Treatment method for household garbage incineration fly ash

Abstract

A treatment method for household garbage incineration fly ash, comprising the steps: S1, immersing raw ash in water to be separated to obtain a leachate and a sediment; S2, curing and granulating the sediment; S3, putting granulated particles into a household garbage incinerator for heat treatment; and S4, evaporating the leachate for salt separation. According to the treatment method, large-scale reduction of pollutants is achieved, carbon emission reduction and energy saving are achieved by means of collaborative heat treatment in a plant, after treatment, fly ash products are fully absorbed or utilized without the need for landfilling, and after detoxification, products serving as resources are stable and harmless.

Description

A method for treating fly ash from incineration of domestic waste Technical Field

[0001] The present invention relates to the technical field of fly ash treatment in environmental management, and in particular to a method for treating fly ash from the incineration of domestic waste. Background Art

[0002] In recent years, my country's waste incineration industry has grown explosively, with the amount of domestic waste incineration reaching 180 million tons / year. The treatment of the generated fly ash has become increasingly important. As of August 27, 2020, the "Technical Specifications for Pollution Control of Domestic Waste Incineration Fly Ash (Trial)" (HJ 1134-2020) standard was released.

[0003] Fly ash from municipal solid waste incineration appears as a loose, gray, powdery solid, an irregular mass composed of particulate matter, reaction products, unreacted products, and condensed products. Its composition reveals high concentrations of water-leaching salts and several hazardous heavy metals, including Cd, Pb, Zn, and Cr. Furthermore, organic pollutants such as dioxins and furans are also concentrated in the fly ash carrier. The presence of these toxic and hazardous pollutants poses potential ecological and health risks to groundwater, the surrounding ecosystem, and human health.

[0004] The current incineration fly ash treatment processes mainly include: cement solidification, water washing and recycling, fly ash melting and fly ash stabilization. Comparing the advantages and disadvantages of the four methods, we get Table 1:

[0005] Table 1: Comparison of the advantages and disadvantages of common fly ash treatment methods

[0006] As can be seen from Table 1, among the four fly ash treatment methods, the cement solidification method has the defects of high volume expansion ratio and secondary risk; water washing resource utilization has bottlenecks such as the need for supporting cement plants and difficult wastewater treatment; fly ash melting treatment is widely used abroad, especially in Japan, but the treatment cost is high and the economy is poor; fly ash stabilization treatment is the current mainstream treatment process, but it does not treat organic pollutants such as dioxins, and cannot achieve resource utilization of fly ash.

[0007] Based on the above-mentioned defects of the existing fly ash treatment methods, in order to comply with the national trend of carbon reduction, a new fly ash treatment method is urgently needed to achieve the harmlessness, economy, resource utilization and reduction of fly ash. Summary of the Invention

[0008] The purpose of the present invention is to provide a method for treating fly ash from the incineration of domestic waste to solve the problems raised in the above background technology.

[0009] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0010] A method for treating fly ash from the incineration of domestic waste is shown in FIG1 as a flow chart of the fly ash treatment method, which includes the following steps:

[0011] S1. Immersing the raw ash in water to separate the leachate and sediment;

[0012] S2. solidifying and granulating the sediment;

[0013] S3. The granulation is placed in a domestic waste incinerator for heat treatment;

[0014] S4. Evaporating the leachate to separate the salt.

[0015] In steps S1 to S4 above, unlike conventional processes, this treatment method utilizes a coordinated thermal treatment of fly ash within a municipal solid waste incineration plant to remove organic pollutants such as dioxins through thermal treatment to obtain granular fly ash. Furthermore, a salt separation process is used to remove heavy metal pollutants from the leachate and obtain salt that can be used as a resource. The remaining 5% of heavy metal-containing sludge and miscellaneous salts are transported for external treatment, resulting in a fly ash reduction rate exceeding 95%.

[0016] Specifically, pollution reduction is manifested in a significant reduction in multiple pollutants (salt / heavy metals / dioxins, and carbon dioxide in fly ash); carbon reduction is manifested in in-plant collaborative heat treatment, energy conservation and carbon reduction without relying on external treatment facilities; full utilization is manifested in the full disposal or utilization of treated fly ash products, eliminating the need for landfill; and safety is manifested in the stability and harmlessness of the detoxified products, which have long-term environmental safety.

[0017] Therefore, compared with the cement solidification method, this treatment method does not increase weight, and organic pollutants such as dioxins will not cause secondary pollution, and has the advantages of reduction and harmlessness;

[0018] Compared with recycling after washing, there is no need to build a supporting cement plant. Instead, the granules can be directly processed in the domestic waste incineration plant after granulation to obtain granules that can be used as building materials, etc., which has the advantages of economy and resource utilization.

[0019] Compared with the fly ash melting method, since it is directly processed in the municipal waste incineration plant, no additional carbon resources are required, so the processing cost is significantly reduced, and no heavy metals will be discharged with the smoke to generate secondary pollution, which has the advantages of being harmless and economical.

[0020] Compared with fly ash stabilization, heat treatment removes organic pollutants such as dioxins, which has the advantages of harmlessness and resource utilization.

[0021] Preferably, the mass ratio of raw ash to water in step S1 is 1:2 to 1:4. This ash-to-water ratio can avoid the agglomeration effect of fly ash and achieve the dissolution of volatile salts and heavy metals in fly ash under the premise of low-proportion water washing.

[0022] Preferably, step S1 further includes adding an acidic regulator, which is used to adjust the alkaline raw ash water and neutralize the calcium hydroxide in the raw ash water so that the two react to generate calcium carbonate that can be deposited, and the calcium carbonate can be used as a building material; wherein the acidic regulator is hydrochloric acid or sulfuric acid.

[0023] Preferably, the length of the granules in step S2 is 2 to 4 cm, and the diameter is 0.8 to 1.2 cm. Granulations of this size are conducive to complete heat treatment, and are also conducive to the transportation of the granules and the shaping of the granules after heat treatment.

[0024] Preferably, step S2 further comprises: performing solid-liquid separation on the sediment before solidification and granulation, granulating the obtained solid, and passing the obtained liquid into the leachate of step S4 for evaporation and salt separation; the purpose of doing so is to further reduce the water content in the sediment, reducing the water content in the sediment to 40%, so as to facilitate the subsequent granulation operation, and the separated liquid enters the salt separation operation.

[0025] Preferably, the heat treatment temperature in step S3 is 600-900°C and the time is 30 minutes to 2 hours. The heat treatment process is used to remove organic pollutants such as dioxins in the granulation, that is, some organic pollutants in the granulation are decomposed in the incinerator, and the remaining organic pollutants will volatilize. In short, all organic pollutants will escape from the granulation, so that building materials without long-term pollution can be obtained.

[0026] Preferably, step S3 further includes passing the dioxins volatilized by the heat treatment into a flue of the domestic waste incinerator, wherein the treatment temperature of the flue is above 850°C and the time is above 2 seconds, so as to completely decompose the remaining dioxins volatilized during the heat treatment process so that the flue gas discharged from the incinerator does not contain dioxin pollutants.

[0027] Preferably, step S4 further comprises: adding a heavy metal capture agent to the leachate before evaporating the salt to precipitate the heavy metals, and then separating the heavy metal sludge in the leachate for external processing as hazardous waste.

[0028] Preferably, the ratio of heavy metal capture agent to leachate in step S4 is 50-300 mg / L.

[0029] Preferably, step S4 further comprises: before evaporating the salt, passing the flue gas discharged from the heat treatment in step S3 into the leaching solution, that is, using the alkaline leaching solution to fix the carbon dioxide in the flue gas generated by the heat treatment, so that the carbon emission reduction can reach 3.97 kg / m 3 leachate.

[0030] Preferably, in step S4, 3 to 5 kilograms of leachate are added per cubic meter of flue gas.

[0031] Preferably, the evaporation and salt separation in step S4 utilizes a multi-effect evaporation process to obtain chloride salt, and evaporates the water to separate the miscellaneous salts. The chloride salt generally includes sodium chloride and potassium chloride, and the chloride salt can be used to prepare industrial salt.

[0032] Preferably, step S4 further includes: using the water separated by evaporation and salt separation as the water source in step S1, so that the water resources can be reused repeatedly.

[0033] Preferably, the water in step S1 also comes from cigarette washing wastewater in a garbage treatment plant, that is, this treatment method can be applied in a garbage treatment plant. If cigarette washing wastewater is generated in a garbage treatment plant, it can also be directly applied to the fly ash treatment process, further saving water resources and achieving economy. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation of the present invention. In the accompanying drawings:

[0035] FIG1 is a schematic flow chart of a method for treating fly ash from incineration of domestic waste according to the present invention. DETAILED DESCRIPTION

[0036] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0037] Technical Specifications for Pollution Control of Fly Ash from Municipal Waste Incineration (Trial) (HJ Article 6.3 of the 1134-2020 standard states that fly ash treatment products used for other utilization methods other than those specified in Article 6.2 must meet the following pollution control requirements: a) The dioxin content in the fly ash treatment products must be controlled. Dioxin decomposition technologies such as low-temperature thermal decomposition, high-temperature sintering, and high-temperature melting can be used. The total amount of dioxin residues in the treatment products must not exceed 50 ng-TEQ / kg (based on the dry weight of the fly ash); b) The heavy metal leaching concentration in the fly ash treatment products must be controlled. The fly ash treatment products must be used to prepare the leachate according to the HJ557 method. The leaching concentration of heavy metals must not exceed the maximum allowable emission concentration limit specified in GB8978 (the maximum allowable emission concentration of Class II pollutants must be implemented in accordance with the first-level standard); c) The soluble chlorine content in the fly ash treatment products must be controlled. High-temperature processes and water washing processes can be used to remove soluble chlorine. The soluble chlorine content in the treatment products (high-temperature treatment products, fly ash after water washing, etc.) must not exceed 2%, and preferably not exceed 1%.

[0038] According to the above standards, the present invention provides Example 1: a method for treating fly ash from domestic waste incineration. The fly ash treated in this method comes from a domestic waste incineration plant in Shanghai. The amount of fly ash treated in this embodiment is 3 tons, and the treatment steps include:

[0039] S1. Immerse the raw ash in water with a mass ratio of raw ash to water of 1:3, and separate by 1.5-stage leaching to obtain a leachate and a sediment;

[0040] S2. The sediment was first subjected to solid-liquid separation, the resulting liquid was passed into the leachate, a stabilizing and curing plasticizer was added to obtain a sediment with a water content of 40%, which was solidified and granulated to a length of 2 cm and a diameter of 0.8 cm.

[0041] S3. The granulation is placed in a domestic waste incinerator for heat treatment at a heat treatment temperature of 600°C for 2h. The dioxins volatilized during heat treatment are passed into a flue of a domestic waste incinerator, wherein the treatment temperature of a flue is above 850°C for more than 2S.

[0042] S4. First, a heavy metal scavenger is added to the leachate at a ratio of 50 mg / L. The heavy metals in the leachate are separated in a secondary sedimentation tank, and the heavy metal sludge is dehydrated and transported for treatment. Then, the flue gas discharged from the heat treatment in step S3 is passed into the leachate to adjust the pH value of the leachate. The leachate absorbs carbon dioxide in the flue gas, equivalent to 3.97 kg of carbon dioxide absorbed per cubic meter of leachate. The leachate is then evaporated and salted using a multi-effect evaporation process. Sodium salt and potassium salt are obtained by step evaporation. The water is evaporated to obtain miscellaneous salts. The sodium salt and potassium salt are processed and used as industrial salt. The miscellaneous salt is transported for treatment, and the evaporated water is used as the water source in step S1.

[0043] Using the process steps of Example 1, 2.4 tons of granules were ultimately obtained for construction use. The total residual dioxins in the granules were 5.3 ngTEQ / kg, which meets the standard of no more than 50 ng-TEQ / kg in the "Technical Specifications for Pollution Control of Fly Ash from Municipal Waste Incineration," and the soluble chlorine content was 0.8%, meeting the standard of no more than 2%. 116 kg of sodium and potassium salts were obtained for industrial use. After heat treatment, the leaching concentration of heavy metal lead in the fly ash was 0.20 mg / L, meeting the maximum allowable emission concentration limit specified in GB8978. Other heavy metal indicators also met the maximum allowable emission concentration limits specified in GB8978. The weight of heavy metal sludge and miscellaneous salt hazardous waste was 150 kg, accounting for 5% of the total fly ash, and the fly ash reduction rate reached 95%, achieving the technical advantages of harmlessness, economy, resource utilization, and reduction.

[0044] Example 2: The difference between Example 2 and Example 1 is that the fly ash treated in this treatment method comes from another domestic waste incineration plant in Shanghai, and the amount of fly ash treated in this example is 2 tons.

[0045] The difference between the processing steps and Example 1 is:

[0046] In step S1, the mass ratio of raw ash to water is 1:4;

[0047] The length of the granules in step S2 is 4 cm and the diameter is 1.2 cm;

[0048] In step S3, the heat treatment temperature is 900°C, the time is 30 minutes, the treatment temperature of the flue is above 850°C, and the time is above 2 seconds;

[0049] In step S4, the ratio of heavy metal capture agent to leachate is 300 mg / L, and the flue gas discharged from the heat treatment is passed into the leachate to adjust the pH value of the leachate. The leachate absorbs carbon dioxide in the flue gas, equivalent to 3.12 kg of carbon dioxide absorbed per cubic meter of leachate;

[0050] Using the process steps of Example 2, 1.7 tons of granules were finally obtained as building materials. The total dioxin residue in the granules was 0.61 ngTEQ / kg, which is in compliance with the standard of no more than 50 ng-TEQ / kg in the "Technical Specifications for Pollution Control of Fly Ash from Municipal Waste Incineration". The soluble chlorine content was 0.73%, which is in compliance with the standard of no more than 2%. 87 kg of sodium salt and potassium salt were obtained as industrial salts. The leaching concentration of heavy metal lead in the fly ash after heat treatment was 0.19 mg / L, which is in compliance with the maximum allowable emission concentration limit specified in GB8978. Other heavy metal indicators also met the maximum allowable emission concentration limit specified in GB8978. The weight of heavy metal sludge and miscellaneous salt hazardous waste was 98 kg, accounting for 4.9% of the total fly ash, and the fly ash reduction rate reached 95.1%. This treatment process achieves the technical advantages of harmlessness, economy, resource utilization, and reduction.

[0051] Example 3: The difference between Example 3 and Example 1 is that the fly ash treated in this treatment method comes from another domestic waste incineration plant in Shanghai, and the amount of fly ash treated in this example is 2 tons;

[0052] The difference between the processing steps and Example 1 is:

[0053] In step S1, the mass ratio of raw ash to water is 1:3;

[0054] The length of the granules in step S2 is 3 cm and the diameter is 1 cm;

[0055] In step S3, the heat treatment temperature is 750°C for 1.2 hours, and the treatment temperature of the flue is above 850°C for more than 2 seconds.

[0056] In step S4, the ratio of heavy metal capture agent to leachate is 170 mg / L. The flue gas discharged from the heat treatment is passed into the leachate to adjust the pH value of the leachate. The leachate absorbs carbon dioxide in the flue gas, equivalent to 4.63 kg of carbon dioxide absorbed per cubic meter of leachate.

[0057] Using the process steps of Example 3, 1.67 tons of granules were finally obtained as building materials. The total dioxin residue in the granules was 0.63 ng-TEQ / kg, which meets the standard of no more than 50 ng-TEQ / kg in the "Technical Specifications for Pollution Control of Fly Ash from Municipal Waste Incineration". The soluble chlorine content was 0.72%, which meets the standard of no more than 2%. 89 kg of sodium salt and potassium salt were obtained as industrial salts. The leaching concentration of heavy metal lead in the fly ash after heat treatment was 0.20 mg / L, which meets the maximum allowable emission concentration limit specified in GB8978. Other heavy metal indicators also meet the maximum allowable emission concentration limit specified in GB8978. The weight of heavy metal sludge and miscellaneous salt hazardous waste was 100 kg, accounting for 5% of the total fly ash, and the fly ash reduction rate reached 95%. This treatment process achieves the technical advantages of harmlessness, economy, resource utilization, and reduction.

[0058] It should be noted that, in this document, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that includes a list of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such process, method, article, or apparatus.

[0059] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art will be able to modify the technical solutions described in the aforementioned embodiments or substitute equivalents for some of the technical features. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A method for treating municipal solid waste incineration fly ash, characterized in that, It includes the following steps: S1. Immerse the original ash in water to separate the leachate and sediment; S2. Solidify and granulate the sediment; S3. Place the granulated product into a domestic waste incinerator for heat treatment; S4. Evaporate and separate salts from the leachate.

2. The treatment method of municipal solid waste incineration fly ash according to claim 1, wherein, In the step S1, the mass ratio of the original ash to water is 1:2 to 1:

4.

3. The treatment method of municipal solid waste incineration fly ash according to claim 1, characterized in that In the step S2, fly ash granulation is achieved by adding a stable solidifying plasticizer to the sediment. The length of the granulation is 2 - 4 cm, and the diameter is 0.8 - 1.2 cm.

4. The treatment method of municipal solid waste incineration fly ash according to claim 1, wherein, In the step S3, the temperature of the heat treatment is 600 - 900 °C, and the time is 30 min - 2 h. The volatilized dioxin is introduced into the first flue of the domestic waste incinerator.

5. The treatment method of municipal solid waste incineration fly ash according to claim 1, characterized in that, The step S4 further includes: adding a heavy metal scavenger to the leachate before evaporating and separating salts to separate heavy metals in the leachate. The ratio of the heavy metal scavenger to the leachate is 50 - 300 mg / L.

6. The treatment method of municipal solid waste incineration fly ash according to claim 1, wherein, The step S4 further includes: introducing the flue gas discharged from the heat treatment in the step S3 into the leachate before evaporating and separating salts.

7. A method for treating domestic waste incineration fly ash according to claim 1, characterized in that, In the step S4, 3 - 5 kg of carbon dioxide is captured per cubic meter of leachate.

8. A method for treating domestic waste incineration fly ash according to claim 1, characterized in that, In the step S4, the evaporation and salt separation utilize a multi-effect evaporation process to obtain chloride salts and evaporate the water to dryness to separate out miscellaneous salts.

9. A method for treating municipal solid waste incineration fly ash according to claim 1, characterized in that, The step S4 further includes: using the water separated by the evaporation and salt separation as the water source in the step S1.

10. A method for treating domestic waste incineration fly ash according to claim 1, characterized in that, The water in the step S1 also comes from the flue gas washing wastewater in the waste treatment plant.

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