Detoxification system for washed household garbage incineration fly ash

Abstract

The invention discloses a detoxification system for washed household garbage incineration fly ash, and belongs to the technical field of hazardous waste treatment. Comprising a fly ash temporary-storage tempering unit, a low-temperature anti-sticking drying unit, a temperature-control anti-scaling pyrolysis unit and a gas-solid separation unit which are connected in sequence. The fly ash caching and tempering unit is provided with a calcium salt content online detector and an anti-caking agent adding device, so that accurate tempering is realized; the low-temperature anti-sticking drying unit realizes low-temperature anti-sticking drying; the temperature-control anti-scaling pyrolysis unit adopts an indirect heating type rotary kiln and is provided with a plasma catalysis assembly, so that medium-temperature degradation of dioxin and scaling prevention are realized; the gas-solid separation unit comprises an efficient cyclone separator, a high-temperature ceramic dust remover and a water-cooled conveyor, and efficient separation and cooling are achieved. Through systematic structural design and integration, the technical problems that the calcium salt-containing fly ash after water washing is prone to caking and scaling in the treatment process, and dioxin degradation is not thorough are effectively solved.

Description

Technical Field

[0001] This invention belongs to the field of hazardous waste treatment technology, specifically relating to a detoxification system for fly ash from municipal solid waste incineration after water washing. Background Technology

[0002] Fly ash produced during the incineration of municipal solid waste is listed in the National Hazardous Waste List (No. HW18). It contains high concentrations of heavy metals (such as lead, cadmium, chromium, mercury, etc.), soluble salts (mainly chloride salts), and highly toxic organic substances such as dioxins. If not properly disposed of, it can easily cause secondary pollution to the soil, groundwater, and atmospheric environment, endangering the ecological environment and human health.

[0003] Currently, fly ash disposal technologies mainly include solidification / stabilization, cement kiln co-processing, wet treatment, and thermochemical treatment. Among these, water washing pretreatment has received widespread attention due to its ability to effectively remove soluble chlorides (removal rate 70%-90%) and some heavy metals (removal rate over 85%), reducing the corrosiveness and leaching toxicity of fly ash. However, after water washing, fly ash still retains a large amount of calcium sulfate (CaSO4) and calcium carbonate (CaCO3), posing new technical challenges to subsequent treatment. Calcium sulfate easily forms crystalline hydrates such as gypsum dihydrate at drying temperatures of 120-180℃, leading to severe adhesion and agglomeration between fly ash particles. This not only forms a hard, dense calcium salt crust on the inner wall of the drying equipment, greatly reducing heat transfer efficiency and forcing frequent equipment shutdowns for cleaning; but also reduces the fluidity of the agglomerated fly ash, resulting in uneven feeding and deterioration of heat and mass transfer in subsequent pyrolysis processes. On the other hand, during high-temperature pyrolysis, calcium carbonate begins to decompose significantly into calcium oxide (CaO) and carbon dioxide (CO2) at temperatures exceeding 600℃ (the thermodynamic decomposition temperature of pure calcium carbonate under standard atmospheric pressure is approximately 898℃; however, in practical engineering, especially in fly ash systems containing various impurities, in complex atmospheres, and with the presence of catalytic substances (such as heavy metal oxides and alkali metal salts in fly ash). The newly formed calcium oxide is highly reactive and readily reacts with trace amounts of water vapor in the pyrolysis gas to form calcium hydroxide (Ca(OH)2), leading to severe scaling and blockage on the inner walls of the pyrolysis furnace, flue, and waste heat boiler. The presence of these calcium-based substances may interfere with or even catalyze the pyrolysis pathway of organic matter in fly ash, causing complex reactions with residual chlorobenzene, chlorophenol, and other precursors. This could lead to the recombination or incomplete degradation of dioxins, making it difficult to consistently meet the toxicity standards of the final product. Summary of the Invention

[0004] The purpose of this invention is to overcome the defects in the existing technology and provide a detoxification system for fly ash from municipal solid waste incineration after water washing.

[0005] To achieve the above objectives, the technical solution of this invention is to design a detoxification system for fly ash from municipal solid waste incineration after water washing, comprising a fly ash buffer conditioning unit, a low-temperature anti-sticking drying unit, a temperature-controlled anti-scaling pyrolysis unit, and a gas-solid separation unit connected in sequence; the fly ash buffer conditioning unit is used to receive and homogenize the water-washed fly ash and add an anti-sticking agent for pretreatment; the low-temperature anti-sticking drying unit is used to dry and crush the fly ash under low-temperature conditions; the temperature-controlled anti-scaling pyrolysis unit is used to perform medium-low temperature pyrolysis on the dried fly ash; the gas-solid separation unit is used to efficiently separate the gas generated by pyrolysis from the solid ash residue and cool the pyrolysis ash.

[0006] The fly ash buffer conditioning unit includes a sealed buffer chamber, a stirrer installed inside the buffer chamber, an anti-caking agent addition device connected to the buffer chamber, and an online calcium salt content detector installed on the buffer chamber. The stirrer is used to thoroughly mix the fly ash with the anti-caking agent. The online calcium salt content detector is used to monitor the total content of calcium sulfate and calcium carbonate in the fly ash in real time, and controls the addition amount of the anti-caking agent addition device based on the monitoring results. The buffer chamber integrates a mechanical stirring component (stirrer), a chemical agent addition interface (anti-caking agent addition device), and a component monitoring sensor (online calcium salt content detector). A heating jacket is installed at the bottom of the buffer chamber to prevent the fly ash from agglomerating at low temperatures. These components are combined through mechanical installation, pipeline connections, and electrical signal lines to form a physical module with conditioning function. The stirrer is preferably a dual-shaft ribbon stirrer, whose blade design enables strong mixing in three-dimensional space, preventing dead zones from forming in the fly ash within the chamber. The anti-caking agent addition device typically includes a storage tank, a metering pump, and a spray head, connected to the upper part or interior of the buffer bin via pipelines. The anti-caking agent is preferably a modified silane coupling agent (γ-aminopropyltriethoxysilane). The online calcium salt content analyzer can employ an online detection device based on near-infrared (NIR) spectroscopy analysis. Its detection signal, along with fly ash batch analysis data and downstream equipment operating parameters (such as the drying kiln drive current), constitutes a composite signal, which is input to the system's central control unit (PLC). A fuzzy PID algorithm controls the addition amount by the metering pump, forming an intelligent closed-loop control.

[0007] The low-temperature anti-sticking drying unit includes a pre-dispersing device, a drum drying kiln, and a deep crushing device arranged sequentially. The pre-dispersing device is used to initially crush the fly ash from the buffer conditioning unit and preheat it with hot air. The drum drying kiln adopts a jacketed indirect heating system with saturated steam as the heat source. Adjustable hollow scrapers are installed on the inner wall of the drum, and steam flows through the inside of these scrapers. The deep crushing device is used to crush the dried fly ash. The pre-dispersing device reduces the feed particle size and initiates preheating, reducing the load on the main drying kiln. The unique scraper design of the drum drying kiln continuously and physically removes adhering materials from the inner wall, ensuring long-term continuous operation. The deep crushing device ensures that the discharge particle size meets downstream requirements. Jacketed indirect heating refers to the double-layer structure of the drying kiln's cylinder. Saturated steam flows within the jacket layer and heats the cylinder wall. Heat is transferred to the material through the cylinder wall, avoiding direct contact between hot air and the material, which could lead to localized overheating. Adjustable hollow scrapers refer to scrapers whose angle or pressure with the cylinder wall can be adjusted via mechanical linkages or hydraulic devices. The scrapers are hollow tubes that can be connected to steam pipes to fill them with steam, maintain high temperature, and prevent material from sticking to them.

[0008] The pre-dispersing device is a twin-shaft shredder, into which 50-60℃ hot air is introduced. The twin-shaft shredder provides powerful mechanical crushing capabilities, ensuring that large pieces of material are effectively broken down. The introduced 50-60℃ hot air serves two purposes: first, it initiates the drying process, reducing the overall drying load; second, it preheats the fly ash, preventing cold, wet fly ash from directly entering the drying kiln and causing a sudden temperature drop and thermal stress, thus promoting stable operation of the drying kiln. The twin-shaft shredder refers to a crushing device equipped with two opposing rotating shafts fitted with staggered blades, primarily shearing and tearing the material. The introduction of 50-60℃ hot air can be achieved by drawing a hot air duct from the system's waste heat pipeline or a separate small hot air generator, connecting it to an air vent above or to the side of the shredder's feed inlet, allowing the hot air to contact the falling fly ash material in the same or opposite direction.

[0009] The temperature-controlled and anti-scaling pyrolysis unit includes a hot blast stove, a medium-high temperature pyrolysis kiln, and a plasma catalytic component. The hot blast stove is connected to the medium-high temperature pyrolysis kiln via a pipeline, and the high-temperature flue gas generated by the hot blast stove is directed to the medium-high temperature pyrolysis kiln. The medium-high temperature pyrolysis kiln is an indirect-heating rotary kiln, with the pyrolysis temperature controlled at 450~550℃, the pyrolysis pressure at -0.05~-0.07MPa, and the material residence time at 40~50min. The plasma catalytic component is located at the gas outlet of the pyrolysis kiln and is a high-frequency pulsed plasma generator. The hot blast stove uses natural gas as its energy source and is equipped with 4~8 burners for heating, providing the generated flue gas as a heat source to the medium-high temperature pyrolysis kiln. The medium-high temperature pyrolysis kiln adopts indirect heating, with uniform heating achieved through the hot air generated by the hot blast stove. The hot blast stove and the medium-high temperature pyrolysis kiln are connected via a high-temperature flue, and the plasma catalytic component is fixed to the outlet pipeline via flanges and other connecting components. Indirect heating rotary kilns refer to kilns with jackets or external combustion chambers. The heat source (high-temperature flue gas) heats the outer wall or jacket of the kiln without entering the inner cylinder where the material is located. A high-frequency pulse electrode is a device that generates a high-frequency, high-voltage pulse electric field. It typically consists of a high-voltage power supply, a pulse generator, and one or more pairs of electrodes, which are installed within an insulated pipe section.

[0010] The high-frequency pulsed plasma generator operates at a frequency of 30-40 kHz and a peak pulse voltage of 10-30 kV. Under these parameters, stable corona discharge or dielectric barrier discharge can be formed in the pyrolysis gas flow, generating low-temperature plasma rich in highly active substances. These active substances can directly decompose gaseous dioxins and further stimulate the catalytic activity of metal oxides on the surface of fly ash particles, achieving deep catalytic oxidation of dioxins on the particle surface. Simultaneously, the plasma highly charges the fly ash particles, and the like-pole repulsion effect effectively inhibits their deposition and scaling in subsequent pipelines.

[0011] The medium-high temperature pyrolysis kiln is equipped with lifting plates. Multiple metal plates of specific shapes (lifting plates) are installed axially and circumferentially on the inner wall of the kiln. These lifting plates are fixed to the inner wall by welding or bolting and move as the kiln rotates. The design of the lifting plates allows them to lift and raise the material at the bottom when the kiln rotates, then allow the material to fall at a certain height, forming a material curtain. This process greatly increases the frequency of material agitation and contact with the hot kiln wall, ensuring uniform heating, precise temperature control, and complete reaction. It also helps prevent material from clumping or sticking to the wall inside the kiln. The shape of the lifting plates can be L-shaped, arc-shaped, or spoon-shaped, etc., and their number and arrangement are designed according to the kiln size and process requirements.

[0012] The gas-solid separation unit includes a high-efficiency cyclone separator, a high-temperature dust collector, and a fly ash cooling conveyor. The high-efficiency cyclone separator is connected to a low-temperature anti-sticking drying unit and a temperature-controlled anti-scaling pyrolysis unit to separate larger particles from the pyrolysis gases. The high-temperature dust collector is connected to the high-efficiency cyclone separator and uses a porous ceramic tube filter element, equipped with a nitrogen backflushing cleaning system to capture fine dust. The fly ash cooling conveyor is a jacketed water-cooled screw conveyor connected to the high-temperature dust collector and the temperature-controlled anti-scaling pyrolysis unit to cool the treated fly ash and transport it to a designated location. The high-efficiency cyclone separator performs coarse separation using centrifugal force, the high-temperature dust collector performs fine separation using filtration, and the separated solids are cooled and transported by the screw conveyor. These components are connected by pipes and an ash hopper. The high-efficiency cyclone separator adopts a tangential inlet structure to separate calcium salt particles with a diameter ≥8μm from fly ash; the high-temperature dust collector uses porous ceramic tubes as the filter element, with a temperature resistance ≥600℃, and is equipped with a nitrogen backflushing device to further trap fine fly ash particles. After plasma catalysis and high-temperature filtration, the concentration of dioxins and solid content in the gas are significantly reduced, and the solid content in the filtered gas is ≤3mg / m³. 3 The separated flue gas can be further purified. The porous ceramic tube filter element is a tubular filter element with uniform micropores made of ceramic materials such as silicon carbide and cordierite. The nitrogen backflushing cleaning system includes a nitrogen storage tank, pulse valves, and blowpipes, periodically injecting high-pressure nitrogen into the filter element to shake off the attached dust. The fly ash cooling conveyor adopts an indirect water-cooling structure, introducing 25-30℃ cooling water to cool the pyrolysis ash to ≤60℃ and transport it to the designated location. The porous ceramic tube filter element of the high-temperature dust collector has a temperature resistance of not less than 600℃. This temperature resistance provides a reliable guarantee for the system to handle high-temperature pyrolysis gas, avoiding equipment damage, production stoppages, replacements, and safety hazards caused by insufficient filter element temperature resistance.

[0013] It also includes waste heat recovery piping; the high-temperature flue gas generated by the hot blast furnace first flows through the jacket of the temperature-controlled, anti-scaling pyrolysis unit for heating, and then is guided to the low-temperature, anti-sticking drying unit as a drying heat source. By adding waste heat recovery piping to the system, the hot flue gas from the hot blast furnace outlet, after heating the pyrolysis kiln, is guided to a specific location in the low-temperature, anti-sticking drying unit (such as a pre-dispersing device or inside a drum drying kiln). This significantly improves the energy efficiency of the entire system. The high-temperature flue gas is first used for the pyrolysis process requiring higher temperatures, and the cooled flue gas is then used for the drying process requiring lower temperatures. This waste heat recovery piping system has a simple structure and significant effects, which can greatly reduce the system's consumption of external fresh steam or fuel, thereby reducing operating costs and improving the system's economy and environmental friendliness.

[0014] The advantages and beneficial effects of this invention are as follows: 1. By integrating the anti-caking agent addition in the buffer conditioning unit, the wall scraping design in the low-temperature anti-sticking drying unit, and the precise temperature control in the temperature-controlled anti-scaling pyrolysis unit, the system effectively solves the problems of calcium sulfate agglomeration and calcium carbonate scaling. In the fly ash buffer conditioning unit, 0.3%-0.5% of modified silane coupling agent is added to reduce the adhesion of calcium sulfate crystal hydrate. This is combined with real-time control by an online calcium salt content detector and a heating jacket at the bottom of the sealed buffer silo to prevent low-temperature agglomeration, thus reducing the tendency of calcium salt adhesion from the source. The low-temperature anti-sticking drying unit uses an adjustable hollow scraper of the drum dryer to scrape off the calcium salt crust on the wall in real time, and a toothed roller crusher to crush the fly ash to a particle size ≤3mm, ensuring that the moisture content of the dried fly ash is ≤2.5% and the calcium salt agglomeration rate is ≤4%. The temperature-controlled anti-scaling pyrolysis unit precisely controls the pyrolysis temperature at 450~550℃ to avoid the decomposition of calcium carbonate at high temperatures. During the pyrolysis process, the calcium carbonate decomposition rate is ≤5%. At the same time, the strong electric field generated by the plasma catalytic component makes the fly ash particles highly charged and dispersed, effectively preventing them from scaling in the pipeline and ensuring that there is no serious scaling on the inner wall of the pyrolysis furnace. The system's operational stability is significantly improved.

[0015] 2. The system demonstrates outstanding performance in detoxification and resource recovery, offering significant environmental benefits and economic value. The temperature-controlled, anti-scaling pyrolysis unit, through precise medium-to-high temperature pyrolysis (450~550℃) and efficient high-frequency pulse ionization, achieves a dioxin removal rate of ≥99.7%, with a solid content in the pyrolysis gas ≤3mg / m³. 3 The solids separated by the gas-solid separation unit are mixed into the fly ash after pyrolysis, and the various indicators of the pyrolysis ash (such as heavy metal leaching concentration and dioxin content) meet the requirements for resource utilization.

[0016] 3. The system utilizes waste heat recovery pipelines to cascade the high-temperature flue gas waste heat from the pyrolysis unit to the drying unit, significantly reducing external energy consumption. Simultaneously, the treated fly ash (pyrolysis ash) exhibits stable properties, low heavy metal leaching toxicity, and meets dioxin content standards, demonstrating its potential for resource utilization as a building material raw material, thus achieving a balance between environmental and economic benefits. Attached Figure Description

[0017] Figure 1 This is a system block diagram of the present invention. Detailed Implementation

[0018] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings and examples. The following examples are only used to more clearly illustrate the technical solutions of the present invention and should not be construed as limiting the scope of protection of the present invention.

[0019] according to Figure 1As shown, this invention is a detoxification system for fly ash from municipal solid waste incineration after water washing. It includes a fly ash buffer conditioning unit, a low-temperature anti-sticking drying unit, a temperature-controlled anti-scaling pyrolysis unit, and a gas-solid separation unit, all connected sequentially by conveying equipment and pipelines. Furthermore, the system includes waste heat utilization pipelines connecting the pyrolysis unit and the low-temperature anti-sticking drying unit, as well as supporting auxiliary facilities such as a central control system (not shown in the figure, such as a PLC or DCS), a power supply system, a water supply and drainage system, and a compressed air / nitrogen system.

[0020] The basic process flow is as follows: Wet fly ash, after pretreatment by water washing, desalination, and heavy metal removal, is transported by sealed tank trucks or a conveyor system to the fly ash buffer conditioning unit, where storage, component detection, addition of anti-caking agents, and homogenization mixing are completed. The conditioned fly ash is then quantitatively fed into a low-temperature anti-sticking drying unit via a sealed conveyor, where it undergoes pre-dispersion crushing and preheating, drum-type indirect heating drying, and deep crushing of the dried material, resulting in a dry powder with low moisture content and uniform particle size. The dry fly ash then enters a temperature-controlled anti-scaling pyrolysis unit, where it undergoes medium-low temperature pyrolysis under precisely controlled temperature (450~550℃) and slight negative pressure, allowing organic matter and dioxins to fully desorb into the gas phase. The desorbed pyrolysis gas immediately enters the plasma catalytic component, where a catalytic degradation reaction occurs under the action of a high-frequency pulsed electric field. The high-temperature gas-solid mixture generated from pyrolysis enters the gas-solid separation unit, where it undergoes coarse particle separation via a high-efficiency cyclone separator, followed by fine dust removal via a high-temperature ceramic filter. The purified gas is either discharged in compliance with standards or enters a subsequent advanced treatment system. The collected pyrolysis ash is rapidly cooled to a safe temperature by a water-cooled conveyor before being transported to the finished product warehouse for storage or resource utilization. The high-temperature flue gas generated by the hot blast furnace heats the pyrolysis kiln, and the waste heat is introduced into the drying unit through waste heat utilization pipelines for utilization, achieving cascaded energy recovery.

[0021] The fly ash buffer conditioning unit is the system's inlet and pretreatment module. Its core function is to receive incoming materials, stabilize their composition, and perform anti-caking pretreatment to provide downstream users with stable fly ash materials. It includes a sealed buffer silo, typically designed as a vertical cylindrical conical-bottom silo or a square silo. The volume is determined by the system's processing scale, ensuring a certain buffer capacity (e.g., meeting 4-8 hour processing capacity). The silo body is made of carbon steel, and the inner wall can be lined with wear-resistant and corrosion-resistant materials (such as stainless steel plates or wear-resistant ceramic sheets). The silo top has a feed inlet (for docking with the unloading device) and a dust collection interface (for connecting a small silo top dust collector to maintain a slight negative pressure inside the silo and prevent dust escape). The silo bottom is conical to ensure smooth gravity flow of fly ash to the discharge outlet.

[0022] A dual-shaft ribbon agitator is installed at the center of the silo. Driven by a motor and reducer, the agitator features continuous spiral ribbons mounted on two parallel shafts, with the ribbons rotating in opposite directions. When the agitator operates, the material is propelled by the ribbons, moving axially and circulating up-and-down and left-and-right within the silo, achieving powerful three-dimensional mixing throughout the entire silo, eliminating dead zones and ensuring high mixing uniformity. The anti-caking agent addition device mainly consists of an anti-caking agent storage tank, a precision metering pump (such as a diaphragm metering pump or screw pump), delivery pipelines, and spray nozzles. The storage tank is typically a small container with agitation, used to store liquid modified silane coupling agents (such as γ-aminopropyltriethoxysilane) and other anti-caking agents. The metering pump outlet is connected via pipeline to multiple spray nozzles at the top of the buffer silo. The spray nozzles should ideally be designed to produce fine droplets, evenly spraying the falling fly ash or the surface of the agitated fly ash within the silo. The start / stop and frequency (i.e., dosage) of the metering pump are automatically adjusted by the system's central controller based on a composite judgment made from the signal from the online calcium salt content analyzer, batch test data of fly ash entering the plant, and the load current of the downstream drying unit's drive motor. This adjustment is achieved through a fuzzy PID algorithm. For example, the basic addition ratio is set to 0.4% of the fly ash mass. When the online analyzer detects a total calcium salt content >20%, the controller increases the metering pump frequency, raising the addition ratio to 0.5%; when the calcium salt content is low, it decreases to 0.3%. This achieves precise and dynamic reagent dosing.

[0023] The online calcium salt content analyzer uses near-infrared (NIR) spectroscopy or X-ray fluorescence (XRF) principles. The probe is directly installed on the side wall or top of the buffer chamber 11, eliminating the need for sampling and enabling real-time, continuous scanning and analysis of the fly ash composition within the chamber. The probe installation location must be representative of the average composition of the material within the chamber, typically chosen on the side wall within the agitator's operating range. The analyzer transmits the real-time percentage signal of the total calcium salt (CaSO4 and CaCO3) content to the central controller via 4-20mA or communication methods (such as Profibus DP).

[0024] The screw feeder is installed below the discharge port at the bottom of the buffer silo to stably and quantitatively transport the conditioned fly ash to the downstream low-temperature anti-sticking drying unit. A shaftless screw conveyor or a sealed twin-screw feeder is typically used to prevent fly ash blockage during transport. The feeder speed is adjustable to achieve stable feed rate control.

[0025] A heating jacket is installed at the bottom of the buffer compartment to prevent fly ash from clumping due to low temperature settling.

[0026] Working process: Wet fly ash enters the buffer silo, and the twin-shaft ribbon agitator starts for initial mixing. An online calcium salt content analyzer analyzes the incoming material composition in real time and transmits the signal to the controller. Based on this signal, the controller calculates the required amount of anti-caking agent to be added and starts the metering pump of the anti-caking agent dosing device, uniformly spraying the anti-caking agent into the fly ash through a spray nozzle. The agitator continues to run for a sufficient time (e.g., 10-20 minutes) to ensure thorough and uniform mixing of the fly ash and anti-caking agent. After mixing is complete, the screw feeder starts, continuously and stably conveying the uniformly conditioned fly ash to the next unit.

[0027] The low-temperature anti-sticking drying unit is responsible for drying the conditioned fly ash with high moisture content to a low moisture content, and ensuring effective inhibition of calcium sulfate agglomeration and wall adhesion throughout the drying process. It includes a pre-dispersing device (twin-shaft shredder), whose shell is a welded box with two parallel rotor shafts driven by a motor reducer mounted inside. Each shaft has multiple moving blades made of high-strength alloy steel arranged alternately. The blades are specially designed to primarily shear and tear the material. A screen plate (approximately 50mm aperture) is located at the bottom of the shell to control the discharge particle size. One or more hot air inlets are located above or to the side of the shredder shell's feed inlet, connected to waste heat recovery pipelines or a separate small hot air generator via insulated pipes. Hot air (50-60℃) is introduced into the crushing chamber, making direct and thorough contact with the falling fly ash material.

[0028] The rotary drum dryer is a large-diameter horizontal rotating cylinder. The cylinder is rolled and welded from boiler steel plates, supported at both ends by large rolling rings on rollers. It is driven by a motor through a reducer and gears to rotate slowly (speed adjustable). The entire cylinder has an inclination of approximately 1°-5°, facilitating the movement of materials towards the discharge end while tumbling. A concentric jacket is installed on the outside of the cylinder. The jacket is a sealed annular space that surrounds most of the cylinder's length. Saturated steam enters from an inlet at one end of the jacket, flows within it, and transfers heat to the cylinder wall. The condensate is discharged from a drain valve at the other end. This indirect heating method avoids localized overheating and a significant increase in exhaust gas volume caused by direct hot air blowing on the material. Multiple rows of hollow scrapers are evenly distributed along the axial and circumferential directions on the inner wall of the cylinder. The scraper base is a long strip made of heat-resistant stainless steel plate, fixed to a bracket on the inner wall of the cylinder via an adjustable linkage mechanism (such as a hinged arm with a locking nut). This allows adjustment of the angle between the scraper and the cylinder wall (typically 30°-60°) and the gap between the tip and the wall surface. The scraper has a hollow pipe structure inside. Each scraper or group of scrapers is connected to an external steam system via a rotary joint and pipeline, allowing steam to enter the scraper. This keeps the scraper itself at a high temperature similar to the cylinder wall. When the drying kiln rotates, the scraper moves with the cylinder wall. Its functions are twofold: first, to scoop up and disperse the material, forming a material curtain to increase the heat transfer area and uniformity; second, its cutting edge continuously scrapes the inner wall of the cylinder, promptly removing any thin layers of calcium salt crust that are just beginning to form or have already adhered, preventing their accumulation and thickening. Because the scraper itself is hot, fly ash does not easily adhere to it, ensuring a long-lasting and effective scraping effect.

[0029] The deep crushing unit (toothed roller crusher) is located below the discharge chute of the rotary drum dryer. A single double-toothed roller crusher is used. Two parallel rollers with staggered teeth rotate in opposite directions. The gap between the rollers (i.e., the discharge particle size) is adjustable, typically set to 1-3 mm. Any small amounts of soft lumps or large particles that may remain after drying are further crushed here, ensuring that the fly ash entering the pyrolysis unit is a uniform fine powder. The discharge port of the screw feeder is connected to the inlet of the pre-dispersing device via a sealed chute. The discharge port of the pre-dispersing device is connected to the feed end (high end) of the rotary drum dryer via an elevator or screw conveyor. The discharge end (low end) of the rotary drum dryer is connected to the deep crushing unit via a chute. The discharge port of the deep crushing unit is then connected to the feed device of the temperature-controlled, anti-scaling pyrolysis unit via a sealed conveying device (such as a bucket elevator).

[0030] Working Process: After conditioning, the wet fly ash first enters the pre-dispersing device (twin-shaft shredder), where it is forcefully crushed to below 5cm by rotating blades. Simultaneously, it comes into contact with hot air at 50-60℃ for initial preheating and surface moisture evaporation. The crushed and preheated fly ash then enters the rotary drum dryer. Inside the kiln, the fly ash is continuously lifted and scattered by the rotating drum and hollow scrapers, forming a uniform material curtain. Heat is transferred to the fly ash through the steam jacket's drum wall via conduction and radiation, causing its moisture to gradually evaporate. The hollow scrapers continuously scrape the drum wall during rotation, preventing any material from adhering. After a set residence time (controlled by kiln speed and inclination angle), the dried fly ash (moisture content ≤2.5%) is discharged from the kiln tail and falls into the deep crushing device (toothed roller crusher), where it is crushed to uniform powder ≤3mm, and then conveyed to the pyrolysis unit.

[0031] The temperature-controlled, scale-preventing pyrolysis unit is the core detoxification component of this system. While inhibiting the decomposition of calcium carbonate, it achieves efficient dioxin degradation through synergistic pyrolysis and plasma catalysis. This includes a hot blast stove, which is an independent gas-fired (e.g., natural gas) hot blast stove. The stove body consists of a combustion chamber, a mixing chamber, and a refractory insulation lining. It is equipped with 4-8 low-NOx burners, arranged circumferentially or tangentially to ensure complete combustion and uniform temperature. The temperature and flow rate of the outlet hot flue gas can be precisely controlled by adjusting the amount of fuel gas and combustion air. The outlet flue gas temperature is typically adjustable within the range of 600-800℃. The hot blast stove is equipped with a comprehensive safety monitoring and control system.

[0032] The medium-high temperature pyrolysis kiln is an indirect heating rotary kiln. Its core is an inner cylinder (reaction chamber) made of heat-resistant alloy steel, where fly ash undergoes pyrolysis. A concentric outer cylinder or a sealed jacketed shell surrounds the inner cylinder, forming an annular flue gas passage (jacket). High-temperature flue gas from the hot blast stove is introduced into the flue gas passage (jacket) of the pyrolysis kiln through a high-temperature flue. The high-temperature flue gas flows around the inner cylinder within the jacket, transferring heat to the inner cylinder wall through radiation and convection, thereby heating the fly ash inside the cylinder. The flue gas does not directly contact the fly ash, ensuring uniform and clean heating. After heating, the cooled flue gas exits from the jacket outlet and enters the waste heat recovery pipeline. Multiple rows of lifting plates are welded or fixed to the inner wall of the inner cylinder. The lifting plates are mostly L-shaped or arc-shaped, arranged spirally along the axial direction. Its function is to lift the fly ash from the bottom to a certain height and then sprinkle it down as the kiln rotates, forming a material curtain. This greatly enhances the heat exchange efficiency and axial movement speed of the material, ensuring uniform heating, complete reaction, and preventing material accumulation. Thermocouples are placed in the interlayer flue gas channel and / or the inner cylinder material layer to monitor the temperature in real time and provide feedback to control the combustion power of the hot blast stove and / or the flow rate of flue gas entering the interlayer, ensuring that the temperature of the inner cylinder material layer is strictly and stably controlled within the target range of 450~550℃. An induced draft fan is connected to the outlet of the pyrolysis kiln. By adjusting the frequency converter of the induced draft fan or the valve opening, a slight negative pressure of -0.05 ~ -0.07 MPa is maintained inside the kiln (inner cylinder). This facilitates the smooth discharge of pyrolysis gas and prevents the leakage of harmful gases. By adjusting the rotation speed and tilt angle of the pyrolysis kiln (usually fixed), the average residence time of fly ash in the kiln is controlled to be 40~50 minutes. This is determined by the feed rate and the kiln filling rate.

[0033] The plasma catalytic assembly is installed on the gas outlet pipe of the pyrolysis furnace. This assembly includes a pipe section made of insulating material (such as ceramic or Teflon). Inside this pipe section, one or more pairs of electrodes made of high-temperature resistant alloys are arranged parallel to the gas flow direction. The electrodes are connected to a high-frequency pulsed high-voltage power supply. This power supply generates a pulsed high voltage with a frequency in the range of 30-40 kHz and a peak voltage of 10-30 kV, which is applied between the electrodes to form a strong pulsed electric field region, i.e., a low-temperature plasma reaction zone, within the reaction tube. When pyrolysis gas carrying desorbed dioxins and fly ash particles pass through this region, corona discharge or dielectric barrier discharge occurs under the action of the high-frequency pulsed electric field, generating a large number of highly reactive free radicals (·OH, ·O, etc.), ozone (O3), and high-energy electrons. These active substances can directly attack and break down gaseous dioxin molecules; simultaneously, the high-energy environment can significantly stimulate the catalytic activity of the inherent metal oxides (such as CuO, Fe2O3) on the surface of the fly ash particles, forming "catalytic hot spots" on the particle surface, achieving deep catalytic oxidation of dioxins. In addition, plasma charges the surface of fly ash particles (usually with the same charge), and the strong electrostatic repulsion effectively inhibits particle aggregation and deposition on pipe walls, fundamentally preventing scaling.

[0034] Dry fly ash from the drying unit is fed into the inner cylinder of the pyrolysis kiln from the feed end (high end) via a closed conveying system. The outlet of the hot blast stove is connected to the flue gas jacket inlet of the pyrolysis kiln via an insulated flue. The gas outlet of the inner cylinder of the pyrolysis kiln is connected to the reaction pipe section of the plasma catalytic module via a flange. The pipeline after the plasma catalytic module is installed is then connected to the gas-solid separation unit. The outlet of the flue gas jacket of the pyrolysis kiln is connected to the waste heat recovery pipeline.

[0035] Working Process: Dry fly ash continuously enters the inner cylinder of the medium-high temperature pyrolysis kiln. Simultaneously, clean, high-temperature flue gas from the hot blast stove enters the kiln's jacket, providing uniform indirect heating to the inner cylinder. Under the action of the lifters, the fly ash is thoroughly agitated and mixed within the kiln, and remains at 450-550℃ under slight negative pressure for 40-50 minutes, completing the thermal desorption of organic matter and dioxins. The gas produced during pyrolysis (containing desorbed dioxins and a small amount of ash) is discharged from the kiln tail and immediately enters the reaction zone of the plasma catalytic component, where a highly efficient catalytic degradation reaction occurs under the action of high-frequency pulsed plasma. Subsequently, the treated gas-solid mixture enters the gas-solid separation unit. The flue gas, cooled after providing heat to the pyrolysis kiln (approximately 250-350℃), is discharged from the jacket and enters the waste heat recovery pipeline.

[0036] The gas-solid separation unit is responsible for the efficient separation, gas purification, and solid cooling of the high-temperature gas-solid mixture generated by pyrolysis. It includes a high-efficiency cyclone separator with a tangential inlet design. The shell is made of wear-resistant steel plate or lined with wear-resistant ceramic. Dust-laden pyrolysis gas enters at a high velocity (e.g., 15-25 m / s) from the tangential inlet at the top of the separator, creating a strong, swirling, downward airflow within the cylinder. Coarse particles (typically ≥8μm) are thrown against the wall by centrifugal force and slide down to the ash collection hopper at the conical bottom. The preliminarily purified gas forms an upward internal vortex in the central region and exits from the central exhaust pipe at the top. Its inlet is connected to the pyrolysis gas outlet pipeline of the self-temperature-controlled, anti-scaling pyrolysis unit via a pipe. An airlock ash discharge valve (e.g., a double-layer flap valve) is installed below its ash discharge port to periodically discharge the collected coarse ash into downstream collection and conveying equipment or directly into a cooling conveyor. Its outlet is connected to a high-temperature dust collector via a pipe.

[0037] The high-temperature dust collector has a heat-resistant steel casing, insulated internally with refractory materials. Several sets of porous ceramic tube filter elements are suspended inside. In this embodiment, the filter element is made of silicon carbide (SiC) or cordierite, with a uniform microporous structure, a porosity of approximately 40-50%, and an average pore size of 10-20 μm. Its key performance characteristics include a long-term operating temperature not lower than 600℃ and resistance to chemical corrosion from pyrolysis gases. It is also equipped with a nitrogen pulse backflushing cleaning system. This system includes a nitrogen storage tank, a pressure reducing valve, a pulse valve, and blowpipes. The blowpipes are arranged corresponding to each row of filter elements. When the dust layer adhering to the outer surface of the filter element reaches a certain thickness, increasing the operating resistance, the control system will sequentially trigger the pulse valves. The instantaneously released compressed nitrogen (pressure 0.4-0.6 MPa) is injected into the filter element through nozzles on the blowpipes, generating a reverse airflow that shakes off the dust layer from the outer surface of the filter element. The cleaning process is performed online and does not affect the continuous operation of the equipment. The dust collector has a conical ash hopper at the bottom to collect the dust that is removed, and it is discharged through the airlock ash discharge valve.

[0038] The fly ash cooling conveyor (jacketed water-cooled screw conveyor) consists of a shaft with helical blades installed in a U-shaped or cylindrical trough. The trough is surrounded by a sealed water-cooling jacket. Cooling water (typically circulating cooling water at 25-30℃) enters from one end of the jacket and exits from the other, continuously removing heat from the conveyor trough and the materials inside. It performs two tasks simultaneously: first, it horizontally (or inclinedly) transports pyrolysis ash (which may reach temperatures as high as 400-500℃) from the cyclone separator, high-temperature dust collector hopper, and temperature-controlled anti-scaling pyrolysis unit to a designated finished product warehouse or packaging point; second, during the conveying process, through indirect heat exchange with the circulating cooling water within the jacket, it rapidly and uniformly reduces the temperature of the pyrolysis ash to a safe storage temperature below 60℃.

[0039] The outlet pipe of the high-efficiency cyclone separator is connected to the inlet chamber of the high-temperature dust collector. The ash hopper outlets at the bottom of the cyclone separator and the high-temperature dust collector are connected to the inlet of the fly ash cooling conveyor via chutes or short-circuit conveyors. The clean gas outlet of the high-temperature dust collector is connected to the main chimney or subsequent flue gas purification systems (such as deacidification towers, activated carbon adsorption devices, etc.).

[0040] Working process: The pyrolysis gas from the pyrolysis unit, which has undergone plasma catalytic treatment, first enters a high-efficiency cyclone separator, where most of the coarser particles are separated. The preliminarily purified gas then enters a high-temperature dust collector. As it passes through a porous ceramic tube filter, fine dust particles are trapped on the outer surface of the filter. After purification, both the dioxin and dust concentrations in the gas are significantly reduced, with the dust concentration reaching ≤3 mg / m³. 3The dust is then discharged. When the filter element resistance increases, the nitrogen pulse backflushing system automatically activates, shaking the dust into the ash hopper. All pyrolysis ash collected from the cyclone separator and high-temperature dust collector enters the fly ash cooling conveyor. Driven by the spiral blades, the pyrolysis ash moves forward, while its heat is continuously carried away by the cooling water flowing in the jacket. After a sufficiently long conveying and cooling section, the pyrolysis ash is cooled to ≤60℃ at the outlet and then discharged, completing the entire detoxification process.

[0041] Waste heat recovery pipeline 5 is not an independent processing unit, but rather an energy recovery network connecting the pyrolysis unit and the drying unit. It mainly consists of insulated steel pipes, regulating valves (such as electric butterfly valves), expansion joints, pipe supports, and possibly a simple settling chamber. The pipeline requires good insulation to reduce heat loss. The pipeline's starting end connects to the flue gas jacket outlet of the high-temperature pyrolysis kiln in the temperature-controlled, anti-scaling pyrolysis unit. Here, the flue gas temperature has dropped to approximately 250-350℃ after being heated by the pyrolysis kiln, but still contains considerable heat energy. At this point, the pipeline splits into two paths or branches: one path leads directly to the hot air inlet of the pre-dispersing device in the low-temperature, anti-sticking drying unit, providing preheated hot air at 50-60℃. The other path (or through the same main pipe) can lead to the feed end of the drum dryer or inside the drum, serving as an auxiliary direct drying heat source, complementing the indirect heating from the jacket steam. The flue gas entering the drying kiln, along with the evaporated water vapor, is finally discharged from the kiln's exhaust port, and after dust removal, is released. Regulating valves are installed on each branch pipeline to adjust the flue gas distribution in real time according to the heat required by the drying unit. Temperature and pressure monitoring points are installed at the beginning of the pipeline or at key nodes, and the signals are connected to the central control system.

[0042] Working process: The medium-temperature flue gas discharged from the jacket of the pyrolysis kiln is transported to the drying unit through the waste heat utilization pipeline. Part of it enters the pre-dispersing device for preliminary preheating and surface drying of the material; the other part is directly used for auxiliary heating of the drum dryer. This realizes the cascade utilization of internal thermal energy (high temperature for pyrolysis, medium and low temperature for drying), significantly reducing the consumption of external fresh steam and fuel.

[0043] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A system for detoxifying fly ash from municipal solid waste incineration after water washing, characterized in that, It includes a fly ash buffer conditioning unit, a low-temperature anti-sticking drying unit, a temperature-controlled anti-scaling pyrolysis unit, and a gas-solid separation unit connected in sequence; The fly ash buffer conditioning unit is used to receive and homogenize the fly ash after water washing, and add an anti-caking agent for pretreatment; The low-temperature anti-sticking drying unit is used to dry and crush fly ash under low-temperature conditions; The temperature-controlled and scale-preventing pyrolysis unit is used to perform medium- and low-temperature pyrolysis on dried fly ash. The gas-solid separation unit is used to efficiently separate the gas generated by pyrolysis from the solid ash residue, and to cool the pyrolysis ash.

2. The system for detoxifying fly ash from municipal solid waste incineration after water washing, as described in claim 1, is characterized in that, The fly ash buffer conditioning unit includes a sealed buffer chamber, a stirrer installed inside the buffer chamber, an anti-caking agent adding device connected to the buffer chamber, and an online calcium salt content detector installed on the buffer chamber; The agitator is used to thoroughly mix fly ash and anti-caking agent; The online calcium salt content detector is used to monitor the total content of calcium sulfate and calcium carbonate in fly ash in real time, and to control the amount of anti-caking agent added by the device based on the monitoring results.

3. The system for detoxifying fly ash from municipal solid waste incineration after water washing, as described in claim 1, is characterized in that... The low-temperature anti-sticking drying unit includes a pre-dispersing device, a drum drying kiln, and a deep crushing device arranged in sequence. The pre-dispersing device is used to initially crush the fly ash from the buffer conditioning unit and preheat it with hot air. The rotary drum drying kiln adopts a jacketed indirect heating system with saturated steam as the heat source. The inner wall of the drum is equipped with adjustable hollow scrapers, and steam is circulated inside the hollow scrapers. The deep crushing device is used to crush the dried fly ash.

4. The system for detoxifying fly ash from municipal solid waste incineration after water washing, as described in claim 3, is characterized in that... The pre-dispersing device is a twin-shaft shredder, and hot air at 50-60℃ is introduced into the pre-dispersing device.

5. The system for detoxifying fly ash from municipal solid waste incineration after water washing, as described in claim 1, is characterized in that... The temperature-controlled and scale-preventing pyrolysis unit includes a hot air furnace, a medium-high temperature pyrolysis kiln, and a plasma catalytic component. The hot blast stove is connected to the medium-high temperature pyrolysis kiln through a pipeline, and the high-temperature flue gas generated by the hot blast stove is directed to the medium-high temperature pyrolysis kiln. The medium-high temperature pyrolysis kiln is an indirect heating rotary kiln, with the pyrolysis temperature controlled at 450~550℃, the pyrolysis pressure at -0.05~-0.07MPa, and the material residence time at 40~50min. The plasma catalytic component is located at the gas outlet of the pyrolysis furnace and is a high-frequency pulsed plasma generator.

6. The system for detoxifying fly ash from municipal solid waste incineration after water washing, as described in claim 5, is characterized in that... The high-frequency pulse electrode operates at a frequency of 30-40kHz.

7. A system for detoxifying fly ash from municipal solid waste incineration after water washing, as described in claim 5, is characterized in that, The medium-high temperature pyrolysis kiln is equipped with a lifting plate.

8. The system for detoxifying fly ash from municipal solid waste incineration after water washing, as described in claim 1, is characterized in that... The gas-solid separation unit includes a high-efficiency cyclone separator, a high-temperature dust collector, and a fly ash cooling conveyor; the high-efficiency cyclone separator is connected to a low-temperature anti-sticking drying unit and a temperature-controlled anti-scaling pyrolysis unit, and is used to separate larger particles in the pyrolysis gas of the two units. The high-temperature dust collector is connected to a high-efficiency cyclone separator. The high-temperature dust collector uses a porous ceramic tube filter element and is equipped with a nitrogen back-flushing cleaning system for collecting fine dust. The fly ash cooling conveyor is a jacketed water-cooled screw conveyor connected to a high-temperature dust collector and a temperature-controlled anti-scaling pyrolysis unit, used to cool the treated fly ash and convey it to a designated location.

9. A system for detoxifying fly ash from municipal solid waste incineration after water washing, as described in claim 8, is characterized in that... The porous ceramic tube filter element of the high-temperature dust collector has a temperature resistance of not less than 600℃.

10. A system for detoxifying fly ash from municipal solid waste incineration after water washing, as described in claim 5, is characterized in that... It also includes waste heat utilization pipelines; the high-temperature flue gas generated by the hot air furnace first flows through the jacket of the temperature-controlled and anti-scaling pyrolysis unit to heat it, and then is led to the low-temperature anti-sticking drying unit as a drying heat source.

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