A system and method for treating municipal solid waste incineration fly ash

Abstract

This invention relates to the field of fly ash treatment technology, and discloses a treatment system and method for fly ash from municipal solid waste incineration. The fly ash treatment system provided by this invention combines a water washing module and a hydrothermal module, enabling simultaneous fly ash water washing and dechlorination, dioxin removal, and heavy metal solidification. The main reactions are all completed within the hydrothermal reactor, reducing equipment costs and operating costs for the harmless disposal of fly ash. The continuous dioxin degradation and heavy metal solidification operations overcome the drawbacks of intermittent operations, such as high energy consumption and high operating costs. The sequence of water washing and hydrothermal treatment can be flexibly switched according to the chlorine content in the fly ash, which helps ensure stable system operation, reduce equipment wear, reduce the amount of washing water and alkali solution used, and effectively control costs. The hydrothermal reactor recovers some heat through heat exchangers, achieving energy saving and consumption reduction. The treated fly ash can be directly used as a raw material for high-value-added building materials or adsorption materials, realizing the resource utilization of fly ash.

Description

Technical Field

[0001] This invention relates to the field of fly ash treatment technology, and in particular to a treatment system and method for fly ash from municipal solid waste incineration. Background Technology

[0002] Waste incineration is the mainstream technology for municipal solid waste treatment, with a large incineration capacity. However, the incineration process generates fly ash, which accounts for approximately 4% of the incinerated waste mass, resulting in a significant fly ash production. Landfilling is the primary method for fly ash disposal, and from the perspective of hazardous waste, fly ash has become the single type of hazardous waste with the largest landfill volume.

[0003] Fly ash from municipal solid waste incineration is classified as hazardous waste and cannot be directly disposed of in landfills. Current technologies mostly involve solidifying / stabilizing the fly ash at the incineration plant using cement or chelating agents, and then sending it to landfills only after it passes quality testing. However, this approach only achieves the harmlessness of the fly ash, not its resource utilization, and it also occupies a large amount of landfill space, posing significant environmental risks. Based on this, the Ministry of Ecology and Environment issued the "Guiding Opinions on Further Strengthening the Environmental Governance of Hazardous Waste and Strictly Preventing Environmental Risks," which explicitly proposes to gradually reduce the amount of municipal solid waste incineration fly ash sent to landfills and encourages the comprehensive utilization of municipal solid waste incineration fly ash after harmless pretreatment to prevent long-term, large-scale stockpiling.

[0004] In addition, some fly ash is sent directly to cement kilns for co-processing. However, with the era of large-scale infrastructure construction and the slump in the real estate market, the production load of cement plants has been continuously reduced. From a spatial distribution perspective, the distribution density of municipal solid waste incineration plants is significantly higher than that of cement kilns. It can be seen that cement kiln co-processing relies on external facilities, and the disposal method is unstable and uncertain.

[0005] In some regions, a melting method is used to treat fly ash. This involves heating the fly ash from waste incineration to a high temperature of around 1400℃ in a fuel furnace using fuel or electricity, melting the fly ash, and then cooling it through a certain process to turn it into slag. The slag can be used as a building material, thus achieving the goals of reducing fly ash volume, rendering it harmless, and recycling it. However, this method has drawbacks such as high costs for dioxin control, high energy consumption, and high carbon emissions, making it difficult to promote and use on a large scale.

[0006] Heavy metals (leaching toxicity) and dioxins are the main limiting factors for the resource utilization of fly ash. Existing technologies often involve multi-stage water washing of fly ash, followed by evaporation, concentration, and salt extraction of the washing liquid. Simultaneously, a low-temperature catalytic cracking process is used to catalytically decompose dioxins in the waste. This method has initially achieved the resource utilization and harmlessness of fly ash, but heavy metals still remain in the treated fly ash, requiring additional chelating agent stabilization or co-processing in a cement kiln.

[0007] CN 116851421 A discloses a continuous fly ash dioxin hydrothermal degradation and heavy metal solidification system and method. By adding one or more of alkaline substances and / or oxidants, and adjusting the temperature and residence time in the reaction, the dioxin degradation efficiency is improved, which helps to solidify heavy metals in fly ash. However, the dioxin and heavy metal content in the fly ash treated by this method still does not meet the requirements of the "Technical Specification for Pollution Control of Fly Ash from Municipal Solid Waste Incineration (Trial)" HJ1134-2020 standard. CN118180110A discloses a system and method for the synergistic removal of dioxins and heavy metals from waste incineration fly ash. The original fly ash is first washed with water, and then the washed fly ash is successively dried, crushed, pyrolyzed at low temperature, and ground to remove dioxins and solidify heavy metals in the fly ash. However, this method still solidifies heavy metals by adding chelating agents, which is the same as the fly ash stabilization principle in municipal solid waste incineration plants. It does not reduce the cost of heavy metal solidification, and the low-temperature pyrolysis for dioxin removal has the problem of exhaust gas treatment.

[0008] Hydrothermal treatment can form stable aluminosilicate minerals in waste incineration fly ash. Heavy metals are fixed within the structure of these minerals through physical / chemical adsorption, ion exchange, and physical encapsulation, thereby improving the stability of heavy metal ions and reducing environmental pollution. Based on the heating method and additives used, hydrothermal methods can be categorized into three types: traditional hydrothermal methods, additive-assisted hydrothermal methods, and microwave hydrothermal methods. Currently, the municipal solid waste industry primarily uses grate furnaces, making additive-assisted hydrothermal methods the most applicable. However, in practical applications, they suffer from high energy and equipment costs.

[0009] Therefore, there is an urgent need to develop a low-cost, high-efficiency fly ash treatment method that can synergistically remove dioxins and heavy metals, so that the dioxin and heavy metal content in the treated fly ash can be reduced to meet the requirements of the "Technical Specification for Pollution Control of Fly Ash from Municipal Solid Waste Incineration (Trial)" HJ1134-2020, and promote the resource utilization of fly ash from municipal solid waste incineration. Summary of the Invention

[0010] The present invention aims to at least solve one of the aforementioned technical problems existing in the prior art. Therefore, one objective of the present invention is to provide a system for treating fly ash from municipal solid waste incineration.

[0011] The second objective of this invention is to provide a method for treating fly ash from municipal solid waste incineration.

[0012] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0013] A first aspect of the present invention provides a system for treating fly ash from municipal solid waste incineration, comprising:

[0014] Original ash warehouse 100;

[0015] The water washing module includes a primary water washing tank 200, a primary dewatering device 210, a secondary water washing tank 300, and a secondary dewatering device 310 arranged sequentially.

[0016] The hydrothermal module includes a mixing chamber 400, a hydrothermal reactor 500, a heat exchanger 600, and a hydrothermal dehydration device 610 arranged sequentially.

[0017] Finished product ash silo 700;

[0018] The ash outlet of the original ash silo 100 is connected to the primary washing tank 200 and the mixing silo 400, respectively.

[0019] The filtrate outlet of the primary dehydration device 210 is connected to the heat exchanger 600;

[0020] The filtrate outlet of the secondary dewatering device 310 is connected to the primary washing tank 200;

[0021] The ash outlet of the secondary dewatering device 310 is connected to the mixing silo 400 and the finished ash silo 700, respectively.

[0022] The filtrate outlet of the hydrothermal dehydration device 610 is connected to the secondary washing tank 300;

[0023] The ash outlet of the hydrothermal dehydration equipment 610 is connected to the primary washing tank 200 and the finished ash silo 700, respectively.

[0024] The outlet of the hydrothermal reactor 500 is connected to the inlet of the heat exchanger 600; the outlet of the heat exchanger 600 is connected to the inlet of the hydrothermal reactor (500) and the hydrothermal dehydration device (610).

[0025] In some embodiments of the present invention, the processing system further includes a washing liquid treatment tank 800, which is connected to the filtrate outlets of the primary dehydration device 210 and the hydrothermal dehydration device 610, respectively.

[0026] In some embodiments of the present invention, the processing system further includes a fresh water tank 900, which is connected to the inlet of the secondary washing tank 300 and the heat exchanger 600, respectively.

[0027] In some embodiments of the present invention, the processing system further includes a silicon-aluminum additive tank 410 and an alkali tank 620, wherein the silicon-aluminum additive tank 410 is connected to the feed inlet of the mixing tank 400, and the alkali tank 620 is connected to the heat exchanger 600.

[0028] In some embodiments of the present invention, the processing system further includes an automatic control unit, which switches the order in which the fly ash in the original ash silo 100 enters the water washing module and the hydrothermal module according to the chlorine content in the fly ash.

[0029] In some embodiments of the present invention, if the chlorine content in the fly ash is >15wt%, the automatic control unit controls the fly ash in the original ash silo 100 to first enter the water washing module; if the chlorine content in the fly ash is ≤15wt%, the automatic control unit controls the fly ash in the original ash silo 100 to first enter the hydrothermal module.

[0030] In some embodiments of the present invention, the automatic control unit is electrically connected to the sensors and actuators of each device.

[0031] In some embodiments of the present invention, the hydrothermal reactor 500 is made of corrosion-resistant stainless steel, has an internal stirring device, an outer wall insulation layer, and is equipped with a temperature sensor and a pressure gauge.

[0032] In some embodiments of the present invention, the hydrothermal reactor 500 is a continuous reaction device that can realize continuous feeding and discharging.

[0033] In some embodiments of the present invention, the primary washing tank 200 and the secondary washing tank 300 are respectively equipped with stirring devices, and the tank bodies are all made of corrosion-resistant materials.

[0034] In some embodiments of the present invention, a screw conveyor is provided at the bottom of the mixing ash silo 400, and the screw conveyor transports the mixed ash in the mixing ash silo 400 to the hydrothermal reactor 500.

[0035] In some embodiments of the present invention, the finished product ash silo 700 is provided with a sampling port and a testing window, and the silo body adopts a sealed design.

[0036] The basic principle of the municipal solid waste incineration fly ash treatment system of the present invention is explained as follows:

[0037] The present invention provides a system for treating fly ash from municipal solid waste incineration. The original ash bin 100 is connected to a primary washing tank 200 of a washing module and a mixing bin 400 of a hydrothermal module. An automatic control unit controls the order in which the fly ash in the original ash bin 100 enters the washing module and the hydrothermal module based on the chlorine content in the fly ash. Specifically:

[0038] When the chlorine content in fly ash is >15wt%, the fly ash in the original ash silo 100 first enters the primary washing tank 200 of the washing module, where it is washed with filtrate from the secondary dewatering device 310. It then enters the primary dewatering device 210 for solid-liquid separation. The filtrate enters the washing liquid treatment tank 800, and the solids enter the secondary washing tank 300. The solids in the secondary washing tank 300 are washed with filtrate from the hydrothermal dewatering device 610, and then enter the secondary dewatering device 310 for solid-liquid separation. The filtrate is returned to the primary washing tank 200, and the washed ash enters the mixing silo 400. The washing module is now complete. (Silica-alumina additive silo) 410 Add silicon-aluminum additives to the mixing bin 400 to adjust the elemental composition of the washed ash. The resulting mixed ash enters the hydrothermal reactor 500 for hydrothermal reaction. The alkali solution bin 620 and the fresh water tank 900 respectively supply alkali solution and water to the heat exchanger 600. After preheating, the mixture enters the hydrothermal reactor 500, and steam is injected to heat it and carry out the hydrothermal reaction. The water-ash mixture discharged from the hydrothermal reactor 500 exchanges heat with the alkali solution / water in the heat exchanger 600 to recover heat, and then enters the hydrothermal dehydration equipment 610 for solid-liquid separation. The resulting filtrate is returned to the secondary washing tank 300, and the solid enters the finished ash bin 700. The fly ash treatment is completed.

[0039] When the chlorine content in fly ash is ≤15wt%, the fly ash in the original ash silo 100 first enters the mixing silo 400 of the hydrothermal module. The silicon-aluminum additive silo 410 adds silicon-aluminum additives to the mixing silo 400 to adjust the elemental composition of the fly ash. The resulting mixed ash enters the hydrothermal reactor 500 for hydrothermal reaction. The alkali solution silo 620 supplies alkali solution to the heat exchanger 600. The filtrate from the primary dewatering device 210 enters the heat exchanger 600. After preheating, the alkali solution and filtrate enter the hydrothermal reactor 500, where steam is injected for heating and hydrothermal reaction. The water-ash mixture discharged from the hydrothermal reactor 500 exchanges heat with the alkali solution / filtrate in the heat exchanger 600 to recover heat before entering the... Solid-liquid separation is performed in the hydrothermal dehydration equipment 610. The resulting filtrate enters the washing liquid treatment tank 800, while the solids enter the primary washing tank 200, completing the hydrothermal treatment. The solids in the primary washing tank 200 are washed with the filtrate from the secondary dehydration equipment 310, and then enter the primary dehydration equipment 210 for solid-liquid separation. The filtrate enters the heat exchanger 600, while the solids enter the secondary washing tank 300. A second washing is performed using water supplied from the fresh water tank 900 to the secondary washing tank 300, followed by solid-liquid separation in the secondary dehydration equipment 310. The filtrate is returned to the primary washing tank 200, while the solids enter the finished product ash silo 700, completing the fly ash treatment.

[0040] The second aspect of the present invention provides a method for treating fly ash from municipal solid waste incineration, comprising using the municipal solid waste incineration fly ash treatment system described in the first aspect of the present invention to perform water washing and dechlorination, dioxin removal and heavy metal solidification on the fly ash.

[0041] In some embodiments of the present invention, the physicochemical parameters of the municipal solid waste incineration fly ash include at least one of the following: dioxin content ≥ 0.2 μg TEQ / kg; Pb content ≥ 1000 mg / kg; Zn content ≥ 3000 mg / kg; Cu content ≥ 500 mg / kg; Cr content ≥ 200 mg / kg; Cd content ≥ 40 mg / kg; As content ≥ 20 mg / kg; Ca content ≥ 20 wt%; Si content ≥ 2 wt%; Al content ≥ 0.5 wt%.

[0042] In some preferred embodiments of the present invention, the physicochemical parameters of the municipal solid waste incineration fly ash include at least one of the following: dioxin content of 0.2-0.5 μg TEQ / kg; Pb content of 1000-2500 mg / kg; Zn content of 3000-5000 mg / kg; Cu content of 500-700 mg / kg; Cr content of 200-400 mg / kg; Cd content of 40-60 mg / kg; As content of 20-40 mg / kg; Ca content of 20wt%-35wt%; Si content of 2wt%-5wt%; and Al content of 0.5wt%-2wt%.

[0043] In some embodiments of the present invention, the process path of the processing method is selected from either path 1 or path 2:

[0044] Path 1: When the chlorine content in fly ash is >15wt%, the fly ash first enters the water washing module from the original ash silo 100 for water washing and dechlorination, and then enters the hydrothermal module for hydrothermal reaction to remove dioxins, solidify heavy metals, and obtain finished ash, which enters the finished ash silo 700.

[0045] Path 2: When the chlorine content in fly ash is ≤15wt%, the fly ash first enters the hydrothermal module from the original ash silo 100 for hydrothermal reaction to remove dioxins and solidify heavy metals, and then enters the water washing module for water washing and dechlorination to obtain finished ash, which enters the finished ash silo 700.

[0046] In some embodiments of the present invention, after the fly ash enters the hydrothermal module, silicon-aluminum additives are added from the silicon-aluminum additive bin 410 to the mixing bin 400 to adjust the CaO, SiO2, and AlO content of the fly ash in the mixing bin 400. 1.5 The mass ratio is (5-6):(3.5-4.5):1, resulting in mixed ash.

[0047] In some preferred embodiments of the present invention, after the fly ash enters the hydrothermal module, the process includes adding silicon-aluminum additives from the silicon-aluminum additive bin 410 to the mixing bin 400 to adjust the CaO, SiO2, and AlO content of the fly ash in the mixing bin 400. 1.5The mass ratio is (5-5.5):(3.5-4):1, resulting in mixed ash.

[0048] In some embodiments of the present invention, the silicon-aluminum additive is selected from at least one of incinerator slag, fly ash, diatomaceous earth, and ferrous sulfate.

[0049] In some embodiments of the present invention, the particle size of the silicon-aluminum additive is less than 90 μm.

[0050] In some embodiments of the present invention, the conditions for the hydrothermal reaction include at least one of the following:

[0051] 1) The solid-liquid ratio is 1g:(2-5)mL;

[0052] 2) pH ≥ 12;

[0053] 3) The temperature is 180-280℃;

[0054] 4) Pressure range: 1.0-6.4 MPa;

[0055] 5) The time is 2-8 hours.

[0056] In some preferred embodiments of the present invention, the conditions for the hydrothermal reaction include at least one of the following:

[0057] 1) The solid-liquid ratio is 1g:(3-4)mL;

[0058] 2) pH = 12-13;

[0059] 3) The temperature is 180-220℃;

[0060] 4) Pressure is 1.0-3.0 MPa;

[0061] 5) The time is 2-5 hours.

[0062] In some embodiments of the present invention, prior to the hydrothermal reaction, the material in the hydrothermal reactor 500 is activated for 2-10 hours.

[0063] In some embodiments of the present invention, after the hydrothermal reaction, the temperature is cooled to 50-60°C by external cooling water through a heat exchanger 600.

[0064] In some embodiments of the present invention, the finished ash in the finished ash silo 700 is periodically sampled and tested. If the soluble chlorine content, heavy metal leaching toxicity and dioxin content in the finished ash meet the requirements of the "Technical Specification for Pollution Control of Fly Ash from Municipal Solid Waste Incineration (Trial)" HJ1134-2020 standard, it can be used as a raw material for high-value-added building materials or adsorbent materials. Finished ash that does not meet the standard requirements is returned to the mixing silo 400 for further processing.

[0065] The basic principle of the method for treating fly ash from municipal solid waste incineration provided by this invention is explained as follows:

[0066] The method for treating fly ash from municipal solid waste incineration provided by this invention can be divided into two main modules: water washing and hydrothermal treatment. In the water washing module, soluble chloride salts in fly ash can be effectively removed by countercurrent water washing (multi-stage water washing + dehydration). In the hydrothermal treatment module, hydrothermal reaction is mainly carried out. In an alkaline hydrothermal environment with high temperature (180-280℃) and high pressure (1.0-6.4MPa), water is in a subcritical state and has strong oxidizing and high solubility. It can promote the breaking of the C-Cl bond of dioxins and degrade them into low-toxicity small molecules through dechlorination reaction. After adding silica-alumina additives (such as slag and fly ash), the hydrothermal reaction generates aluminosilicate minerals (such as zeolite substances). Heavy metals can be fixed in the mineral lattice through physical adsorption, ion exchange or chemical bonding, reducing their leaching toxicity, thereby achieving dioxin removal and heavy metal solidification.

[0067] Furthermore, this invention determines the order of water washing dechlorination and hydrothermal reaction based on the chlorine content in fly ash, forming two process paths: "water washing first, then hydrothermal reaction" and "hydrothermal reaction first, then water washing".

[0068] When the chlorine content in fly ash is greater than 15 wt%, it is classified as high-chlorine fly ash. High concentrations of chloride salts (such as NaCl and KCl) will accelerate the corrosion of the reactor in a high-temperature and high-pressure hydrothermal environment, especially chloride stress corrosion cracking of metal parts. The presence of chloride salts will also interfere with the formation of aluminosilicate minerals in the hydrothermal reaction and affect the stabilization of heavy metals. It is also necessary to increase the amount of alkali solution used in the hydrothermal reaction process to neutralize the chloride salts. Therefore, this invention adopts the method of "washing first and then hydrothermal" for high-chlorine fly ash. Most of the soluble chloride salts are removed by washing first, and the chlorine content in the washed ash is greatly reduced, thereby reducing the corrosion risk of the hydrothermal reactor and ensuring that the hydrothermal reaction is carried out more efficiently. It can also reduce the amount of alkali solution used and reduce costs.

[0069] When the chlorine content in fly ash is ≤15wt%, it is considered low-chlorine fly ash and does not require priority desalination. Therefore, the "hydrothermal treatment followed by water washing" method is adopted, allowing the fly ash to directly enter the hydrothermal reactor. The high-temperature and high-pressure hydrothermal conditions are used to increase the solubility of residual chloride salts in the fly ash, causing chloride ions to be released in the form of HCl and neutralized by alkaline solution. This achieves pre-dechlorination while decomposing dioxins and solidifying heavy metals, reducing the load on the water washing module, making water washing more efficient, using less water, and reducing equipment investment and energy costs.

[0070] Compared with the prior art, the beneficial effects of the present invention are:

[0071] 1) The municipal solid waste incineration fly ash treatment system provided by this invention combines a water washing module and a hydrothermal module, which can simultaneously achieve fly ash water washing dechlorination, dioxin removal, and heavy metal solidification. The main reactions are all completed in the hydrothermal reactor, which reduces the equipment cost and operating cost of fly ash harmless disposal. The continuous dioxin degradation and heavy metal solidification operation overcomes the defects of high energy consumption and high operating cost of intermittent operation. The order of water washing and hydrothermal treatment can be flexibly switched according to the chlorine content in the fly ash, which helps to ensure the stable operation of the system, reduce equipment wear, reduce the amount of water washing and alkali solution used, and effectively control costs. The hydrothermal reactor recovers part of the heat through heat exchanger, realizing energy saving and consumption reduction.

[0072] 2) The method for treating fly ash from municipal solid waste incineration provided by this invention can reduce the chlorine content of the dry basis of the washed ash to below 1 wt%, and reduce the dioxin content and the leaching concentrations of heavy metals Pb, Zn, Cu, Cr, and Cd to below the standard limits in the "Technical Specification for Pollution Control of Fly Ash from Municipal Solid Waste Incineration (Trial)" HJ1134-2020. The treated fly ash can be directly used as a raw material for high-value-added building materials or adsorbent materials, thus realizing the resource utilization of fly ash. Attached Figure Description

[0073] Figure 1 This is a schematic diagram of the structure of the municipal solid waste incineration fly ash treatment system of the present invention;

[0074] Figure 2 This is a schematic diagram of the system used for treating fly ash from municipal solid waste incineration in Example 1;

[0075] Figure 3 This is a schematic diagram of the system used for treating fly ash from municipal solid waste incineration in Example 2;

[0076] Appendix Figure 1-3 mark:

[0077] 100 - Raw ash silo, 200 - Primary washing tank, 210 - Primary dewatering equipment, 300 - Secondary washing tank, 310 - Secondary dewatering equipment, 400 - Mixing silo, 410 - Silicon-aluminum additive silo, 500 - Hydrothermal reactor, 600 - Heat exchanger, 610 - Hydrothermal dewatering equipment, 620 - Alkali solution silo, 700 - Finished ash silo, 800 - Washing liquid treatment tank, 900 - Fresh water tank. Detailed Implementation

[0078] The present invention will be further described in detail below through specific embodiments. Unless otherwise specified, the raw materials, reagents, or apparatus used in the embodiments can be obtained from conventional commercial sources or by existing technical methods. Unless otherwise specified, the experimental or testing methods are conventional methods in the art.

[0079] Figure 1 This is a schematic diagram of the structure of the municipal solid waste incineration fly ash treatment system of the present invention. Figure 1 It can be known that:

[0080] The municipal solid waste incineration fly ash treatment system provided by this invention mainly includes a water washing module and a hydrothermal module. When the fly ash in the original ash silo 100 first enters the water washing module, the fly ash first enters the primary water washing tank 200 of the water washing module, where it is washed with filtrate from the secondary dewatering device 310. Then, it enters the primary dewatering device 210 for solid-liquid separation. The filtrate enters the water washing liquid treatment tank 800, and the solids enter the secondary water washing tank 300. The solids in the secondary water washing tank 300 are washed with filtrate from the hydrothermal dewatering device 610, and then enter the secondary dewatering device 310 for solid-liquid separation. The filtrate is returned to the primary water washing tank. The washed ash enters the mixing chamber 400 from the pool 200. The silicon-aluminum additive chamber 410 adds silicon-aluminum additive to the mixing chamber 400 to adjust the elemental composition of the washed ash. The resulting mixed ash enters the hydrothermal reactor 500 for hydrothermal reaction. The alkali solution chamber 620 and the fresh water tank 900 respectively supply alkali solution and water to the heat exchanger 600. After preheating, the alkali solution and water enter the hydrothermal reactor 500 to participate in the hydrothermal reaction. The water-ash mixture discharged from the hydrothermal reactor 500 exchanges heat with the alkali solution / water in the heat exchanger 600 to recover heat. Then, it enters the hydrothermal dehydration equipment 610 for solid-liquid separation. The resulting filtrate is returned to the secondary washing pool 300, and the solid enters the finished ash silo 700.

[0081] When the fly ash in the original ash silo 100 enters the hydrothermal module, controlled by the automatic control unit, the fly ash first enters the mixing silo 400 of the hydrothermal module. The silicon-aluminum additive silo 410 adds silicon-aluminum additives to the mixing silo 400 to adjust the elemental composition of the fly ash. The resulting mixed ash enters the hydrothermal reactor 500 for hydrothermal reaction. The alkali solution silo 620 supplies alkali solution to the heat exchanger 600. The filtrate from the primary dewatering device 210 enters the heat exchanger 600. After preheating, the alkali solution and filtrate enter the hydrothermal reactor 500 to participate in the hydrothermal reaction. The water-ash mixture discharged from the hydrothermal reactor 500 reacts with the alkali solution / filtrate in the heat exchanger 600. After heat recovery via liquid heat exchange, the solids enter the hydrothermal dehydration equipment 610 for solid-liquid separation. The resulting filtrate enters the washing liquid treatment tank 800, while the solids enter the primary washing tank 200. The solids are then washed with the filtrate from the secondary dehydration equipment 310 and subsequently enter the primary dehydration equipment 210 for solid-liquid separation. The filtrate enters the heat exchanger 600, while the solids enter the secondary washing tank 300. The solids are then washed a second time with water supplied from the fresh water tank 900 to the secondary washing tank 300 and subsequently enter the secondary dehydration equipment 310 for solid-liquid separation. The filtrate is returned to the primary washing tank 200, while the solids enter the finished product ash silo 700.

[0082] Example 1

[0083] This embodiment provides a method for treating fly ash from municipal solid waste incineration. The fly ash has a chlorine content of 16.89 wt%, classifying it as high-chlorine fly ash. The method employs a process of "pre-washing followed by hydrothermal treatment." Figure 2 This is a schematic diagram of the system used for treating fly ash from municipal solid waste incineration in Example 1.

[0084] The specific steps for treating fly ash from municipal solid waste incineration are as follows:

[0085] S1. Fly ash (raw ash) enters the primary washing tank 200 from the raw ash silo 100 (0.5h). The fly ash is washed with water using the filtrate from the secondary dewatering equipment 310, and then enters the primary dewatering equipment 210 for solid-liquid separation (0.5h). The filtrate enters the washing liquid treatment tank 800, and the solids enter the secondary washing tank 300. The solids in the secondary washing tank 300 are washed with water using the filtrate from the hydrothermal dewatering equipment 610 (0.5h), and then enter the secondary dewatering equipment 310 for solid-liquid separation (0.5h). The filtrate is returned to the primary washing tank 200, and the washed ash (moisture content less than 30wt%) enters the mixing tank 400 to complete the water washing and dechlorination of the fly ash. The chlorine content of the washed ash is less than 1wt% (dry basis), and the dechlorination efficiency reaches more than 99%.

[0086] S2. Silicon-aluminum additives, specifically municipal solid waste incineration plant slag and diatomaceous earth, are added to the mixing chamber 400 in the silicon-aluminum additive bin 410. The particle size of both is less than 90μm. The mass ratio of incineration plant slag, diatomaceous earth, and raw ash is 1:1:8. This mixture forms a mixed ash, which is then conveyed by a screw conveyor to the hydrothermal reactor 500 for hydrothermal reaction. Fresh water tank 900 supplies water at a liquid-to-solid ratio of 3.5mL:1g. 30wt% sodium hydroxide is added to the alkali solution bin 620. The water and 30wt% sodium hydroxide are preheated by heat exchanger 600. After heating, the material enters the hydrothermal reactor 500 to participate in the hydrothermal reaction. After activating the material for 8 hours, steam is used to pressurize and heat the hydrothermal reactor 500. The pressure inside the reactor is 2.5 MPa, the temperature is 200℃, and the pH is 13. The hydrothermal reaction lasts for 2 hours. The water-ash mixture discharged from the hydrothermal reactor 500 enters the heat exchanger 600 and is indirectly cooled to below 50℃ by water. It then enters the hydrothermal dehydration equipment 610 for solid-liquid separation (0.5 hours). The resulting filtrate is returned to the secondary washing tank 300, and the solid enters the finished ash silo 700.

[0087] S3. Test the soluble chlorine content, heavy metal leaching toxicity, and dioxin content of the finished ash in the finished ash silo 700.

[0088] Table 1. Elemental composition of raw ash, incinerator slag, diatomaceous earth, and mixed ash in Example 1

[0089]

[0090] Table 2. Treatment effect of fly ash from municipal solid waste incineration in Example 1

[0091]

[0092] The standard limits are based on the "Technical Specification for Pollution Control of Fly Ash from Municipal Solid Waste Incineration (Trial)" HJ1134-2020.

[0093] Table 2 shows the treatment effect of municipal solid waste incineration fly ash in Example 1. As can be seen from Table 2, for high-chlorine fly ash (chlorine content > 15 wt%), the municipal solid waste incineration fly ash treatment system provided by this invention, using the process path of "first water washing and then hydrothermal treatment", has a good dechlorination effect, which greatly reduces the corrosion of soluble chloride salts on the hydrothermal reactor and the impact on the hydrothermal reaction process. After the water-washed ash undergoes hydrothermal reaction, the dioxin content and the leaching concentrations of heavy metals Pb, Zn, Cu, Cr, and Cd are all lower than the standard limits in the "Technical Specification for Pollution Control of Municipal Solid Waste Incineration Fly Ash (Trial)" HJ1134-2020. It can be directly used as a raw material for high-value-added building materials or adsorption materials, realizing the resource utilization of fly ash.

[0094] Example 2

[0095] This embodiment provides a method for treating fly ash from municipal solid waste incineration. The chlorine content of the treated fly ash is 11.95 wt%, which is classified as low-chlorine fly ash. The method employs a process of "hydrothermal treatment followed by water washing". Figure 3 This is a schematic diagram of the system used for treating fly ash from municipal solid waste incineration in Example 2.

[0096] The specific steps for treating fly ash from municipal solid waste incineration are as follows:

[0097] S1. Fly ash (raw ash) enters the mixing silo 400 from the raw ash silo 100. Silicon-aluminum additives, specifically municipal solid waste incineration plant slag and diatomaceous earth, are added to the mixing silo 400 from the silicon-aluminum additive silo 410. The particle size of both is less than 90μm, and the mass ratio of incineration plant slag, diatomaceous earth, and raw ash is 1:1:8. This mixture forms a mixed ash, which is then conveyed by a screw conveyor into the hydrothermal reactor 500 for hydrothermal reaction. The primary dewatering equipment 210 delivers filtrate at a liquid-to-solid ratio of 3.5mL:1g. 30wt% sodium hydroxide is added to the alkali solution silo 620. The filtrate and 30wt% sodium hydroxide are preheated by the heat exchanger 600 before entering the hydrothermal reactor. The reactor 500 participates in the hydrothermal reaction. After the material is activated for 8 hours, steam is used to pressurize and heat the hydrothermal reactor 500. The pressure inside the reactor is 2.5 MPa, the temperature is 200℃, and the pH is 13. The hydrothermal reaction lasts for 2 hours. The water-ash mixture discharged from the hydrothermal reactor 500 enters the heat exchanger 600 and is indirectly cooled to below 50℃ by the filtrate or water from the preceding dewatering equipment. The cooled water-ash mixture enters the hydrothermal dewatering equipment 610 for solid-liquid separation (0.5 hours). The resulting filtrate enters the washing liquid treatment tank 800, while the solid enters the primary washing tank 200 to complete the dioxin removal and heavy metal solidification of fly ash.

[0098] S2. The solids in the primary washing tank 200 are washed with filtrate from the secondary dewatering equipment 310 for 0.5 hours, and then enter the primary dewatering equipment 210 for solid-liquid separation for 0.5 hours. The filtrate enters the heat exchanger 600, and the solids enter the secondary washing tank 300. The solids are washed a second time with water supplied from the fresh water tank 900 to the secondary washing tank 300 for 0.5 hours, and then enter the secondary dewatering equipment 310 for solid-liquid separation for 0.5 hours. The filtrate is returned to the primary washing tank 200, and the solids enter the finished product ash silo 700.

[0099] S3. Test the soluble chlorine content, heavy metal leaching toxicity, and dioxin content of the finished ash in the finished ash silo 700.

[0100] Table 3. Elemental composition of raw ash, incinerator slag, diatomaceous earth, and mixed ash in Example 2.

[0101]

[0102] Table 4. Treatment effect of fly ash from municipal solid waste incineration in Example 2

[0103]

[0104] The standard limits are based on the "Technical Specification for Pollution Control of Fly Ash from Municipal Solid Waste Incineration (Trial)" HJ1134-2020.

[0105] Table 4 shows the treatment effect of municipal solid waste incineration fly ash in Example 2. As can be seen from Table 4, for low-chlorine fly ash (chlorine content ≤15wt%), the municipal solid waste incineration fly ash treatment system provided by this invention, using the process path of "first hydrothermal treatment followed by water washing", resulted in dioxin content and leaching concentrations of heavy metals Pb, Zn, Cu, Cr, and Cd in the fly ash being lower than the standard limits in the "Technical Specification for Pollution Control of Municipal Solid Waste Incineration Fly Ash (Trial)" HJ1134-2020. The hydrothermal reaction achieved pre-dechlorination, reduced the processing pressure of the water washing module, and saved water consumption. The chlorine content of the washed ash was below 1wt% (dry basis), and the dechlorination efficiency reached over 99%, demonstrating good dechlorination effect. The treated fly ash can be directly used as raw material for high-value-added building materials or adsorption materials, realizing the resource utilization of fly ash.

Claims

1. A system for treating fly ash from municipal solid waste incineration, characterized in that, include: Original ash bin(100); The water washing module includes a primary water washing tank (200), a primary dewatering device (210), a secondary water washing tank (300), and a secondary dewatering device (310) arranged sequentially. The hydrothermal module includes a mixing chamber (400), a hydrothermal reactor (500), a heat exchanger (600), and a hydrothermal dehydration device (610) arranged sequentially. Finished product ash silo (700); The ash outlet of the original ash silo (100) is connected to the primary washing tank (200) and the mixing silo (400) respectively; The filtrate outlet of the primary dehydration device (210) is connected to the heat exchanger (600); The filtrate outlet of the secondary dewatering device (310) is connected to the primary washing tank (200); The ash outlet of the secondary dewatering device (310) is connected to the mixing silo (400) and the finished ash silo (700) respectively; The filtrate outlet of the hydrothermal dehydration equipment (610) is connected to the secondary washing tank (300); The ash outlet of the hydrothermal dehydration equipment (610) is connected to the primary washing tank (200) and the finished ash silo (700) respectively; The outlet of the hydrothermal reactor (500) is connected to the inlet of the heat exchanger (600); the outlet of the heat exchanger (600) is connected to the inlet of the hydrothermal reactor (500) and the hydrothermal dehydration device (610) respectively. The processing system also includes an automatic control unit, which switches the order in which the fly ash in the original ash silo (100) enters the water washing module and the hydrothermal module according to the chlorine content in the fly ash, specifically: If the chlorine content in the fly ash is >15wt%, the automatic control unit controls the fly ash in the original ash bin (100) to first enter the water washing module; if the chlorine content in the fly ash is ≤15wt%, the automatic control unit controls the fly ash in the original ash bin (100) to first enter the hydrothermal module.

2. The processing system according to claim 1, characterized in that, The processing system also includes a washing liquid treatment tank (800), which is connected to the filtrate outlets of the primary dehydration device (210) and the hydrothermal dehydration device (610).

3. The processing system according to claim 2, characterized in that, The processing system also includes a fresh water tank (900), which is connected to the inlet of the secondary washing tank (300) and the heat exchanger (600).

4. The processing system according to claim 3, characterized in that, The processing system also includes a silicon-aluminum additive tank (410) and an alkali tank (620). The silicon-aluminum additive tank (410) is connected to the inlet of the mixing tank (400), and the alkali tank (620) is connected to the heat exchanger (600).

5. A method for treating fly ash from municipal solid waste incineration, characterized in that, This includes using the municipal solid waste incineration fly ash treatment system described in claim 4 to perform water washing and dechlorination, dioxin removal, and heavy metal solidification on the fly ash.

6. The processing method according to claim 5, characterized in that, The physicochemical parameters of the municipal solid waste incineration fly ash include at least one of the following: dioxin content ≥ 0.2 μg TEQ / kg; Pb content ≥ 1000 mg / kg; Zn content ≥ 3000 mg / kg; Cu content ≥ 500 mg / kg; Cr content ≥ 200 mg / kg; Cd content ≥ 40 mg / kg; As content ≥ 20 mg / kg; Ca content ≥ 20 wt%; Si content ≥ 2 wt%; Al content ≥ 0.5 wt%.

7. The processing method according to claim 5 or 6, characterized in that, The process path of the processing method is selected from either path 1 or path 2: Path 1: When the chlorine content in fly ash is >15wt%, the fly ash first enters the water washing module from the original ash silo (100) for water washing and dechlorination, and then enters the hydrothermal module for hydrothermal reaction to remove dioxins, solidify heavy metals, and obtain finished ash, which then enters the finished ash silo (700). Path 2: When the chlorine content in fly ash is ≤15wt%, the fly ash first enters the hydrothermal module from the original ash silo (100) for hydrothermal reaction to remove dioxins and solidify heavy metals, and then enters the water washing module for water washing and dechlorination to obtain finished ash, which then enters the finished ash silo (700).

8. The processing method according to claim 7, characterized in that, After the fly ash enters the hydrothermal module, it includes adding silicon-aluminum additives from the silicon-aluminum additive bin (410) to the mixing bin (400) to adjust the CaO, SiO2, and AlO content of the fly ash in the mixing bin (400). 1.5 The mass ratio is (5-6): (3.5-4.5): 1, resulting in a mixed ash.

9. The processing method according to claim 7, characterized in that, The conditions for the hydrothermal reaction include at least one of the following: 1) The solid-liquid ratio is 1g: (2-5)mL; 2) pH ≥ 12; 3) The temperature is 180-280℃; 4) Pressure range: 1.0-6.4 MPa; 5) The time is 2-8 hours.

Images