Fly ash dioxin low-temperature removal system and method

Abstract

The present invention discloses a low-temperature dioxin removal system and method for fly ash. The fly ash low-temperature dioxin removal system includes a low-temperature pyrolysis device, a multi-stage countercurrent washing device, and a solid-liquid separation unit. The low-temperature pyrolysis device includes a device body, a feeding mechanism, an inert gas mechanism, a conveying mechanism, and a cooling mechanism. The feeding mechanism is located at the feeding port at the top of the device body, and the conveying mechanism is located within the device body. The multi-stage countercurrent washing device includes a fly ash conveying mechanism and a plurality of water washing tanks arranged in series, each of which is provided with a liquid distribution member and a stirring mechanism. The solid-liquid separation unit includes a filter press mechanism, a sodium chloride continuous crystallizer, and a potassium chloride continuous crystallizer. The filtrate from the filter press mechanism is fed into the sodium chloride continuous crystallizer. The fly ash low-temperature dioxin removal system provided by the present invention has the advantages of low fly ash processing energy consumption and high resource utilization rate.

Description

Technical Field

[0001] The present invention relates to the technical field of dioxin removal, and in particular to a low-temperature dioxin removal system and method for fly ash. Background Art

[0002] Currently, dioxins in municipal solid waste incineration fly ash are difficult to degrade, high-temperature treatment consumes a lot of energy, and water washing pretreatment produces large amounts of secondary pollutants, leading to low resource utilization. Related technologies often use high-temperature treatment methods, which are energy-intensive, result in significant secondary pollutant migration during the co-treatment process, and pose serious environmental risks. For example, carbonation treatment of fly ash suffers from low carbonation efficiency, poor heavy metal solidification, and inability to degrade dioxins. Alternatively, low-temperature treatment of fly ash results in low resource utilization and significant heavy metal pollution after enrichment. Alternatively, large amounts of wastewater are generated, requiring chelation prior to landfill, wasting land resources. Furthermore, high requirements for fly ash raw materials result in low dioxin degradation efficiency and high residual dioxins. Summary of the Invention

[0003] This invention is based on the inventors' discovery and understanding of the following facts and problems: existing fly ash treatment processes are costly and inefficient. The present invention aims to address, at least to some extent, one of the technical issues in the related art. To this end, embodiments of the present invention provide a low-temperature dioxin removal system for fly ash, which offers the advantages of low fly ash treatment energy consumption and high resource utilization.

[0004] According to the fly ash dioxin low-temperature removal system of the embodiment of the present invention, the fly ash dioxin low-temperature removal system includes a low-temperature pyrolysis device, a multi-stage countercurrent washing device and a solid-liquid separation unit, the low-temperature pyrolysis device includes a device body, a feeding mechanism, an inert gas mechanism, a conveying mechanism and a cooling mechanism, the feeding mechanism is located at the feeding port on the top of the device body to control the entry of fly ash, the conveying mechanism is located in the device body to carry and convey the fly ash, the inert gas mechanism is used to convey inert gas to the fly ash in the device body to form a low-oxygen environment, the cooling mechanism is located at the discharge port at the bottom of the device body to cool the fly ash after pyrolysis, the multi-stage countercurrent washing device includes A fly ash conveying mechanism and multiple water washing tanks arranged in series, each of the water washing tanks is provided with a liquid distributing member for feeding washing liquid and a stirring mechanism for stirring fly ash, the fly ash conveying mechanism transports the fly ash from the first-stage water washing tank to the next-stage water washing tank in forward direction, the solid-liquid separation unit includes a filter press mechanism, a sodium chloride continuous crystallizer and a potassium chloride continuous crystallizer, the filter press mechanism is used to dehydrate the washing residue from the multi-stage countercurrent washing device, the filtrate of the filter press mechanism is fed into the sodium chloride continuous crystallizer, the filtrate is circulated for crystallization and desalination in the sodium chloride continuous crystallizer and the potassium chloride continuous crystallizer for multiple times, and the desalted wastewater is returned to the multi-stage countercurrent washing device.

[0005] The low-temperature dioxin removal system for fly ash according to the embodiment of the present invention has the advantages of low fly ash treatment energy consumption and high resource utilization rate. This application has the following advantages: high efficiency, low cost, low energy consumption, low carbon and environmental protection, high acceptance of raw ash, and can be used to treat various fly ashes without pretreatment of fly ash; heavy metals as non-ferrous metallurgical raw materials and salts as industrial salts can be effectively recovered, with high resource utilization rate; the equipment reaction is carried out at low temperature and normal pressure, the process flow is simple, no harmful substances are generated during the process, and it is low carbon and environmentally friendly. This application uses waste incineration fly ash as raw material, and after low-temperature heat treatment to degrade dioxins, combined with water washing to enrich heavy metals and separate and recover potassium and sodium salts, and the washed ash is utilized as a resource. The entire process has no wastewater discharge and no hazardous waste output, realizing a green, low-carbon and environmentally friendly fly ash disposal and resource utilization of "one waste in, multiple resources out, and full resource utilization". The low-temperature removal technology effectively reduces the dioxin content while reducing energy consumption. The water washing and salt separation process not only removes harmful heavy metals from the fly ash, but also recovers valuable heavy metal resources and salt resources.

[0006] In some embodiments, the feed mechanism includes a manual gate valve and a solenoid gate valve, which are arranged vertically in sequence, with a distance between the manual gate valve and the two solenoid gate valves. Fly ash between the two solenoid gate valves serves as a material seal.

[0007] In some embodiments, the inert gas mechanism includes a first direction blowing pipeline and a second direction blowing pipeline, the first direction is opposite to the forward direction of the fly ash on the conveying mechanism, and the second direction is perpendicular to the forward direction of the fly ash on the conveying mechanism.

[0008] In some embodiments, the cooling mechanism includes a conveyor belt and a cooling water circulation pipe. The conveyor belt is used to receive the fly ash after pyrolysis. The cooling water circulation pipe is arranged on the outer shell of the conveyor belt to cool the fly ash after pyrolysis.

[0009] In some embodiments, two electromagnetic gate valves are provided at the discharge port at the bottom of the device body to control the discharge amount, and a heat exchange component is also provided at the discharge port to exchange heat with the inert gas in the device body.

[0010] In some embodiments, the three water washing tanks are respectively a primary water washing tank, a secondary water washing tank and a tertiary water washing tank. The fly ash enters the secondary water washing tank from the primary water washing tank and then enters the tertiary water washing tank. The washing liquid flows from the tertiary water washing tank to the secondary water washing tank and then enters the primary water washing tank. A fly ash feed port is set at the top of the primary water washing tank, and the outlet of the tertiary water washing tank is connected to the filter press mechanism.

[0011] In some embodiments, the liquid distribution member includes a spray head and a liquid distribution pipe. The spray head is connected to the liquid distribution pipe, and the liquid distribution pipe is used to ensure that the washing liquid rises evenly.

[0012] In some embodiments, the fly ash conveying mechanism is a screw conveyor or a scraper conveyor, which conveys the fly ash step by step to the water washing tank in the direction of the filter press mechanism, and the first conveying mechanism is a heated grate conveyor belt.

[0013] According to the low-temperature removal method of dioxins from fly ash according to an embodiment of the present invention, the low-temperature removal method of dioxins from fly ash comprises the following steps:

[0014] Fly ash is fed into a low-temperature pyrolysis device, where the fly ash remains in the low-temperature pyrolysis device at a temperature range of 300° C. to 400° C. for a preset time, and an inert gas is blown into the low-temperature pyrolysis device to remove degradation products on the surface of the fly ash and form a low-oxygen environment;

[0015] The fly ash after pyrolysis is cooled to below the target temperature by a cooling mechanism to obtain pyrolysis ash and discharged;

[0016] The pyrolysis ash is contacted with a washing liquid in a countercurrent manner in a multi-stage countercurrent washing device for washing, so as to wash away soluble pollutants in the pyrolysis ash and obtain washing residue and washing liquid;

[0017] A heavy metal remover is added to the water washing liquid to obtain a heavy metal residue. The washing residue and the heavy metal residue are sent to a filter press mechanism for solid-liquid separation. The water washing liquid and the filtrate obtained by the filter press are subjected to multiple evaporation and crystallization to recover potassium salt and sodium salt in the filtrate. The remaining part of the filtrate is refluxed to a multi-stage countercurrent washing device.

[0018] In some embodiments, the washing liquid portion of the multi-stage countercurrent washing device uses cooling circulating water from a cooling mechanism, and the high-temperature gas from the low-temperature pyrolysis device is purified and sent to the primary water washing tank for heat exchange with the washing liquid. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 Schematic diagram of the structure of a low-temperature pyrolysis device of a low-temperature dioxin removal system for fly ash according to an embodiment of the present invention.

[0020] Figure 2 Schematic diagram of the structure of a multi-stage countercurrent washing device and a solid-liquid separation unit of a low-temperature dioxin removal system for fly ash according to an embodiment of the present invention.

[0021] Figure numerals: 1. Manual gate valve; 2. Solenoid gate valve; 3. First conveying mechanism; 4. First direction blowing pipeline; 5. Second direction blowing pipeline; 6. Conveyor belt; 7. Cooling water circulation pipe; 8. Heat exchanger; 9. Primary water washing tank; 10. Secondary water washing tank; 11. Tertiary water washing tank; 12. Filter press mechanism; 13. Sodium chloride continuous crystallizer. DETAILED DESCRIPTION

[0022] The embodiments of the present invention are described in detail below, and examples of the embodiments are shown in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to be used to explain the present invention, but should not be understood as limiting the present invention.

[0023] According to an embodiment of the present invention, a low-temperature dioxin removal system for fly ash includes a low-temperature pyrolysis device, a multi-stage countercurrent washing device and a solid-liquid separation unit. The low-temperature pyrolysis device includes a device body, a feeding mechanism, an inert gas mechanism, a conveying mechanism and a cooling mechanism. The feeding mechanism is located at a feeding port on the top of the device body to control the entry of fly ash. The conveying mechanism is located in the device body to carry and convey fly ash. The conveying mechanism can be a heated grate conveyor belt. The movement of the grate conveyor belt can increase the heating of the fly ash and the effective contact with the inert gas, thereby accelerating the degradation of dioxins. The temperature of the heated grate conveyor belt is 300°C to 400°C, which can directly supply energy to the fly ash, provide the energy required for breaking the C-Cl bond, and promote the dechlorination and degradation of dioxins.

[0024] The inert gas mechanism is used to transport inert gas to the fly ash in the device body to form a low-oxygen environment. The cooling mechanism is located at the discharge port at the bottom of the device body to cool the fly ash after pyrolysis. The multi-stage countercurrent washing device includes a fly ash conveying mechanism and a plurality of water washing tanks arranged in series. Each water washing tank is provided with a liquid distribution member for feeding washing liquid and a stirring mechanism for stirring fly ash. The fly ash conveying mechanism transports the fly ash from the first-stage water washing tank 9 to the next-stage water washing tank 9 in forward direction. The solid-liquid separation unit includes a filter press mechanism 12, a sodium chloride continuous crystallizer and a potassium chloride continuous crystallizer. The filter press mechanism 12 is used to dehydrate the washing residue from the multi-stage countercurrent washing device. The filtrate of the filter press mechanism 12 is fed into the sodium chloride continuous crystallizer. The filtrate is circulated multiple times in the sodium chloride continuous crystallizer and the potassium chloride continuous crystallizer for crystallization and desalination. The desalted wastewater is returned to the multi-stage countercurrent washing device. Low-temperature pyrolysis units create a low-oxygen environment by delivering inert gas to the fly ash surface, causing it to pyrolyze at temperatures between 300°C and 400°C. During the incineration of chlorine-containing plastics, dioxins are generated at temperatures between 250°C and 500°C. In this temperature range, chlorine readily combines with amorphous carbon species to form highly toxic dioxins. In the presence of oxygen in the ambient atmosphere, it preferentially reacts with hydroxyl groups or reducing gases, thereby inhibiting dioxin degradation. The low-oxygen environment created by the inert gas promotes chlorination substitution reactions between hydroxyl groups or reducing species and dioxins, promoting dioxin dechlorination. Residual calcium hydroxide and silica in the fly ash provide abundant surface hydroxyl groups, further facilitating dechlorination. Furthermore, the inert gas removes degradation products from the fly ash surface, promoting the forward chlorination reaction and accelerating dioxin dechlorination. The multi-stage countercurrent scrubbing unit removes soluble contaminants from the fly ash through multiple washes, using countercurrent contact between scrubbing liquid and the pyrolyzed fly ash. The fly ash after low-temperature pyrolysis has a uniform particle size distribution and a moisture content of less than 2%, resulting in excellent fluidity. Washing the fly ash with a washing solution effectively avoids problems such as difficult raw ash conveying, agglomeration during washing, low heavy metal dissolution rates, and high reagent dosages. Residual free chlorine in the washed fly ash can be reduced to less than 0.5%. Reusing the washing solution multiple times conserves water and reduces costs. The solid-liquid separation unit achieves solid-liquid separation using a filter press 12. Sodium chloride and potassium chloride in the filtrate are crystallized and desalinated using a continuous evaporation crystallizer. The remaining supernatant can be recycled as washing solution, reducing environmental pollution. The filter press 12 utilizes a plate and frame filter press, with acid- and alkali-resistant filter cloths, to achieve deep dehydration of the washing residue (moisture content ≤ 20%). The treated filtrate then flows back to the multi-stage countercurrent washing unit.The sodium chloride continuous crystallizer is an MVR evaporation and concentration continuous crystallizer. It consists of an evaporation chamber, a separator, a crystallizer, and an MVR mechanism. The evaporation chamber is equipped with a heating pipe or plate heat exchanger. High-temperature steam from the MVR mechanism heats the raw liquid to promote water evaporation. The separator is located above the evaporation chamber and uses a gas-liquid separation structure to separate the secondary steam generated by evaporation from the suspension containing sodium chloride crystals. The upper outlet of the separator is connected to a pipeline for discharging low-sodium supernatant, and the lower outlet of the separator is used to discharge the slurry containing sodium chloride crystals. The crystallizer is connected to the lower outlet of the separator, providing space for crystal growth. A stirring element is installed in the crystallizer to prevent crystal sedimentation and promote uniform crystal growth. The MVR mechanism includes a steam compressor, a condenser, and a circulation pipeline. The MVR mechanism compresses and heats the secondary steam and returns it to the evaporation chamber, achieving heat recycling. The bottom of the crystallizer is connected to a solid-liquid separator, which separates the sodium chloride and potassium chloride crystals. The filtrate is returned to the corresponding crystallizer or sent to a multi-stage countercurrent washing device. The structure of the potassium chloride continuous crystallizer is similar to that of the MVR evaporation concentration continuous crystallizer and will not be described in detail.

[0025] In some embodiments, the feeding mechanism includes a manual gate valve 1 and an electromagnetic gate valve 2, which are arranged in sequence in the vertical direction, and there is a distance between the manual gate valve 1 and the two electromagnetic gate valves 2.

[0026] Specifically, the switching time and sequence of the two electromagnetic gate valves 2 are regulated to achieve stable and continuous discharge of raw ash. The fly ash between the two electromagnetic gate valves 2 acts as a material seal to effectively ensure the airtightness of the device. At the same time, the open discharge space can avoid clogging caused by foreign matter in the fly ash. The manual gate valve 1 is convenient for operators to manually open or close the feed in the event of power failure or other emergency situations to ensure the safe operation of the system. Precise feed control can reduce the accumulation of fly ash at the feed port and avoid affecting the normal operation of the system due to fly ash blockage. The good seal brought by the material seal can prevent outside air from entering the low-temperature pyrolysis device, ensuring a low-oxygen environment in the device and further improving the pyrolysis effect of dioxins. Precise feed control and good sealing can reduce the wear and corrosion of the equipment by fly ash and extend the service life of the equipment.

[0027] Optionally, a material level sensor is installed between the manual gate valve 1 and the electromagnetic gate valve 2 to detect the fly ash material level. When the material level reaches a preset value, the material level sensor is triggered, which in turn controls the electromagnetic gate valve 2 to achieve precise feed control and avoid overfeeding or underfeeding. This helps stabilize the material flow within the low-temperature pyrolysis unit and improve pyrolysis efficiency and quality.

[0028] In some embodiments, the inert gas mechanism includes a first direction blowing pipeline 4 and a second direction blowing pipeline 5, the first direction is opposite to the forward direction of the fly ash on the conveying mechanism, and the second direction is perpendicular to the forward direction of the fly ash on the conveying mechanism.

[0029] Specifically, the inert gas is injected in two directions. The first direction, counter to the direction of the fly ash's movement on the conveyor, replenishes heat and removes surface degradation products. The second direction, perpendicular to the direction of the fly ash's movement on the conveyor, creates a weakly fluidized state. Nitrogen can be used as the inert gas. Weakly fluidized states can be understood as the effect of the hot nitrogen injection, which causes the fly ash to be partially suspended but not fully fluidized. When the hot nitrogen is injected perpendicular to the fly ash, it only slightly "loosens" the fly ash particles, forming a loose, stacked structure similar to a slight boil, but does not achieve full fluidization, or the free flow of a liquid. In this weakly fluidized state, the interparticle spaces increase, allowing the hot nitrogen to more evenly penetrate the ash layer, fully contacting pollutants such as dioxins, improving heat transfer and degradation efficiency, and accelerating the removal of pyrolysis products. Compared to strong fluidization, weak fluidization reduces the violent movement of particles, preventing excessive carryover of ash into downstream systems while ensuring that impurity gases generated by pyrolysis are effectively removed by the countercurrent nitrogen injection. By optimizing the injection of inert gas, the low-oxygen environment in the device can be maintained more effectively, reducing the generation and emission of dioxins.

[0030] Optionally, the injection ports of the first direction injection pipeline 4 and the second direction injection pipeline 5 of the inert gas mechanism are provided with angle adjustment members for adjusting the injection direction, and the injection angle is adjusted according to the fly ash particle size and conveying speed.

[0031] Before entering the injection pipeline, the inert gas, such as nitrogen, can be preheated to a temperature close to the pyrolysis temperature (e.g., 200°C to 300°C). This preheated inert gas not only helps maintain a stable temperature within the device but also improves pyrolysis efficiency. Injecting the inert gas into the device itself maintains a slightly positive pressure within the system, minimizing oxygen concentrations within the device and facilitating the smooth flow of fly ash.

[0032] In some embodiments, the cooling mechanism includes a conveyor belt 6 and a cooling water circulation pipe 7. The conveyor belt 6 is used to receive the fly ash after pyrolysis. The cooling water circulation pipe 7 is arranged on the outer shell of the conveyor belt 6 to cool the fly ash after pyrolysis.

[0033] Specifically, cooling water circulation pipe 7 cools the outer shell of conveyor belt 6 with cooling water, rapidly cooling the pyrolysis ash to below 70°C, effectively preventing the regeneration of toxic dioxins. A variable-frequency speed-regulating motor is installed on conveyor belt 6, flexibly adjusting its speed based on the fly ash cooling requirements and subsequent processing steps. When the fly ash temperature is high, the speed of conveyor belt 6 can be appropriately reduced to extend the cooling time.

[0034] Optionally, a temperature sensor is provided on the cooling water circulation pipe 7 to detect the cooling water temperature, and a heat exchanger is provided on the cooling water circulation pipe 7 to adjust the cooling water temperature. By adjusting the temperature of the cooling water, the cooling rate of the fly ash after pyrolysis is controlled. According to the temperature of the fly ash and the subsequent processing requirements, the temperature of the cooling water can be flexibly adjusted to ensure that the fly ash does not agglomerate due to too low a temperature or affect subsequent operations due to too high a temperature during the cooling process. By adjusting the temperature of the cooling water, the cooling process can be accurately controlled according to the temperature of the fly ash and the cooling requirements. Adjusting the cooling water flow rate can ensure that the cooling water can efficiently cool the fly ash under different working conditions, while avoiding the waste of cooling water and reducing operating costs.

[0035] In some embodiments, two electromagnetic gate valves 2 are provided at the discharge port at the bottom of the device body to control the discharge amount, and a heat exchange element 8 is also provided at the discharge port to exchange heat with the inert gas in the device body.

[0036] Specifically, two electromagnetic gate valves 2 are spaced apart vertically. The pyrolysis fly ash stored between the two electromagnetic gate valves 2 acts as a material seal, preventing the escape of inert gas and the ingress of external oxygen. When the first electromagnetic gate valve 2 is closed, the second electromagnetic gate valve 2 is opened, and vice versa, thus ensuring the continuity and stability of the discharge process.

[0037] The heat exchange element 8 can use cooling water or compressed air or inert gas to exchange heat with the inert gas. The high-temperature inert gas in the device body can be used to preheat the inert gas to reduce heat energy waste.

[0038] In some embodiments, the three water washing tanks are respectively a primary water washing tank 9, a secondary water washing tank 10 and a tertiary water washing tank 11. The fly ash enters the secondary water washing tank 10 from the primary water washing tank 9 and then enters the tertiary water washing tank 11. The washing liquid flows from the tertiary water washing tank 11 to the secondary water washing tank 10 and then enters the primary water washing tank 9. A fly ash feed port is set at the top of the primary water washing tank 9, and the outlet of the tertiary water washing tank 11 is connected to the filter press mechanism 12.

[0039] Specifically, the fly ash enters the secondary water washing tank 10 from the primary water washing tank 9, and then enters the tertiary water washing tank 11, while the washing liquid flows from the tertiary water washing tank 11 to the secondary water washing tank 10, and finally enters the primary water washing tank 9. The washing liquid that has been washed twice in the primary water washing tank 9 performs the initial washing on the fly ash, the washing liquid that has been washed once in the secondary water washing tank 10 performs the secondary washing on the fly ash, and the fresh washing liquid in the tertiary water washing tank 11 performs the tertiary washing on the fly ash. This countercurrent washing method can ensure that pollutants in the fly ash are removed to the maximum extent. The subsequent purification of the washing liquid can be used to recycle the washing liquid to reduce wastewater discharge and reduce the impact on the environment. The water washing tank is a rectangular tank. Paddle-type or anchor-type stirring elements are set in the water washing tank to ensure full contact between the fly ash and the washing liquid.

[0040] Optionally, a heat exchanger is installed on the flow pipeline of the washing liquid to adjust the temperature of the washing liquid according to the requirements of the washing process to improve the washing efficiency. Adjusting the temperature of the washing liquid helps to increase the solubility of soluble substances in the fly ash.

[0041] In some embodiments, the liquid distribution component includes a spray head and a liquid distribution pipe. The spray head is connected to the liquid distribution pipe, and the liquid distribution pipe is used to ensure that the washing liquid rises evenly.

[0042] Specifically, the liquid distribution unit can be configured as a spray pipe with multiple branches to ensure that the washing liquid is evenly distributed throughout the washing tank, avoiding local insufficient or excessive washing liquid. The spray head can be an adjustable nozzle to adjust the spray intensity according to the flow rate and concentration of the fly ash.

[0043] In some embodiments, the fly ash conveying mechanism is a screw conveyor or a scraper conveyor, which conveys the fly ash step by step to the water washing tank in the direction of the filter press mechanism 12, and the first conveying mechanism 3 is a heated grate conveyor belt.

[0044] Specifically, fly ash is transported from one level to the next via a screw conveyor or scraper to ensure that the fly ash is in full contact with the washing liquid during transportation. The washing liquid concentration and temperature of each washing tank can be adjusted according to the composition and treatment requirements of the fly ash to achieve the best washing effect. The spacing and pitch of the spiral blades of the screw conveyor can be optimized according to the particle size and density of the fly ash to improve the transportation efficiency and reduce the accumulation and blockage of fly ash during transportation. The shape and spacing of the scraper conveyor can be adjusted according to the fluidity of the fly ash. At the same time, baffles are set on the scraper to prevent the fly ash from detaching during transportation and ensure transportation efficiency. Both screw conveyors and scraper conveyors can adopt a closed body, which can effectively prevent fly ash from flying during transportation and reduce dust pollution. The heated grate conveyor belt combines heating and material conveying functions. The grate can stably convey materials in a high-temperature environment. A heat source is set on or around the grate to heat the grate. The conveyor belt drives the grate to move the material along the target path. The heated grate conveyor belt realizes continuous heating and conveying of the material, ensuring that the material is heated evenly during the heating process, thereby improving product quality.

[0045] According to the low-temperature removal method of dioxins from fly ash according to an embodiment of the present invention, the low-temperature removal method of dioxins from fly ash comprises the following steps:

[0046] Fly ash is fed into a low-temperature pyrolysis unit, where it remains within a temperature range of 300°C to 400°C for a predetermined time. Inert gas is then injected into the unit to remove degradation products from the fly ash surface and create a low-oxygen environment. The fly ash remains within the unit for 0.5 to 1 hour, promoting deep dechlorination and degradation of dioxins into non-toxic amorphous carbon species. The inert gas used is nitrogen with a purity of 99.9% or higher, and the nitrogen injection temperature is between 200°C and 400°C. The oxygen content within the unit is below 4%, and the pressure is maintained between -100 Pa and 500 Pa. The unit's residence time is maintained between 0.5 and 1 hour, promoting deep dechlorination and degradation of dioxins into non-toxic amorphous carbon species.

[0047] After pyrolysis, the fly ash is cooled by a cooling mechanism to below the target temperature of 70°C, resulting in pyrolysis ash, which is then discharged. This cooling process is divided into two steps. Initial cooling involves heat exchange with nitrogen at the discharge port of the low-temperature pyrolysis unit, recovering heat energy. Secondary cooling involves rapid cooling with cooling water by the cooling mechanism to prevent the regeneration of dioxins. The high-temperature flue gas discharged from the low-temperature pyrolysis unit contains nitrogen and impurities, which can be purified to produce ammonia water with a concentration of 3% to 10%, achieving resource recovery.

[0048] The pyrolysis ash is washed in a multi-stage countercurrent washing device in countercurrent contact with the washing liquid to wash the soluble pollutants in the pyrolysis ash, thereby obtaining washing residue and washing liquid. The multi-stage countercurrent washing device achieves efficient elution of soluble pollutants (such as heavy metals and salts) in the fly ash through countercurrent contact. The multiple rectangular tanks connected in series in the multi-stage countercurrent washing device wash the fly ash multiple times, and the washing residue is squeezed and dehydrated using a plate and frame filter press.

[0049] A heavy metal remover is added to the washing liquid to obtain a heavy metal residue. The washing residue and the heavy metal residue are sent to a filter press mechanism 12 for solid-liquid separation. The water washing liquid and the filtrate obtained by the filter press are subjected to multiple evaporation crystallizations to recover the potassium salt and sodium salt in the filtrate. The remaining part of the filtrate is refluxed to a multi-stage countercurrent washing device. The washing liquid and the filtrate contain a large amount of chlorine-rich calcium salts. Direct discharge will not only cause pollution, but also cause a large amount of waste of chlorine-rich calcium salt resources. After the cooling water is heat-exchanged with the fly ash after pyrolysis, the temperature can be raised to 50°C to 80°C. Using part of the cooling water as a washing liquid can accelerate the dissolution of heavy metals and salts and reduce the energy consumption required for reheating the washing liquid. In addition, the temperature increase helps to reduce the solubility of carbonates and promote the complete precipitation of miscellaneous ions such as calcium and magnesium.

[0050] The washing liquid and the filtrate are sent to the MVR evaporation and concentration continuous crystallizer as the raw liquid, so that the raw liquid is evaporated, concentrated, and hot crystallized to precipitate sodium chloride. The low sodium supernatant on the upper part of the separator of the MVR evaporation and concentration continuous crystallizer is sent to the potassium chloride continuous crystallizer to crystallize and precipitate potassium chloride. The low potassium supernatant on the upper part of the potassium chloride continuous crystallizer is then sent to the MVR evaporation and concentration continuous crystallizer. The low sodium supernatant and the low potassium supernatant are continuously circulated back and forth in the MVR evaporation and concentration hot continuous crystallizer and the potassium chloride continuous crystallizer, so that sodium chloride is continuously precipitated in the MVR evaporation and concentration continuous crystallizer, and potassium chloride is continuously precipitated in the potassium chloride continuous crystallizer, thereby evaporating the wastewater raw liquid and separating potassium and sodium salts. The desalted wastewater can be recycled and used as washing liquid.

[0051] This method provides a new route for the recycling of all fly ash components and materials. Furthermore, its application in low-temperature flue gas purification systems, the full utilization of waste heat, and the recovery of steam heat all improve overall system efficiency and reduce operating costs. This method is not only applicable to waste-to-energy plants but can also be expanded to other industrial sectors requiring fly ash treatment.

[0052] In some embodiments, the washing liquid portion of the multi-stage countercurrent washing device uses cooling circulating water from a cooling mechanism, and the high-temperature gas from the low-temperature pyrolysis device is purified and sent to the primary water washing tank 9 to exchange heat with the washing liquid.

[0053] Specifically, the temperature of the high-temperature gas purified by the low-temperature pyrolysis device is 80°C to 100°C. The high-temperature gas is fed into the primary water washing tank 9. The washing liquid can absorb the waste heat of the high-temperature gas. The preheated washing liquid can also accelerate the dissolution of heavy metals and salts, promote the precipitation of carbonates, and reduce the energy consumption required for reheating the washing liquid. The heat provided to the fly ash and nitrogen in the low-temperature pyrolysis device is reused to the maximum extent through the circulating water and flue gas-water washing heat exchange, thereby fully realizing energy saving.

[0054] Example 1: The dioxin content in fly ash from a grate furnace waste incineration plant was 160 ng-TEQ / kg. The process of this application was used to treat the fly ash. The reaction temperature was controlled at 350°C, the reaction time was 50 minutes, the oxygen content in the reaction system was maintained at less than 1% (volume fraction), and the pressure in the reaction system was maintained at 50 Pa (gauge pressure). The temperature of the fly ash after pyrolysis was reduced to 60°C within 2 minutes. The dioxin content in the fly ash after pyrolysis was 0.3 ng-TEQ / kg, and no dioxin was detected in the flue gas. The degradation rate of dioxins in the fly ash after pyrolysis was 99.81%. The ammonia concentration recovered by the flue gas purification system was 5%, and the recovered salt purity reached 98%. After pyrolysis and water washing, the heavy metal concentration of fly ash increases from 11.58mg / L Cu, 39.41mg / L Pb, 233.02mg / L Zn, 1.45mg / L Ni, 0.97mg / L Cr, and 7.79mg / L Cd to 0.079mg / L Cu, 0.18mg / L Pb, 56mg / L Zn, 0.15mg / L Ni, 0.17mg / L Cr, and 0.09mg / L Cd. The heavy metal-enriched bottom slag is used as a smelting concentrate ingredient. The power consumption for dioxin removal per ton of fly ash is 80-100 degrees, and the heat recycling rate reaches more than 80%.

[0055] Example 2: The dioxin content in fly ash from a grate furnace waste incineration plant was 85 ng-TEQ / kg. Using the treatment method of the present invention, the reaction temperature was controlled at 340°C, the reaction time was 45 minutes, the oxygen content in the reaction system was maintained at less than 1% (volume fraction), and the pressure in the reaction system was maintained at -10 Pa (gauge pressure). After pyrolysis, the temperature of the fly ash was reduced to 50°C within 2 minutes. The dioxin content in the fly ash after pyrolysis was measured to be 0.77 ng-TEQ / kg, and no dioxins were detected in the flue gas, resulting in a dioxin degradation rate of 99.09%. The ammonia concentration recovered by the flue gas purification system was 5%, and the recovered salt purity reached 96%. After pyrolysis and water washing, the heavy metal concentration of fly ash increases from 10.07mg / L Cu, 34.94mg / L Pb, 243.05mg / L Zn, 1.76mg / LNi, 0.78mg / L Cr, and 7.21mg / L Cd to 0.087mg / L Cu, 0.11mg / L Pb, 61mg / L Zn, 0.18mg / L Ni, 0.21mg / L Cr, and 0.11mg / L Cd. The heavy metal enriched bottom slag is used as a smelting concentrate ingredient. The power consumption for dioxin removal per ton of fly ash is 80-100 degrees, and the heat recycling rate reaches more than 80%.

[0056] Example 3: The dioxin content in fly ash from a grate furnace waste incineration plant was 102 ng-TEQ / kg. Using the treatment method of the present invention, the reaction temperature was controlled at 330°C, the reaction time was 50 minutes, the oxygen content in the reaction system was maintained at less than 1% (volume fraction), and the pressure in the reaction system was maintained at 18 Pa (gauge pressure). After pyrolysis, the temperature of the fly ash was reduced to 50°C within 2 minutes. The dioxin content in the fly ash after pyrolysis was measured to be 5.98 ng-TEQ / kg, and no dioxins were detected in the flue gas, resulting in a dioxin degradation rate of 94.14%. The ammonia concentration recovered by the flue gas purification system was 6%, and the recovered salt purity reached 96%. After pyrolysis and water washing, the heavy metal concentration of fly ash increases from 11.01mg / L Cu, 35.71mg / L Pb, 237.01mg / L Zn, 1.58mg / LNi, 0.87mg / L Cr, and 7.29mg / L Cd to 0.089mg / L Cu, 0.20mg / L Pb, 59mg / L Zn, 0.18mg / L Ni, 0.15mg / L Cr, and 0.06mg / L Cd. The heavy metal enriched bottom slag is used as a smelting concentrate ingredient. The power consumption for dioxin removal per ton of fly ash is 80-100 degrees, and the heat recycling rate reaches more than 80%.

[0057] Example 4: The dioxin content in fly ash from a grate furnace waste incineration plant was 131 ng-TEQ / kg. Using the treatment method of the present invention, the reaction temperature was controlled at 380°C, the reaction time was 45 minutes, the oxygen content in the reaction system was maintained at less than 1% (volume fraction), and the pressure in the reaction system was maintained at 39 Pa (gauge pressure). After pyrolysis, the temperature of the fly ash was reduced to 50°C within 2 minutes. The dioxin content in the fly ash after pyrolysis was measured to be 0.48 ng-TEQ / kg, and no dioxins were detected in the flue gas, resulting in a dioxin degradation rate of 99.63%. The ammonia concentration recovered by the flue gas purification system was 4%, and the recovered salt purity reached 98%. After pyrolysis and water washing, the heavy metal concentration of fly ash increases from 10.98mg / L Cu, 37.11mg / L Pb, 238.52mg / L Zn, 165mg / L Ni, 0.87mg / L Cr, and 7.49mg / L Cd to 0.069mg / L Cu, 0.19mg / L Pb, 72mg / L Zn, 0.18mg / L Ni, 0.21mg / L Cr, and 0.11mg / L Cd. The heavy metal enriched bottom slag is used as a smelting concentrate ingredient. The power consumption for dioxin removal per ton of fly ash is 80-100 degrees, and the heat recycling rate reaches more than 80%.

[0058] Example 5: The dioxin content in fly ash from a grate furnace waste incineration plant was 249 ng-TEQ / kg. Using the treatment method of the present invention, the reaction temperature was controlled at 400°C, the reaction time was 60 minutes, the oxygen content in the reaction system was maintained at less than 1% (volume fraction), and the pressure in the reaction system was maintained at -5 Pa (gauge pressure). After pyrolysis, the temperature of the fly ash was reduced to 70°C within 2 minutes. The dioxin content in the fly ash after pyrolysis was measured to be 0.61 ng-TEQ / kg, and no dioxins were detected in the flue gas, resulting in a dioxin degradation rate of 99.75%. The concentration of ammonia recovered by the flue gas purification system was 3%, and the recovered salt had a purity of 98%. After pyrolysis and water washing, the heavy metal concentration of fly ash increases from 10.77mg / L Cu, 33.81mg / L Pb, 230.62mg / L Zn, 1.85mg / LNi, 0.82mg / L Cr, and 7.34mg / L Cd to 0.061mg / L Cu, 0.11mg / L Pb, 59mg / L Zn, 0.19mg / L Ni, 0.12mg / L Cr, and 0.12mg / L Cd. The heavy metal enriched bottom slag is used as a smelting concentrate ingredient. The power consumption for dioxin removal per ton of fly ash is 80-100 degrees, and the heat recycling rate reaches more than 80%.

[0059] Example 6: The dioxin content in fly ash from a grate furnace waste incineration plant was 163 ng-TEQ / kg. According to the treatment method of the present invention, the reaction temperature was controlled at 300°C, the reaction time was 60 minutes, the oxygen content in the reaction system was maintained at less than 1% (volume fraction), and the pressure in the reaction system was maintained at 35 Pa (gauge pressure). After pyrolysis, the temperature of the fly ash was reduced to 50°C within 2 minutes. The dioxin content in the fly ash after pyrolysis was measured to be 29.86 ng-TEQ / kg, and no dioxins were detected in the flue gas, resulting in a dioxin degradation rate of 81.68%. The concentration of ammonia recovered by the flue gas purification system was 8%, and the recovered salt purity reached 95%. After pyrolysis and water washing, the heavy metal concentration of fly ash increases from 10.99 mg / L Cu, 34.91 mg / L Pb, 230.56 mg / L Zn, 1.37 mg / L Ni, 0.82 mg / L Cr, and 7.14 mg / L Cd to 0.065 mg / L Cu, 0.13 mg / L Pb, 67 mg / L Zn, 0.12 mg / L Ni, 0.11 mg / L Cr, and 0.13 mg / L Cd. The heavy metal-enriched bottom slag is used as a smelting concentrate ingredient. The power consumption for dioxin removal per ton of fly ash is 80-100 degrees, and the heat recycling rate reaches more than 80%.

[0060] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like to indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0061] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of the technical features being referred to. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one such feature. In the description of the present invention, "plurality" means at least two, such as two, three, etc., unless otherwise specifically defined.

[0062] In the present invention, unless otherwise specified or limited, the terms "installed," "connected," "connect," "fixed," etc. should be understood in a broad sense. For example, they can refer to fixed connection, detachable connection, or integration; mechanical connection, electrical connection, or communication; direct connection or indirect connection through an intermediate medium; internal communication between two elements or interaction between two elements, unless otherwise specified. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0063] In the present invention, unless otherwise expressly specified or limited, when a first feature is "above" or "below" a second feature, it may mean that the first and second features are in direct contact, or that the first and second features are in indirect contact through an intermediary. Furthermore, when a first feature is "above," "above," or "above" a second feature, it may mean that the first feature is directly above or diagonally above the second feature, or simply means that the first feature is at a higher level than the second feature. When a first feature is "below," "below," or "below" a second feature, it may mean that the first feature is directly below or diagonally below the second feature, or simply means that the first feature is at a lower level than the second feature.

[0064] In the present invention, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples" mean that the specific features, structures, materials, or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in any appropriate manner in any one or more embodiments or examples. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification, as well as features of different embodiments or examples, unless they are mutually inconsistent.

[0065] Although the embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are illustrative and are not to be construed as limitations on the present invention. Any changes, modifications, substitutions and variations of the above embodiments by those skilled in the art are within the scope of protection of the present invention.

Claims

1. A fly ash dioxin low temperature removal system, characterized in that: include: A low-temperature pyrolysis device, comprising a device body, a feeding mechanism, an inert gas mechanism, a first conveying mechanism, and a cooling mechanism. The feeding mechanism is located at a feeding port at the top of the device body to control the entry of fly ash. The first conveying mechanism is located within the device body to carry and convey the fly ash. The inert gas mechanism is used to convey inert gas to the fly ash in the device body to form a low-oxygen environment. The cooling mechanism is located at a discharge port at the bottom of the device body to cool the fly ash after pyrolysis. A multi-stage countercurrent washing device, comprising a fly ash conveying mechanism and a plurality of water washing tanks arranged in series, each of the water washing tanks being provided with a liquid distributing member for feeding washing liquid and a stirring mechanism for stirring fly ash, wherein the fly ash conveying mechanism conveys the fly ash from the first-stage water washing tank to the next-stage water washing tank in a forward direction; a solid-liquid separation unit comprising a filter press mechanism, a sodium chloride continuous crystallizer, and a potassium chloride continuous crystallizer; the filter press mechanism is used to dehydrate the washing residue from the multi-stage countercurrent washing device; the filtrate from the filter press mechanism is fed into the sodium chloride continuous crystallizer; the filtrate is circulated multiple times in the sodium chloride continuous crystallizer and the potassium chloride continuous crystallizer for crystallization and desalination; and the desalted wastewater is returned to the multi-stage countercurrent washing device; The inert gas mechanism includes a first-direction blowing pipeline and a second-direction blowing pipeline. The first direction is opposite to the forward direction of the fly ash on the first conveying mechanism, and the second direction is perpendicular to the forward direction of the fly ash on the first conveying mechanism, so that the fly ash forms a weak fluidized state. The weak fluidized state is a state in which the fly ash is partially suspended but not completely fluidized through the blowing action of the hot inert gas. When the hot inert gas is blown perpendicular to the fly ash, the gas only slightly "loosens" the fly ash particles, forming a loose stacking structure similar to slight boiling, but does not achieve complete fluidization, that is, free flow like liquid.

2. The fly ash dioxin low temperature removal system according to claim 1, characterized in that: The feeding mechanism includes a manual gate valve and an electromagnetic gate valve, which are arranged in sequence in the vertical direction, and there is a distance between the manual gate valve and the two electromagnetic gate valves.

3. The fly ash dioxin low temperature removal system according to claim 1, characterized in that: The cooling mechanism includes a conveyor belt and a cooling water circulation pipe. The conveyor belt is used to receive the fly ash after pyrolysis. The cooling water circulation pipe is arranged on the outer shell of the conveyor belt to cool the fly ash after pyrolysis.

4. The fly ash dioxin low temperature removal system according to claim 1, characterized in that: Two electromagnetic gate valves are provided at the discharge port at the bottom of the device body to control the discharge amount. A heat exchange component is also provided at the discharge port to exchange heat with the inert gas in the device body.

5. The fly ash dioxin low temperature removal system according to claim 1, characterized in that: The three water washing tanks are respectively a primary water washing tank, a secondary water washing tank and a tertiary water washing tank. The fly ash enters the secondary water washing tank from the primary water washing tank and then enters the tertiary water washing tank. The washing liquid flows from the tertiary water washing tank to the secondary water washing tank and then enters the primary water washing tank. A fly ash feed port is provided on the top of the primary water washing tank, and the outlet of the tertiary water washing tank is connected to the filter press mechanism.

6. The fly ash dioxin low temperature removal system according to claim 1, characterized in that: The liquid distribution component includes a spray head and a liquid distribution pipe. The spray head is connected to the liquid distribution pipe, and the liquid distribution pipe is used to ensure that the washing liquid rises evenly.

7. The fly ash dioxin low temperature removal system according to claim 1, characterized in that: The fly ash conveying mechanism is a screw conveyor or a scraper conveyor, which conveys the fly ash step by step to the water washing tank in the direction of the filter press mechanism. The first conveying mechanism is a heated grate conveyor belt.

8. A method for removing dioxins from fly ash at low temperature, characterized in that: The fly ash dioxin low-temperature removal system according to any one of claims 1 to 7 is used, and the removal method comprises the following steps: Fly ash is fed into a low-temperature pyrolysis device, where the fly ash remains in the low-temperature pyrolysis device at a temperature range of 300° C. to 400° C. for a preset time, and an inert gas is blown into the low-temperature pyrolysis device to remove degradation products on the surface of the fly ash and form a low-oxygen environment; The fly ash after pyrolysis is cooled to below the target temperature by a cooling mechanism to obtain pyrolysis ash and discharged; The pyrolysis ash is contacted with a washing liquid in a countercurrent manner in a multi-stage countercurrent washing device for washing, so as to wash away soluble pollutants in the pyrolysis ash and obtain washing residue and washing liquid; A heavy metal remover is added to the water washing liquid to obtain a heavy metal residue. The washing residue and the heavy metal residue are sent to a filter press mechanism for solid-liquid separation. The water washing liquid and the filtrate obtained by the filter press are subjected to multiple evaporation and crystallization to recover potassium salt and sodium salt in the filtrate. The remaining part of the filtrate is refluxed to a multi-stage countercurrent washing device.

9. The low-temperature removal method for dioxins in fly ash according to claim 8, characterized in that: The washing liquid portion of the multi-stage countercurrent washing device uses cooling circulating water from a cooling mechanism, and the high-temperature gas from the low-temperature pyrolysis device is purified and sent to the primary water washing tank for heat exchange with the washing liquid.

Images