specific surface area is not less than 100 m 2 / g.

[0025] More preferably, the biochar in step N1 is ground to a particle size of less than 150 μm; the iron salt comprises ferric chloride, ferric nitrate or ferric sulfate; the stirring speed is 300~500 rpm, and the stirring temperature is 60~80℃.

[0026] More preferably, the mass ratio of C, Fe, OH in the biochar, iron salt, sodium hydroxide or ammonia water in step N2 is 1:0.8~1.5:1.2~2.0; the centrifugal speed in step N3 is 3000~5000 rpm, and the time is 5~10 min.

[0027] Preferably, the specific steps of step S2 include:

[0028] B1, the fly ash after water washing is mixed with the catalyst at a mass ratio of 5:1~15:1, and then shaped into spherical or cylindrical particles with a diameter of 1~3 cm;

[0029] B2, catalytic pyrolysis is carried out under a micro-oxygen atmosphere at a temperature of 250~350℃ for 30~120 minutes, and the flue gas generated by pyrolysis is introduced into an incinerator for heat treatment.

[0030] More preferably, the micro-oxygen atmosphere in step B2 is an atmosphere mainly composed of nitrogen or argon, with an oxygen concentration of ≤1%.

[0031] More preferably, in the micro-oxygen atmosphere in step B2, Fe2O3 and Fe have a synergistic catalytic effect; Fe2O3 provides active oxygen atoms to promote the oxidative cleavage of dioxin molecules; Fe provides electrons and activates the C-Cl bond to promote the dechlorination of dioxin; and the carrier C provides π electrons to enhance the adsorption and activation of dioxin molecules.

[0032] Preferably, the specific steps of step S3 include:

[0033] C1, sodium sulfide or sodium carbonate is added to the water washing waste liquid to a concentration of 0.3~1.2 g / L to precipitate heavy metals and calcium ions; then Fenton reagent is added and the pH is adjusted to 2~4, H2O2 and Fe 2+ molar ratio of 2:1~4:1 to oxidize organic matter; then the pH value is adjusted to 7.0~9.0; and 20~60 mg / L of polyaluminum chloride and 1~8 mg / L of polyacrylamide are added or not added according to the type of impurities in the water washing waste liquid, and flocculation and sedimentation are carried out to remove calcium ions and heavy metals;

[0034] C2, the water washing waste liquid after impurity removal is treated by ultrafiltration membrane and / or nanofiltration membrane to remove suspended solids and organic matter, and monovalent and multivalent ions are separated according to the needs of inorganic salt component recovery;

[0035] C3, the treated water washing waste liquid is subjected to mechanical vapor recompression or multi-effect evaporation crystallizer staged recovery of sodium sulfate, potassium chloride and sodium chloride at different temperatures, and the condensed water is recovered for use in the fly ash primary water washing plus leaching step.

[0036] Further, the soluble chlorine of the final treated fly ash is <1%, the leaching liquid obtained according to HJ 557-2010 'Solid Waste Leaching Toxicity Level Oscillation Method' has Pb <1.0 mg / L, and the dioxin toxicity equivalent is <20 ng TEQ / kg.

[0037] The beneficial technical effects of the present application are that:

[0038] 1, the present application utilizes fly ash primary water washing plus forced leaching to effectively remove chlorine salts and easily soluble heavy metals in fly ash, and by removing a large amount of inorganic chlorine in fly ash, the resynthesis of dioxin catalytic cracking process is blocked, the directional decomposition and conversion of dioxin are promoted, and the technical difficulty of reaction control is reduced.

[0039] 2, the present application prepares a new type of oxygen-resistant catalyst which can tolerate <1% oxygen concentration, improves the oxygen tolerance of the system, reduces equipment investment and operating cost, and promotes the directional conversion of dioxin; fly ash and catalyst are mixed and granulated before catalytic cracking, which is beneficial to the full contact and reduction of dust or sticking of the two, and facilitates system control.

[0040] 3, the present application recovers inorganic salts such as sodium sulfate, potassium chloride and sodium chloride in stages, can obtain inorganic salts with high purity, is convenient for sale and profit, has the advantages of high treatment efficiency, less secondary pollution, simple operation, etc., and provides a new technical approach for the safe disposal of municipal solid waste incineration fly ash. BRIEF DESCRIPTION OF DRAWINGS

[0041] Figure 1 The figure is a schematic diagram of the component regulation and directional conversion treatment method of the present application. DETAILED DESCRIPTION

[0042] The present application will be described in detail below in conjunction with the drawings and examples. Obviously, the described examples are only a part of the examples of the present application, not all the examples. Based on the examples in the present application, all other examples obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0043] Example 1:

[0044] This embodiment provides a preparation method of Fe2O3 / Fe / C composite catalyst, the specific steps are as follows:

[0045] 10 g of biochar was ground to a particle size of less than 150 μm, ultrasonically dispersed in 100 ml of deionized water for 30 minutes to make a suspension. Under the condition of stirring at 400 rpm and temperature of 65℃, 180 ml of iron chloride solution with a concentration of 1 mol / L was added drop by drop; then 95 ml of sodium hydroxide solution with a concentration of 4 mol / L was slowly added drop by drop, the dropping speed was controlled at 2 ml / min, the pH of the reaction system was maintained at 9, and the reaction time was 3 hours. After the reaction was completed, the reaction system was allowed to stand at room temperature for 9 hours, and then centrifugal separation was carried out at a speed of 3000 rpm for 10 minutes. The washing liquid was washed with deionized water until the pH was close to neutral, and then dried in an oven at 105℃ for 18 hours. Under the mixed gas atmosphere of H2:N2=1:1, the Fe2O3 / Fe / C composite catalyst with core-shell structure was formed by selective reduction at 300℃ for 2.5 hours.

[0046] It was found by laser particle size analyzer and BET instrument that the particle size of the obtained catalyst was mainly distributed in 200~400 μm, and the specific surface area was 148.6 m 2 / g. TEM detection confirmed that the catalyst was a core-shell structure.

[0047] Example 2:

[0048] A waste incineration power plant daily handles 2000 tons of waste, adopts grate furnace incineration process, and the production of fly ash is about 80 tons per day, and the annual output is about 25,000 tons. The main components of fly ash are chlorine content of 12.5%, calcium content of 28.3%, potassium content of 3.1%, sodium content of 5.8%, silicon content of 15.8%, aluminum content of 2.2%, and iron content of 2.1%; heavy metal content: Pb 4500 mg / kg, Cd 150 mg / kg, Zn 8500 mg / kg. Dioxin toxicity equivalent 80 ng TEQ / kg.

[0049] The above-mentioned waste incineration fly ash component regulation and directional conversion treatment method is provided in this embodiment, and the process flow is as shown in Figure 1 , which comprises the following steps:

[0050] S1, primary water washing and forced rinsing, the steps are as follows:

[0051] A1, 1 kg of fly ash is mixed with 3 L of condensed water (liquid-solid ratio 3 L / kg, and if the condensed water is insufficient, make up with water); stirred at room temperature at a speed of 350 r / min for 30 min, and then separated by centrifugation to obtain solid residue and the first batch of water washing waste liquid;

[0052] A2, use 0.5 L of water to wash the solid residue (liquid-solid ratio 0.5 L / kg); after solid-liquid separation, the water-washed fly ash and the second batch of water washing waste liquid are obtained; the water-washed fly ash is about 750 g of dry solid;

[0053] S2, after mixing with catalyst, catalytic pyrolysis, the steps are as follows:

[0054] B1, after washing with water, the fly ash dry solid is mixed with 75 g of Fe2O3 / Fe / C composite catalyst prepared in Example 1, and is pressed into a spherical shape with a diameter of 1.5 cm;

[0055] B2, under a nitrogen atmosphere (oxygen content is about 0.8%), the temperature is raised to 300°C, and pyrolysis is carried out at constant temperature for 60 min, to obtain a solid residue, and the generated flue gas is introduced into a co-processing furnace for heat treatment.

[0056] The dioxin toxicity equivalent of the obtained solid residue is less than 10 ng TEQ / kg. The microspherical Fe2O3 catalyst with a particle size of 250-400 μm and a specific surface area of 60.5 m 2 / g is used for catalytic pyrolysis under the same conditions, and the dioxin toxicity of the solid residue is 25-40 ng TEQ / kg.

[0057] S3, after pretreatment, the two batches of water washing waste liquid are subjected to evaporation and quality crystallization to recover inorganic salt components, and the steps are as follows:

[0058] C1, about 3 L of water washing waste liquid generated by water washing and enhanced forced washing is added with 2.5 g of sodium carbonate to precipitate heavy metals and calcium salts, and is adjusted to pH=4, and then 30% hydrogen peroxide and 0.6 g of ferrous sulfate are added to form Fenton reagent with a molar ratio of 3:1 to oxidize organic matter; after treatment, there is little suspended matter in the waste liquid, so polyaluminum chloride and polyacrylamide are not added for flocculation and precipitation.

[0059] C2, the pH of the water washing waste liquid after impurity removal is adjusted to 7.0 by using sodium hydroxide solution, and residual trace organic matter and divalent ions are removed by using an ultrafiltration membrane with a molecular weight cut-off of 400 Da and a nanofiltration membrane with a molecular weight cut-off of 100 Da;

[0060] C3, by evaporating and crystallizing at different temperature sections at 60°C and 25°C respectively, 50 g of NaCl and 20 g of KCl can be recovered, and no sodium sulfate is produced from the fly ash sample used in this example. The condensed water obtained after treatment can be reused in step S1.

[0061] The dioxin toxicity equivalent of the solid residue is less than 10 ng TEQ / kg; the soluble chlorine content is less than 1%; the leaching liquid obtained according to the "Solid Waste Leaching Toxicity Level Oscillation Method" (HJ 557-2010) has Pb less than 1.0 mg / L, Zn less than 2.0 mg / L, and Cd less than 0.1 mg / L.

[0062] Example 3:

[0063] A waste incineration power plant daily handles 600 tons of waste, adopts fluidized bed incineration process, and the fly ash production is about 90 tons per day, and the annual output is about 30,000 tons. The main components of fly ash are chlorine content 15.2%, calcium content 22.1%, silicon content 18.5%, aluminum content 8.3%, iron content 5.2%, potassium content 2.1%, sodium content 3.6%, and sulfur content 2%; heavy metal content: Pb 2800 mg / kg, Zn 4200 mg / kg; dioxin toxicity equivalent is 110 ng TEQ / kg.

[0064] The above-mentioned waste incineration fly ash component regulation and directional conversion treatment method is provided, and the process flow is as shown in Figure 1 The method comprises the following steps:

[0065] S1, primary water washing and forced leaching, the steps are as follows:

[0066] A1, 90 tons of fly ash in original state are put into the reactor, and 360 m 3 of clean water are added according to the liquid-solid ratio of 4 L / kg, stirring at 300 r / min at 25℃ for 30 minutes, and then solid-liquid separation is carried out to obtain about 335 m 3 of first batch of water washing waste liquid and about 110 tons of solid residue.

[0067] A2, then the solid residue is leached according to the liquid-solid ratio of 0.7 L / kg, 63 m 3 of clean water are added, and leaching treatment is carried out for 5 minutes to obtain about 105 tons of final desalted fly ash residue with a water content of about 45%. The chlorine content of the treated fly ash is reduced to 0.42%.

[0068] S2, after mixing with the catalyst, catalytic pyrolysis is carried out, and the steps are as follows:

[0069] B1, the catalyst prepared in example 1 is used in an amount of 3.8 tons, and the mass ratio of the water washed fly ash to the catalyst is about 1:15 (the dry basis mass of the fly ash is only used for calculation, and drying is not required during granulation). After the water washed fly ash and the catalyst are uniformly mixed, they are pressed into cylindrical particles with a diameter of about 1.2 cm and a length of 2 cm, and the water content is adjusted to 8%.

[0070] B2, catalytic pyrolysis is carried out in a fixed bed reactor, nitrogen is introduced for protection, the oxygen content is maintained to be less than 1%, preferably between 0.5% and 1%, pyrolysis is carried out at 250℃ for 100 minutes, and the generated flue gas is introduced into a incinerator for cooperative heat treatment.

[0071] The dioxin toxicity equivalent of the treated fly ash is less than 10 ng TEQ / kg. According to the HJ 557-2010 standard leaching test, the lead leaching concentration is 0.9 mg / L, and other heavy metals are not detected. At the same time, a commercial catalyst (microspherical Fe2O3, particle size of 200-400 μm, specific surface area of 62 m 2 / g) is used, the oxygen concentration is controlled to be less than 0.1% according to the manufacturer's requirements, and the mixing ratio is 10:1. The dioxin toxicity equivalent of the treated fly ash is 20 ng TEQ / kg.

[0072] S3, two batches of water washing waste liquid are pretreated and then subjected to stepwise evaporation and quality-specific crystallization to recover inorganic salt components, and the steps are as follows:

[0073] C1, the total amount of water washing waste liquid is about 400 m 3 L, sodium carbonate is added to 0.6 g / L to precipitate calcium ions and heavy metals; the pH is adjusted to 4.0, Fenton reagent is used, the molar ratio of H2O2 to Fe 2+ is 2.5:1, and organic matter is oxidized; the pH is adjusted to 8.0, 45 mg / L of polyaluminum chloride and 3 mg / L of polyacrylamide are added, and flocculation and sedimentation are performed;

[0074] C2, the ultrafiltration membrane with a molecular weight cut-off of 500 Da is used to remove suspended solids and organic matter;

[0075] C3, MVR is used for quality-specific crystallization, in which potassium chloride crystallization is carried out at 58℃, about 1 ton of potassium chloride is obtained per day, and the purity is 90.8%; sodium chloride crystallization is carried out at 25℃, about 2.5 tons of sodium chloride crystals are precipitated per day, and the purity is 97.6%; the remaining mother liquor continues to precipitate sodium sulfate, about 1.0 tons of sodium sulfate crystals are obtained per day, and the purity is 85.2%.

[0076] Although the embodiments of the present application have been disclosed as above, they are not limited to the applications listed in the specification and embodiments, and can be fully applied to various fields suitable for the present application. For those skilled in the art, for those skilled in the art, various changes, modifications, replacements and modifications can be made to these embodiments without departing from the principles and spirits of the present application, and therefore the present application is not limited to specific details without departing from the general concept defined by the claims and equivalent ranges.

Claims

1. A method for the controlled and directed conversion of municipal solid waste incineration fly ash components, comprising: The method comprises the following steps: ​ S1, the waste incineration fly ash is first washed with water to remove soluble chlorides and heavy metals, and the obtained solid after solid-liquid separation is then subjected to forced leaching using reclaimed water or clean water to obtain washed fly ash and water washing waste liquid, and deeply separate the residual soluble chlorides and heavy metals, and remove the chlorine source for the re-synthesis of dioxins; S2, a core-shell structure Fe2O3 / Fe / C composite catalyst is prepared, mixed with the washed fly ash to form granules, and then subjected to catalytic pyrolysis in an inert or micro-oxygen environment to crack dioxin organic matter; S3, the water washing waste liquid is pretreated and then subjected to stepwise evaporation and quality-based crystallization to recover inorganic salt components, and the flue gas is introduced into an incinerator for cooperative thermal treatment; The preparation method of the Fe2O3 / Fe / C composite catalyst in step S2 comprises the following steps: N1, a suspension is prepared by dispersing biochar as a carrier in deionized water under ultrasonic dispersion; then, an iron salt solution is added dropwise under stirring; N2, then, a sodium hydroxide or ammonia water solution is slowly added dropwise, the dropping speed is controlled to be 1-3 ml / min, the pH of the reaction system is maintained at 8-10, and the reaction time is 2-4 hours; N3, after the reaction is completed, the system is allowed to stand for 6-12 hours, and then subjected to centrifugal separation, and washed with deionized water until the pH of the washing liquid is neutral; N4, the obtained product is dried at 80-120℃ for 12-24 hours, Fe2O3 is loaded on the biochar carrier through the co-precipitation method in the above steps, and the Fe loading amount is 10-20 wt%; N5. The dried product is selectively reduced at 280-320℃ for 2-3 hours under a H2 / N2 mixed atmosphere to form a core-shell Fe2O3 / Fe / C composite catalyst; the obtained Fe2O3 / Fe / C composite catalyst has a particle size of 200-500 μm and a specific surface area of ​​not less than 100 m². 2 / g.

2. The method of claim 1, wherein, The specific steps of the forced leaching of the fly ash in step S1 comprise: A1, the waste incineration fly ash is mixed with the condensate water obtained from the quality-based recovery of inorganic salts in step S3 and supplemented clean water according to a liquid-solid ratio of 2-5 L / kg, then stirred at 200-500 r / min at room temperature for 15-60 min, and then subjected to solid-liquid separation to obtain a solid and a first batch of water washing waste liquid; A2, the obtained solid is uniformly leached with clean water according to a liquid-solid ratio of 0.5-1 L / kg, and then subjected to solid-liquid separation again to obtain washed fly ash and a second batch of water washing waste liquid; the soluble chlorine content in the washed fly ash is less than 1%, and the chlorine source for the re-synthesis of dioxins is reduced.

3. The method of claim 1, wherein, The biochar in step N1 is ground to a particle size of less than 150 μm; the iron salt includes ferric chloride, ferric nitrate or ferric sulfate; the stirring speed is 300-500 rpm, and the stirring temperature is 60-80℃.

4. The method of claim 1, wherein, The mass ratio of C, Fe and OH in the biochar, iron salt and sodium hydroxide or ammonia water in step N2 is 1:0.8-1.5:1.2-2.0; the centrifugal separation speed in step N3 is 3000-5000 rpm, and the time is 5-10 min.

5. The method of claim 1, wherein, The specific steps of the catalytic pyrolysis of the washed fly ash mixed with the catalyst in step S2 comprise: B1, the washed fly ash and the catalyst are uniformly mixed according to a mass ratio of 5:1-15:1, and then shaped into spherical or cylindrical particles with a diameter of 1-3 cm; B2, the catalytic pyrolysis is carried out at a temperature of 250-350℃ for 30-120 min in a micro-oxygen atmosphere, and the flue gas generated by the pyrolysis is introduced into an incinerator for cooperative thermal treatment.

6. The method of claim 5, wherein, The micro-oxygen atmosphere in step B2 is nitrogen or argon with an oxygen concentration of less than or equal to 1%.

7. The method of claim 5, wherein, Step B2: Fe2O3 and Fe synergistically catalyze the reaction in a micro-oxygen atmosphere; Fe2O3 provides active oxygen atoms to promote the oxidative cleavage of dioxin molecules; Fe provides electrons and activates the C-Cl bond to promote dioxin dechlorination; and the carrier C provides π electrons to enhance the adsorption and activation of dioxin molecules.

8. The method of claim 1, wherein, The specific steps of recovering the inorganic salt components from the pretreated water washing waste liquid by section evaporation and quality crystallization in step S3 include: C1, add sodium sulfide or sodium carbonate to 0.3~1.2 g / L in the water washing waste liquid, precipitate heavy metals and calcium ions; then add Fenton reagent and adjust pH to 2~4, H2O2 and Fe 2+ molar ratio of 2:1~4:1, oxidize organic matter; then adjust pH to 7.0~9.0; then add or do not add 20~60 mg / L polyaluminum chloride and 1~8 mg / L polyacrylamide according to the impurity type of the water washing waste liquid, flocculate and precipitate, remove calcium ions and heavy metals; C2: The water washing waste liquid after impurity removal is treated by ultrafiltration and / or nanofiltration membranes to remove suspended solids and organic matter, and monovalent and multivalent ions are separated according to the inorganic salt component recovery requirements; C3: The treated water washing waste liquid is recovered by mechanical vapor recompression or multi-effect evaporation crystallizer at different temperatures to recover sodium sulfate, potassium chloride and sodium chloride, and the condensed water is recovered for use in the first-stage water washing and leaching step of fly ash.

9. The method of claim 1, wherein, The soluble chlorine content of the finally treated fly ash is less than 1%, and the dioxin toxicity equivalent is less than 20 ng TEQ / kg.

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