Reducing and recycling harmless system for waste incineration fly ash and working method

Abstract

The invention relates to the technical field of waste incineration, in particular to a waste incineration fly ash reduction and recycling harmless system and a working method. The system comprises a dioxin mechanical detoxification subsystem, a multi-stage countercurrent water washing subsystem, a quaternary system evaporation salt separation subsystem and a heavy metal pickling recovery subsystem, and according to the working method of the system, low-temperature mechanical detoxification, multi-stage countercurrent fly ash water washing, heavy metal pickling recovery and low-cost quaternary system evaporation salt separation are organically combined; the low-cost reduction, harmless and resourceful treatment of the fly ash is realized, the treated fly ash can be directly used for preparing materials such as building materials, and the method has a wide application prospect. In addition, no flue gas is generated, a flue gas treatment system is not needed, secondary fly ash and wastewater discharge is avoided, and near-zero discharge can be realized.

Description

Technical Field

[0001] The invention relates to the technical field of waste incineration, and in particular to a waste incineration fly ash reduction, resource utilization and harmlessness system and a working method. Background Art

[0002] Waste incineration fly ash refers to the collection of the flue gas purification system of the waste incineration facility and the bottom ash settled at the bottom of the flue and chimney, referred to as fly ash. During the incineration of domestic waste, harmful substances such as heavy metals and dioxins will enter the purification system with the flue gas. Through the treatment of SDA deacidification tower and bag filter, pollutants such as HCl, heavy metals and dioxins in the flue gas can be effectively removed to ensure that the flue gas emissions meet the relevant pollutant emission standards. However, the fly ash generated in this process, as the collection of the flue gas purification system, is rich in soluble salts such as Na, K, Ca, and heavy metals such as Cu, Pb, Hg, Zn and dioxins. It is classified as hazardous waste and is difficult to handle. Special treatment measures are required. The current common treatment method is chelation + landfill, that is, the heavy metals are solidified by chelating agents to meet the leaching standards and then landfilled. However, this method not only occupies a large amount of land resources, but also has the risk of secondary leaching of heavy metals, and cannot effectively achieve the reasonable disposal and resource utilization of fly ash.

[0003] In view of the resource utilization value of soluble salts and various heavy metals contained in waste incineration fly ash, fly ash resource utilization technology has emerged. Existing technologies include water washing + cement kiln synergy, high temperature melting, low temperature pyrolysis and other methods, but they all have their own limitations and shortcomings. For example, the water washing + cement kiln synergy method is limited by the cement production capacity, and it is impossible to achieve continuous processing of fly ash, and the heavy metals in the fly ash will affect the purity of the water washing salt; although high temperature melting can completely decompose dioxins, it consumes huge energy, and the flue gas and secondary fly ash generated still need further processing, and the resource utilization rate is not high; low temperature pyrolysis is difficult to meet the strict requirements of dioxin emissions.

[0004] In the prior art, the low-temperature thermal decomposition method has a significant energy consumption problem, and the emission concentrations of pollutants such as nitric oxide and carbon monoxide during the reaction process are high, which makes it difficult to meet the emission standards and the cost of treatment is expensive. In addition, due to the use of complexing agents for heavy metal extraction, the heavy metal extraction rate in fly ash is generally low, and the cost of the extraction process is high, and the economic benefits are poor. On the other hand, after the fly ash is treated with three-stage countercurrent water washing, the salt content in the obtained washing liquid is relatively low, which directly leads to an increase in the cost of subsequent evaporation treatment. More importantly, in the water treatment link before the washing liquid is evaporated and salted, it is necessary to add additional decalcifying agents such as sodium sulfate and sodium carbonate to remove the calcium component, which not only increases the cost of the reagents, but also further increases the complexity and cost burden of the overall treatment process. Summary of the invention

[0005] In response to the above problems, the present invention provides a waste incineration fly ash reduction, resource utilization and harmless treatment system and working method, which adopts "low-temperature mechanical detoxification + multi-stage countercurrent water washing + low-cost evaporation and salt separation + heavy metal acid washing and recovery". This method aims to achieve low-cost detoxification of fly ash and maximize its resource utilization benefits at the same time, providing an innovative solution to the limitations and deficiencies in the existing technology and can significantly reduce the current technology cost.

[0006] In order to solve the above technical problems, this application provides the following technical solutions: A waste incineration fly ash reduction and resource-based harmless system, including a dioxin mechanical detoxification subsystem, a multi-stage countercurrent water washing subsystem, a quaternary system evaporation and salt separation subsystem, and a heavy metal acid washing and recovery subsystem; The dioxin mechanical detoxification subsystem includes a fly ash bin, a primary mechanical ball mill, a secondary mechanical ball mill and a buffer bin which are connected in sequence; the outlet of the buffer bin is connected to a regulating tank; the outlet of the regulating tank is connected to a primary slurry mixing tank; The multi-stage countercurrent water washing subsystem comprises a primary slurry mixing tank, a primary water washing filter press, a secondary slurry mixing tank, a secondary water washing filter press, a tertiary slurry mixing tank, a tertiary water washing filter press and a vacuum belt dehydrator which are connected in sequence; the filtrate outlet of the primary water washing filter press is connected to the primary filtrate tank, and the outlet of the primary filtrate tank is connected to the reaction tank; the filtrate outlet of the secondary water washing filter press is connected to the secondary filtrate tank, and the outlet of the secondary filtrate tank is connected to the primary slurry mixing tank; the filtrate outlet of the tertiary water washing filter press is connected to the tertiary filtrate tank, and the outlet of the tertiary filtrate tank is connected to the secondary slurry mixing tank; the outlet of the vacuum belt dehydrator is connected to the pickling tank; The quaternary system evaporation and salt separation subsystem comprises a reaction tank, a plate and frame filter press, a purification reaction tank, a primary evaporator, a secondary evaporator and a tertiary evaporator which are connected in sequence; The heavy metal pickling recovery subsystem comprises a pickling tank, a first filter press, a water washing tank, a second filter press and a stabilization tank which are connected in sequence, and the filtrate outlets of the first filter press and the second filter press are connected to the heavy metal precipitation tank.

[0007] Wherein, the fly ash bin is provided with an original fly ash inlet.

[0008] Wherein, the three-stage slurry mixing tank is provided with a water supply port.

[0009] The reaction tank is provided with a heavy metal precipitant addition port, the filter cake of the plate and frame filter press contains heavy metals, the first-stage evaporator recovers sodium chloride, the second-stage evaporator recovers sodium chloride and potassium chloride, and the third-stage evaporator recovers calcium chloride.

[0010] Among them, sulfuric acid and hydrochloric acid solutions are added to the pickling tank, the wastewater of the heavy metal precipitation tank is recycled to the multi-stage countercurrent water washing subsystem, an alkaline stabilizer is added to the stabilization tank, and the stabilization tank discharges a detoxified mud cake.

[0011] A working method of a waste incineration fly ash reduction resource harmless system comprises the following steps: ① The original fly ash is first sent to the fly ash bin for storage through a conveying device; then, the fly ash is ball-milled and detoxified in a primary mechanical ball mill, and then enters a secondary mechanical ball mill, where appropriate amounts of CaO and Al are added for combined grinding; the fly ash after ball-milling and detoxification enters a buffer bin for subsequent treatment; ② The fly ash in the buffer bin enters the regulating tank through the conveyor belt, and then enters the primary slurry mixing tank. The stirred slurry enters the primary water-washing filter press. The filtrate after filtration enters the primary filtrate tank. The filter cake is sent to the secondary slurry mixing tank. The stirred slurry enters the secondary water-washing filter press. The secondary water-washing filtrate enters the primary slurry mixing tank through the secondary filtrate tank. The secondary water-washing filter cake enters the tertiary slurry mixing tank. The stirred slurry enters the tertiary water-washing filter press. The filtrate enters the secondary slurry mixing tank through the tertiary filtrate tank for repeated use. The filter cake enters the vacuum belt dehydrator to ensure that the moisture content of the obtained tertiary water-washed ash is not higher than 10%; ③ The filter cake after dehydration by the vacuum belt dehydrator enters the pickling tank, desalted water is added to the pickling tank, and then sulfuric acid and hydrochloric acid solutions are slowly added, and fully stirred and mixed at room temperature; the mixed solution enters the first filter press, and the filtrate produced after the first filter press works enters the heavy metal precipitation tank, and the extraction rates of heavy metals lead, zinc and copper all reach more than 80%; A chelating agent is added to the heavy metal precipitation tank to remove heavy metals, and the pH is controlled at 8-9. The reaction is carried out under rapid stirring until the filtrate does not change color or no precipitation is produced, which proves that the heavy metals have been completely removed, and the wastewater is reused in the multi-stage countercurrent washing subsystem; the filter cake produced after the first filter press is operated enters the washing tank, is mixed with process water for washing, and after sufficient stirring, the slurry enters the second filter press, and the filtrate after filtration enters the heavy metal precipitation tank to precipitate heavy metals; the filter cake after filtration by the second filter press enters the stabilization tank, and after adding an alkaline stabilizer, a detoxified mud cake is obtained, which can be used as a resource; ④ The filtrate in the primary filtrate tank enters the reaction tank, and a heavy metal precipitant is added to the water washing liquid in the reaction tank to precipitate the heavy metals and sulfate ions in the water washing liquid. The mixture is then sent to a plate and frame filter press for filtration to obtain a filter cake with a high heavy metal content and a filtrate free of heavy metals and sulfate ions. After the filtrate enters the purification reaction tank for filtration, the main components are calcium chloride, potassium chloride and sodium chloride. The filtrate passes through a primary evaporator, a secondary evaporator and a tertiary evaporator to recover calcium chloride, potassium chloride and sodium chloride. The water finally produced by evaporation is reused in the tertiary slurry mixing tank in the multi-stage countercurrent water washing subsystem, and no wastewater is generated.

[0012] Among them, in the first-stage mechanical ball mill, the mass ratio of stainless steel balls to fly ash is 30:0.5, the rotation speed is 700r / min, and the ball milling is 10h; the rotation speed of the second-stage mechanical ball mill is 700r / min, and the grinding is 10h.

[0013] The water-cement ratio in the first-stage slurry mixing tank is controlled at 3:1, the temperature is controlled at 30°C, and the mixture is stirred for 30 minutes; the water-cement ratio in the second-stage slurry mixing tank is controlled at 3:1, the temperature is controlled at 30°C, and the mixture is stirred for 30 minutes; the third-stage slurry mixing tank is replenished with desalted water at a water-cement ratio of 3:1, and stirred at 30°C for 30 minutes; Among them, the moisture content of the filter cake produced by each stage of the first and second stage water washing filter press is strictly controlled below 30%.

[0014] Among them, deionized water is added to the pickling tank at a water-cement ratio of 4:1, and the stirring time after adding sulfuric acid and hydrochloric acid solutions is 60 minutes; in the water washing tank, the ratio of filter cake to water is 1:10, and the stirring time is 30-60 minutes.

[0015] Among them, the dioxin mechanical detoxification subsystem detoxifies dioxins in fly ash through low-temperature mechanical detoxification technology. Low-temperature mechanical detoxification has no heating process and does not produce flue gas, so it can solve the problem of high carbon monoxide and nitrogen monoxide emission concentrations in the application process of existing low-temperature thermal decomposition technology, significantly reduce pollutant emissions, and improve environmental protection performance.

[0016] The multi-stage countercurrent washing subsystem adopts multi-stage countercurrent fly ash washing to reduce the water-ash ratio. When the total amount of fly ash is constant, according to the mass balance, the water volume is reduced, which can increase the salt content in the washing liquid, thereby reducing the amount of evaporated washing liquid and further reducing the evaporation cost per ton of fly ash.

[0017] In the heavy metal pickling recovery subsystem, heavy metals in fly ash are pickled and recovered by mixing sulfuric acid and hydrochloric acid. The price of sulfuric acid is low, while hydrochloric acid has a better extraction effect on heavy metals. Therefore, combining the two can not only reduce the cost of pickling, but also improve the effect of heavy metal leaching. It can solve the problem of low extraction rate and high extraction cost of complexing agents for heavy metals. Through pickling recovery, not only the extraction rate of heavy metals is improved, but also the extraction cost is reduced, realizing the efficient recovery and utilization of heavy metals.

[0018] The quaternary system evaporation and salt separation subsystem adopts low-cost quaternary system evaporation and salt separation, which does not need to remove calcium ions in the water wash liquid, and eliminates the addition of sodium carbonate and sodium sulfate in the traditional evaporation and salt separation process, thereby saving the cost of removing calcium ions in water treatment in traditional evaporation and salt separation technology.

[0019] The heavy metal content and dioxin content in the mud cake produced after fly ash treatment meet the standards and can be utilized; by adjusting the ratio of sulfuric acid and hydrochloric acid, the amount of mud cake after multi-stage countercurrent water washing treatment can be adjusted. After dehydration by a dehydrator, the moisture content of the mud cake is 10-25%, and the cake base weight can reach 20~60% of the original fly ash weight.

[0020] The system of the present invention adopts the above core technical links comprehensively, realizes the low-cost recovery of heavy metals, sodium salts, potassium salts and calcium salts in fly ash, and realizes the detoxification of dioxins and heavy metals in fly ash, greatly reducing the cost of fly ash disposal. In addition, water is recycled in the whole process, so there is no wastewater discharge.

[0021] Compared with the prior art, the waste incineration fly ash reduction resource harmless system and working method of the present invention have at least the following beneficial effects: The waste incineration fly ash reduction, resource utilization and harmless treatment system of the present invention can achieve: (1) reduction, the mass of the detoxified filter cake after treatment is 20% to 40% of the original fly ash mass, that is, the fly ash is reduced by 60% to 80%; (2) resource utilization, the heavy metals, sodium salts, potassium salts and calcium salts in the fly ash are recovered and resourced, and the fly ash after detoxification and resource extraction can be used to prepare building materials, realizing full resource utilization; (3) harmlessness, the heavy metal content and dioxin content in the products after fly ash detoxification and resource extraction meet the requirements of "Technical Specifications for Pollutant Control of Municipal Waste Incineration Fly Ash" (HJ1134-2020).

[0022] The waste incineration fly ash reduction, resource utilization and harmless treatment system of the present invention realizes low-cost fly ash reduction, harmlessness and resource treatment. The treated fly ash can be directly used to prepare building materials and other materials, and has broad application prospects. In addition, no smoke is generated, no smoke treatment system is required, no secondary fly ash and wastewater are discharged, and near-zero emissions can be achieved. The present invention also helps to promote the promotion and application of fly ash zero landfill technology, which is of great significance for achieving sustainable treatment and utilization of waste incineration fly ash.

[0023] The waste incineration fly ash reduction, resource utilization and harmless treatment system and working method of the present invention are further described below in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a schematic diagram of the flow of the waste incineration fly ash reduction, resource utilization and harmless treatment system of the present invention.

[0025] Among them, 1-dioxin mechanical detoxification subsystem, 2-multi-stage countercurrent water washing subsystem, 3-quaternary system evaporation and salt separation subsystem, 4-heavy metal acid washing and recovery subsystem; 101-fly ash bin, 102-primary mechanical ball mill, 103-secondary mechanical ball mill, 104-buffer bin; 201-first-stage slurry mixing tank, 202-first-stage water-washing filter press, 203-second-stage slurry mixing tank, 204-second-stage water-washing filter press, 205-third-stage slurry mixing tank, 206-third-stage water-washing filter press, 207-vacuum belt dehydrator, 208-first-stage filtrate tank, 209-second-stage filtrate tank, 210-third-stage filtrate tank; 301-reaction tank, 302-plate and frame filter press, 303-purification reaction tank, 304-primary evaporator, 305-secondary evaporator, 306-tertiary evaporator; 307-adjustment tank; 401-pickling tank, 402-first filter press, 403-water washing tank, 404-second filter press, 405-stabilization tank, 406-heavy metal precipitation tank. DETAILED DESCRIPTION

[0026] like Figure 1 As shown, a waste incineration fly ash reduction and resource-based harmless treatment system includes a dioxin mechanical detoxification subsystem 1, a multi-stage countercurrent water washing subsystem 2, a quaternary system evaporation and salt separation subsystem 3 and a heavy metal acid washing recovery subsystem 4.

[0027] The dioxin mechanical detoxification subsystem 1 comprises a fly ash bin 101, a primary mechanical ball mill 102, a secondary mechanical ball mill 103 and a buffer bin 104 which are connected in sequence; the outlet of the buffer bin 104 is connected to the regulating tank 307; the outlet of the regulating tank 307 is connected to the primary slurry mixing tank 201. The fly ash bin 101 is provided with an original fly ash inlet.

[0028] The multi-stage countercurrent water washing subsystem 2 can realize the effective separation of the soluble and insoluble parts in the fly ash so as to make resource utilization for them respectively. The invention comprises a first-stage slurry mixing tank 201, a first-stage water-washing filter press 202, a second-stage slurry mixing tank 203, a second-stage water-washing filter press 204, a third-stage slurry mixing tank 205, a third-stage water-washing filter press 206 and a vacuum belt dehydrator 207 which are connected in sequence; the filtrate outlet of the first-stage water-washing filter press 202 is connected to the first-stage filtrate tank 208, and the outlet of the first-stage filtrate tank 208 is connected to the reaction tank 301; the filtrate outlet of the second-stage water-washing filter press 204 is connected to the second-stage filtrate tank 209, and the outlet of the second-stage filtrate tank 209 is connected to the first-stage slurry mixing tank 201; the filtrate outlet of the third-stage water-washing filter press 206 is connected to the third-stage filtrate tank 210, and the outlet of the third-stage filtrate tank 210 is connected to the second-stage slurry mixing tank 203; the outlet of the vacuum belt dehydrator 207 is connected to the pickling tank 401. The third-stage slurry mixing tank 205 is provided with a water supply port.

[0029] The quaternary system evaporation and salt separation subsystem 3 includes a reaction tank 301, a plate-frame filter press 302, a purification reaction tank 303, a primary evaporator 304, a secondary evaporator 305 and a tertiary evaporator 306 which are connected in sequence. The reaction tank 301 is provided with a heavy metal precipitant addition port, the filter cake of the plate-frame filter press 302 contains heavy metals, the primary evaporator 304 recovers sodium chloride, the secondary evaporator 305 recovers sodium chloride and potassium chloride, and the tertiary evaporator 306 recovers calcium chloride.

[0030] The heavy metal pickling recovery subsystem 4 comprises a pickling tank 401, a first filter press 402, a water washing tank 403, a second filter press 404 and a stabilization tank 405 which are connected in sequence, and the filtrate outlets of the first filter press 402 and the second filter press 404 are connected to a heavy metal precipitation tank 406. Sulfuric acid and hydrochloric acid solutions are added to the pickling tank 401, and the wastewater of the heavy metal precipitation tank 406 is reused to the multi-stage countercurrent water washing subsystem, and an alkaline stabilizer is added to the stabilization tank 405, and the stabilization tank 405 discharges a detoxified mud cake.

[0031] The working method of the waste incineration fly ash reduction and resource-based harmless treatment system realizes efficient, low-cost, harmless and resource-based treatment of fly ash through the mutual coordination of four subsystems. The specific steps are as follows: (1) The raw fly ash is first transported to the fly ash bin for storage through a conveying device. Subsequently, the fly ash is detoxified by ball milling in a full-range planetary ball mill. Through experimental comparison, stainless steel balls have high grinding properties and low cost (other materials themselves are not hard enough and are not very helpful for detoxification).

[0032] The mass ratio of stainless steel balls to fly ash is 30:0.5. The fly ash is firstly milled in a primary mechanical ball mill at a speed of 700r / min for 10h (setting a suitable speed can increase the energy input during the ball milling process). At a higher speed, the impact and friction of the ball on the fly ash are greater, which can more effectively reduce the fly ash particle size through physical action. The smaller particle size increases the specific surface area of ​​the fly ash, which increases the decomposition reaction activity of dioxins. With the increase in reaction activity, dioxins are more likely to undergo decomposition reactions, thereby reducing their content.

[0033] Then, it enters the secondary mechanical ball mill, and adds appropriate amounts of CaO and Al for combined grinding. The speed is set to 700r / min and the grinding is carried out for 10 hours to promote the removal of chloride ions. The grinding process causes the wear of the balls and the ball mill jars, and introduces metal impurities into the fly ash. These metal impurities react with dioxins and promote the decomposition of dioxins. For example, some metal ions (such as iron ions) may act as catalysts to accelerate the decomposition reaction of dioxins. The introduction of metal impurities such as iron can change the physical and chemical properties of fly ash, increase the reaction activity of dioxin generation and decomposition in fly ash, and the detoxification efficiency reaches more than 85%. The fly ash detoxified by ball milling enters the buffer bin for subsequent treatment.

[0034] The following tests were performed for this step: Experimental conditions: omnidirectional planetary ball mill, ball mill jar 250 mL, rotation speed 700 r / min, rotation: revolution = 2:1, flip speed 12 r / min, total ball milling time 24h (forward rotation 0.5h, reverse rotation 0.5h, pause 0.5h cycle in sequence). Stainless steel ball sizes: 10mm, 8mm, 5mm.

[0035] The ratio is stainless steel ball: original ash: CaO: Al (mass ratio) = 30: 0.5: 0.4: 0.1, and the actual mass is 202.5 g: 3.38 g: 2.70 g: 0.68g.

[0036] The test results are shown in Table 1. The removal ratio (absolute) of dioxin toxicity was 87.5%.

[0037] Table 1

[0038] (2) The fly ash that passes through the low-temperature detoxification system and reaches the buffer bin enters the regulating tank through a conveyor belt, and then enters the first-level slurry mixing tank. The water-cement ratio in the slurry mixing tank is controlled at 3:1, the temperature is controlled at 30°C, and after stirring for 30 minutes, the slurry enters the first-level water-washing filter press. The filtrate after filtration enters the first-level filtrate tank. The filter cake is sent to the second-level slurry mixing tank. The water-cement ratio is also controlled at 3:1, the temperature is 30°C, and after stirring for 30 minutes, the slurry enters the second-level water-washing filter press. The secondary water-washing filtrate enters the first-level slurry mixing tank through the second-level filtrate tank. The second-level water-washing filter cake enters the third-level slurry mixing tank. Desalted water is added at a water-cement ratio of 3:1 for water replenishment. After stirring at 30°C for 30 minutes, the slurry enters the third-level water-washing filter press. The filtrate enters the second-level slurry mixing tank through the third-level filtrate tank for repeated use. The filter cake enters the vacuum belt dehydrator to ensure that the moisture content of the obtained third-level water-washed ash is not higher than 10%.

[0039] The moisture content of the filter cake produced by each filter press of the first and second stage water washing is strictly controlled to be less than 30% to ensure the treatment effect. After the three-stage countercurrent water washing, the soluble and insoluble parts in the fly ash are effectively separated, and CaCl2, NaCl, and KCl solutions are separated. At the same time, if the separated soluble part is tested after the three-stage countercurrent water washing and it is found that the salt concentration therein has not reached the ideal state, or when considering the subsequent evaporation cost, resource recovery efficiency and other factors, it is considered necessary to further reduce the water-ash ratio to increase the salt concentration in the washing liquid, this system can also be flexibly set to a four-stage, five-stage or even more-stage countercurrent water washing system to reduce the water-ash ratio and increase the salt concentration in the washing liquid, thereby significantly reducing the evaporation cost.

[0040] There are several reasons for reducing the evaporation cost: ① When the salt content in the solution increases, it means that the amount of water that needs to be evaporated per unit volume of solution is relatively reduced. In the evaporation process, the main energy consumption is to convert water from liquid to gas, and the presence of salt does not require a lot of energy for evaporation. Therefore, after increasing the salt content, the amount of water that needs to be evaporated is reduced, thereby reducing the energy consumption required for evaporation, and thus reducing the evaporation cost; ② As the salt content in the solution increases, the boiling point of the solution may increase. Within a certain range, a higher boiling point can make the evaporation process more stable and reduce the energy loss caused by temperature fluctuations. At the same time, a higher salt concentration may also affect the physical properties of the solution, such as viscosity, so that the heat transfer and mass transfer efficiency during the evaporation process is improved, further improving the evaporation efficiency and reducing the cost; ③ If the salt content in the solution is low, in order to achieve a certain resource recovery effect, a large amount of solution may need to be processed. This requires a larger-scale evaporation equipment, and the equipment will also have a longer operating time. After increasing the salt content in the solution, the volume of solution that needs to be processed can be reduced, the utilization rate of the equipment can be improved, and the investment and operating costs of the equipment can be reduced. In addition, the filter cake after the filter press will be sent to the acid washing heavy metal recovery subsystem to further extract the heavy metal resources therein, realizing the comprehensive resource utilization of fly ash.

[0041] (3) After being dehydrated by the vacuum belt dehydrator in the multi-stage countercurrent water washing subsystem, the filter cake enters the pickling tank, desalted water is added to the pickling tank at a water-cement ratio of 4:1, and then sulfuric acid and hydrochloric acid solutions are slowly added (first adjust the solution to pH = 7 with sulfuric acid, and then add hydrochloric acid solution at a ratio of 0.1 times), and the mixture is fully stirred at room temperature for 60 minutes.

[0042] The mixed solution enters the first filter press, and the filtrate produced after the filter press works enters the heavy metal precipitation tank. At this time, the extraction rate of heavy metals lead, zinc, and copper reaches more than 80%. (Different heavy metals have different reactivity with sulfuric acid and hydrochloric acid. For heavy metals with high content and difficult to dissolve, it may be necessary to increase the proportion of acid appropriately to ensure sufficient reaction. For example, if the fly ash contains more heavy metals such as lead and zinc, the proportion of acid solution needs to be adjusted according to their chemical properties and content.) Adding the following chelating agents to the precipitation tank can effectively achieve heavy metal removal. The mechanism is as follows: the chelating agent coordinates with the metal ions simultaneously through multiple coordinating atoms in its molecules to form a stable ring structure, and the formed chelate is generally soluble. The stability of the chelate allows the metal ions to exist in a chelated state in the solution, changing the chemical and physical properties of the metal ions, such as color, redox properties, etc. For example, polyethyleneimine can form stable complexes with heavy metal ions such as copper and lead. Add an appropriate amount of polyethyleneimine according to the pH, control the pH at 8-9, and react for 2-5 minutes at a rapid stirring of 150 rpm until the filtrate does not change color or no precipitation is produced, which proves that the heavy metals have been removed. The wastewater is reused to the multi-stage countercurrent water washing subsystem.

[0043] The filter cake produced after entering the first filter press enters the washing tank and is mixed with process water for washing. The ratio of filter cake to water is 1:10, and the stirring time is 30-60 minutes. After sufficient stirring, the slurry enters the second filter press, and the filtrate after filtration enters the heavy metal precipitation tank to precipitate heavy metals such as lead and zinc. The filter cake after filtration enters the stabilization tank, and alkaline stabilizers such as calcium hydroxide are added (3-5g calcium hydroxide is added to 700g filter cake) to obtain detoxified mud cake, which can be sold for resource utilization.

[0044] The following test was performed for this step.

[0045] Test conditions: The mass ratio of raw ash A1: primary washing liquid is 1:3 (i.e. 300:900), stirred at room temperature for 15 minutes, filtered with medium-speed filter paper, and then placed in a 105℃ oven for 24 hours; According to the mass of fly ash after drying, add deionized water at a ratio of sulfuric acid to hydrochloric acid (mass ratio) = 1:1 and a solid-liquid ratio of 1:4, stir at room temperature for 60 minutes, and filter with medium-speed filter paper; Add new desalted water at a solid-liquid ratio of 1:10, stir at room temperature for 15 minutes, filter with medium-speed filter paper, put the filter cake into a 105℃ oven for 24 hours, and send it for inspection.

[0046] The test results are shown in Table 2-4.

[0047] Table 2 Fly ash samples and filtrate quality

[0048] Table 3 Heavy metal contents in fly ash samples and filtrates Extraction rate calculation formula: [1-(A3 mass × heavy metal content per kg of A3) / (A1 mass × heavy metal content per kg of A1)]*100% Table 4 Heavy metal extraction rate

[0049] (4) The filtrate in the primary filtrate tank enters the reaction tank, where a heavy metal precipitant (such as sodium sulfide) is added to the water wash in an amount of 5% to 10% of the total filtrate; the heavy metals and sulfate ions in the water wash are precipitated, and then the mixture is sent to a plate and frame filter press for filtration to obtain a filter cake with a high heavy metal content and a filtrate without heavy metals and sulfate ions. The filter cake is rich in heavy metals and is sold for use. After the filtrate enters the purification reaction tank for filtration, the main components are calcium chloride, potassium chloride and sodium chloride. The filtrate passes through the primary, secondary and tertiary evaporators to recover calcium chloride, potassium chloride and sodium chloride. The water produced by evaporation is reused in the third-stage slurry mixing tank in the multi-stage countercurrent water system, and no wastewater is generated.

[0050] In summary, the system of the present invention organically combines low-temperature mechanical detoxification, multi-stage countercurrent fly ash washing, heavy metal acid washing recovery and low-cost quaternary system evaporation and salt separation technologies to achieve low-cost, reduced, harmless and resource-based treatment of fly ash. (1) The dioxins in fly ash are detoxified by low-temperature mechanical detoxification technology, which solves the problem of high emission concentrations of carbon monoxide and nitrogen monoxide during low-temperature thermal decomposition. (2) Multi-stage countercurrent fly ash washing solves the problem of low salt content and high evaporation cost in the washing liquid obtained by traditional three-stage countercurrent washing, increases the salt content of the washing liquid, and reduces the cost for subsequent evaporation treatment. (3) Sulfuric acid and hydrochloric acid are mixed to acid wash and recover heavy metals in fly ash, which solves the problem of low extraction rate and high extraction cost of heavy metals by complexing agents. Through acid washing and recovery, not only the extraction rate of heavy metals is improved, but also the extraction cost is reduced, realizing efficient recovery and utilization of heavy metals. (4) The application of low-cost quaternary system evaporation and salt separation technology solves the problem of high consumption and high cost of sodium carbonate and sodium sulfate in traditional evaporation and salt separation. Through the quaternary system evaporation salt separation system, the consumption of sodium sulfate and sodium carbonate reagents is eliminated, and the cost of water washing liquid pretreatment is reduced.

[0051] The heavy metal content and dioxin content in the mud cake produced after fly ash treatment in this system meet the standards and can be utilized; the fly ash reduction is achieved, and the moisture content of the mud cake after multi-stage countercurrent water washing treatment is 10-25% after dehydration by a dehydrator, and the cake base weight is 20~60% of the original fly ash weight; the fly ash resource utilization is achieved, including heavy metal recovery, sodium salt, potassium salt and calcium salt recovery; near-zero emissions are achieved, no tail gas is generated, no secondary fly ash, and no wastewater is discharged; at the same time, the fly ash reduction, resource utilization and harmlessness processes are carried out simultaneously, greatly reducing the treatment cycle.

[0052] The embodiments described above are merely descriptions of preferred implementation modes of the present invention and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A working method of a waste incineration fly ash reduction resource harmless system, characterized in that: The following steps are involved: ① The original fly ash is first sent to the fly ash bin for storage through a conveying device; then, the fly ash is ball-milled and detoxified in a primary mechanical ball mill, and then enters a secondary mechanical ball mill, where appropriate amounts of CaO and Al are added for combined grinding; the fly ash after ball-milling and detoxification enters a buffer bin for subsequent treatment; ② The fly ash in the buffer bin enters the regulating tank through the conveyor belt, and then enters the primary slurry mixing tank. The stirred slurry enters the primary water-washing filter press. The filtrate after filtration enters the primary filtrate tank. The filter cake is sent to the secondary slurry mixing tank. The stirred slurry enters the secondary water-washing filter press. The secondary water-washing filtrate enters the primary slurry mixing tank through the secondary filtrate tank. The secondary water-washing filter cake enters the tertiary slurry mixing tank. The stirred slurry enters the tertiary water-washing filter press. The filtrate enters the secondary slurry mixing tank through the tertiary filtrate tank for repeated use. The filter cake enters the vacuum belt dehydrator to ensure that the moisture content of the obtained tertiary water-washed ash is not higher than 10%; ③ The filter cake after dehydration by the vacuum belt dehydrator enters the pickling tank, desalted water is added to the pickling tank, and then sulfuric acid and hydrochloric acid solutions are slowly added, and fully stirred and mixed at room temperature; the mixed solution enters the first filter press, and the filtrate produced after the first filter press works enters the heavy metal precipitation tank, and the extraction rates of heavy metals lead, zinc and copper all reach more than 80%; A chelating agent is added to the heavy metal precipitation tank to remove heavy metals, and the pH is controlled at 8-9. The reaction is carried out under rapid stirring until the filtrate does not change color or no precipitation is produced, which proves that the heavy metals have been completely removed, and the wastewater is reused in the multi-stage countercurrent washing subsystem; the filter cake produced after the first filter press is operated enters the washing tank, is mixed with process water for washing, and after sufficient stirring, the slurry enters the second filter press, and the filtrate after filtration enters the heavy metal precipitation tank to precipitate heavy metals; the filter cake after filtration by the second filter press enters the stabilization tank, and after adding an alkaline stabilizer, a detoxified mud cake is obtained, which can be used as a resource; ④ The filtrate in the primary filtrate tank enters the reaction tank, and a heavy metal precipitant is added to the water washing liquid in the reaction tank to precipitate the heavy metals and sulfate ions in the water washing liquid. The mixture is then sent to a plate and frame filter press for filtration to obtain a filter cake with a high heavy metal content and a filtrate free of heavy metals and sulfate ions. After the filtrate enters the purification reaction tank for filtration, the main components are calcium chloride, potassium chloride and sodium chloride. The filtrate passes through a primary evaporator, a secondary evaporator and a tertiary evaporator to recover calcium chloride, potassium chloride and sodium chloride. The water finally produced by evaporation is reused in the tertiary slurry mixing tank in the multi-stage countercurrent water washing subsystem, and no wastewater is generated.

2. The working method of the waste incineration fly ash reduction resource harmless system according to claim 1 is characterized by: In the first-stage mechanical ball mill, the mass ratio of stainless steel balls to fly ash is 30:0.5, the rotation speed is 700 r / min, and the ball milling is performed for 10 hours; the rotation speed of the second-stage mechanical ball mill is 700 r / min, and the grinding is performed for 10 hours.

3. The working method of the waste incineration fly ash reduction resource harmless system according to claim 2 is characterized by: The water-cement ratio in the first-stage slurry mixing tank is controlled at 3:1, the temperature is controlled at 30°C, and stirring is performed for 30 minutes; the water-cement ratio in the second-stage slurry mixing tank is controlled at 3:1, the temperature is controlled at 30°C, and stirring is performed for 30 minutes; the third-stage slurry mixing tank is supplemented with desalted water at a water-cement ratio of 3:1, and stirring is performed at 30°C for 30 minutes; Among them, the moisture content of the filter cake produced by each stage of the first and second stage water washing filter press is strictly controlled below 30%.

4. The working method of the waste incineration fly ash reduction resource harmless system according to claim 3 is characterized by: Deionized water is added to the acid washing tank at a water-cement ratio of 4:1, and the stirring time after adding sulfuric acid and hydrochloric acid solutions is 60 minutes; in the water washing tank, the ratio of filter cake to water is 1:10, and the stirring time is 30-60 minutes.

5. The working method of the waste incineration fly ash reduction resource harmless system according to claim 4 is characterized by: The first-stage evaporator recovers sodium chloride, the second-stage evaporator recovers sodium chloride and potassium chloride, and the third-stage evaporator recovers calcium chloride.

6. The waste incineration fly ash reduction and resource-based harmless system used in the working method according to any one of claims 1 to 5 is characterized by: It includes a dioxin mechanical detoxification subsystem (1), a multi-stage countercurrent water washing subsystem (2), a quaternary system evaporation and salt separation subsystem (3) and a heavy metal acid washing and recovery subsystem (4); The dioxin mechanical detoxification subsystem (1) comprises a fly ash bin (101), a primary mechanical ball mill (102), a secondary mechanical ball mill (103), and a buffer bin (104) which are connected in sequence; the outlet of the buffer bin (104) is connected to a regulating tank (307); the outlet of the regulating tank (307) is connected to a primary slurry mixing tank (201); The multi-stage countercurrent water washing subsystem (2) comprises a primary slurry mixing tank (201), a primary water washing filter press (202), a secondary slurry mixing tank (203), a secondary water washing filter press (204), a tertiary slurry mixing tank (205), a tertiary water washing filter press (206) and a vacuum belt dehydrator (207) which are connected in sequence; the filtrate outlet of the primary water washing filter press (202) is connected to the primary filtrate tank (208), and the outlet of the primary filtrate tank (208) is connected to the reaction tank ( The filtrate outlet of the secondary water-washing filter press (204) is connected to the secondary filtrate tank (209), and the outlet of the secondary filtrate tank (209) is connected to the primary slurry mixing tank (201); the filtrate outlet of the tertiary water-washing filter press (206) is connected to the tertiary filtrate tank (210), and the outlet of the tertiary filtrate tank (210) is connected to the secondary slurry mixing tank (203); the outlet of the vacuum belt dehydrator (207) is connected to the pickling tank (401); The quaternary system evaporation and salt separation subsystem (3) comprises a reaction tank (301), a plate and frame filter press (302), a purification reaction tank (303), a primary evaporator (304), a secondary evaporator (305) and a tertiary evaporator (306) which are connected in sequence; The heavy metal pickling recovery subsystem (4) comprises a pickling tank (401), a first filter press (402), a water washing tank (403), a second filter press (404) and a stabilization tank (405) which are connected in sequence, and the filtrate outlets of the first filter press (402) and the second filter press (404) are connected to a heavy metal precipitation tank (406).

7. The waste incineration fly ash reduction and resource-based harmless system according to claim 6 is characterized by: The fly ash bin (101) is provided with a raw fly ash inlet.

8. The waste incineration fly ash reduction and resource-based harmless system according to claim 7 is characterized by: The third-stage slurry mixing tank (205) is provided with a water replenishment port.

9. The waste incineration fly ash reduction and resource-based harmless system according to claim 8 is characterized by: The reaction tank (301) is provided with a heavy metal precipitant addition port, the filter cake of the plate and frame filter press (302) contains heavy metals, the first-stage evaporator (304) recovers sodium chloride, the second-stage evaporator (305) recovers sodium chloride and potassium chloride, and the third-stage evaporator (306) recovers calcium chloride.

10. The waste incineration fly ash reduction and resource-based harmless system according to claim 9 is characterized by: Sulfuric acid and hydrochloric acid solutions are added to the pickling tank (401), wastewater from the heavy metal precipitation tank (406) is recycled to the multi-stage countercurrent water washing subsystem, an alkaline stabilizer is added to the stabilization tank (405), and the stabilization tank (405) discharges a detoxified mud cake.

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