System and method for detoxifying fly ash from garbage incineration

Abstract

The present invention discloses a waste incineration fly ash detoxification system, comprising an ash feeding device, a low-temperature thermal decomposition device, a fly ash cooling device, a fly ash washing device, a heavy metal solidification device, a pyrolysis gas treatment device, a wastewater pretreatment device and an evaporation and salt separation device. The system adopts the method recorded in the invention to perform low-temperature thermal decomposition on waste incineration fly ash, with low comprehensive energy consumption, which is beneficial to energy saving. The present invention can achieve efficient removal of dioxin-like organic compounds, soluble salts and heavy metals. After treatment, the leaching of dioxins and heavy metals in the waste incineration fly ash is lower than the standard limit, which is safe and reliable. The detoxified waste incineration fly ash can be utilized as building materials and landfilled harmlessly, ultimately achieving the harmlessness, resource utilization and reduction of the waste incineration fly ash.

Description

Technical Field

[0001] The present invention relates to the technical field of waste incineration treatment, and in particular to a system and method for detoxifying waste incineration fly ash. Background Art

[0002] my country's urban domestic waste is growing rapidly. From 2010 to 2020, the national waste collection volume increased significantly, more than doubling from 108.05 million tons to 235.12 million tons. Waste-to-energy incineration is gaining popularity due to its advantages in volume reduction, energy recovery, and energy recovery. In July 2020, the National Development and Reform Commission, the Ministry of Housing and Urban-Rural Development, the Ministry of Ecology and Environment, and other three departments jointly issued the "Implementation Plan for Addressing Shortcomings and Strengthening Weaknesses in Urban Domestic Waste Sorting and Treatment Facilities," comprehensively promoting the development of incineration treatment capacity and accelerating the construction of fly ash disposal facilities. Due to the complex composition of fly ash, including heavy metals, dioxin-like organic compounds, and chloride salts, its high pollutant content is difficult to remove. Improper disposal can cause serious environmental problems. Chinese laws and regulations classify fly ash as hazardous waste. In 2020, my country's waste incineration fly ash production exceeded 7 million tons. Therefore, the proper detoxification and disposal of waste incineration fly ash has become a widespread and urgent need.

[0003] Currently, the main methods for treating waste incineration fly ash include high-temperature melting, low-temperature thermal decomposition, hydrothermal treatment, bioleaching, chemical extraction, and mechanochemical methods. However, due to the complex nature of waste incineration pollutants and the difficulty in resource utilization, a single technology cannot meet the requirements for waste incineration fly ash detoxification. For example, high-temperature melting technology has high energy consumption and costs, low-temperature thermal decomposition cannot stabilize heavy metals, hydrothermal treatment has weak technical adaptability, bioleaching has a long cycle and low efficiency, and chemical extraction has unstable results. Currently, there are some comprehensive waste incineration fly ash treatment systems and methods, such as CN113714246A, which describes a waste incineration fly ash treatment system and method. This system utilizes a pyrolyzer, a roaster, a melting furnace, a quenching device, a metal recovery device, and a heat exchanger. Through treatment in three temperature stages: low-temperature pyrolysis pretreatment, high-temperature chlorination roasting, and melting, it achieves metal chlorination separation and enrichment in the fly ash, complete decomposition of dioxins, and ultimately achieves fly ash detoxification. However, the entire treatment process requires relatively high temperatures. Currently, the issue of dioxin regeneration during the cooling process of hot fly ash after pyrolysis has been largely overlooked. Therefore, it is crucial to design a method and system for detoxifying waste incineration fly ash to address issues such as high fly ash disposal costs, poor heavy metal stabilization, poor adaptability, low disposal efficiency, and the secondary generation of dioxins during the fly ash cooling process, ultimately achieving the goal of detoxifying and harmless waste incineration fly ash. Summary of the Invention

[0004] The purpose of the present invention is to overcome the shortcomings of the existing technology and propose a method and system for detoxifying waste incineration fly ash to fully remove dioxin-like organic compounds, heavy metals and soluble salts in waste incineration fly ash, thereby achieving harmlessness, resource utilization and reduction of waste incineration fly ash.

[0005] In order to achieve the above object, the present invention provides the following technical solutions:

[0006] A first aspect of the present invention provides a waste incineration fly ash detoxification system, comprising:

[0007] Ash feeding device: It consists of an ash storage bin, a bag dust collector, a discharge valve and a screw conveyor. It is used to continuously feed the system. Nitrogen is introduced into the bottom of the ash storage bin.

[0008] Low-temperature thermal decomposition device: includes a preheating chamber and a holding chamber connected in sequence, with an exhaust port at the end of the preheating chamber; the discharge port of the screw conveyor is connected to the feed port of the preheating chamber, and nitrogen is introduced into the discharge port of the holding chamber;

[0009] The fly ash cooling device includes a first-stage fly ash water-cooled screw conveyor, a fly ash buffer bin, and a second-stage fly ash water-cooled screw conveyor connected in sequence. The first-stage fly ash water-cooled screw conveyor and the second-stage fly ash water-cooled screw conveyor have the same structure and are respectively provided with a feed port, a discharge port, a water inlet, and a water outlet. The discharge port of the insulation chamber is connected to the feed port of the first-stage fly ash water-cooled screw conveyor, and nitrogen is introduced into the bottom of the fly ash buffer bin.

[0010] Fly ash washing device: includes a primary stirring kettle, a primary pump, a primary dehydration device, a bidirectional conveyor, a secondary stirring kettle, a secondary pump, a secondary dehydration device, and a unidirectional conveyor; it is used to remove heavy metals from fly ash by water washing; the discharge port of the secondary fly ash water-cooled screw conveyor is connected to the primary stirring kettle, and the wastewater generated by the dehydration device enters the wastewater pretreatment system;

[0011] Heavy metal solidification device: The fly ash circulating slurry tank, fly ash slurry circulating pump, and wet continuous ball mill are connected via a slurry pipeline to form a circulation loop; an on-off valve A is provided on the slurry pipeline between the fly ash slurry circulating pump and the wet continuous ball mill; the feed port of the wet continuous ball mill is provided with a reagent addition device; the on-off valve A and the fly ash slurry circulating pump are connected to the tertiary dehydration device via a branch slurry pipeline, and the branch slurry pipeline is provided with an on-off valve B; the discharge port of the one-way conveyor of the fly ash washing device is connected to the fly ash circulating slurry tank;

[0012] The pyrolysis gas treatment device comprises an activated carbon injection device, a bag dust collector, a spray tower and an induced draft fan connected in sequence; the exhaust port at the end of the preheating chamber is connected to the pyrolysis gas treatment device through a pipeline between the activated carbon injection device and the bag dust collector.

[0013] Furthermore, an oxygen content meter is provided at the exhaust outlet of the low-temperature thermal decomposition device.

[0014] Furthermore, the preheating chamber and the holding chamber of the low-temperature thermal decomposition device are both indirect heating spiral propulsion structures, and the two are arranged in parallel. The preheating chamber is above the holding chamber, and the discharge port of the preheating chamber is connected to the feed port of the holding chamber.

[0015] Furthermore, the first-level stirring kettle, first-level pump, first-level dehydration device, and bidirectional conveyor of the fly ash washing device are connected in sequence, one discharge end of the bidirectional conveyor is connected to the first-level stirring kettle, and the other discharge end is connected to the second-level stirring kettle. The second-level stirring kettle is connected in sequence to the second-level pump, second-level dehydration device, and one-way conveyor.

[0016] Furthermore, the wastewater pretreatment system includes a wastewater pretreatment device and an evaporation and salt separation device. The wastewater pretreatment device includes a regulating tank, a decalcification reaction tank, a heavy metal removal tank, a sedimentation tank, a pH adjustment tank, a sand filter tank and a clean water tank connected in sequence, and also includes a sludge sedimentation tank. The clean water tank is connected to the evaporation and salt separation device through a lifting pump. The sludge in the regulating tank, decalcification reaction tank, heavy metal removal tank, sedimentation tank and pH adjustment tank enters the sludge sedimentation tank, and the sludge sedimentation tank is connected to the first-level stirring tank of the fly ash washing device through a sludge pump.

[0017] The second aspect of the present invention is to provide a method for detoxifying waste incineration fly ash using the waste incineration fly ash detoxification system described above, the method specifically comprising:

[0018] S1, continuously inputting waste incineration fly ash to be processed into the system through the ash feeding device, and continuously introducing nitrogen into the system; the fly ash enters the low-temperature thermal decomposition device with a nitrogen environment, the preheating temperature in the preheating chamber is 200-400℃, the heating temperature in the holding chamber is 200-400℃, and the residence time is 10-60 minutes; the fly ash is thermally decomposed at low temperature to form hot ash and pyrolysis gas;

[0019] S2, the pyrolysis gas enters the pyrolysis gas purification device through the exhaust port at the end of the preheating chamber. The oxygen content in the system is detected by the oxygen content meter at the exhaust port, and the oxygen content is controlled at 0-1%;

[0020] S3, the hot ash enters the fly ash cooling device with a nitrogen environment, where it is cooled by a two-stage water cooling device to prevent dioxin from re-generating;

[0021] S4, the cooled fly ash enters the fly ash washing device and undergoes three-stage washing. During the washing process, the ash-to-water ratio is 1:2 to 1:4, and it is stirred for 10 to 60 minutes. The washing filtrate enters the wastewater treatment system. The wastewater is treated by the pretreatment device and then enters the evaporation and salt separation device; the fly ash solids after washing enter the heavy metal solidification device for treatment.

[0022] Furthermore, when the fly ash solid is processed in the heavy metal solidification device, when the wet continuous ball mill disposes of the fly ash, the switch valve A is opened, the switch valve B is closed, and a heavy metal solidification agent is added to the wet continuous ball mill. The heavy metal solidification agent includes NaH2PO4 and CaO, wherein NaH2PO4 accounts for 20% to 80% of the mass fraction of the heavy metal solidification agent, and the amount of heavy metal solidification agent added is 1% to 20% of the mass of the fly ash.

[0023] Furthermore, when process water is added to the fly ash circulation slurry pool, the solid concentration of the fly ash slurry is controlled at 10% to 50%.

[0024] Furthermore, the fly ash solids are treated in the heavy metal solidification unit for 30 to 240 minutes. When the set value is reached, valve B opens and valve A closes. The fly ash then passes through a three-stage dehydration unit to remove water, ensuring the water content is no more than 30%. The treated fly ash is then used for building materials or landfilled.

[0025] In the present invention, during the low-temperature thermal decomposition process of fly ash, the oxygen content is controlled between 0-1%. The low-temperature thermal decomposition device adopts an indirect heating spiral propulsion structure. The fly ash is fully heat-exchanged with the furnace wall while being mixed, stirred and transported to the rear end. The upper part of the low-temperature thermal decomposition device is a preheating chamber. In this space, the temperature of the fly ash continues to rise to 200-400°C as the transportation distance increases, and the moisture in the fly ash evaporates due to heat; the lower part is an insulation chamber. In this stage, the fly ash stays at a temperature of 200-400°C for 10-60 minutes. Organic pollutants such as dioxins in the fly ash are continuously decomposed in an oxygen-deficient environment, and form pyrolysis waste gas together with the introduced nitrogen to be discharged from the low-temperature thermal decomposition device. This part of the pyrolysis gas is treated by a subsequent pyrolysis gas treatment device and then discharged into the chimney.

[0026] Oxygen is the oxygen source for the de novo dioxin synthesis reaction and is crucial for this process. Reducing the oxygen content in the reaction atmosphere can reduce dioxin formation during thermal desorption. Dioxins are degraded when fly ash is heated in a nitrogen atmosphere. When fly ash is heated at 300°C for 30 minutes in a nitrogen atmosphere, virtually no dioxin is generated. However, when the fly ash contains 10% oxygen, the same experiment results in higher dioxin formation, and dioxin formation increases with increasing oxygen content (0-10%). Therefore, to prevent dioxin regeneration during pyrolysis, the low-temperature thermal decomposition unit requires continuous nitrogen flow during operation to keep the internal oxygen content below 1%.

[0027] In the process of heavy metal solidification of fly ash solids, the heavy metal solidification agent is mainly composed of NaH2PO4 and CaO, which mainly uses the reaction of heavy metals with NaH2PO4 and PO4. 3-The reaction generates insoluble phosphate precipitate, and the alkaline reaction environment provided by CaO can promote the precipitation reaction. The content of NaH2PO4 accounts for 20%-80% of the mass fraction of the heavy metal solidification agent.

[0028] During the pyrolysis gas purification process of fly ash, the pyrolysis gas purification device mainly uses the treatment process of bag dust collector + activated carbon adsorption + wet deacidification spray tower to treat the pyrolysis waste gas of domestic waste incineration fly ash containing a small amount of dust, acidic substances and dioxins, so that the waste gas emission standards meet the GB18485-2020 standard.

[0029] A. Bag filter: The dust-laden gas is sent into the bag filter from the exhaust outlet of the low-temperature thermal decomposition device. As the bag filter runs, the dust and particles contained in the flue gas form filter cakes on the outer surface of the filter bag due to inertial impact, direct interception, diffusion and electrostatic attraction.

[0030] B. Activated carbon injection device: Activated carbon is used to absorb toxic substances such as dioxins and heavy metals in the flue gas to achieve the purpose of efficient flue gas purification. After the activated carbon and the flue gas are strongly and evenly mixed, it achieves a high-efficiency adsorption effect, achieving the adsorption and purification of pollutants such as dioxins and heavy metals in the flue gas.

[0031] C. Spray tower (wet deacidification): The waste gas enters from the air inlet located at the bottom of the spray tower. During the rising process, the waste gas mixes with the alkaline solution sprayed from the spray device at the top of the tower to react and remove acidic gases such as HCl and SO2 in the flue gas. A circulation pool is set at the bottom of the spray tower. After the pH value is adjusted in the circulation pool, the circulating alkaline solution is pumped to the top of the spray tower to continue washing the flue gas. The purified flue gas rises and enters the demister device to ensure that the moisture content of the waste gas at the outlet of the spray tower is not more than 75mg / Nm 3 .

[0032] In the wastewater treatment system for fly ash washing wastewater, the fly ash filtrate contains not only soluble salts such as potassium and sodium salts, but also calcium, magnesium, and heavy metal sludge. If these substances were directly introduced into the evaporation and salt separation system, they would cause scaling, blockage, and other problems. Therefore, a wastewater pretreatment device was installed to ensure that the fly ash filtrate meets the process requirements of the subsequent evaporation and salt separation (MVR) device after pretreatment.

[0033] The wastewater pretreatment device includes a regulating tank, a decalcification reaction tank, a heavy metal removal tank, a sedimentation tank, a pH adjustment tank, a sand filter tank, a clean water tank, and a sludge sedimentation tank.

[0034] Adjustment tank: Used to store high-chlorine wastewater generated by fly ash washing, it has the function of homogenizing and balancing the amount of wastewater. The wastewater flows by gravity into the adjustment tank, and then is continuously transported to the decalcification reaction tank for treatment by the sewage lift pump.

[0035] Decalcification reaction tank: Sodium carbonate is added as a precipitant to react with calcium ions in the wastewater to form a water-insoluble precipitate. Sodium carbonate dissolves in the washing wastewater and undergoes hydrolysis, which produces a large amount of OH - , HCO 3- 、CO3 2- , which increases the alkalinity in the system. The washing wastewater contains a large amount of Ca 2+ , can be combined with CO3 2- CaCO3 precipitate is formed, and CaCO3 is a loose precipitate material.

[0036] Heavy Metal Removal Tank: In addition to chelating agents, the heavy metal removal tank also incorporates polymer flocculants such as polyaluminium chloride (PAC) and polyacrylamide (PAM). Polyaluminium chloride, as a coagulant, and polyacrylamide, as a coagulant aid, achieve rapid flocculation and sedimentation, operating over a wide pH range. They effectively remove heavy metals such as SS, COD, BOD, and heavy metal ions such as arsenic and mercury from water. Heavy metals in the wash wastewater flocculate under the action of polyaluminium chloride, removing them from the water. The flocculation process also precipitates heavy metals and suspended solids previously precipitated by the precipitant, removing them from the water. The post-reaction wash wastewater containing the precipitate flows into a sedimentation tank for solid-liquid separation.

[0037] Sedimentation tank: Separates the precipitate generated by the reaction from the wastewater. The precipitate settles to the bottom of the tank and is regularly drained through the sludge valve. The sludge is then pumped into the sludge pump for subsequent treatment. The supernatant enters the pH adjustment tank.

[0038] pH adjustment tank: By adding 30% hydrochloric acid to neutralize the alkali in the wastewater, the hydrochloric acid is diluted to 10% in the metering tank and pumped into the pH adjustment tank below the liquid level through the metering pump to avoid the generation of acid mist.

[0039] Sand filter tanks: These use a multi-media filter filled with gravel, quartz sand, and other media to filter, coagulate, and settle suspended solids in the effluent. After a period of operation, sand filters require regular backwashing to remove suspended solids trapped by the filter media and ensure effective filtration. Backwash water can be returned to the conditioning tank.

[0040] Clean water tank: used to store pre-treated water, which is connected to the subsequent evaporation and salt separation equipment through a lifting pump.

[0041] Sludge sedimentation tank: The sludge sedimentation tank is in the shape of a mud bucket and is used to store the sludge produced by the regulating tank, decalcification reaction tank, heavy metal removal tank, sedimentation tank, and pH adjustment tank. The sludge is transported to the first-level stirred tank of the fly ash washing device through a sludge pump.

[0042] The evaporation and salt separation device uses conventional equipment already available in the industry, primarily consisting of an evaporation chamber, a gas-liquid separator, and a mechanical steam compressor. The evaporation and salt separation device can separate the sodium chloride and potassium chloride resources in the fly ash wash water from the wastewater, producing industrial-grade sodium chloride and potassium chloride products that can be sold externally.

[0043] The beneficial effects of the present invention are as follows: the present invention uses the waste incineration fly ash detoxification system to efficiently remove dioxin-like pyrolysis gas generated by waste incineration fly ash, heavy metals in fly ash solids, and soluble salts and heavy metals in water-washing waste liquid: the fly ash is placed in a low-temperature thermal decomposition device, under the conditions of nitrogen and oxygen content of 0-1%, the preheating chamber and the insulation chamber are continuously heated to 200-400°C, the fly ash is kept at this temperature for 10-60 minutes, the dioxins and other organic pollutants in the fly ash are continuously decomposed, and together with the nitrogen introduced, pyrolysis waste gas is formed. After the pyrolysis waste gas is treated by the bag filter + activated carbon adsorption + wet deacidification spray tower of the pyrolysis gas treatment device, the waste gas is discharged. The emission standard meets the GB18485-2020 standard and is discharged directly from the chimney; the heavy metals in the fly ash solids are transferred to the wastewater through the fly ash washing device, and the other part is solidified in the heavy metal solidification device by adding a heavy metal solidifying agent with a mass fraction of NaH2PO4 of 20~80%. Under the conditions of wet continuous ball milling, the heavy metals in the fly ash are solidified. After dehydration, the fly ash with a water content of no more than 30% can be used for building material utilization or harmless landfill. The fly ash washing wastewater is treated by the wastewater pretreatment device and the evaporation and salt separation device to meet the harmlessness requirements. At the same time, industrial-grade sodium chloride and potassium chloride are separated from the fly ash wastewater.

[0044] The waste incineration fly ash treated by the waste incineration fly ash detoxification system and method of the present invention has dioxin and heavy metal leaching below the standard limit, which is safe and reliable; the detoxified waste incineration fly ash can be used as building materials and landfilled harmlessly; the use of the present invention can achieve continuous and uninterrupted disposal of waste incineration fly ash with high disposal efficiency; the waste incineration fly ash is subjected to low-temperature thermal decomposition, the comprehensive energy consumption is low, and it is conducive to energy saving. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 This is a schematic diagram of the process flow of the waste incineration fly ash detoxification system of the present invention;

[0046] Figure 2 This is a schematic structural diagram of the ash feeding device of the waste incineration fly ash detoxification system of the present invention;

[0047] Figure 3 This is a schematic structural diagram of a low-temperature thermal decomposition device of a waste incineration fly ash detoxification system according to the present invention;

[0048] Figure 4 This is a schematic structural diagram of a fly ash cooling device of a waste incineration fly ash detoxification system according to the present invention;

[0049] Figure 5 This is a schematic structural diagram of a fly ash washing device in a waste incineration fly ash detoxification system according to the present invention;

[0050] Figure 6 This is a schematic structural diagram of the heavy metal solidification device of the waste incineration fly ash detoxification system of the present invention;

[0051] Figure 7 This is a schematic structural diagram of a pyrolysis gas treatment device for a waste incineration fly ash detoxification system according to the present invention;

[0052] Figure 8 This is a schematic structural diagram of a wastewater pretreatment device for a waste incineration fly ash detoxification system according to the present invention;

[0053] Among them, 1. Ash feeding device; 101. Ash storage bin; 102. Bag dust collector; 103. Discharge valve; 104. Screw conveyor; 105. Discharge port of screw conveyor; 2. Low-temperature thermal decomposition device; 201. Preheating chamber; 202. Holding chamber; 203. Exhaust port; 204. Preheating chamber feed port; 205. Holding chamber discharge port; 206. Preheating chamber discharge port; 207. Holding chamber feed port; 208. Oxygen content Measuring instrument; 3. Fly ash cooling device; 301. First-stage fly ash water-cooled screw conveyor; 302. Fly ash buffer bin; 303. Second-stage fly ash water-cooled screw conveyor; 304. Feed inlet; 305. Discharge outlet; 306. Water inlet; 307. Water outlet; 4. Fly ash washing device; 401. First-stage stirring kettle; 402. First-stage pump; 403. First-stage dehydration device; 404. Bidirectional conveyor; 405. Second-stage stirring kettle; 406, secondary pump; 407, secondary dehydration device; 408, one-way conveyor; 409, one-way conveyor outlet; 5, heavy metal solidification device; 501, fly ash circulation slurry tank; 502, fly ash slurry circulation pump; 503, wet continuous ball mill; 504, tertiary dehydration device; 505, slurry pipeline; 506, on-off valve A; 507, on-off valve B; 508, reagent addition device; 509, branch slurry Liquid pipeline; 6. Pyrolysis gas treatment device; 601. Activated carbon injection device; 602. Bag dust collector; 603. Spray tower; 604. Induced draft fan; 7. Wastewater pretreatment device; 701. Adjustment tank; 702. Decalcification reaction tank; 703. Heavy metal removal tank; 704. Sedimentation tank; 705. pH adjustment tank; 706. Sand filter tank; 707. Clear water tank; 708. Sludge sedimentation tank; 8. Evaporation and salt separation device. DETAILED DESCRIPTION

[0054] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0055] like Figures 1 to 8 As shown, the waste incineration fly ash detoxification system of the present invention includes:

[0056] Ash feeding device 1: It consists of an ash storage bin 101, a bag filter 102, a discharge valve 103 and a screw conveyor 104. It is used to continuously feed the system. Nitrogen is introduced into the bottom of the ash storage bin 101.

[0057] Low-temperature thermal decomposition device 2: includes a preheating chamber 201 and a holding chamber 202 connected in sequence, with an exhaust port 203 provided at the end of the preheating chamber 201; an oxygen content meter is provided at the exhaust port 203; the screw conveyor discharge port 105 is connected to the preheating chamber feed port 204, and nitrogen is introduced into the holding chamber discharge port 205; the preheating chamber 201 and the holding chamber 202 of the low-temperature thermal decomposition device 2 are both indirect heating spiral propulsion structures, and the two are arranged in parallel, the preheating chamber 201 is above the holding chamber 202, and the preheating chamber discharge port 206 is connected to the holding chamber feed port 207.

[0058] Fly ash cooling device 3: includes a first-stage fly ash water-cooled screw conveyor 301, a fly ash buffer bin 302, and a second-stage fly ash water-cooled screw conveyor 303 connected in sequence. The first-stage fly ash water-cooled screw conveyor 301 and the second-stage fly ash water-cooled screw conveyor 303 have the same structure and are respectively provided with a feed inlet 304, a discharge port 305, a water inlet 306, and a water outlet 307. The discharge port 205 of the insulation chamber is connected to the feed inlet 304 of the first-stage fly ash water-cooled screw conveyor. Nitrogen is introduced into the bottom of the fly ash buffer bin 302.

[0059] Fly ash washing device 4: includes a first-level stirring kettle 401, a first-level pump 402, a first-level dehydration device 403, a bidirectional conveyor 404, a second-level stirring kettle 405, a second-level pump 406, a second-level dehydration device 407, and a one-way conveyor 408; is used for washing and removing heavy metals from fly ash; the discharge port 305 of the second-level fly ash water-cooled screw conveyor is connected to the first-level stirring kettle 401, and the wastewater generated by the dehydration device enters the wastewater treatment system; the first-level stirring kettle 401, the first-level pump 402, the first-level dehydration device 403, and the bidirectional conveyor 404 of the fly ash washing device 4 are connected in sequence, one discharge end of the bidirectional conveyor 404 is connected to the first-level stirring kettle 405, and the other discharge end is connected to the second-level stirring kettle 405, and the second-level stirring kettle 405 is connected in sequence to the second-level pump 406, the second-level dehydration device 407, and the one-way conveyor 408.

[0060] Heavy metal solidification device 5: includes a fly ash circulating slurry tank 501, a fly ash slurry circulating pump 502, a wet continuous ball mill 503, a tertiary dehydration device 504, a slurry pipeline 505, a switch valve A506, a switch valve B507 and a reagent adding device 508; the fly ash circulating slurry tank 501, the fly ash slurry circulating pump 502 and the wet continuous ball mill 503 are connected through the slurry pipeline 505 to form a circulation loop; the slurry pipeline 505 between the fly ash slurry circulating pump 502 and the wet continuous ball mill 503 is provided with a switch valve A506, the feed port of the wet continuous ball mill 503 is provided with a reagent adding device 508, the switch valve A506 and the fly ash slurry circulating pump 502 are connected to the tertiary dehydration device 504 through a branch slurry pipeline 509, and the branch slurry pipeline 509 is provided with a switch valve B 507; fly ash washing device one-way conveyor discharge port 409 is connected to the fly ash circulating slurry pool 501;

[0061] The pyrolysis gas treatment device 6 includes an activated carbon injection device 601, a bag dust collector 602, a spray tower 603 and an induced draft fan 604 connected in sequence; the exhaust port 203 at the end of the preheating chamber 201 is connected to the pyrolysis gas treatment device 6 through a pipeline between the activated carbon injection device 601 and the bag dust collector 602.

[0062] The wastewater pretreatment system includes a wastewater pretreatment device 7 and an evaporation and salt separation device 8. The wastewater pretreatment device 7 includes a regulating tank 701, a decalcification reaction tank 702, a heavy metal removal tank 703, a precipitation tank 704, a pH adjustment tank 705, a sand filter tank 706 and a clean water tank 707 connected in sequence, and also includes a sludge sedimentation tank 708. The clean water tank 707 is connected to the evaporation and salt separation device 8 through a lifting pump. The sludge in the regulating tank 701, the decalcification reaction tank 702, the heavy metal removal tank 703, the precipitation tank 704 and the pH adjustment tank 705 enters the sludge sedimentation tank 708, and the sludge sedimentation tank 708 is connected to the first-level stirring tank 402 of the fly ash washing device 4 through a sludge pump.

[0063] The method for detoxifying waste incineration fly ash using the waste incineration fly ash detoxification system of the present invention is as follows:

[0064] The waste incineration fly ash to be processed is continuously fed into the system through the ash feeding device, and nitrogen is continuously introduced into the system at the same time; the fly ash enters the low-temperature thermal decomposition device, the preheating temperature of the preheating chamber is 200-400℃, the heating temperature of the insulation chamber is 200-400℃, and the residence time is 10-60min; the fly ash forms hot ash and pyrolysis gas after low-temperature thermal decomposition; the pyrolysis gas enters the pyrolysis gas purification device through the exhaust port at the end of the preheating chamber, and the oxygen content in the system is detected by the oxygen content meter at the exhaust port at the end of the preheating chamber, and the oxygen content is controlled at 0-1%; the exhaust gas treated by the pyrolysis gas purification device can meet the emission standard requirements and is finally discharged into the atmosphere through the chimney.

[0065] The hot ash enters the fly ash cooling unit, which is located in a nitrogen atmosphere. It is then cooled by a two-stage water cooling unit to prevent dioxin regeneration. The cooled fly ash then enters the fly ash washing unit, where it undergoes three-stage water washing. The washing process maintains an ash-to-water ratio of 1:2 to 1:4 and is stirred for 10 to 60 minutes. The wash filtrate enters the wastewater treatment system, where it is pretreated and then fed into the evaporation and desalination unit. The washed fly ash solids enter the heavy metal solidification unit. The evaporation and desalination unit separates the sodium chloride and potassium chloride resources from the wastewater, producing industrial-grade sodium chloride and potassium chloride products for sale.

[0066] During fly ash solids treatment in the heavy metal solidification unit, when the wet continuous ball mill is processing fly ash, valve A is opened and valve B is closed. A heavy metal solidification agent, consisting of NaH2PO4 and CaO, is added to the wet continuous ball mill. NaH2PO4 accounts for 20-80% of the heavy metal solidification agent by mass, and the dosage is 1-20% of the fly ash mass. When process water is added to the fly ash circulating slurry tank, the solids concentration of the fly ash slurry is controlled at 10-50%. The fly ash solids treatment time in the heavy metal solidification unit is set at 30-240 minutes. When the set treatment time is reached, valve B is opened and valve A is closed. The fly ash is then dehydrated through a tertiary dehydration unit to ensure that the water content does not exceed 30%. The treated fly ash is then used for building material utilization or landfilled.

[0067] The principle of low-temperature thermal decomposition in the present invention is as follows: oxygen is the oxygen source for the de novo synthesis of dioxins and is crucial for the de novo synthesis of dioxins. Reducing the oxygen content in the reaction atmosphere can reduce the amount of dioxins generated during the thermal desorption process; dioxins will be degraded when fly ash is heated in a nitrogen atmosphere.

[0068] Example 1

[0069] The dioxin toxicity equivalent concentration in fly ash from a grate furnace is 427.24 ng TEQ / kg. The waste incineration fly ash detoxification system described above is used. The specific disposal method is as follows:

[0070] The waste incineration fly ash to be processed is continuously fed into the system through the ash feeding device, and nitrogen is continuously introduced into the system; the fly ash enters the low-temperature thermal decomposition device, the heat source of which comes from natural gas combustion. The preheating temperature of the preheating chamber is 350℃, the heating temperature of the insulation chamber is 350℃, and the residence time is 30 minutes. The natural gas consumption per ton of fly ash is 23.7Nm 3 / t; fly ash is thermally decomposed at low temperature to form hot ash and pyrolysis gas;

[0071] The pyrolysis gas enters the pyrolysis gas purification device through the exhaust port at the end of the preheating chamber. The oxygen content in the system is detected by the oxygen content meter at the exhaust port, and the oxygen content is controlled at 0.2%;

[0072] The hot ash enters the fly ash cooling device with a nitrogen environment to prevent dioxin from re-generating. It is cooled by a two-stage water cooling device in a nitrogen environment and the temperature drops to about 70°C.

[0073] The cooled fly ash enters the fly ash washing device and undergoes three-stage washing. During the washing process, the ash-to-water ratio is 1:3, and it is stirred for 30 minutes. The washing filtrate enters the wastewater treatment system, and the wastewater enters the evaporation and salt separation device after pretreatment; the washed fly ash solids enter the heavy metal solidification device for treatment; a heavy metal solidification agent composed of NaH2PO4 and CaO is added to the wet continuous ball mill through the agent adding device, wherein NaH2PO4 accounts for 60% of the mass fraction of the heavy metal solidification agent, and the dosage of the heavy metal solidification agent is 2% of the fly ash mass. The solid concentration in the fly ash circulating slurry pool is controlled at 30%. After the fly ash is continuously ground in the ball mill for 30 minutes, it is finally dehydrated by the dehydration device to complete the discharge.

[0074] The heavy metal leaching concentrations of fly ash before and after treatment are shown in Table 1.

[0075] After disposal, samples were collected for testing, revealing a dioxin toxicity equivalent concentration (TEQ) of 1.67 ng TEQ / kg in the fly ash, which complies with the "Technical Specifications for Pollution Control of Fly Ash from Municipal Waste Incineration." The dioxin degradation rate was 99.61%. Heavy metal leaching concentrations are shown in Table 1. All indicators met the "GB 16889-2008 Municipal Waste Landfill Pollution Control Standard."

[0076] Table 1 Comparison of heavy metal leaching concentrations (mg / L)

[0077]

[0078] Example 2

[0079] The dioxin toxicity equivalent concentration in fly ash from a grate furnace is 630.52 ng TEQ / kg. The waste incineration fly ash detoxification system described above is used. The specific treatment method is as follows:

[0080] The waste incineration fly ash to be processed is continuously fed into the system through the ash feeding device, and nitrogen is continuously introduced into the system; the fly ash enters the low-temperature thermal decomposition device, the heat source of which comes from natural gas combustion. The preheating temperature of the preheating chamber is 350℃, the heating temperature of the holding chamber is 350℃, and the residence time is 60 minutes. The natural gas consumption per ton of fly ash is 27.6Nm 3 / t; fly ash is thermally decomposed at low temperature to form hot ash and pyrolysis gas;

[0081] The pyrolysis gas enters the pyrolysis gas purification device through the exhaust port at the end of the preheating chamber. The oxygen content in the system is detected by the oxygen content meter at the exhaust port, and the oxygen content is controlled at 0.2%;

[0082] The hot ash enters the fly ash cooling device with a nitrogen environment to prevent dioxin from re-generating. It is cooled by a two-stage water cooling device in a nitrogen environment and the temperature drops to about 70°C.

[0083] The cooled fly ash enters the fly ash washing device and undergoes three-stage washing. During the washing process, the ash-to-water ratio is 1:3, and it is stirred for 30 minutes. The washing filtrate enters the wastewater treatment system, and the wastewater enters the evaporation and salt separation device after pretreatment; the washed fly ash solids enter the heavy metal solidification device for treatment; a heavy metal solidification agent composed of NaH2PO4 and CaO is added to the wet continuous ball mill through the agent adding device, wherein NaH2PO4 accounts for 60% of the mass fraction of the heavy metal solidification agent, and the dosage of the heavy metal solidification agent is 5% of the fly ash mass. The solid concentration in the fly ash circulating slurry pool is controlled at 30%. After the fly ash is continuously ground in the ball mill for 60 minutes, it is finally dehydrated by the dehydration device to complete the discharge.

[0084] The heavy metal leaching concentrations of fly ash before and after treatment are shown in Table 2.

[0085] After disposal, samples were collected for testing, revealing a dioxin toxicity equivalent concentration (TEQ) of 2.32 ng TEQ / kg in the fly ash, which complies with the "Technical Specifications for Pollution Control of Fly Ash from Municipal Waste Incineration." The dioxin degradation rate was 99.63%. Heavy metal leaching concentrations are shown in Table 2. All indicators met the "GB 16889-2008 Municipal Waste Landfill Pollution Control Standard."

[0086] Table 2 Comparison of heavy metal leaching concentrations (mg / L)

[0087]

[0088] It can be seen from the data in the above table that after the waste incineration fly ash is treated with the waste incineration fly ash detoxification system and method of the present invention, the heavy metal leaching concentration has been greatly reduced and is much lower than the standard limit, which is safe and reliable.

[0089] Example 3

[0090] The dioxin toxic equivalent concentration (TEQ) in fly ash from a grate furnace for incineration of domestic waste was 427.24 ng TEQ / kg. Other conditions were the same as in Example 1. After a 30-min dwell time at 300° C., different oxygen concentrations were used during the treatment process. The dioxin equivalent concentration in the fly ash was finally measured. The results are shown in Table 3.

[0091] Table 3 Dioxin equivalent concentrations in fly ash at different oxygen concentrations

[0092]

[0093] Example 4

[0094] The dioxin toxic equivalent concentration in fly ash from a grate furnace for incineration of domestic waste was 630.52 ng TEQ / kg. Other conditions were the same as those in Example 2. After a 30-min dwell time at 300° C., different oxygen concentrations were used during the treatment process. The dioxin equivalent concentration in the fly ash was finally measured. The results are shown in Table 4:

[0095] Table 4 Dioxin equivalent concentrations in fly ash at different oxygen concentrations

[0096]

[0097] From the results of Examples 3 and 4, it can be seen that when the fly ash is reacted at 300°C for 30 minutes under the condition of 0 oxygen content, almost no dioxin is generated; when the oxygen content is 10%, the amount of dioxin generated is large, and the amount of dioxin generated increases with the increase of oxygen content from 0 to 10%.

[0098] Comparing the results of Example 1 and Example 3, and Comparing Example 2 and Example 4, it can be seen that, for different dioxin toxicity equivalent concentrations of the original fly ash, different oxygen content, pyrolysis temperature and pyrolysis time during the pyrolysis of fly ash will have a certain impact on the treatment results. The detoxification treatment of fly ash is a comprehensive treatment process, and the treatment effects of each step will affect each other. The final treatment effect of the entire system of the invention is the result of the coordinated treatment between each step.

[0099] Example 5

[0100] No nitrogen was introduced into the fly ash cooling device, and other conditions were the same as in Example 1 and Example 2. The dioxin equivalent concentration in the fly ash was finally detected. The results are shown in Table 5:

[0101] Table 5 Dioxin equivalent concentrations in fly ash under different cooling conditions

[0102]

[0103] The results in the above table show that cooling in a nitrogen environment can effectively inhibit the regeneration of dioxins and improve the storage effect of dioxins in fly ash detoxification treatment.

[0104] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the invention can be embodied in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as illustrative and non-restrictive, and the scope of the invention is defined by the appended claims rather than the foregoing description, and it is intended that all variations that come within the meaning and range of equivalents of the claims be embraced therein.

Claims

1. A waste incineration fly ash detoxification system, characterized in that: include: Ash feeding device (1): composed of an ash storage bin (101), a bag dust collector (102), a discharge valve (103) and a screw conveyor (104), used for continuously feeding into the system, with nitrogen introduced into the bottom of the ash storage bin (101); A low-temperature thermal decomposition device (2) comprises a preheating chamber (201) and a holding chamber (202) connected in sequence, wherein an exhaust port (203) is provided at the end of the preheating chamber (201); a screw conveyor discharge port (105) is connected to a preheating chamber feed port (204), and nitrogen is introduced into the holding chamber discharge port (205); The fly ash cooling device (3) comprises a first-stage fly ash water-cooling screw conveyor (301), a fly ash buffer bin (302), and a second-stage fly ash water-cooling screw conveyor (303) connected in sequence, wherein the first-stage fly ash water-cooling screw conveyor (301) and the second-stage fly ash water-cooling screw conveyor (303) have the same structure and are respectively provided with a feed port (304), a discharge port (305), a water inlet (306), and a water outlet (307); the discharge port (205) of the insulation chamber is connected to the feed port of the first-stage fly ash water-cooling screw conveyor (301), and nitrogen is introduced into the bottom of the fly ash buffer bin (302); The fly ash washing device (4) comprises a first-stage stirring kettle (401), a first-stage pump (402), a first-stage dehydration device (403), a bidirectional conveyor (404), a second-stage stirring kettle (405), a second-stage pump (406), a second-stage dehydration device (407), and a unidirectional conveyor (408); the device is used for washing and removing heavy metals from the fly ash; the discharge port (305) of the second-stage fly ash water-cooled screw conveyor (303) is connected to the first-stage stirring kettle (401), and wastewater generated by the dehydration device enters the wastewater pretreatment system; Heavy metal solidification device (5): a fly ash circulating slurry pool (501), a fly ash slurry circulating pump (502), and a wet continuous ball mill (503) are connected via a slurry pipe (505) to form a circulation loop; a switch valve A (506) is provided on the slurry pipe (505) between the fly ash slurry circulating pump (502) and the wet continuous ball mill (503); a reagent adding device (508) is provided at the feed port of the wet continuous ball mill (503); the switch valve A (506) and the fly ash slurry circulating pump (502) are connected to the tertiary dehydration device (504) via a branch slurry pipe (509); the branch slurry pipe (509) is provided with a switch valve B (507); the fly ash washing device one-way conveyor discharge port (409) is connected to the fly ash circulating slurry pool (501); The pyrolysis gas treatment device (6) comprises an activated carbon injection device (601), a bag dust collector (602), a spray tower (603) and an induced draft fan (604) connected in sequence; the exhaust port (203) at the end of the preheating chamber (201) is connected to the pyrolysis gas treatment device (6) through a pipeline between the activated carbon injection device (601) and the bag dust collector (602).

2. The waste incineration fly ash detoxification system according to claim 1, characterized in that: An oxygen content meter (208) is provided at the exhaust port (203) of the low-temperature thermal decomposition device (2).

3. The waste incineration fly ash detoxification system according to claim 1, characterized in that: The preheating chamber (201) and the holding chamber (202) of the low-temperature thermal decomposition device (2) are both of an indirect heating spiral propulsion structure, and are arranged in parallel. The preheating chamber (201) is above the holding chamber (202), and the preheating chamber discharge port (206) is connected to the holding chamber feed port (207).

4. The waste incineration fly ash detoxification system according to claim 1, characterized in that: The fly ash washing device (4) is connected in sequence to a primary stirring kettle (401), a primary pump (402), a primary dehydration device (403), and a bidirectional conveyor (404); one discharge end of the bidirectional conveyor (404) is connected to the primary stirring kettle (401), and the other discharge end is connected to a secondary stirring kettle (405); and the secondary stirring kettle (405) is connected in sequence to a secondary pump (406), a secondary dehydration device (407), and a unidirectional conveyor (408).

5. The waste incineration fly ash detoxification system according to claim 1, characterized in that: The wastewater pretreatment system comprises a wastewater pretreatment device (7) and an evaporation and salt separation device (8). The wastewater pretreatment device (7) comprises a regulating tank (701), a decalcification reaction tank (702), a heavy metal removal tank (703), a sedimentation tank (704), a pH regulating tank (705), a sand filter tank (706) and a clean water tank (707) which are connected in sequence. The wastewater pretreatment system also comprises a sludge sedimentation tank (708). The clean water tank (707) is connected to the evaporation and salt separation device (8) via a lifting pump. The sludge in the regulating tank (701), the decalcification reaction tank (702), the heavy metal removal tank (703), the sedimentation tank (704) and the pH regulating tank (705) enters the sludge sedimentation tank (708). The sludge sedimentation tank (708) is connected to the first-stage stirring tank (401) of the fly ash washing device (4) via a sludge pump.

6. A method for detoxifying waste incineration fly ash using the waste incineration fly ash detoxification system according to any one of claims 1 to 5, characterized in that: The method specifically includes: S1, the waste incineration fly ash to be processed is continuously fed into the system through the ash feeding device, and nitrogen is continuously introduced into the system; the fly ash enters the low-temperature thermal decomposition device with a nitrogen environment, the preheating temperature in the preheating chamber is 200-400℃, the heating temperature in the holding chamber is 200-400℃, and the residence time is 10-60 minutes; the fly ash is thermally decomposed at low temperature to form hot ash and pyrolysis gas; S2, the pyrolysis gas enters the pyrolysis gas purification device through the exhaust port at the end of the preheating chamber. The oxygen content in the system is detected by the oxygen content meter at the exhaust port, and the oxygen content is controlled at 0-1%; S3, the hot ash enters the fly ash cooling device with a nitrogen environment, where it is cooled by a two-stage water cooling device to prevent dioxin from re-generating; S4, the cooled fly ash enters the fly ash washing device and undergoes three-stage washing. During the washing process, the ash-to-water ratio is 1:2 to 1:4, and it is stirred for 10 to 60 minutes. The washing filtrate enters the wastewater treatment system and enters the evaporation and salt separation device after treatment by the wastewater pretreatment device; the fly ash solids after washing enter the heavy metal solidification device for treatment.

7. The method for detoxifying fly ash from waste incineration according to claim 6, characterized in that: During the treatment of the fly ash solid in the heavy metal solidification device, when the wet continuous ball mill disposes of the fly ash, the switch valve A is opened, the switch valve B is closed, and a heavy metal solidification agent is added to the wet continuous ball mill. The heavy metal solidification agent includes NaH2PO4 and CaO, wherein NaH2PO4 accounts for 20% to 80% of the mass fraction of the heavy metal solidification agent, and the amount of the heavy metal solidification agent added is 1% to 20% of the mass of the fly ash.

8. The method for detoxifying fly ash from waste incineration according to claim 6, characterized in that: When process water is added to the fly ash circulation slurry pool, the solid concentration of the fly ash slurry is controlled at 10% to 50%.

9. The method for detoxifying fly ash from waste incineration according to claim 6, characterized in that: When the fly ash solid is treated in the heavy metal solidification device, the fly ash treatment time is set to 30 to 240 minutes. When the set value is reached, the switch valve B is opened and the switch valve A is closed. The fly ash is dehydrated through the three-stage dehydration device to ensure that the water content of the fly ash is no more than 30%.

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