Method for synchronous dechlorination of household garbage incineration fly ash by high-temperature melting

Abstract

The present application relates to a kind of household garbage incineration fly ash high temperature melting synchronous dechlorination method, the household garbage incineration fly ash is mixed with organic matter and silico-aluminous auxiliary material according to proportion after granulation, then the granulation product is sent into high temperature melting furnace and is melted treatment;By regulating the ratio of silicon and aluminum component, adjust CaO-SiO2-Al2O3 ternary system, reduce the basicity of system, further reduce the residual chlorine content in molten slag;Preheating is carried out at 1100 DEG C or more for 1h or more before melting, ensure that organic matter is completely decomposed before the massive volatilization of chlorides, pore structure formation.When temperature continues to rise to melting stage, the massive volatilization of chlorides just occurs in the particle in which pore has been fully developed, the effect of pore-forming intensifies mass transfer to the greatest extent, realize synchronous efficient dechlorination in the high temperature melting process of fly ash, and the total chlorine content in final melting product can be reduced to 0.5% or less.Compared with prior art, the present application has the characteristics of simple process, low cost, green environmental protection.

Description

Technical Field

[0001] This invention belongs to the field of solid waste treatment and resource utilization technology, and relates to a method for simultaneous dechlorination of fly ash from municipal solid waste incineration at high temperature. Background Technology

[0002] With the acceleration of urbanization and the continuous increase in the amount of municipal solid waste generated in my country, municipal solid waste incineration has been widely used due to its significant volume reduction and waste reduction effects. However, the incineration process produces a large amount of fly ash, accounting for approximately 3-5% of the incinerated waste. Fly ash contains high concentrations of soluble chloride salts (mainly NaCl, KCl, CaCl2, etc.), heavy metals (Pb, Cd, Zn, Cu, etc.), and persistent organic pollutants such as dioxins, and is listed in the "National Hazardous Waste List," requiring safe disposal.

[0003] High-temperature melting technology is one of the important technical approaches for the harmless disposal and resource utilization of fly ash. This technology heats fly ash to temperatures above 1300℃, causing the mineral components in the fly ash to form a glassy slag, thereby stabilizing and solidifying heavy metals within the glassy network structure, while simultaneously decomposing dioxin-like organic pollutants. Furthermore, during the high-temperature melting process, some chloride salts volatilize in gaseous form, achieving a certain degree of dechlorination.

[0004] However, existing high-temperature melting processes for fly ash suffer from incomplete chlorine volatilization. Studies show that chlorine in fly ash mainly exists in the form of alkali metal chlorides (NaCl, KCl) and alkaline earth metal chlorides (CaCl2). During high-temperature melting, NaCl and KCl are more easily volatilized due to their lower boiling points (1465℃ and 1420℃, respectively), while CaCl2 has a boiling point above 1600℃ and high solubility in silicate slag, making it difficult to completely remove through simple high-temperature heating. After conventional melting treatment, the residual chlorine content in the slag is typically between 1% and 3%, and in some cases even exceeds 5%.

[0005] Residual chlorine in the molten products not only affects their resource utilization as building material raw materials (excessive chlorine content can lead to steel corrosion), but also poses a long-term leaching risk, potentially causing secondary pollution to the environment. Currently, to address the problem of incomplete dechlorination during fly ash melting, industrial processes typically employ a water washing pretreatment method. This involves first washing the fly ash to remove most of the soluble chloride salts before melting. For example, patent CN117125913A discloses a method for preparing a solidified body fed into the furnace from municipal solid waste incineration fly ash through melting. This method involves first washing the fly ash using a three-stage countercurrent rinsing process, then compounding fluxing materials, pore-forming materials, and cementing materials, followed by melting the solidified body into the furnace to improve melting efficiency and achieve waste resource utilization. However, the water washing process generates a large amount of high-salt wastewater, requiring additional wastewater treatment facilities, increasing treatment costs and process complexity. Simultaneously, some heavy metals are lost with the washing liquid during the washing process, increasing the difficulty of subsequent treatment.

[0006] In addition, some studies have used methods such as vacuum melting and adding chlorinating agents to enhance dechlorination. However, vacuum melting has high equipment requirements, high energy consumption, and limited processing scale. Although adding chlorinating agents (such as CaCl2, MgCl2, etc.) can promote the volatilization of heavy metals, it will increase the total chlorine content of the system, which may lead to an increase in the residual chlorine content in the slag.

[0007] Therefore, developing a simple, efficient, and water-washing-free method for simultaneous high-temperature melting and dechlorination of fly ash is of great practical significance and application value for the safe disposal and resource utilization of fly ash. Summary of the Invention

[0008] The purpose of this invention is to provide a method for simultaneous dechlorination of fly ash from municipal solid waste incineration through high-temperature melting, so as to achieve efficient dechlorination of fly ash during the melting process without the need for water washing pretreatment. This method is simple and effective.

[0009] The objective of this invention can be achieved through the following technical solutions: This invention provides a method for simultaneous dechlorination of fly ash from municipal solid waste incineration through high-temperature melting. The core ideas of this method are as follows: (1) Mechanism of pore formation by thermal decomposition of organic matter: During the preheating stage, the organic matter inside the particles undergoes thermal decomposition, releasing gases such as CO2, H2O, and CO. As these gases escape from the inside of the particles to the outside, they leave behind a large number of micropores and mesopores inside the particles, forming an interconnected network of pores. As the temperature continues to rise to above 1100℃, the low-melting-point components in the fly ash begin to soften, but since the organic matter has been completely decomposed at this time, the pore structure is preserved and further expanded, forming interconnected mass transfer channels from the particle surface to the inside.

[0010] (2) Enhanced mass transfer mechanism for chloride volatilization: During the high-temperature melting stage, chlorides (NaCl, KCl, CaCl2, etc.) in fly ash evaporate or decompose upon heating, generating HCl gas. In traditional direct melting processes, fly ash particles are dense, and the chloride vapor generated inside needs to diffuse through solid phase or viscous fluid to reach the particle surface, resulting in high mass transfer resistance and making it difficult for the internal chlorides to fully volatilize. In this invention, the interconnected channels formed by the decomposition of organic matter provide a rapid diffusion channel for chloride vapor. Chloride vapor can directly reach the particle surface and enter the gas phase through the channels, significantly reducing mass transfer resistance and thus significantly improving dechlorination efficiency.

[0011] (3) Mechanism of silicon-aluminum composition regulation: The addition of SiO2 and Al2O3 not only regulates the melting temperature and viscosity of the system, but also affects the form and solubility of chlorine in the slag. Studies have shown that in high basicity (high CaO) systems, CaCl2 has a high solubility in silicate slag and is difficult to completely volatilize and remove; while appropriately increasing the content of SiO2 and Al2O3 can reduce the basicity of the system, promote the reaction of CaCl2 with silicates to release HCl gas (CaCl2+SiO2+H2O→CaSiO3+2HCl↑), thereby further reducing the residual chlorine content in the slag.

[0012] (4) Preheating-Melting Two-Stage Synergistic Mechanism: This invention sets a preheating stage above 1100℃ to ensure that the organic matter is completely decomposed before the chloride salts volatilize in large quantities, and the pore structure is fully formed. When the temperature continues to rise to the melting stage, the large-scale volatilization of chloride salts occurs precisely in the particles where the pores have been fully developed, and the effect of pore-forming and mass transfer enhancement is maximized. If the preheating stage is missing, the decomposition of organic matter and the volatilization of chloride salts will occur simultaneously, and the chloride salts will begin to volatilize in large quantities before the pores are formed, which will greatly reduce the effect of pore-forming and mass transfer enhancement.

[0013] This invention provides a method for simultaneous dechlorination of fly ash from municipal solid waste incineration at high temperature, comprising the following steps: (1) Mixing of ingredients: The fly ash from municipal solid waste incineration, organic matter and silica-alumina auxiliary materials are mixed in proportion to obtain a mixture containing a variety of oxides; (2) Granulation: The mixture is placed in a granulator, a binder is added to obtain granular material, and then dried; (3) Preheating: The granular material is fed into a high-temperature furnace for preheating and temperature maintenance; (4) High-temperature melting: The preheated granular material is heated and kept at the temperature to melt, thus obtaining the molten product; (5) Cooling: Cool the molten product to obtain dechlorinated slag.

[0014] Further, the organic matter mentioned in step (1) is one or more of biomass, straw, rice husk, sawdust, organic sludge, and waste wood; the amount of organic matter added is 3-15% of the total mass of the mixture.

[0015] Further, the aluminosilicate additives mentioned in step (1) are one or more combinations of glass powder, fly ash, aluminum ash, kaolin, bentonite, and coal gangue. The functions of the aluminosilicate additives include: ① adjusting the ratio of silicon, aluminum, and calcium in the system to optimize the melting temperature and degree of vitrification; ② SiO2 and Al2O3 are the main components for forming a glassy network structure, which helps to stabilize and solidify heavy metals; ③ an appropriate amount of Al2O3 can reduce the solubility of CaCl2 in the slag and promote the volatilization and removal of chlorine.

[0016] Further, the oxides mentioned in step (1) are CaO, SiO2 and Al2O3; the content of CaO is 20-50%, the content of SiO2 is 20-40%, and the content of Al2O3 is 10-30% by mass fraction of oxides.

[0017] Further, the granulator mentioned in step (2) is a disc granulator or an extrusion granulator, the binder is water, the amount of water added is 8-15% of the total mass of the mixture, the particle size of the granules is 5-30mm, and the drying temperature is 100~110℃, preferably 105℃.

[0018] Furthermore, the purpose of granulation in step (2) is to uniformly solidify fly ash, organic matter and silicon-aluminum additives together, ensuring that the channels generated by the decomposition of organic matter can penetrate the entire particle, while avoiding the powdery material being carried away by the airflow in the high-temperature furnace.

[0019] Furthermore, in step (3), the preheating rate is 5-10℃ / min, the preheating temperature is 1100-1200℃, and the holding time is 1-3h.

[0020] Furthermore, the purpose of preheating in step (3) is that at a temperature above 1100°C, the organic matter has been completely decomposed and the pore structure has been fully formed; at the same time, this temperature is lower than the volatilization temperature of chloride salts, so that chloride salts only begin to volatilize in large quantities after the pores are formed, thereby making full use of the mass transfer enhancement effect of the pores.

[0021] Furthermore, the heating rate in step (4) is 3-10℃ / min, the melting temperature is 1320-1400℃, within this temperature range, the silicate components in the fly ash are fully melted to form a glass phase, while the chloride salts are rapidly volatilized and removed through the channels, and the holding time is 1.5-2.5h.

[0022] Furthermore, the heating rate in step (4) is 3-8 °C / min.

[0023] Furthermore, the total chlorine content of the molten product in step (4) is less than 0.5%, and the soluble chlorine content is less than 0.1%.

[0024] Furthermore, the phase of the molten product in step (4) is glassy, ​​and the concentration of heavy metal leaching is lower than the limit of the "Identification Standard for Hazardous Waste: Leaching Toxicity Identification" (GB5085.3-2007).

[0025] Furthermore, in step (4), the chlorine-containing flue gas generated during the high-temperature melting process is treated by dust removal and alkaline absorption to meet emission standards; the recovered chloride salts can be used for industrial chlor-alkali production or as road de-icing agents, thus realizing the recycling of resources.

[0026] Compared with the prior art, the present invention has the following advantages: (1) This invention utilizes the pore-forming effect of organic matter thermal decomposition to form a large number of interconnected channels inside the particles, which significantly reduces the mass transfer resistance of chloride salts diffusing from the inside of the particles to the surface, allowing chloride salts to volatilize and be removed more fully. Compared with the traditional direct melting process, the total chlorine content of the melt product can be reduced from 1-3% to below 0.5%, and the dechlorination efficiency is increased by more than 60%, effectively solving the problem of high chlorine leaching risk in the melt product.

[0027] (2) The present invention achieves dechlorination simultaneously during the melting process, eliminating the water washing pretreatment step in the traditional process, avoiding the generation of high-salt wastewater, greatly simplifying the process flow, and reducing treatment costs and secondary pollution risks.

[0028] (3) The organic matter (biomass, straw, organic sludge, etc.) used in this invention are all common solid wastes, widely available and inexpensive. At the same time, it realizes the co-processing of organic waste, which is in line with the circular economy concept of "treating waste with waste".

[0029] (4) The silicon-aluminum auxiliary materials (glass powder, fly ash, aluminum ash, etc.) used in this invention are all industrial solid wastes. They not only adjust the chemical composition of the system and optimize the melting performance, but also realize the synergistic disposal and resource utilization of various solid wastes.

[0030] (5) By optimizing the ratio of the CaO-SiO2-Al2O3 ternary system, the present invention forms a stable glassy structure in the molten product, with good heavy metal solidification effect and leaching toxicity far below the national standard limit, thus realizing the resource utilization of fly ash.

[0031] (6) The method of the present invention is simple and low in cost. It can adapt to the fluctuation of fly ash composition by adjusting the auxiliary material ratio. It is applicable to fly ash from municipal solid waste incineration of different sources and compositions, and is easy to promote and apply in industrial applications. Detailed Implementation

[0032] The present invention will now be described in detail with reference to specific embodiments. These embodiments are based on the technical solution of the present invention and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0033] It is worth noting that, unless otherwise specified, all raw materials used in this invention are commercially available; and all methods and equipment used are common in the field.

[0034] The fly ash from municipal solid waste incineration used in the following examples and comparative examples was taken from the fly ash of a bag filter dust collector in a municipal solid waste incineration power plant. Its main chemical composition is shown in Table 1.

[0035] Table 1. Main chemical components (wt%) of fly ash from municipal solid waste incineration The organic matter used was corn stalk powder (particle size <0.5mm, industrial analysis: moisture 6.8%, ash 5.2%, volatile matter 72.5%, fixed carbon 15.5%); the silicon-aluminum auxiliary materials included glass powder (SiO2 72.5%, Al2O3 2.3%, CaO 10.5%), fly ash (SiO2 52.3%, Al2O3 28.6%, CaO 5.8%) and aluminum ash (Al2O3 65.2%, SiO2 8.5%, MgO 2.1%).

[0036] Chlorine content was determined by X-ray fluorescence spectroscopy (XRF) combined with ion chromatography (IC); soluble chlorine content was determined by ion chromatography after deionized water extraction (liquid-to-solid ratio 10:1, shaking for 24 h); heavy metal leaching toxicity was determined according to the "Leaching Toxicity of Solid Waste - Acetic Acid Buffer Solution Method" (HJ / T300-2007).

[0037] Example 1: This embodiment provides a method for simultaneous dechlorination of fly ash from municipal solid waste incineration through high-temperature melting. The specific steps are as follows: (1) Mixing of ingredients: Take 1000g of the above-mentioned municipal solid waste incineration fly ash, add 80g of corn stalk powder (accounting for 6.5% of the mixture), 350g of glass powder, and 200g of fly ash, and mix thoroughly. The content of each oxide in the mixture is as follows: CaO 28.6%, SiO 28.3%, Al2O3 10.8%.

[0038] (2) Granulation: Add the mixture into the disc granulator, and spray an appropriate amount of water (about 10% of the mass of the mixture) while rotating to granulate and obtain spherical particles with a particle size of 10-20 mm; then dry the particles in an oven at 105℃ until the moisture content is less than 2%.

[0039] (3) Preheating: Place the dried granular material into a corundum crucible and place it in a high-temperature box-type resistance furnace; heat it to 1150℃ at a rate of 8℃ / min and hold it at that temperature for 1.5h for preheating treatment. During this stage, the organic matter is completely thermally decomposed, forming a large number of interconnected micropores inside the particles.

[0040] (4) High-temperature melting: Continue to heat up to 1350℃ at a rate of 5℃ / min and keep it at the temperature for 2 hours; during the melting process, chloride salts volatilize rapidly through the channels and are discharged with the flue gas.

[0041] (5) Cooling: After melting, the furnace is cooled to room temperature to obtain a glassy slag product.

[0042] The total chlorine content of the molten product obtained in this embodiment was 0.38%, and the soluble chlorine content was 0.06%. The product was dark brown and glassy with no obvious crystalline phase. The leaching concentrations of heavy metals Pb, Cd, Zn, and Cu were 0.85 mg / L, 0.05 mg / L, 2.36 mg / L, and 0.42 mg / L, respectively, all of which were far below the limits of GB5085.3-2007.

[0043] Example 2: This embodiment provides a method for simultaneous dechlorination of fly ash from municipal solid waste incineration through high-temperature melting. The difference from Embodiment 1 lies in the amount of organic matter added. The specific steps are as follows: (1) Mixing of ingredients: Take 1000g of fly ash from municipal solid waste incineration, add 150g of corn stalk powder (accounting for 10.3% of the mixture), 300g of glass powder, and 180g of fly ash, and mix thoroughly. The content of each oxide in the mixture is: CaO 29.8%, SiO 27.5%, Al 2O 3 10.2%.

[0044] (2) Granulation: Same as in Example 1, the particle size after granulation is 8-15mm, and dried at 105℃ until the moisture content is less than 2%.

[0045] (3) Preheating: Heat to 1100℃ at a rate of 10℃ / min and keep warm for 2 hours for preheating treatment.

[0046] (4) High-temperature melting: Continue to heat up to 1320℃ at a rate of 5℃ / min, and keep it at the temperature for 2.5h.

[0047] (5) Cooling: Cool the furnace to room temperature to obtain glassy slag product.

[0048] Testing revealed that the total chlorine content of the molten product obtained in this embodiment was 0.29%, and the soluble chlorine content was 0.04%. Due to the increased amount of organic matter added, the pore-forming effect was more significant, and the dechlorination efficiency was further improved. The leaching concentrations of heavy metals all met the national standards.

[0049] Example 3: This embodiment provides a method for simultaneous dechlorination of fly ash from municipal solid waste incineration through high-temperature melting. The difference from Embodiment 1 lies in the use of different combinations of silicon-aluminum auxiliary materials and the melting temperature. The specific steps are as follows: (1) Mixing of ingredients: Take 1000g of fly ash from municipal solid waste incineration, add 60g of sawdust (accounting for 4.8% of the mixture), 400g of fly ash, and 120g of aluminum ash, and mix thoroughly. The content of each oxide in the mixture is: CaO 25.2%, SiO 25.6%, Al2O3 22.8%.

[0050] (2) Granulation: Granulation is carried out using an extrusion granulator with a particle size of 5-10 mm and dried at 105℃.

[0051] (3) Preheating: Heat to 1200℃ at a rate of 6℃ / min and keep warm for 1 hour for preheating treatment.

[0052] (4) High temperature melting: Continue to heat up to 1380℃ at a rate of 5℃ / min, and keep it at the temperature for 1.5h.

[0053] (5) Cooling: Cool the furnace to room temperature to obtain glassy slag product.

[0054] The total chlorine content of the molten product obtained in this embodiment was 0.42%, and the soluble chlorine content was 0.07%. Due to the high Al2O3 content, the viscosity of the slag increased, and the volatilization rate of chlorine decreased slightly, but it still achieved a good dechlorination effect. The glassy structure with high aluminum content has a better curing effect on heavy metals.

[0055] Example 4: This embodiment provides a method for simultaneous dechlorination of fly ash from municipal solid waste incineration through high-temperature melting. The difference from Embodiment 1 is the use of organic sludge as the organic matter. The specific steps are as follows: (1) Mixing of ingredients: Take 1000g of fly ash from municipal solid waste incineration, add 180g of dewatered organic sludge (dry basis, accounting for 12.1% of the mixture), 280g of glass powder, and 250g of fly ash, and mix thoroughly. The content of each oxide in the mixture is: CaO 26.8%, SiO 26.2%, Al 2O 3 11.5%.

[0056] (2) Granulation: The mixture is added to a disc granulator for granulation. The particle size is 15-25 mm. The mixture is then dried at 105℃.

[0057] (3) Preheating: Heat to 1150℃ at a rate of 5℃ / min and keep warm for 1.5h for preheating treatment.

[0058] (4) High-temperature melting: Continue to heat up to 1350℃ at a rate of 3℃ / min and keep it at that temperature for 2 hours.

[0059] (5) Cooling: Cool the furnace to room temperature to obtain glassy slag product.

[0060] Testing revealed that the total chlorine content of the molten product obtained in this embodiment was 0.35%, and the soluble chlorine content was 0.05%. The organic matter in the organic sludge also exhibited good pore-forming effects, thus achieving the co-treatment of municipal sludge. The leaching concentrations of heavy metals all met national standards.

[0061] Example 5: This embodiment provides a method for simultaneous dechlorination of fly ash from municipal solid waste incineration through high-temperature melting, employing a high CaO content ratio. The specific steps are as follows: (1) Mixing of ingredients: Take 1000g of fly ash from municipal solid waste incineration, add 50g of rice husk powder (accounting for 3.6% of the mixture), 180g of glass powder, and 150g of fly ash, and mix thoroughly. The content of each oxide in the mixture is: CaO 35.2%, SiO2 20.5%, Al2O3 10.3%.

[0062] (2) Granulation: Disc granulation, particle size is 10-20mm, dried at 105℃.

[0063] (3) Preheating: Heat to 1150℃ at a rate of 8℃ / min and keep warm for 1.5h.

[0064] (4) High-temperature melting: Continue to heat up to 1400℃ at a rate of 5℃ / min, and keep it at the temperature for 3 hours to melt.

[0065] (5) Cooling: Cool the furnace to room temperature to obtain glassy slag product.

[0066] The total chlorine content of the molten product obtained in this embodiment was 0.46%, and the soluble chlorine content was 0.08%. Due to the high CaO content, the alkalinity of the system increased, and the solubility of CaCl2 in the slag increased. However, by increasing the melting temperature and extending the holding time, a good dechlorination effect could still be achieved. A small amount of crystalline phase was present in the product, but the degree of vitrification still met the requirements, and the heavy metal leaching met the standards.

[0067] Comparative Example 1: The difference between this comparative example and Example 1 is that no organic matter (corn straw powder) is added; all other conditions are the same as in Example 1. The specific steps are as follows: (1) Mixing of ingredients: Take 1000g of fly ash from municipal solid waste incineration, add 350g of glass powder and 200g of fly ash, and mix thoroughly. The content of each oxide in the mixture is: CaO 29.8%, SiO 29.5%, Al2O3 11.2%.

[0068] (2) Granulation: Same as in Example 1, the particle size after granulation is 10-20 mm, and dried at 105℃.

[0069] (3) Preheating: Heat to 1150℃ at a rate of 8℃ / min and keep warm for 1.5h.

[0070] (4) High-temperature melting: Continue to heat up to 1350℃ at a rate of 5℃ / min, and keep it at the temperature for 2 hours to melt.

[0071] (5) Cooling: Cool the furnace to room temperature to obtain slag product.

[0072] The total chlorine content of the molten product obtained in this comparative example was 1.52%, and the soluble chlorine content was 0.58%. Due to the lack of pore-forming effect of organic matter, the chloride salts mainly rely on the volatilization of the particle surface. The internal chloride salt diffusion resistance is large, the dechlorination efficiency is significantly lower than that of Example 1, the residual chlorine content is high, and there is a greater risk of leaching.

[0073] Comparative Example 2: The difference between this comparative example and Example 1 is that it omits the preheating and holding stage above 1100°C and directly heats to the melting temperature. The specific steps are as follows: (1) Ingredient mixing: Same as in Example 1, 1000g fly ash + 80g corn stalk powder + 350g glass powder + 200g fly ash.

[0074] (2) Granulation: Same as in Example 1.

[0075] (3) High temperature melting: The granular material is directly heated to 1350℃ at a rate of 5℃ / min and kept at the temperature for 2 hours without going through a preheating and heat preservation stage above 1100℃.

[0076] (4) Cooling: Cool the furnace to room temperature to obtain slag product.

[0077] Testing revealed that the total chlorine content of the molten product obtained in this comparative example was 0.86%, and the soluble chlorine content was 0.18%. Compared to Example 1, due to the lack of a preheating stage, the decomposition of organic matter and the large-scale volatilization of chloride salts occurred almost simultaneously. Chlorine salts began to volatilize in large quantities before the pores were fully formed, thus the effect of pore-forming and mass transfer enhancement was not fully realized, resulting in a lower dechlorination efficiency than in Example 1. This demonstrates that the preheating stage is crucial for ensuring effective dechlorination.

[0078] Comparative Example 3: The difference between this comparative example and Example 1 is that the amount of silicon-aluminum additives added is less, and the content of SiO2 and Al2O3 is lower than the range specified in this invention. The specific steps are as follows: (1) Mixing of ingredients: Take 1000g of fly ash from municipal solid waste incineration, add 80g of corn stalk powder, 80g of glass powder, and 50g of fly ash, and mix thoroughly. The content of each oxide in the mixture is: CaO 38.5%, SiO2 12.6%, Al2O3 5.8%.

[0079] (2) Granulation: Same as in Example 1.

[0080] (3) Preheating: Same as in Example 1, keep warm at 1150℃ for 1.5h.

[0081] (4) High temperature melting: Same as in Example 1, keep warm at 1350℃ for 2 hours.

[0082] (5) Cooling: Cool to room temperature along with the furnace.

[0083] The total chlorine content of the product obtained in this comparative example was 1.15%, and the soluble chlorine content was 0.42%. Compared with Example 1, the system was not fully melted due to the low content of SiO2 and Al2O3, resulting in poor glass transition. In addition, the high solubility of CaCl2 in the high calcium environment led to poor chlorine volatilization and removal. At the same time, the product contained a large amount of crystalline phase, resulting in poor heavy metal curing effect. The Pb leaching concentration was 5.2 mg / L, exceeding the standard limit.

[0084] Comparative Example 4: The difference between this comparative example and Example 1 is that the melting temperature is lower than the range defined in this invention. The specific steps are as follows: (1) Ingredient mixing: Same as in Example 1.

[0085] (2) Granulation: Same as in Example 1.

[0086] (3) Preheating: Same as in Example 1, keep warm at 1150℃ for 1.5h.

[0087] (4) High temperature melting: Heat to 1250℃ and keep warm for 2 hours to melt.

[0088] (5) Cooling: Cool to room temperature along with the furnace.

[0089] The total chlorine content of the product obtained in this comparative example was 0.98%, and the soluble chlorine content was 0.25%. Compared with Example 1, due to the low melting temperature, the system was not completely melted, the slag viscosity was high, the resistance to chloride diffusion and volatilization increased, and the dechlorination effect was significantly reduced. At the same time, the product had a low degree of glassization and was in a sintered state rather than a molten state, resulting in poor solidification of heavy metals and failing to meet the requirements for safe disposal.

[0090] Comparative Example 5: This comparative example uses a traditional direct fly ash melting process without adding any auxiliary materials or organic matter. The specific steps are as follows: (1) Take the fly ash from the incineration of raw domestic waste and put it directly into the corundum crucible without any pretreatment.

[0091] (2) High temperature melting: Heat to 1350℃ at a rate of 5℃ / min and hold for 2 hours to melt.

[0092] (3) Cooling: Cool to room temperature with the furnace.

[0093] The test results showed that the total chlorine content of the molten product obtained in this comparative example was 2.86%, and the soluble chlorine content was 1.35%. Compared with Example 1, when fly ash was directly melted, the melting effect was poor due to the lack of silicon and aluminum component adjustment, and there was no pore-forming to enhance mass transfer. Chlorine volatilization was very incomplete, the residual chlorine content was very high, and the risk of leaching was extremely high. At the same time, the product contained a large amount of crystalline phase, and the concentration of heavy metal leaching generally exceeded the standard, which could not meet the requirements for safe disposal.

[0094] The main experimental results of each embodiment and comparative example are summarized in Table 2.

[0095] Table 2 Comparison of experimental results between each embodiment and the comparative example. As can be seen from Table 2: (1) After being treated by the method of the present invention in Examples 1-5, the total chlorine content of the molten products was less than 0.5%, and the soluble chlorine content was less than 0.1%, with significant dechlorination effect, achieving the expected goal.

[0096] (2) Comparing Example 1 and Comparative Example 1, it can be seen that the addition of organic matter has a decisive effect on the dechlorination effect. After adding 6.5% straw powder, the total chlorine content decreased from 1.52% to 0.38%, and the dechlorination efficiency increased by about 75%, which fully demonstrates the mechanism of organic matter in creating pores and enhancing the mass transfer of chlorine volatilization.

[0097] (3) Comparing Example 1 and Comparative Example 2, it can be seen that the setting of the preheating stage is crucial to the dechlorination effect. Without the preheating stage, the total chlorine content is 0.86%, which is significantly higher than 0.38% with preheating. This indicates that only by keeping the temperature above 1100℃ to allow the organic matter to fully decompose and the channels to be fully formed before entering the melting stage can the pore-forming and mass transfer-enhancing effects be maximized.

[0098] (4) Comparing Example 1 and Comparative Example 3, it can be seen that a reasonable material ratio is a prerequisite for ensuring the dechlorination and vitrification effects. When the content of SiO2 and Al2O3 is too low, not only is the dechlorination effect poor, but the degree of vitrification is also insufficient, and the curing effect of heavy metals cannot be guaranteed.

[0099] (5) Comparing Example 1 and Comparative Example 4, it can be seen that the melting temperature must be high enough to ensure sufficient melting and effective volatilization of chlorine. When the temperature is too low, the system viscosity is high, the chloride diffusion resistance is high, and the dechlorination and glass transition effects are not ideal.

[0100] (6) Comparing Example 1 and Comparative Example 5, it can be seen that the dechlorination effect of traditional direct melting of fly ash is extremely poor, with a total chlorine content as high as 2.86%, which is far from meeting the requirements for safe disposal and resource utilization. The method of the present invention has significant technological progress compared with the traditional process.

[0101] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A method for simultaneous dechlorination of fly ash from municipal solid waste incineration at high temperature, characterized in that, Includes the following steps: (1) Mixing of ingredients: The fly ash from municipal solid waste incineration, organic matter and silica-alumina auxiliary materials are mixed in proportion to obtain a mixture containing a variety of oxides; (2) Granulation: The mixture is placed in a granulator, a binder is added to obtain granular material, and then dried; (3) Preheating: The granular material is fed into a high-temperature furnace for preheating and temperature maintenance; (4) High-temperature melting: The preheated granular material is heated and kept at the temperature to melt, thus obtaining the molten product; (5) Cooling: Cool the molten product to obtain dechlorinated slag.

2. The method for simultaneous dechlorination of fly ash from municipal solid waste incineration at high temperature according to claim 1, characterized in that, The organic matter mentioned in step (1) is one or more of the following: biomass, straw, rice husk, sawdust, organic sludge, and waste wood; the amount of organic matter added is 3-15% of the total mass of the mixture.

3. The method for simultaneous dechlorination of fly ash from municipal solid waste incineration at high temperature according to claim 1, characterized in that, The silicon-aluminum auxiliary material mentioned in step (1) is one or more of glass powder, fly ash, aluminum ash, kaolin, bentonite, and coal gangue.

4. The method for simultaneous dechlorination of fly ash from municipal solid waste incineration at high temperature according to claim 1, characterized in that, The oxides mentioned in step (1) are CaO, SiO2 and Al2O3; the content of CaO is 20-50%, the content of SiO2 is 20-40%, and the content of Al2O3 is 10-30% by mass fraction of oxides.

5. The method for simultaneous dechlorination of fly ash from municipal solid waste incineration at high temperature according to claim 1, characterized in that, The granulator mentioned in step (2) is a disc granulator or an extrusion granulator, the binder is water, the amount of water added is 8-15% of the total mass of the mixture, the particle size of the granules is 5-30mm, and the drying temperature is 100~110℃.

6. The method for simultaneous dechlorination of fly ash from municipal solid waste incineration at high temperature according to claim 1, characterized in that, The preheating rate in step (3) is 5-10℃ / min, the preheating temperature is 1100-1200℃, and the holding time is 1-3h.

7. The method for simultaneous dechlorination of fly ash from municipal solid waste incineration at high temperature according to claim 1, characterized in that, The heating rate in step (4) is 3-10℃ / min, the melting temperature is 1320-1400℃, and the holding time is 1.5-2.5h.

8. The method for simultaneous dechlorination of fly ash from municipal solid waste incineration at high temperature according to claim 1, characterized in that, The total chlorine content of the molten product in step (4) is less than 0.5%, and the soluble chlorine content is less than 0.1%.

9. The method for simultaneous dechlorination of fly ash from municipal solid waste incineration at high temperature according to claim 1, characterized in that, The phase of the molten product in step (4) is glassy, ​​and the concentration of heavy metal leaching is lower than the limit in GB5085.3-2007 of the "Identification Standard for Hazardous Waste: Leaching Toxicity Identification".

10. The method for simultaneous dechlorination of fly ash from municipal solid waste incineration at high temperature according to claim 1, characterized in that, The chlorine-containing flue gas generated during the high-temperature melting process is treated by dust removal and alkaline absorption before being discharged in compliance with standards; the recovered chloride salts are used in industrial chlor-alkali production or as road de-icing agents.

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