Harmless and resourceful treatment process for household garbage incineration fly ash

Abstract

The invention discloses a harmless and resourceful treatment process for household garbage incineration fly ash, and relates to the technical field of fly ash resourceful utilization. The process comprises the following steps: efficiently removing soluble chlorine salt in fly ash through a circulating thickening washing system to obtain dechlorinated fly ash and salt-containing wastewater; the method comprises the following steps: carrying out thickening circulation reuse on salt-containing wastewater, carrying out quality-divided crystallization evaporation on a thickening mother solution to recover salt, dehydrating a precipitate / filter-press solid, and then doping the dehydrated precipitate / filter-press solid into a dechlorinated fly ash system to realize closed-loop circulation; adding a chelating agent with a specific formula into the dechlorinated fly ash, and curing to stably cure heavy metals; the cured fly ash is subjected to heat treatment in a rotary kiln at the temperature of 600-900 DEG C for 10-30 min so as to decompose solid-phase dioxin and promote mineralization; after dioxin and semi-volatile organic compounds enter the flue gas pipeline, the dioxin and the semi-volatile organic compounds are quenched to 200 DEG C or below so as to inhibit regeneration. According to the method, the synergistic effects of heavy metal leaching standard reaching, dioxin control and fly ash resource utilization are achieved.

Description

Technical Field

[0001] This application relates to the field of fly ash resource utilization technology, and in particular to a process for the harmless and resource-based treatment of fly ash from municipal solid waste incineration. Background Technology

[0002] Fly ash from municipal solid waste incineration, or simply "fly ash," refers to the residue collected in the flue gas purification system (such as bag filters and scrubbing towers) of municipal solid waste incineration plants. It is not the slag discharged from the grate, but rather extremely fine particulate matter captured after being discharged with the flue gas. Fly ash is listed in the "National Hazardous Waste List," and its hazards mainly stem from two aspects: high levels of heavy metals and highly toxic persistent organic pollutants.

[0003] Currently, the main technologies for the harmless utilization of fly ash resources, including pretreatment and treatment, are: 1. Water washing and desalination + cement kiln co-processing of fly ash; 2. High-temperature fusion vitrification technology; 3. High-temperature sintering ceramsite technology; 4. In-situ low-carbon synergistic reduction and harmless treatment process for fly ash in the furnace (FAST process).

[0004] Water washing and desalination combined with cement kiln co-processing of fly ash involves separating chloride salts from fly ash through water washing to produce salt, and then co-processing the dechlorinated fly ash in a cement kiln at high temperature to produce cement clinker. However, the cement produced by this method has a much higher heavy metal content than ordinary cement, and there is a risk of heavy metal leaching when it is used as building material.

[0005] High-temperature molten vitrification technology involves adding flux to fly ash, then melting it at high temperatures (1300-1600℃) and rapidly cooling it to form a dense glassy body. This process inhibits the re-precipitation and crystallization of heavy metals. The glassy body is then crushed and screened to obtain aggregates of different particle sizes for use as road base aggregates and building fillers. This method requires high temperatures, consumes a lot of energy, and has high equipment investment and operating costs. Moreover, the melting of lead oxides at 1300-1500℃ results in a Pb leaching concentration of 3-4.4 mg / L, which is far greater than the 0.25 mg / L requirement of GB 16889-2008 "Standard for Pollution Control of Municipal Solid Waste Landfill".

[0006] High-temperature sintered ceramsite is produced by mixing fly ash with flux to form granules, heating and sintering at 850-1100℃, and then screening different particle sizes after natural cooling or air cooling for use in building materials or roadbed materials. However, most of the heavy metals and chlorides in the flue gas produced by this method are captured and collected into the concentrated ash. As hazardous waste, it is necessary to entrust professional third-party compliant disposal or further separate and recover heavy metals and salts, so the operating cost is relatively high.

[0007] The FAST process mainly includes three systems: a desalination and heavy metal removal system (decomposing pollutants, separating heavy metals and recovering industrial salts), a salt separation and recovery system (purifying industrial salts such as sodium chloride and potassium chloride), and a co-heat treatment system (reducing dioxin concentration through in-furnace low-carbon treatment to achieve harmless treatment of fly ash). In this method, the salt separation and recovery system of FAST technology discharges sludge containing heavy metals and miscellaneous salts (5-8%), which, as hazardous waste, requires the expenditure of entrusting a professional third party for compliant disposal. Summary of the Invention

[0008] This application provides a process for the harmless and resource-based treatment of fly ash from municipal solid waste incineration, in order to solve the problems of high energy consumption, high cost, and high concentration of heavy metal leaching in existing technologies.

[0009] Firstly, this application provides a process for the harmless and resource-based treatment of fly ash from municipal solid waste incineration, which adopts the following technical solution: A process for the harmless and resource-based treatment of fly ash from municipal solid waste incineration includes the following steps: S1. Circulating thickening and washing desalination: A circulating thickening and washing system is used to wash the fly ash with water and separate the solid and liquid to obtain dechlorinated fly ash and saline wastewater; the saline wastewater is thickened and recycled, and the thickening mother liquor is subjected to fractional crystallization and evaporation to recover salt; S2. Chelation stabilization: Add chelating agent to dechlorinated fly ash, stir evenly, and let stand for 3-7 days to allow heavy metals to fully react with chelating agent and obtain chelated fly ash sludge. The chelating agent comprises the following components in parts by weight: 20-40 parts phosphate, 15-25 parts silicate, 20-30 parts bentonite, 20-30 parts kaolin, and 5-15 parts calcium oxide; wherein the phosphate comprises NaH2PO4 and / or Ca(H2PO4)2, and the silicate comprises Na2SiO3 and / or CaSiO3; S3. Medium-high temperature reaction: Heat the fly ash sludge to 600-900℃ and react it in an atmosphere with an oxygen volume concentration of 2-6% for 10-30 minutes to obtain stabilized fly ash products. S4. Flue gas rapid cooling and purification: The flue gas generated during the heating process in step S3 is rapidly cooled to a temperature below 200℃ to inhibit the regeneration of dioxins; the rapidly cooled flue gas is then purified through heat exchange to recover waste heat, bag filter dust removal and wet desulfurization processes before being discharged in compliance with standards.

[0010] By adopting the above technical solution, a circulating concentration washing system is used to preferentially transfer soluble salts such as Cl- to the circulating mother liquor. Salt recovery and low evaporation operation are achieved through closed-loop circulation of the mother liquor and discharge-concentration-separation crystallization. Thus, a high chlorine removal rate (≥98%) can still be obtained under the condition of a water-ash ratio of 1:1. Before the discharge concentrate enters the evaporation crystallization, it can be pretreated by sedimentation / filtration. The resulting solid phase is then filtered and returned to the system, reducing the burden of external transportation and disposal.

[0011] Adding a chelating agent to dechlorinated fly ash, followed by thorough mixing and settling, achieves significant and long-term stability in the fixation of heavy metals. The chelating agent used in this process also accelerates the catalytic destruction of dioxins, shortening the oxidation combustion time. This avoids the decomposition and release of heavy metals from the stabilized heavy metal products caused by prolonged high-temperature oxidation and sintering. The chelating agent also contains flux and binder, exhibiting a certain sintering effect during oxidation combustion, resulting in a dense material that can be directly incorporated into the resource recovery process.

[0012] The chelated fly ash sludge is heated to 600-900℃, causing dioxins in the fly ash to decompose into smaller, non-toxic fragments of the chelating agent and promoting the mineralization and consolidation of the inorganic phase. During this process, the chelating agent system can stabilize and solidify heavy metals and inhibit their reactivation / reoxidation reactions under an oxygen-containing atmosphere, thus eliminating the need to construct an oxygen-deficient environment to obtain stabilized products. In some embodiments, the oxygen volume fraction can be controlled at 2-6% to further optimize the valence stability of elements such as chromium. This rapid cooling treatment effectively prevents flue gas from remaining in the dioxin regeneration sensitive temperature range of 250-400℃, thereby inhibiting the resynthesis of dioxins on the fly ash surface and under metal catalytic conditions.

[0013] The process described in this application has four major technical advantages: 1. It does not generate secondary pollution risks or hazardous waste byproducts (such as heavy metal sludge and miscellaneous salts or concentrated ash containing heavy metals and chlorides), and does not require the expenditure of entrusting professional third-party compliant disposal or further separation and recycling of heavy metals and salts, thus reducing costs. 2. Avoid energy consumption from combustion alone. This avoids the high energy consumption associated with high-temperature melting; it can be achieved by modifying the waste heat from the tail section or the gas in the secondary combustion chamber, eliminating the need for a new melting device. 3. It has strong adaptability and can handle multiple types of fly ash, including fly ash from municipal solid waste incineration, fly ash from hazardous waste, and sludge drying residue; it also has good adaptability to fly ash with high chlorine, high heavy metal, and high water content. 4. Simple process, low investment cost, and short process: water washing → chelation → curing → pyrolysis → resource recovery; few equipment required: only water washing system, stirring curing system, and low temperature pyrolysis device are needed; small investment: about 1 / 3 of the high temperature melting line, payback period of 2-3 years, can be modularly added to the waste heat zone of the tail section of the existing incineration plant without affecting the operation of the main system.

[0014] The specific steps of S1 are as follows: (1) Wetting and premixing: Add the fly ash to be treated to the water washing mixing tank, introduce the circulating washing liquid from the mother liquor tank to wet and premix the fly ash, stir, so that the particles are fully dispersed and the soluble salts migrate to the liquid phase. (2) Circulating concentrated water washing: Under continuous circulating stirring conditions, add recycled condensate and / or fresh water according to the dry weight of fly ash, so that the mass ratio of the added water to the fly ash is 1:1, and stir and wash. (3) Solid-liquid separation: The washed slurry is subjected to solid-liquid separation to obtain dechlorinated fly ash filter cake and saline wastewater; the dechlorinated fly ash is dehydrated to a moisture content of 18-22%, and the overall chloride ion removal rate is ≥98%; (4) Closed-loop circulation and concentration discharge of mother liquor: The saline wastewater enters the mother liquor tank and is reused in step (2) to reduce the amount of fresh water replenishment; in order to control the accumulation of salt, a portion of the saline wastewater is introduced into the concentration crystallization unit as the concentration discharge liquid, and the amount introduced is 20-40% of the amount of circulating water washing replenishment water; (5) Concentration and fractional crystallization: The concentrated liquid is concentrated by evaporation to obtain concentrated brine and condensate. The condensate is recycled to step (2) as supplementary water. The concentrated brine is fractionally crystallized and solid-liquid separation is performed to obtain crystalline salt product and mother liquor. The mother liquor is returned to the evaporation concentration unit or mother liquor tank for continued circulation.

[0015] By adopting the above technical solution: the circulating concentrated water washing achieves a high chloride ion removal rate (≥98%) under low water replenishment ratio conditions. The washing liquid is circulated in a closed loop and the salt is recovered through discharge-concentration-separation crystallization, which reduces the liquid volume entering the evaporation crystallization unit by about 2 / 3 compared with a single water washing. The sedimentation / pressure filter solid phase generated during the water washing process can be recycled back into the system (recycled to step S2 or enters step S3 together with dechlorinated fly ash) to achieve by-product reduction and the solid products meet the requirements of building material resource utilization.

[0016] Preferably, in step S2, the amount of chelating agent used is 8-15 wt% of the dry weight of the dechlorinated fly ash.

[0017] By adopting the above technical solution, the amount of chelating agent used is limited, thus ensuring the effectiveness of the chelating agent.

[0018] It should be noted that "dry weight of dechlorination fly ash" refers to the mass of dechlorination fly ash when dried to constant weight.

[0019] Preferably, in step S2, the amount of chelating agent used is 10-12 wt% of the dry weight of the dechlorinated fly ash.

[0020] Preferably, in step S3, the heating conditions are as follows: heating to 150-200℃ at a heating rate of 5-10℃ / min, continuing to heat to 450-500℃ at a heating rate of 10-20℃ / min, and continuing to heat to 600-900℃ at a heating rate of 5-10℃ / min.

[0021] By adopting the above technical solution, the temperature is raised to 150-200℃ at a heating rate of 5-10℃ / min. This process removes the moisture from the chelated fly ash sludge. The temperature is then raised to 450-500℃ at a rate of 10-20℃ / min. By increasing the heating rate, the residence time in the 200-500℃ range is shortened, thereby reducing the regeneration of dioxins.

[0022] Preferably, in step S4, the rapid cooling conditions are as follows: Rapidly cool to below 200℃ under a cooling rate ≥100℃ / s.

[0023] By adopting the above technical solution, rapid cooling is achieved, reducing the regeneration of dioxins.

[0024] Secondly, this application provides a fly ash product obtained by using the above-mentioned harmless and resource-based treatment process for fly ash from municipal solid waste incineration.

[0025] Thirdly, this application provides an application of the aforementioned fly ash product in non-fired bricks, ceramsite, roadbed materials, or landscape stones.

[0026] In summary, the present invention has at least one of the following beneficial technical effects: 1. This application employs a synergistic approach of "specific chelating agent formulation + curing to form a gel / precipitate network + specific heat treatment window + rapid cooling rate": the chelating agent is a specific ratio of phosphate / silicate / bentonite / kaolin / CaO; curing for 3-7 days promotes the full formation of heavy metal precipitation and gel network; then heat treatment in a rotary kiln at 600-900℃ for 10-30 min decomposes solid-phase dioxins and promotes mineralization and consolidation; dioxins and semi-volatile organic compounds generated during heating are rapidly cooled to <200℃ at a cooling rate ≥100℃ / s after entering the flue gas and are treated in conjunction with subsequent flue gas purification units; this synergistic approach can achieve heavy metal leaching compliance while ensuring solid-phase / flue gas dioxins reach ND, and also improve Cl... - The removal rate is ≥98%, and it can avoid failures caused by factors such as "no rapid cooling / no chelation / insufficient time".

[0027] 2. This application utilizes a chelating agent to react with heavy metal ions at room temperature, causing the heavy metal ions to precipitate. At high temperature, lattice rearrangement occurs. The chelating agent reacts with metal oxides in fly ash to generate spinel-type or silicate-type minerals. At the same time, silicates and fly ash will undergo mineralization, forming a coexistence system of glass phase + crystal phase, which helps to encapsulate and imprison metal compounds, thereby reducing the leaching toxicity of heavy metals in fly ash and achieving harmless treatment. 3. The process of this application is simple and the overall system management is easy. The equipment investment, operating costs and energy consumption are low. It can be completed by modifying the waste heat of the tail section of the existing incineration plant or the gas of the secondary combustion chamber. There is no need to build a new melting device, which solves the problem of high energy consumption of high temperature melting. Detailed Implementation

[0028] The present application will be further described in detail below with reference to the embodiments and comparative examples. The raw materials involved in the present application can all be obtained commercially.

[0029] Fly ash raw material source: secondary dust collectors or fly ash collection systems in municipal solid waste incineration plants. Specific components are shown in the table below:

[0030] Heavy metal analysis is as follows:

[0031] Example Example 1

[0032] A process for the harmless and resource-based treatment of fly ash from municipal solid waste incineration includes the following steps: S1. Water washing to remove salt: (1) Circulating concentrated water washing: Take 200 kg of fly ash raw material and add it to the water washing mixing tank. Introduce circulating mother liquor to wet and premix the fly ash for 3 min. Add 200 kg of recycled condensate or fresh water as makeup water under stirring at 200 rpm, so that the mass ratio of makeup water to fly ash is 1:1. Continue washing for 20 min. (2) Solid-liquid separation: The washing slurry is filtered by pressure to obtain dechlorination fly ash filter cake and saline wastewater; the dechlorination fly ash is dehydrated to a moisture content of 20%, and the overall chloride ion removal rate is ≥98%; (3) Closed-loop circulation of mother liquor: saline wastewater enters the mother liquor tank and is reused as the circulating washing liquid for the next batch of water washing steps to reduce the amount of fresh water replenishment; (4) Pretreatment and re-mixing of concentrated wastewater: In order to control the accumulation of salt, a portion of the saline wastewater is introduced into the concentration crystallization unit as concentrated liquid (the amount introduced is 1 / 3 of the amount of circulating water washing makeup water). The concentrated liquid enters the sedimentation unit to remove suspended solids. The solid phase obtained from sedimentation is dewatered by pressure filtration and then re-mixed into the dechlorination fly ash system (re-mixed into step S2 or entered into step S3 together with dechlorination fly ash). (5) Concentration and fractional crystallization: The pretreated concentrated liquid enters the MVR evaporator for concentration to obtain concentrated brine and condensate. The evaporated condensate is reused for water washing as makeup water. The concentrated brine enters the fractional crystallization unit, where it is crystallized in stages and the solid and liquid are separated to obtain crystalline salt products and mother liquor. The mother liquor is returned to the evaporator or mother liquor tank for continued circulation. S2, Chelation Stabilization: The dechlorinated fly ash obtained in step S1 and the chelating agent are mixed at a dry weight ratio of 10:1 for the dechlorinated fly ash to the chelating agent. After stirring evenly, the mixture is allowed to stand and cured for 5 days at 30°C, 55% humidity and pH 9 to obtain chelated and cured fly ash sludge. S3, Medium and high temperature reaction: The fly ash sludge after chelation and curing in step S2 is heated to 850℃ at a heating rate of 10℃ / min and reacted in an atmosphere with an oxygen volume concentration of 4% for 25min to obtain stabilized fly ash product. S4. Flue gas rapid cooling and purification: During the heating and heat preservation process in step S3, dioxins and semi-volatile organic compounds can volatilize / be carried into the flue gas pipeline with the flue gas; the flue gas is cooled to 180°C at a cooling rate of 110°C / s to avoid the sensitive regeneration temperature range of 250-400°C, and the flue gas after rapid cooling is purified by heat exchange to recover waste heat, bag filter dust removal and wet desulfurization process to meet emission standards, or in other embodiments, the flue gas can be directly connected to the flue gas purification and treatment system of the waste incineration power plant.

[0033] In step S2, the chelating agent is obtained by conventionally mixing phosphate, silicate, bentonite, kaolin and calcium oxide in a weight ratio of 30:20:25:25:10. The phosphate is obtained by mixing NaH2PO4 and Ca(H2PO4)2 in a weight ratio of 1:1, and the silicate is obtained by mixing Na2SiO3 and CaSiO3 in a weight ratio of 1:1. Example 2

[0034] A process for the harmless and resource-based treatment of fly ash from municipal solid waste incineration includes the following steps: S1. Water washing to remove salt: (1) Circulating concentrated water washing: Take 200 kg of fly ash raw material and add it to the water washing mixing tank. Introduce circulating mother liquor to wet and premix the fly ash for 3 min. Add 200 kg of recycled condensate or fresh water as makeup water under stirring at 200 rpm, so that the mass ratio of makeup water to fly ash is 1:1. Continue washing for 15 min. (2) Solid-liquid separation: The washing slurry is filtered by pressure to obtain dechlorination fly ash filter cake and saline wastewater; the dechlorination fly ash is dehydrated to a moisture content of 18%, and the overall chloride ion removal rate is ≥98%; (3) Closed-loop circulation of mother liquor: saline wastewater enters the mother liquor tank and is reused as the circulating washing liquid for the next batch of water washing steps to reduce the amount of fresh water replenishment; (4) Pretreatment and re-mixing of concentrated wastewater: In order to control the accumulation of salt, a portion of the saline wastewater is introduced into the concentration and crystallization unit as concentrated liquid (the amount introduced is 20% of the amount of circulating water washing makeup water). The concentrated liquid enters the sedimentation unit to remove suspended solids. The solid phase obtained from sedimentation is dewatered by pressure filtration and then re-mixed into the dechlorination fly ash system (re-mixed into step S2 or entered into step S3 together with dechlorination fly ash). (5) Concentration and fractional crystallization: The pretreated concentrated liquid enters the MVR evaporator for concentration to obtain concentrated brine and condensate. The evaporated condensate is reused for water washing as makeup water. The concentrated brine enters the fractional crystallization unit, where it is crystallized in stages and the solid and liquid are separated to obtain crystalline salt products and mother liquor. The mother liquor is returned to the evaporator or mother liquor tank for continued circulation. S2, Chelation Stabilization: The dechlorinated fly ash obtained in step S1 and the chelating agent are mixed at a dry weight ratio of 10:1 for the dechlorinated fly ash to the chelating agent. After stirring evenly, the mixture is allowed to stand and cured for 3 days at 20℃, 55% humidity and pH 10 to obtain chelated and cured fly ash sludge. S3, Medium and high temperature reaction: The fly ash sludge after chelation and curing in step S2 is heated to 600℃ at a heating rate of 5℃ / min and reacted in an atmosphere with an oxygen volume concentration of 6% for 10min to obtain stabilized fly ash product. S4. Flue gas rapid cooling and purification: During the heating and heat preservation process in step S3, dioxins and semi-volatile organic compounds can volatilize / be carried into the flue gas pipeline with the flue gas; the flue gas is cooled to 190°C at a cooling rate of 120°C / s to avoid the sensitive regeneration temperature range of 250-400°C, and the flue gas after rapid cooling is purified by heat exchange to recover waste heat, bag filter dust removal and wet desulfurization process to meet emission standards, or in other embodiments, the flue gas can be directly connected to the flue gas purification and treatment system of the waste incineration power plant.

[0035] In step S2, the chelating agent is obtained by conventionally mixing phosphate NaH2PO4, silicate Na2SiO3, bentonite, kaolin, and calcium oxide in a weight ratio of 30:20:25:25:10. Example 3

[0036] A process for the harmless and resource-based treatment of fly ash from municipal solid waste incineration includes the following steps: S1. Water washing to remove salt: (1) Circulating concentrated water washing: Take 200 kg of fly ash raw material and add it to the water washing mixing tank. Introduce circulating mother liquor to wet and premix the fly ash for 3 min. Add 200 kg of recycled condensate or fresh water as makeup water under stirring at 200 rpm, so that the mass ratio of makeup water to fly ash is 1:1. Continue washing for 25 min. (2) Solid-liquid separation: The washing slurry is filtered by pressure to obtain dechlorination fly ash filter cake and saline wastewater; the dechlorination fly ash is dewatered to a moisture content of 22%, and the overall chloride ion removal rate is ≥98%; (3) Closed-loop circulation of mother liquor: The saline wastewater enters the mother liquor tank and is reused as the circulating washing liquid for the next batch of water washing steps to reduce the amount of fresh water replenishment; (4) Pretreatment and re-mixing of concentrated wastewater: In order to control salt accumulation, a portion of the saline wastewater is introduced into the concentration crystallization unit as concentrated liquid (the amount introduced is 40% of the amount of circulating water washing makeup water). The concentrated liquid enters the sedimentation unit to remove suspended solids. The solid phase obtained from sedimentation is dewatered by pressure filtration and then re-mixed into the dechlorination fly ash system (re-mixed into step S2 or entered into step S3 together with dechlorination fly ash). (5) Concentration and fractional crystallization: The pretreated concentrated liquid enters the MVR evaporator for concentration to obtain concentrated brine and condensate. The evaporated condensate is reused for water washing as makeup water. The concentrated brine enters the fractional crystallization unit, where it is crystallized in stages and the solid and liquid are separated to obtain crystalline salt products and mother liquor. The mother liquor is returned to the evaporator or mother liquor tank for continued circulation. S2, Chelation Stabilization: The dechlorinated fly ash obtained in step S1 and the chelating agent are mixed at a dry weight ratio of 10:1 for the dechlorinated fly ash to the chelating agent. After stirring evenly, the mixture is allowed to stand and cured for 7 days at 35°C, 55% humidity and pH 11 to obtain chelated and cured fly ash sludge. S3. High-temperature reaction: The fly ash sludge after chelation and curing in step S2 is heated to 900℃ at a heating rate of 15℃ / min and reacted in an atmosphere with an oxygen volume concentration of 6% for 10min to obtain the stabilized fly ash product.

[0037] S4. Flue gas rapid cooling and purification: During the heating and heat preservation process in step S3, dioxins and semi-volatile organic compounds can be volatilized / entrained into the flue gas pipeline with the flue gas; the flue gas is cooled at a rate of 115℃ / s to 185℃ to avoid the sensitive temperature zone of 250-400℃ for regeneration, and the flue gas after rapid cooling is purified by heat exchange to recover waste heat, bag filter dust removal and wet desulfurization process to meet emission standards, or in other embodiments, the flue gas can be directly connected to the flue gas purification and treatment system of the waste incineration power plant.

[0038] In step S2, the chelating agent is obtained by conventionally mixing phosphate Ca(H2PO4)2, silicate CaSiO3, bentonite, kaolin, and calcium oxide in a weight ratio of 30:20:25:25:10.

[0039] Examples 4-5 Examples 4-5 are based on Example 1, the difference being that the proportions of each component in the chelating agent component are different in step S2: In Example 4, the weight ratio of phosphate, silicate, bentonite, kaolin, and calcium oxide was 20:15:30:20:5.

[0040] In Example 5, the weight ratio of phosphate, silicate, bentonite, kaolin, and calcium oxide was 40:25:20:30:15.

[0041] Examples 6-8 Examples 6-8 are based on Example 1, the difference being that the proportion of chelating agent added in step S2 is different. In Example 6, the dry weight ratio of dechlorinated fly ash to chelating agent in step S2 is 100:8.

[0042] In Example 7, the dry weight ratio of dechlorinated fly ash to chelating agent in step S2 is 100:12.

[0043] In Example 8, the dry weight ratio of dechlorinated fly ash to chelating agent in step S2 is 100:15.

[0044] Examples 9-11 Examples 9-11 are based on Example 1, except that the heating rate and intermediate temperature in step S3 are different; the other steps remain the same as in Example 1. Specifically, In Example 9, the heating process in step S3 is adjusted to heat to 200°C at a heating rate of 8°C / min, to 500°C at a heating rate of 15°C / min, and then to 850°C at a heating rate of 8°C / min.

[0045] In Example 10, the heating process in step S3 is adjusted to heat to 150°C at a heating rate of 10°C / min, to 450°C at a heating rate of 20°C / min, and then to 600°C at a heating rate of 10°C / min.

[0046] In Example 11, the heating process in step S3 is adjusted to heat to 150°C at a heating rate of 5°C / min, to 450°C at a heating rate of 10°C / min, and then to 900°C at a heating rate of 5°C / min.

[0047] Comparative Example 1

[0048] Comparative Example 1 is based on Example 1, except that the proportions of the components in the chelating agent are different, specifically: The weight ratio of phosphate, silicate, bentonite, kaolin, and calcium oxide is 25:0:10:15:50.

[0049] Comparative Example 2

[0050] Comparative Example 2 is based on Example 1, except that the dry weight ratio of dechlorinated fly ash to chelating agent is 100:5.

[0051] Comparative Example 3

[0052] Comparative Example 3 is based on Example 1, except that the dry weight ratio of dechlorinated fly ash to chelating agent is 100:20.

[0053] Comparative Example 4

[0054] Comparative Example 4 is based on Example 1, except that in step S2, the chelating agent is mixed with dechlorinated fly ash and left to stand for 1 day.

[0055] Comparative Example 5

[0056] Comparative Example 5 is based on Example 1, except that in step S3, the reaction time after heating the fly ash sludge obtained in step S2 to 850°C is 5 minutes, and the atmosphere is a nitrogen atmosphere.

[0057] Comparative Example 6

[0058] A process for treating fly ash from municipal solid waste incineration differs from Example 1 in that it does not include step S2, but instead treats the dechlorinated fly ash obtained in step S1 in step S3.

[0059] Based on the dosage of the reagent in Example 1, the resulting precipitated dry solids are approximately 32 kg / batch. With the sludge moisture content after filtration being 80%, the wet sludge yield is approximately 0.16 t / batch, which is equivalent to approximately 0.8 t / t fly ash (wet basis).

[0060] Comparative Example 7

[0061] A process for treating fly ash from municipal solid waste incineration differs from Example 1 in that it does not include step S3.

[0062] Detection methods

[0063] Heavy metal leaching tests were conducted on the stabilized fly ash products obtained from the examples and comparative treatments. The experimental methods were in accordance with GB 5085.3-2007 "Identification Standard for Hazardous Waste: Leaching Toxicity Identification". The test results are shown in Table 1 below.

[0064] 1. Heavy metal leaching test shall be conducted in accordance with GB 5085.3-2007 "Identification Standard for Hazardous Waste - Leaching Toxicity Identification".

[0065] 2. The determination of water-soluble chloride ion content shall be carried out in accordance with HJ / T 84-2001 "Determination of Inorganic Anions in Water - Ion Chromatography Method": Sample preparation: Take 5g of stabilized fly ash product, add 100mL of deionized water, shake at 200rpm for 60min, allow to stand and precipitate, filter, and collect the supernatant for later use; Determination conditions: Chromatographic column: anion exchange column; Mobile phase: carbonate / bicarbonate system; Flow rate: 1.0 mL / min; Detector: conductivity detector; Quantitative method: external standard method; Calculation results: The water-soluble chlorine content in fly ash is calculated using the following formula: Cl - (wt%) = mC × V × 100%. Where C is the Cl in the extract. - Concentration (mg / L), V is the volume of the extract (L), and m is the mass of the fly ash sample (mg).

[0066] 3. Dioxin detection: The isotope dilution high-resolution gas chromatography-high-resolution mass spectrometry method specified in HJ 77.3-2008 was used for detection, and the results are expressed as ng TEQ / g (dry basis).

[0067] 4. Detection of dioxins in flue gas generated after medium and high temperature treatment: The detection shall be carried out in accordance with HJ 77.2-2008 "Determination of dioxins in ambient air and exhaust gas by isotope dilution high-resolution gas chromatography and high-resolution mass spectrometry".

[0068] Table 1 Concentration of pollutants in fly ash product leachate

[0069] Note: ND means not detected; the detection limit for dioxins in solid phase is 0.1 ng TEQ / g (dry basis); the detection limit for dioxins in flue gas is 0.1 ng TEQ / m³ (standard state, dry basis, converted to 11% O2).

[0070] Referring to Table 1, the treatment processes in Examples 1-3 employ specific chelation and specific processes to achieve low heavy metal leaching concentrations, high chlorine removal rates, and no dioxin regeneration in the stabilized fly ash products obtained from the treatment. In contrast, Comparative Example 5 showed pyrolysis failure, with almost no decomposition of solid-phase dioxins, resulting in a dioxin content similar to that of untreated fly ash. Simultaneously, primary dioxins could volatilize or be entrained into the flue gas duct during the heating process. Therefore, in addition to requiring sufficient temperature and residence time within the dioxin decomposition temperature zone, this application employs a combination of "rapid cooling (≥100℃ / s cooling to <200℃) + heat exchange + bag filter + wet desulfurization (or connection to the existing flue gas purification and treatment system of the incinerator)" to simultaneously control gaseous dioxins and associated heavy metals and acidic gases, avoiding insufficient control of volatile dioxins due to rapid cooling alone.

[0071] Comparative Example 6, which did not use a chelating agent, showed a high concentration of heavy metal leaching, indicating that chlorine must first be removed and heavy metals stabilized through S1-S2 before heat treatment in S3 can efficiently degrade solid-phase dioxins. At the same time, rapid cooling in S4 must follow closely and be combined with subsequent purification units to ensure that gaseous pollutants are not regenerated or re-adsorbed back into the solid phase in the sensitive temperature range of 250-400℃. All three steps are indispensable.

[0072] Comparative Example 7 lacks quenching. Since most of the native dioxins are destroyed during the S3 pyrolysis stage, the lack of S4 quenching causes the high-temperature flue gas to regenerate during the subsequent slow cooling process (especially in the 250-400°C range). This results in a small amount of dioxins being regenerated on the surface of the fly ash particles and partially adsorbed by the fly ash, leading to a higher content than in Example 1.

[0073] Based on the analysis of the test results of Examples 1, 6-8 and Comparative Examples 2-3, the dosage of chelating agent added in step S2 is 8-15%. The heavy metal concentration of the leachate of the obtained fly ash product meets the national standard. Too low or too high dosage of chelating agent will affect the leaching toxicity of fly ash product. When the dosage of chelating agent is 10-12%, the heavy metal content of the leachate of the fly ash product is lower.

[0074] Specifically, based on the analysis of the test results of Examples 1 and 9-11, by controlling the heating conditions in step S3, the fly ash product obtained has a leachate concentration that meets national standards.

[0075] Specifically, based on the test results of Example 1 and Comparative Example 5, the fly ash product obtained by reacting at medium and high temperatures under a 2-6% oxygen atmosphere for 10-30 minutes had a heavy metal concentration in its leachate that met national standards. However, in Comparative Example 5, which used a nitrogen atmosphere for 5 minutes, the heavy metal concentration increased.

[0076] The fly ash product after high-temperature oxidation has a grayish-white porous structure, a pH of 9-11, and a heavy metal leaching concentration below the limit. It can be directly used as raw material for non-fired bricks, ceramsite, roadbed material, or landscape stone.

[0077] The embodiments described herein are preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Therefore, all equivalent changes made in accordance with the structure, shape, and principle of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A process for the harmless and resource-based treatment of fly ash from municipal solid waste incineration, characterized in that, Includes the following steps: S1. Circulating thickening and washing desalination: A circulating thickening and washing system is used to wash the fly ash with water and separate the solid and liquid to obtain dechlorinated fly ash and saline wastewater; the saline wastewater is thickened and recycled, and the thickening mother liquor is subjected to fractional crystallization and evaporation to recover salt; S2. Chelation stabilization: Add chelating agent to dechlorinated fly ash, stir evenly, and let stand for 3-7 days to allow heavy metals to fully react with chelating agent to obtain chelated fly ash sludge. The chelating agent comprises the following components in parts by weight: 20-40 parts phosphate, 15-25 parts silicate, 20-30 parts bentonite, 20-30 parts kaolin, and 5-15 parts calcium oxide; wherein the phosphate comprises NaH2PO4 and / or Ca(H2PO4)2, and the silicate comprises Na2SiO3 and / or CaSiO3; S3. Medium-high temperature reaction: Heat the fly ash sludge to 600-900℃ and react it in an atmosphere with an oxygen volume concentration of 2-6% for 10-30 minutes to obtain stabilized fly ash products. S4. Flue gas rapid cooling and purification: The flue gas generated during the heating process in step S3 is rapidly cooled to a temperature below 200℃ to inhibit the regeneration of dioxins; the rapidly cooled flue gas is then purified through heat exchange to recover waste heat, bag filter dust removal and wet desulfurization processes before being discharged in compliance with standards.

2. The process for harmless and resource-based treatment of fly ash from municipal solid waste incineration according to claim 1, characterized in that, The specific steps of S1 are as follows: (1) Wetting and premixing: Add the fly ash to be treated to the water washing mixing tank, introduce the circulating washing liquid from the mother liquor tank to wet and premix the fly ash, stir, so that the particles are fully dispersed and the soluble salts migrate to the liquid phase. (2) Circulating concentrated water washing: Under continuous circulating stirring conditions, add recycled condensate and / or fresh water according to the dry weight of fly ash, so that the mass ratio of the added water to the fly ash is 1:1, and stir and wash. (3) Solid-liquid separation: The washed slurry is subjected to solid-liquid separation to obtain dechlorinated fly ash filter cake and saline wastewater; the dechlorinated fly ash is dehydrated to a moisture content of 18-22%, and the overall chloride ion removal rate is ≥98%; (4) Closed-loop circulation and concentration discharge of mother liquor: The saline wastewater enters the mother liquor tank and is reused in step (2) to reduce the amount of fresh water replenishment; in order to control the accumulation of salt, a portion of the saline wastewater is introduced into the concentration crystallization unit as the concentration discharge liquid, and the amount introduced is 20-40% of the amount of circulating water washing replenishment water; (5) Concentration and fractional crystallization: The concentrated liquid is evaporated and concentrated to obtain concentrated brine and condensate. The condensate is recycled to step (2) as supplementary water. The concentrated brine is fractionally crystallized and solid-liquid separation is performed to obtain crystalline salt product and mother liquor. The mother liquor is returned to the evaporation and concentration unit or mother liquor tank for continued circulation.

3. The process for harmless and resource-based treatment of fly ash from municipal solid waste incineration according to claim 1, characterized in that, In step S2, the amount of chelating agent used is 8-15 wt% of the dry weight of the dechlorinated fly ash.

4. The process for harmless and resource-based treatment of fly ash from municipal solid waste incineration according to claim 3, characterized in that, In step S2, the amount of chelating agent used is 10-12 wt% of the dry weight of the dechlorinated fly ash.

5. The process for harmless and resource-based treatment of fly ash from municipal solid waste incineration according to claim 1, characterized in that, In step S3, the heating conditions are as follows: Heat to 150-200℃ at a rate of 5-10℃ / min. Continue heating at a rate of 10-20℃ / min to 450-500℃. Continue heating at a rate of 5-10℃ / min to 600-900℃.

6. The process for harmless and resource-based treatment of fly ash from municipal solid waste incineration according to claim 1, characterized in that, In step S4, the rapid cooling conditions are: rapid cooling to below 200°C at a cooling rate ≥100°C / s.

7. A fly ash product obtained by the harmless and resource-based treatment process of municipal solid waste incineration fly ash as described in any one of claims 1-6.

8. The application of the fly ash product as described in claim 7 in non-fired bricks, ceramsite, roadbed materials, or landscape stones.

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