Waste incineration power generation flue gas desulfurization and fly ash cooperative treatment method and baking-free brick

Abstract

The invention provides a waste incineration power generation flue gas desulfurization and fly ash cooperative treatment method. The method comprises the following steps that 1, fly ash in flue gas is collected and pretreated to remove impurities, and the water content is adjusted; step 2, performing sodium-based wet desulfurization on the flue gas to obtain a desulfurization solution; 3, the pretreated fly ash, a desulfurization solution, a biological chelating agent and a gel additive are subjected to distribution chelation curing, and a fly ash cured product is obtained; step 4, crushing the fly ash cured material and then coating to obtain coated powder so as to improve the compressive strength and impermeability of the fly ash cured material; and step 5, finely grinding the coated powder, mixing the ground coated powder with aggregate and other raw materials, and carrying out compression molding to obtain the unfired brick. According to the invention, the chelate condensate is coated, so that the compressive strength and the impermeability of the chelate condensate as the road brick material are improved. The invention further provides the baking-free brick which is prepared through the waste incineration power generation flue gas desulfurization and fly ash cooperative treatment method and is high in impermeability and pressure resistance.

Description

Technical Field

[0001] This application relates to the field of waste incineration power generation technology, and in particular to a method for desulfurization of flue gas and co-treatment of fly ash in waste incineration power generation, and non-fired bricks. Background Technology

[0002] The flue gas from waste-to-energy plants contains large amounts of sulfides and fly ash. The current method for treating sulfides is desulfurization. During desulfurization, some smaller fly ash particles enter the desulfurization liquid. This desulfurization liquid is typically used to prepare desulfurized gypsum, which can easily lead to excessive heavy metal content in the gypsum.

[0003] Existing treatment methods for fly ash include collecting it, chelating it, and then landfilling it, or using the chelated solidified material to make roadbed materials, bricks, etc. For example, in patent number 202310918648.6, a chelating agent and its preparation method and lightweight bricks are described, in which the lightweight bricks are made from the following raw materials in parts by weight: 50-130 parts fly ash; 7-9 parts cement; 10-16 parts chelating solution; wherein the chelating solution includes a chelating agent and water.

[0004] Fly ash landfill requires significant space and is highly concentrated. Fly ash contains large amounts of heavy metals, which, when exposed to rainwater over a long period, easily leach from the solidified material, leading to excessive heavy metal levels in the soil. Furthermore, fly ash chelation is costly, resulting in high landfill expenses.

[0005] When fly ash chelated solids are used as roadbed materials, they have poor compressive strength and must be mixed with natural aggregates. Furthermore, they can only be used on road sections with low traffic loads. Additionally, fly ash is classified as hazardous waste, and improper handling when used as roadbed materials can lead to excessive levels of heavy metals.

[0006] When fly ash chelated solidified products are used as wall bricks, their high heavy metal content makes them unacceptable for residential wall applications. Most businesses use railings for exterior walls, requiring very little wall brick material.

[0007] When fly ash chelated solids are used as paving bricks, frequent vehicle traffic causes the chelates to crumble easily due to their low compressive strength. With rainwater leaching, the chelated state of these solids is difficult to maintain, and heavy metals will gradually leach from the solids and diffuse into the surrounding soil within 2-3 years. Although some heavy metals can be absorbed by plants, the high concentration prevents complete absorption. The remaining heavy metals will gradually flow into groundwater or natural water systems, impacting the ecosystem. Therefore, paving bricks made from fly ash pose a high risk of contamination.

[0008] In summary, due to issues with compressive strength and heavy metal leaching, the application scenarios of fly ash products are currently very limited, and the resource utilization rate in China is less than 10%. Summary of the Invention

[0009] In view of this, this application proposes a method for the co-treatment of flue gas desulfurization and fly ash in waste incineration power generation. The desulfurization liquid after flue gas desulfurization is chelated with fly ash to prepare non-fired bricks with strong impermeability and compressive strength, and which do not easily leach heavy metals. This solves the problem of treating desulfurization liquid after flue gas desulfurization and the problem of treating fly ash chelated solids, and improves the resource utilization rate of fly ash products.

[0010] This application also proposes a method for preparing non-fired bricks with strong impermeability and compressive strength by a method for co-processing flue gas desulfurization and fly ash treatment in waste incineration power generation.

[0011] A method for co-treating flue gas desulfurization and fly ash from waste incineration power generation includes the following steps: Step 1: Collect fly ash from the flue gas and pre-treat the fly ash to remove impurities and adjust the moisture content; Step 2: Sodium-based wet desulfurization of flue gas to obtain desulfurization liquid; Step 3: The pretreated fly ash is distributed and chelated with desulfurization liquid, biological chelating agent and gelling agent to obtain solidified fly ash; Step 4: After crushing the solidified fly ash, it is coated to obtain coated powder, which improves the compressive strength and impermeability of the solidified fly ash. Step 5: Grind the coated powder into fine powder, then mix it with other raw materials as aggregate and press it into shape to obtain non-fired bricks.

[0012] A method for preparing non-fired bricks using a waste incineration power generation flue gas desulfurization and fly ash co-treatment method includes coating powder, cement, and sand.

[0013] The technical advantage of this application is that it uses desulfurization liquid to make bricks from fly ash, thus avoiding the problem of excessive heavy metals in desulfurized gypsum.

[0014] This application utilizes distributed chelation to ensure that fly ash reacts fully with the chelating agent, preventing some fly ash from being encapsulated by solidified material without being chelated.

[0015] This application improves the compressive strength and impermeability of chelated solidified materials as paving bricks by coating them with a coating agent.

[0016] The unfired bricks prepared in this application have good impermeability and compressive strength, and exhibit strong compressive strength and impermeability during long-term use. Attached Figure Description

[0017] Figure 1 This is a process flow diagram of the waste incineration power generation flue gas desulfurization and fly ash co-treatment method of this application. Detailed Implementation

[0018] The embodiments of the technical solution of this application will now be described in detail with reference to the accompanying drawings. These embodiments are only used to more clearly illustrate the technical solution of this application and are therefore merely examples, and should not be used to limit the scope of protection of this application.

[0019] A method for co-treating flue gas desulfurization and fly ash from waste incineration power generation includes the following steps: Step 1: Collect fly ash from the flue gas and pre-treat the fly ash to remove impurities and adjust the moisture content and pH. Step 2: Sodium-based wet desulfurization of flue gas to obtain desulfurization liquid; Step 3: The pretreated fly ash is distributed and chelated with desulfurization liquid, biological chelating agent and gelling agent to obtain solidified fly ash; Step 4: After crushing the solidified fly ash, it is coated to obtain coated powder, which improves the compressive strength and impermeability of the solidified fly ash. Step 5: Grind the coated powder into fine powder, then mix it with other raw materials as aggregate and press it into shape to obtain non-fired bricks.

[0020] In a preferred embodiment, the biochelating agent is humic acid.

[0021] In a preferred embodiment, the gelling agent is a sodium silicate solution.

[0022] This application uses a bag filter to collect fly ash. To further reduce the fly ash content in the flue gas, an electrostatic precipitator can be used for further dust removal. The composition of fly ash is relatively complex, requiring pretreatment before chelation; otherwise, the chelation effect will be poor, and heavy metals will easily leach out.

[0023] In a preferred embodiment, the pretreatment of fly ash includes screening, magnetic separation for iron removal, and moisture content adjustment. These steps can be performed simultaneously or sequentially, and the order is not required.

[0024] The purpose of screening is primarily to remove large particulate impurities such as metal shavings and glass fragments from fly ash. These large particles have high density and smooth surfaces, which can cause localized accumulation during chelation and stirring, hindering the contact between fine fly ash particles and the chelating agent. This leads to an imbalance in the distribution, where there is a lack of chelating agent around the impurities and an excess of chelating agent in the fine particle area. After screening, the fly ash particles are uniformly sized, allowing the chelating agent to quickly penetrate into the micropores of the fly ash through stirring, ensuring a full reaction between the fly ash particles and the chelating agent.

[0025] Magnetic separation for iron removal has two advantages. Firstly, it can recover ferromagnetic materials, increasing the efficiency of fly ash recovery. Secondly, ferromagnetic materials readily react with chelates, interfering with the reaction between heavy metal ions and chelating agents, thus reducing the efficiency of heavy metal fixation. Magnetic separation reduces the consumption of chelating agents and ensures more thorough chelation of heavy metal ions.

[0026] When the initial moisture content of fly ash is less than 10%, the fine particles are prone to dust generation and have excessive fluidity, making it difficult to mix evenly with liquid chelating agents and easily forming dry clumps. Adjusting the fly ash moisture content to 20%–25% allows it to reach a state where it “can be clumped together without crumbling, but easily dispersed upon touch,” with moderate interparticle adhesion. During stirring, a uniform fly ash-chelating agent paste system can be formed, avoiding incomplete local reactions. Simultaneously, the increased moisture content creates a water film on the surface of the fine fly ash particles, which can suppress dust generation during screening and conveying, reducing fly ash loss.

[0027] The sodium-based wet flue gas desulfurization method of this application mainly removes SO2 from flue gas and generates a desulfurization liquid mainly composed of sodium sulfite (Na2SO3), which serves as a reducing agent and inorganic complexing agent for fly ash chelation.

[0028] In a preferred embodiment, the desulfurizing agent is a 20% sodium hydroxide solution, with a liquid-to-gas ratio of 12–15 L / m³. 3 The resulting desulfurization solution contains 6-8% Na2SO3, 3-4% Na2SO4, and trace amounts of NaCl, with a pH of 9-10.

[0029] Next, the pretreated fly ash is subjected to distribution chelation. The distribution chelation of fly ash includes the following steps: Step 31: Mix fly ash and desulfurization liquid with a liquid-to-solid mass ratio of 2:1; SO3 2- The fly ash contains highly toxic Cr 6+ Reduced to easily chelated, low-toxicity Cr 3+ The reaction that occurs is as follows:

[0030] SO4 2- With Pb 3+ Cd 2+ It forms insoluble sulfates, thus initially fixing heavy metals.

[0031] Step 32: Sprinkle the humic acid powder evenly into the product from the previous step and stir continuously to obtain a chelated suspension; Humic acid contains a large number of active groups such as -COOH and -OH, which react with Cr 3+ Cu 2+ Zn 2+ Cd 2+ A stable chelate is formed, and at the same time, the biomolecule chains of humic acid entangle and encapsulate the inorganic sulfate precipitate, resulting in a chelated suspension.

[0032] Step 33: Spray the sodium silicate solution into the chelation suspension and stir continuously to obtain a chelation gel; After sodium silicate solution is sprayed into the chelating suspension, it hydrolyzes to generate SiO2·nH2O gel, which fills the gaps between particles, encapsulates the chelate, and reduces the porosity.

[0033] Step 34: The chelating gel is air-dried and cured to obtain the fly ash solidified product.

[0034] Specifically, after standing for 24 hours, the chelate gel hardens to form a fly ash solid with preliminary strength.

[0035] After the chelate gel hardens, it forms a dense three-dimensional network structure in which heavy metal chelates are uniformly encapsulated in the network pores.

[0036] The coating process for solidified fly ash is as follows.

[0037] Step 41: Crush the solidified fly ash after stepwise chelation to a particle size of 3-5 mm and dry it to obtain solidified particles; After the fly ash solidified material is broken down, each chelated particle still retains a complete gel network, and the fly ash solidified material does not break free from the network. Breakdown only increases the surface area of ​​the gel, but the internal structure of each particle remains unchanged. The fly ash solidified material is still fixed by the network and will not be directly exposed to a free state due to physical breakage.

[0038] Step 42: Mix cement, slag powder, fiber, coupling agent and water according to the predetermined ratio to form a uniform slurry without lumps.

[0039] Cement provides early compressive strength, while the CSH gel formed during subsequent cement hydration has low permeability and chemical inertness, physically preventing external corrosive media such as water, acid, and oxygen from contacting the internal chelated solidified material. Slag powder fills pores through secondary hydration, improving impermeability. Fibers inhibit shrinkage cracking of the coating layer and, in conjunction with cement, enhance compressive strength. Coupling agents improve the interfacial adhesion between the coating layer and the chelated solidified material particles, preventing subsequent peeling due to compression. The synergistic effect of these components gives the fly ash solidified material coating strong compressive strength and impermeability.

[0040] Step 43: Spray the slurry evenly onto the surface of the solidified particles so that the solidified particles are completely covered by the coating layer; In a preferred embodiment, the spraying is performed using a roller sprayer with a rotation speed of 30 r / min and a coating thickness of 0.5 to 1 mm. The coating thickness is controlled by adjusting the spraying amount.

[0041] Step 44: Pre-cur the coated particles for a predetermined time to allow the coating layer to initially hydrate, and then allow it to air dry and solidify naturally to obtain the coated powder.

[0042] In a preferred embodiment, the coated particles are pre-cured for 24 hours at a temperature of 20–25°C and a humidity of ≥90%.

[0043] After coating, the compressive strength of the particles is significantly improved, providing a high-strength precursor for subsequent high-pressure molding of bricks and preventing the bricks from cracking during molding or use.

[0044] In a preferred embodiment, the mass ratio of cement, slag powder, fiber, and coupling agent is 20:10:0.1:0.5.

[0045] In a preferred embodiment, the fiber is a polypropylene fiber with a length ≥ 6 mm.

[0046] In a preferred embodiment, the coupling agent is a silane coupling agent.

[0047] For ease of description, the coating of fly ash solidified material by cement, slag powder, fiber, and coupling agent will be referred to as cement coating.

[0048] The coating effects of gel and cement address different needs, and their combination achieves a synergistic effect of chemical stabilization and physical curing. Gel coating forms a semi-solid network that can lock chelates and fly ash particles, but it has low mechanical strength and is easily broken; it also has poor impermeability and is prone to leaching with prolonged water contact. Cement coating, on the other hand, forms a high-strength, low-porosity solid that is impermeable and resistant to acid and alkali corrosion, providing long-term protection for fly ash chelates. In combination, gel coating prevents the migration of heavy metals during cement mixing, while cement coating compensates for the mechanical defects of the gel, providing a long-term physical barrier for the chelates and reducing environmental risks.

[0049] After obtaining the coated powder, the coated powder is finely ground, then mixed with other raw materials as aggregate and pressed into shape to obtain non-fired bricks. In a preferred embodiment, the steps are as follows.

[0050] Step 51: Grind the coated powder to a particle size ≤0.15mm and use it as aggregate for brick making; Step 52: Mix the coating powder, cement, and sand, then press the mixture into shape and autoclave to obtain non-fired bricks.

[0051] In a preferred embodiment, the mass ratio of the coating powder, cement, and sand is (40%–50%): (20%–25%): (15%–30%).

[0052] In a preferred embodiment, the sand material includes quartz sand and river sand.

[0053] The other raw materials mentioned in this application are materials other than the coating powder used in the preparation of non-fired bricks. Common raw materials for non-fired bricks include cement, quartz sand, and river sand. Some also contain additives, such as binders and pH adjusters, to ensure that the non-fired bricks meet relevant requirements.

[0054] The present application will now describe the solution in detail with reference to specific embodiments.

[0055] Example 1 Fly ash pretreatment Screening: Use a 10mm square-hole sieve to remove large particles of impurities; Magnetic separation for iron removal: Drum magnetic separator removes ferromagnetic materials with a magnetic field strength of 1200 Gs; Moisture content adjustment: Add water to the spray to 23% to achieve a state where it "can be clumped together without falling apart when squeezed, but can be easily dispersed when touched", thus suppressing dust and ensuring uniform mixing.

[0056] Stepwise chelation curing Desulfurization liquid reduction pretreatment: Fly ash and desulfurization liquid are mixed at a liquid-to-solid ratio of 2:1 and stirred for 30 minutes. Desulfurization liquid parameters: Na2SO3 37%, Na2SO4 3.5%, pH=9.5.

[0057] humic acid chelation Add 5% (by weight of fly ash) of humic acid powder and stir for 60 minutes.

[0058] Spray a 30% sodium silicate solution at 8% of the fly ash mass, stir for 45 minutes, and let stand for 24 hours to form a dense solidified fly ash.

[0059] The solidified fly ash was crushed to a particle size of 4 mm and dried at 105℃ until the moisture content was ≤5%. Preparation of coating slurry Mixing ratio: P.O42.5 cement, S95 slag powder, 8mm polypropylene fiber, KH550 silane coupling agent, and water are mixed evenly and without lumps in a mass ratio of 20%:10%:0.1%:0.5%:69.4%. Roller spray coating The coating slurry was sprayed onto the surface of the chelated gel solidified material at a rotation speed of 30 r / min, with a coating layer thickness of 0.7 mm. Pre-curing High-strength coated powder was obtained by curing at 23℃ and 92% humidity for 24 hours.

[0060] Road brick forming and maintenance Raw material ratio: The ground coated powder, P.O42.5 cement, quartz sand and river sand are mixed in a mass ratio of 48%:22%:18% and 12% to obtain the mixture; High-pressure molding: The mixture is held under pressure of 20MPa for 30s, and the molding size is 200×100×60mm; Autoclaving: Curing at 185℃ and 0.8MPa steam pressure for 10 hours yields unfired bricks.

[0061] Comparative Example 1 No chelation, only gel and cement coating, otherwise the same as in Example 1.

[0062] Comparative Example 2 No gel coating, only chelation and cement coating, otherwise the same as in Example 1.

[0063] Comparative Example 3 No cement coating, only chelation and gel coating, otherwise the same as in Example 1.

[0064] Comparative Example 4 No desulfurization liquid was used; direct chelation was employed; otherwise, it was the same as in Example 1.

[0065] The performance of the non-fired bricks prepared in Example 1 and Comparative Examples 1-4 was tested, and the results are shown in Table 1.

[0066] Table 1

[0067] As can be seen from Table 1, in all embodiments and comparative examples, Embodiment 1 and Comparative Example 2 meet the national standard requirements. Comparative Example 1: Pb, Cd, Cr 6+ The leaching exceeded the standard; the compressive strength of Comparative Example 3 did not meet the national standard requirements; and the Cr content of Comparative Example 4 was higher than that of Comparative Example 4. 6+ The leaching level exceeded the standard.

[0068] Furthermore, this application simulates the erosion of paving bricks under long-term use in rainy, freeze-thaw, acid rain, and salt spray environments, conducting four accelerated aging tests on Example 1 and Comparative Example 2 to verify the long-term leaching resistance of the paving bricks in this application. The test parameters refer to GB / T14506.30-2019 "Methods for Chemical Analysis of Silicate Rocks" and HJ 557-2010 "Leaching Toxicity Methods for Solid Waste".

[0069] Among them, the rainy test is a rainy-drying alternation, that is, soaking in deionized water for 24 hours → drying at 60℃ for 24 hours, and repeating this cycle 100 times; The freeze-thaw test involves alternating freeze-thaw cycles in cold regions, i.e., freezing at -20℃ for 12 hours and thawing at 20℃ for 12 hours, repeating this cycle 60 times. The acid rain erosion test involved immersion in an acetic acid solution with a pH of 4.5 for 14 days.

[0070] The salt spray environment test is a composite salt spray-dry-wet cycle, that is, spraying 5% NaCl salt spray for 8 hours → soaking in deionized water for 16 hours → drying at 60℃ for 24 hours, and repeating this cycle 50 times.

[0071] The experimental results are shown in Table 2.

[0072] Table 2:

[0073] As shown in Table 2, in all accelerated aging tests, the heavy metal leaching concentration in Example 1 was consistently far below the national standard limit, while in Comparative Example 2, only Pb did not exceed the limit during freeze-thaw cycles. This demonstrates that the non-fired bricks of this application have significant anti-leaching properties. Within the brick's lifespan, heavy metal pollution of the surrounding environment can be avoided.

[0074] The bricks prepared in this application can be used as paving bricks or wall bricks.

[0075] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A method for co-treating flue gas desulfurization and fly ash from waste incineration power generation, characterized in that: Includes the following steps: Step 1: Collect fly ash from the flue gas and pre-treat the fly ash to remove impurities and adjust the moisture content; Step 2: Sodium-based wet desulfurization of flue gas to obtain desulfurization liquid; Step 3: The pretreated fly ash is distributed and chelated with desulfurization liquid, biological chelating agent and gelling agent to obtain solidified fly ash; Step 4: After crushing the solidified fly ash, coat it to obtain coated powder, so as to improve the compressive strength and impermeability of the solidified fly ash; Step 5: Grind the coated powder into fine powder, then mix it with other raw materials as aggregate and press it into shape to obtain non-fired bricks.

2. The method for desulfurization of flue gas and co-treatment of fly ash from waste incineration power generation as described in claim 1, characterized in that: The biochelating agent is humic acid.

3. The method for desulfurization of flue gas and co-treatment of fly ash from waste incineration power generation as described in claim 1, characterized in that: The gelling agent is a sodium silicate solution.

4. The method for desulfurization of flue gas and co-treatment of fly ash in waste incineration power generation as described in claim 1, characterized in that: The distribution, chelation, and solidification of fly ash includes the following steps: Step 31: Mix fly ash and desulfurization liquid with a liquid-to-solid mass ratio of 2:1; Step 32: Sprinkle the humic acid powder evenly into the product from the previous step and stir continuously to obtain a chelated suspension; Step 33: Spray the sodium silicate solution into the chelation suspension and stir continuously to obtain a chelation gel; Step 34: The chelating gel is air-dried and cured to obtain the fly ash solidified product.

5. The method for desulfurization of flue gas and co-treatment of fly ash in waste incineration power generation as described in claim 1, characterized in that: The coating of solidified fly ash includes the following steps: Step 41: Crush the fly ash solidified material to a particle size of 3-5 mm and dry it to obtain solidified material particles; Step 42: Mix cement, slag powder, fiber, coupling agent and water according to the predetermined ratio to form a uniform slurry without lumps; Step 43: Spray the slurry evenly onto the surface of the solidified particles so that the solidified particles are completely covered by the coating layer; Step 44: Pre-cur the coated particles for a predetermined time to allow the coating layer to initially hydrate, and then allow it to air dry and solidify naturally to obtain the coated powder.

6. The method for co-treatment of flue gas desulfurization and fly ash from waste incineration power generation as described in claim 5, characterized in that: The mass ratio of the cement, slag powder, fiber, and coupling agent is 20:10:0.1:0.

5.

7. The method for co-treatment of flue gas desulfurization and fly ash from waste incineration power generation as described in claim 5, characterized in that: The fiber is a polypropylene fiber with a length ≥ 6 mm.

8. The method for co-treatment of flue gas desulfurization and fly ash from waste incineration power generation as described in claim 5, characterized in that: The coupling agent is a silane coupling agent.

9. The non-fired bricks prepared by the method as described in claim 1, characterized in that: This includes coated powder, cement, and sand.

10. The non-fired brick as described in claim 9, characterized in that: The mass ratio of the coating powder, cement, and sand is (40%–50%): (20%–25%): (15%–30%).

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