Methods for treating fly ash from household waste incineration

Abstract

This invention relates to the field of fly ash treatment technology in environmental management and discloses a method for treating fly ash from domestic waste incineration, including step S1 of soaking the raw ash in water to separate it into leachate and sediment, step S2 of solidifying the sediment and granulating it, step S3 of introducing the granulated material into a domestic waste incinerator for heat treatment, and step S4 of evaporating the leachate to separate salts. The treatment method disclosed in this invention significantly reduces the amount of pollutants, and achieves carbon emission reduction and energy savings through coordinated heat treatment at the plant. The treated fly ash product can be absorbed or utilized in its entirety, eliminating the need for landfill disposal. After detoxification, the product is stable and harmless as a resource, ensuring long-term environmental safety.

Description

[Technical Field]

[0001] The present invention relates to the field of fly ash treatment technology in environmental management, specifically to a method for treating domestic waste incineration fly ash. [Background technology]

[0002] In recent years, China's waste incineration industry has grown explosively, with the annual amount of household waste incinerated reaching 180 million tons. The treatment of the resulting incineration fly ash has become increasingly important, and on August 27, 2020, the "Technical Specifications for the Control of Pollution from Household Waste Incineration Fly Ash (Trial)" (HJ 1134~2020) was issued.

[0003] Fly ash from household waste incineration appears as a gray, bulky, powdery solid, and is an irregular mass formed by the aggregation of particulate matter, reaction products, unreacted products, and condensation products. Fly ash contains high concentrations of water-soluble salts and various toxic heavy metals such as Cd, Pb, Zn, and Cr. Furthermore, organic pollutants such as dioxins and furans are concentrated in the fly ash carrier. The presence of these toxic and harmful pollutants poses potential ecological and health risks to groundwater, the surrounding ecosystem, and human health.

[0004] The main treatment processes for incineration fly ash currently in use include cement solidification, water washing and recycling, fly ash melting, and fly ash stabilization. The advantages and disadvantages of these four methods are compared in Table 1.

[0005] [Table 1]

[0006] As can be seen from Table 1, of the four fly ash treatment methods, the cement solidification method has the disadvantage of a high volume increase rate and a high possibility of secondary risks, the water washing and recycling method has issues such as the need for a cement plant tailored to the treatment and the difficulty of wastewater treatment, the fly ash melting treatment is commonly used overseas, especially in Japan, but has high treatment costs and is not economical, and the fly ash stabilization treatment is currently the mainstream treatment process, but it cannot treat organic pollutants such as dioxins, making it impossible to realize fly ash recycling.

[0007] Based on the above-mentioned deficiencies of the existing fly ash treatment methods, in order to respond to the trend of promoting carbon emission reduction in China, there is an urgent need for a new fly ash treatment method that can make fly ash harmless, economical, recyclable, and reduce its volume. Summary of the Invention [Problem to be solved by the invention]

[0008] SUMMARY OF THE INVENTION An object of the present invention is to provide a method for treating domestic waste incineration fly ash to solve the problems presented in the background art above. [Means for solving the problem]

[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 domestic waste incineration, in which FIG. 1 is a schematic flow chart of the method; Step S1: soaking raw ash in water to separate it into leachate and sediment; Step S2 of solidifying and granulating the precipitate; Step S3: heat-treating the granulated material in a household waste incinerator; and step S4 of evaporating the leachate to separate the salts.

[0011] The difference between the above steps S1 to S4 and the conventional process is that in this treatment method, the heat treatment of the fly ash is carried out in cooperation with a household waste incineration plant, organic contaminants such as dioxins are removed by the heat treatment to obtain granulated fly ash, heavy metal contaminants in the leachate are removed by a salt separation process to obtain usable salt, and the remaining 5% of the sludge containing heavy metals and miscellaneous salt are transported outside for treatment, thereby achieving a fly ash weight reduction rate of more than 95%.

[0012] Specifically, pollution reduction is manifested as a significant reduction in the amount of various pollutants (salts, heavy metals, dioxins, and carbon dioxide in fly ash); carbon emission reduction is manifested as energy savings and carbon emission reduction achieved through coordinated heat treatment at the plant, without relying on external treatment facilities; total volume reduction is manifested as the entire amount of treated fly ash product being treated and absorbed or utilized, eliminating the need for landfill disposal; and safety is manifested as the detoxified product being stable and harmless, with long-term environmental safety.

[0013] As a result, compared to the cement solidification method, this treatment method has the advantages of not increasing the weight, not causing secondary contamination by organic pollutants such as dioxins, and reducing the weight and making the waste harmless. Compared to the water washing and recycling method, there is no need to build a cement factory for processing. After granulation, the granules can be directly processed at a household waste incineration plant to obtain particulate matter that can be used as building materials, which has the advantages of economy and recycling. Compared to the fly ash melting method, this method does not require additional input of carbon resources and is directly processed at household waste incineration plants, which significantly reduces processing costs. In addition, since no heavy metals are emitted along with the smoke and dust, there is no secondary pollution, making it harmless and economical. Compared to the fly ash stabilization method, this method has the advantage of removing organic contaminants such as dioxins through heat treatment, making the waste harmless and recycling it.

[0014] Preferably, in step S1, the mass ratio of raw ash to water is 1:2 to 1:4, which can avoid the agglomeration effect of fly ash and realize the dissolution of volatile salts and heavy metals in fly ash under low-ratio water washing conditions.

[0015] Preferably, step S1 further includes adding an acidity adjuster, which is used to adjust the alkaline raw ash water and neutralize calcium hydroxide in the raw ash water so that precipitateable calcium carbonate is produced after the reaction between the two, and the calcium carbonate can be used as a building material, and the acidity adjuster is hydrochloric acid or sulfuric acid.

[0016] Preferably, in step S2, the granules have a length of 2 to 4 cm and a diameter of 0.8 to 1.2 cm, and granules of this size are advantageous for complete heat treatment, transportation of the granules, and granulation after heat treatment.

[0017] Preferably, step S2 further comprises, before solidification and granulation, performing solid-liquid separation on the precipitate, granulating the obtained solid, and introducing the obtained liquid into the leachate in step S4 for evaporation and salt separation, the purpose of which is to further reduce the moisture content in the precipitate, and to reduce the moisture content in the precipitate to 40% to facilitate the subsequent granulation operation, and the separated liquid is used for salt separation.

[0018] Preferably, in step S3, the heat treatment temperature is 600-900°C and the time is 30 min-2 h. The heat treatment process is used to remove organic contaminants such as dioxins during granulation. That is, some of the organic contaminants during granulation are decomposed in the incinerator, and the remaining organic contaminants are volatilized. In any case, all organic contaminants are removed from the granules, so that long-term pollution-free building materials can be obtained.

[0019] Preferably, step S3 further includes introducing the dioxins volatilized by the thermal treatment into the flue of a domestic waste incinerator, wherein the treatment temperature of the flue is 50°C or higher and the treatment time is 2S or higher, which is used to thoroughly decompose the remaining dioxins volatilized by the thermal treatment process, so as to make the smoke discharged from the incinerator free of dioxin contaminants.

[0020] Preferably, step S4 further includes adding a heavy metal capture agent to the leachate before evaporation and salt separation to precipitate heavy metals, and then separating the heavy metal sludge from the leachate and transporting it to the outside as hazardous waste for processing.

[0021] Preferably, in step S4, the compounding ratio of the heavy metal scavenger to the leachate is 50 to 300 mg / L.

[0022] Preferably, step S4 further includes introducing the smoke emitted in the heat treatment in step S3 into the leaching solution before evaporation and salt separation, i.e., fixing carbon dioxide in the smoke generated in the heat treatment with the alkaline leaching solution, and adding the carbon dioxide to the leaching solution. 3 This reduces carbon emissions by up to 3.97 kg per unit.

[0023] Preferably, in step S4, 3 to 5 kilograms of exudate is mixed per cubic meter of smoke.

[0024] Preferably, the evaporation and salt separation in step S4 is performed by using a multi-effect evaporation process to obtain chloride salts, and evaporating water to dryness to separate miscellaneous salts. Chloride salts generally include sodium chloride and potassium chloride, and the chloride salts can be produced into industrial salt for use.

[0025] Preferably, step S4 further includes using the water separated by evaporation and salt separation as the water source for step S1, thereby realizing repeated use of water resources.

[0026] Preferably, the water in step S1 is also sourced from smoke washing wastewater from a refuse treatment plant, i.e., this treatment method is applicable to refuse treatment plants. When smoke washing wastewater is generated in a refuse treatment plant, it can be directly applied to the fly ash treatment process, which further saves water resources and realizes economy. [Brief explanation of the drawings]

[0027] The drawings are used to provide a further understanding of the present invention, constitute a part of the specification, and, together with the examples of the present invention, are used to interpret the present invention and are not intended to limit the present invention. [Figure 1] 1 is a schematic flowchart of a method for treating household waste incineration fly ash according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0028] Hereinafter, the technical solutions of the embodiments of the present invention will be described clearly and completely with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and are not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative efforts fall within the protection scope of the present invention.

[0029] Section 6.3 of the Technical Specifications for the Control of Pollution from Domestic Waste Incineration Fly Ash (Trial) (HJ 1134-2020) proposes that when fly ash treatment products are used in ways other than those specified in Section 6.2, the following pollution control requirements a), b), and c) must be met simultaneously: a) The dioxin content in the treated fly ash product must be controlled. Dioxin decomposition techniques such as low-temperature pyrolysis, high-temperature sintering, and high-temperature melting can be used. The total residual dioxin content in the product must not exceed 50 ng-TEQ / kg (based on the dry weight of the fly ash). b) The leaching concentration of heavy metals in the treated fly ash product must be controlled. The leachate from the treated fly ash product must be prepared according to the HJ557 method. The leaching concentration of heavy metals must not exceed the maximum allowable emission concentration limit specified in GB 8978. (The maximum allowable emission concentration for Class 2 pollutants is enforced according to the first-class standards.) c) The content of soluble chlorine in the fly ash treatment product should be controlled. Soluble chlorine can be removed by high-temperature treatment, water washing, etc. The content of soluble chlorine in the treatment product (high-temperature treatment product, fly ash after water washing, etc.) should not exceed 2%, and preferably be 1% or less.

[0030] Based on the above criteria, the present invention provides the following Example 1, which is a method for treating fly ash from domestic waste incineration, in which the fly ash treated by the method is from a domestic waste incineration plant in Shanghai, the amount of fly ash treated in this example is 3 tons, and the treatment steps include S1 to S4.

[0031] In S1, the raw ash is immersed in water, the mass ratio of raw ash to water is 1:3, and leachate and sediment are obtained by leaching separation at a level of 1.5.

[0032] In S2, the precipitate is first separated into solid and liquid, and the resulting liquid is introduced into the leachate. Stabilizing, solidifying, and plasticizing agents are added to obtain a precipitate with a moisture content of 40%, which is then solidified and granulated. The granules are 2 cm long and 0.8 cm in diameter.

[0033] In S3, the granulated material is put into a household waste incinerator for heat treatment at a temperature of 600°C for 2 hours, and the dioxin volatilized by the heat treatment is introduced into the flue of the household waste incinerator, where the treatment temperature in the flue is 850°C or higher for 2 seconds or more.

[0034] In S4, first, a heavy metal trapping agent is added to the leachate, and the mixing ratio of the heavy metal trapping agent to the leachate is 50 mg / L. The heavy metals in the leachate are separated in the secondary sedimentation tank. The heavy metal sludge is dehydrated and then transported outside for treatment. Next, in step S3, the smoke emitted by the heat treatment is introduced into the leachate to adjust the pH value of the leachate. The carbon dioxide in the smoke is absorbed by the leachate, and 3.97 kg of carbon dioxide is absorbed per cubic meter of leachate. Then, the leachate is evaporated using a multi-effect evaporation process to separate the salts. Sodium salt and potassium salt are obtained by stepwise evaporation, and the water is evaporated to dryness to obtain miscellaneous salt. The sodium salt and potassium salt are processed into industrial salt and used. The miscellaneous salt is transported outside for treatment, and the water obtained by evaporation is used as the water source for step S1.

[0035] Using the process steps of Example 1, 2.4 tons of granules are finally obtained as building materials. The total residual amount of dioxins in the granules is 5.3 ng TEQ / kg, which meets the standard of not exceeding 50 ng TEQ / kg in the Technical Specification for the Control of Pollution from Household Waste Incineration Fly Ash. The soluble chlorine content is 0.8%, which meets the standard of not exceeding 2%. 116 kg of sodium salts and potassium salts are obtained as industrial salts. After heat treatment, the leaching concentration of heavy metal lead in the fly ash was 0.20mg / L, which meets the maximum allowable discharge concentration limit specified in GB8978, and the indicators of other heavy metals also meet the maximum allowable discharge concentration limit specified in GB8978. The weight of hazardous waste, which is heavy metal sludge and miscellaneous salt, is 150kg, accounting for 5% of the total fly ash, and the fly ash reduction rate reaches 95%, so that this treatment process has the technical advantages of detoxification, economy, resource recovery and volume reduction.

[0036] Example 2 The fly ash treated by this treatment method is from another domestic waste incineration plant in Shanghai, and the difference between Example 2 and Example 1 is that the amount of fly ash treated in this example is 2 tons.

[0037] The differences between the processing steps in the first embodiment and the second embodiment are as follows:

[0038] In step S1, the mass ratio of raw ash to water is 1:4.

[0039] In step S2, the granules are 4 cm long and 1.2 cm in diameter.

[0040] In step S3, the heat treatment temperature is 900°C, the time is 30min, the treatment temperature of the flue is 850°C or more, and the time is 2s or more.

[0041] In step S4, the mixing ratio of the heavy metal capture agent to the leachate is 300 mg / L, and the smoke emitted by the heat treatment is introduced into the leachate to adjust the pH value of the leachate. The carbon dioxide in the smoke is absorbed by the leachate, and 3.12 kg of carbon dioxide is absorbed per cubic meter of leachate.

[0042] Using the process steps of Example 2, 1.7 tons of granulated material was finally obtained for construction materials. The total residual amount of dioxins in the granulated material was 0.61 ng TEQ / kg, which met the standard of not exceeding 50 ng TEQ / kg set forth in the "Technical Specifications for the Control of Pollution from Household Waste Incineration Fly Ash." The soluble chlorine content was 0.73%, which met the standard of not exceeding 2%. 87 kg of sodium salt and potassium salt obtained were used as industrial salt. After heat treatment, the leaching concentration of heavy metal lead in the fly ash was 0.19 mg / L, which met the maximum allowable discharge concentration limit specified in GB8978. The indicators of other heavy metals also met the maximum allowable discharge concentration limit specified in GB8978. The weight of hazardous waste, including heavy metal sludge and miscellaneous salt, was 98 kg, accounting for 4.9% of the total fly ash. The fly ash weight reduction rate reached 95.1%, so that this treatment process achieved the technical advantages of detoxification, economy, resource recovery, and weight reduction.

[0043] Example 3 The fly ash treated by this treatment method is from another domestic waste incineration plant in Shanghai, and the amount of fly ash treated in this example is 2 tons, which is the difference between Example 3 and Example 1.

[0044] The differences between the processing steps in the first embodiment and the second embodiment are as follows:

[0045] In step S1, the mass ratio of raw ash to water is 1:3.

[0046] In step S2, the granules are 3 cm long and 1 cm in diameter.

[0047] In step S3, the heat treatment temperature is 750°C, the time is 1.2h, the flue treatment temperature is 850°C or more, and the time is 2s or more.

[0048] In step S4, the mixing ratio of the heavy metal capture agent to the leachate is 170 mg / L, and the smoke emitted by the heat treatment is introduced into the leachate to adjust the pH value of the leachate. The carbon dioxide in the smoke is absorbed by the leachate, and 4.63 kg of carbon dioxide is absorbed per cubic meter of leachate.

[0049] Using the process steps of Example 3, 1.67 tons of granules were finally obtained for use as building materials. The total residual dioxins content in the granules was 0.63ng TEQ / kg, which met the standard of not exceeding 50ng TEQ / kg set forth in the Technical Specifications for the Control of Pollution from Household Waste Incineration Fly Ash. The soluble chlorine content was 0.72%, which met the standard of not exceeding 2%. 89 kg of sodium salt and potassium salt were obtained for industrial use. After heat treatment, the leaching concentration of heavy metal lead in the fly ash was 0.20mg / L, which met the maximum allowable discharge concentration limit specified in GB8978. The indicators of other heavy metals also met the maximum allowable discharge concentration limit specified in GB8978. The weight of hazardous waste, including heavy metal sludge and miscellaneous salt, was 100 kg, accounting for 5% of the total fly ash. The fly ash weight reduction rate reached 95%. This treatment process thus achieved the technical advantages of detoxification, economy, resource recycling, and weight reduction.

[0050] It should be noted that, in this specification, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not require or imply the existence of any actual relationship or order between those entities or operations. And, "comprise," "contain," or any other variant thereof is intended to include a non-exclusive inclusion, whereby a process, method, article, or device comprising a series of elements not only includes those elements, but also other elements not expressly listed, or further elements inherent in such process, method, article, or device.

[0051] Finally, the above are only 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 above embodiments, it should be noted that those skilled in the art may modify the technical solutions described in the above embodiments or equivalently replace some of the technical features therein. Any modifications, equivalent replacements, improvements, etc. made without departing from the spirit and principle of the present invention shall fall within the protection scope of the present invention.

Claims

1. Step S1: immersing raw ash in water to separate it into a leachate and a precipitate; Step S2 of solidifying and granulating the precipitate; Step S3: Heat-treating the granulated material in a household waste incinerator; Step S4 of evaporating the leachate to separate the salts. A method for treating fly ash from domestic waste incineration, comprising:

2. In step S1, the mass ratio of raw ash to water is 1:2 to 1:

4.

2. The method for treating household waste incineration fly ash according to claim 1.

3. In step S2, a stabilizing, solidifying and plasticizing agent is added to the sediment to granulate the fly ash, and the granulated material has a length of 2-4 cm and a diameter of 0.8-1.2 cm.

2. The method for treating household waste incineration fly ash according to claim 1.

4. In step S3, the heat treatment temperature is 600-900°C, and the heat treatment time is 30 minutes to 2 hours. The evaporated dioxins are introduced into the flue of a household waste incinerator.

2. The method for treating household waste incineration fly ash according to claim 1.

5. Step S4 further includes adding a heavy metal capture agent to the leachate before evaporation and salt separation to separate heavy metals in the leachate, and the compounding ratio of the heavy metal capture agent to the leachate is 50 to 300 mg / L.

2. The method for treating household waste incineration fly ash according to claim 1.

6. Step S4 further includes introducing smoke emitted in the heat treatment of step S3 into the infusion solution before evaporation and salt separation.

2. The method for treating household waste incineration fly ash according to claim 1.

7. In step S4, 3 to 5 kilograms of carbon dioxide is captured per cubic meter of leachate.

2. The method for treating household waste incineration fly ash according to claim 1.

8. The evaporation and salt separation in step S4 is to obtain chloride salt by using a multi-effect evaporation process, and to evaporate water to dryness to separate miscellaneous salt.

2. The method for treating household waste incineration fly ash according to claim 1.

9. Step S4 further includes using the water separated by evaporation and salt separation as the water source for step S1.

2. The method for treating household waste incineration fly ash according to claim 1.

10. The water in step S1 is further sourced from wastewater from a waste treatment plant.

2. The method for treating household waste incineration fly ash according to claim 1.

Images