Fly ash harm reduction system and method based on closed isothermal segmented thermal response and reset coupling

Abstract

The invention discloses a fly ash harm reduction system and method based on closed isothermal segmented thermal response and reset coupling. The system comprises a closed heating kettle body, a stirring device, a chemical additive adding device, a segmented condensation and enrichment module and a quenching and tail gas purification device. The fly ash is subjected to isothermal heating under the conditions of closed micro-negative pressure and stirring and turning achieved through low-speed rotation and a material lifting plate, alkaline and oxidizing solid auxiliaries are added, and chemical condition resetting is achieved; preferably separating and enriching mercury; migrating other heavy metals and cracking dioxin; and the high-temperature flue gas is quickly cooled to block resynthesis of dioxin, and finally the dioxin is purified and discharged. Through cooperative regulation and control of a physical field and a chemical field, cooperative deep treatment of heavy metal and dioxin in fly ash is achieved, the problems that in the prior art, the tail gas load is large, dioxin is likely to be regenerated, and equipment is likely to be coked and blocked are effectively solved, and the method has the advantages of being thorough in treatment, controllable in process and low in environmental risk.

Description

Technical Field

[0001] This invention relates to a fly ash harm reduction system and method based on closed isothermal segmented thermal response and reset coupling, belonging to the field of solid waste treatment technology, and is classified under classification number B09B. Background Technology

[0002] Fly ash from municipal solid waste and hazardous waste incineration is rich in heavy metals and dioxins, posing significant environmental risks. Current mainstream technologies, such as cement solidification, can only physically encapsulate pollutants and cannot eliminate the risk of long-term leaching and release. Conventional rotary kiln heat treatment processes suffer from uneven furnace temperatures, leading to fly ash sintering, material adhesion and coking, and ultimately equipment blockage. More importantly, these processes typically operate under atmospheric pressure or positive pressure, generating large volumes of exhaust gas and increasing the load on subsequent purification systems. They also fail to disrupt the inherent chlorine-based metal catalytic centers in the fly ash, and the flue gas slowly passes through the dioxin resynthesis sensitive temperature range of 200-500°C during the cooling phase, making dioxin resynthesis difficult to avoid. Existing technologies mostly focus on end-of-pipe control at single stages, lacking a systematic solution encompassing source control, process coordination, and resource recovery, resulting in incomplete treatment, difficulties in resource recovery, and high overall environmental risks.

[0003] Therefore, the existing technology has problems and needs further improvement and development. Summary of the Invention

[0004] (I) Purpose of the invention: In order to solve the problems existing in the prior art, the purpose of the present invention is to provide a fly ash reduction system and method based on closed isothermal segmented thermal response and reset coupling.

[0005] (II) Technical Solution: To solve the above-mentioned technical problems, this technical solution provides a fly ash harm reduction method based on closed isothermal segmented thermal response and reset coupling, including the following steps: Step S1: Under the closed and slightly negative pressure conditions controlled by the pressure sensor and controller, heat energy is applied to the fly ash, and the fly ash is stirred and turned at the same time to enhance heat and mass transfer. Step S2: Heat the system to the target temperature range and add alkaline and oxidizing solid additives to the fly ash to chemically reset the halogen source and metal catalyst species in the fly ash. The additives include at least one of calcium oxide, calcium hydroxide and calcium peroxide. After the additives are added, continue to heat the system to enter the first temperature range for mercury removal treatment. The additive is used to deactivate and solidify non-volatile metals, eliminate the precursor basis of dioxin formation by destroying the heterogeneous catalytic active sites of dioxin synthesis, and volatilize and separate volatile metals in a chlorination environment. Step S3: In the first temperature range, mercury in fly ash is preferentially volatilized, and mercury-containing gas is extracted for first condensation and enrichment; Step S4: At a second temperature range higher than the first temperature range, the target heavy metals in the fly ash are volatilized and dioxin-like pollutants are decomposed, and the generated heavy metal-containing gas is discharged for second condensation enrichment. Step S5: The high-temperature gas generated in step S4 is rapidly cooled to quickly cross the temperature range of 200°C to 500°C. The slight negative pressure in step S1 is used to ensure that the gas flows out in one direction during the treatment process and to prevent the pollutants from leaking out; the stirring and turning in step S1 is used to achieve isothermal heating conditions where the temperature difference between the inner wall of the reactor and the fly ash pile does not exceed 15°C.

[0006] Furthermore, in step S1, the range of the micro-negative pressure is -10 Pa to -200 Pa.

[0007] Furthermore, the range of the micro-negative pressure is further limited to -50Pa to -150Pa.

[0008] Furthermore, through the stirring and agitation, the temperature difference between the inner wall of the heating device and the fly ash pile is kept to no more than 15°C.

[0009] Furthermore, in step S2, the amount of the additive added is 1% to 20% of the fly ash mass.

[0010] Furthermore, in step S5, the rapid cooling process is achieved through spray cooling or heat exchange cooling, so that the temperature of the high-temperature gas drops to below 200°C within 5 seconds.

[0011] Furthermore, the target temperature range is 100℃~220℃, the first temperature range is 220℃~350℃, and the second temperature range is 600℃~1050℃.

[0012] Furthermore, in step S2, the auxiliary agent is an alkaline compound containing calcium and / or magnesium, used to capture / neutralize free halogen sources, reduce catalytic active centers such as Cu / Fe, and reduce the leaching migration of some residual heavy metals, thereby promoting the stabilization / reduction of leaching of metals Cu and Fe.

[0013] Furthermore, step S3 is performed under inert or slightly oxygenated atmosphere conditions.

[0014] Furthermore, it also includes real-time monitoring and closed-loop control of the pressure in step S1, the temperature and temperature difference between steps S1 and S2, and the stirring speed.

[0015] A fly ash hazard reduction system based on a closed isothermal segmented thermal response and reset coupling system includes: A sealed heating vessel is used to contain fly ash and apply heat to it. The micro negative pressure control unit, including a blower, a pressure sensor and a controller, is used to establish and maintain a micro negative pressure inside the sealed heating vessel. A stirring and turning device is installed inside the sealed heating vessel to turn the material to achieve isothermal heating; A chemical additive dosing device is connected to the sealed heating vessel and is used to add the alkaline and oxidizing solid additives; The first condensation enrichment module and the second condensation enrichment module are connected to the exhaust port of the sealed heating vessel through parallel pipelines, and each pipeline is equipped with a controlled valve. A rapid cooling device, connected to the outlet of the second condensation enrichment module, is used to rapidly cool high-temperature gas to below 200°C; An exhaust gas purification device is connected to the outlet of the quenching device; The central control unit is electrically connected to the pressure sensor, the temperature sensor of the sealed heating vessel, the controlled valve, the stirring and agitating device, and the heating unit, respectively. The central control device is used to maintain a target slight negative pressure by adjusting the opening of the induced draft fan and the inlet / outlet valves according to the feedback signal of the pressure sensor; the central control device is used to adjust the heating power or stirring speed according to the temperature of the inner wall of the vessel and the material temperature fed back by the temperature sensor to control the temperature difference to not exceed 15°C; the central control device is used to control the opening and closing of the controlled valves according to the temperature signal of the sealed heating vessel to guide the gas in different temperature ranges to the first condensation enrichment module or the second condensation enrichment module respectively.

[0016] Furthermore, the stirring and turning device includes a stirring shaft and blades disposed on the stirring shaft. The blades are provided with lifting plates. The stirring shaft passes through the wall of the sealed heating vessel and is provided with a sealing structure at the penetration point.

[0017] Furthermore, the stirring shaft has a hollow structure, and its interior is equipped with a temperature sensor for directly measuring the material temperature and / or an inert gas delivery channel.

[0018] Furthermore, the operating temperature range of the first condensation enrichment module is 0℃~80℃; the operating temperature range of the second condensation enrichment module is 150℃~300℃.

[0019] Furthermore, it also includes a high-temperature pyrolysis chamber connected between the sealed heating vessel and the second condensation enrichment module.

[0020] (III) Beneficial Effects: This invention operates under a fully closed, slightly negative pressure system, enabling directional and quantitative collection of exhaust gases. This significantly reduces the amount of ineffective gases and lowers the processing load and energy consumption of subsequent purification systems. By chemically resetting the precursors at the source and combining this with rapid cooling during directional process interruption, a dual mechanism ensures that dioxins are efficiently eliminated and no longer synthesized, resulting in more thorough treatment. Isothermal stirring ensures uniform heating of the materials, avoiding melting and sintering caused by localized high temperatures. Simultaneously, the addition of alkaline additives neutralizes acidic components, further inhibiting the formation and adhesion of low-temperature eutectic compounds, ensuring long-term stable operation of the system. This invention achieves segmented resource recovery of heavy metals, improves the stability of treated products, and constructs a complete pollution control chain from source to end, resulting in significant comprehensive environmental and economic benefits. Attached Figure Description

[0021] Figure 1 This is a flowchart of the steps of the fly ash harm reduction method based on closed isothermal segmented thermal response and reset coupling of the present invention; Figure 2 This is a schematic diagram of the structure of the fly ash reduction system based on the closed isothermal segmented thermal response and reset coupling of the present invention. Detailed Implementation

[0022] The present invention will be further described in detail below with reference to preferred embodiments. More details are set forth in the following description in order to provide a full understanding of the present invention. However, the present invention can obviously be implemented in many other ways different from those described herein. Those skilled in the art can make similar extensions and derivations based on actual application situations without departing from the spirit of the present invention. Therefore, the scope of protection of the present invention should not be limited by the content of this specific embodiment.

[0023] The accompanying drawings are schematic diagrams of embodiments of the present invention. It should be noted that these drawings are for illustrative purposes only and are not drawn to scale, and should not be construed as limiting the actual scope of protection of the present invention.

[0024] like Figure 1 As shown, the fly ash harm reduction method based on closed isothermal segmented thermal response and reset coupling includes the following steps: Step S1: Under the closed and slightly negative pressure conditions controlled by the pressure sensor and controller, heat energy is applied to the fly ash, and the fly ash is stirred and turned at the same time to enhance heat and mass transfer. Step S2: Heat the system to the target temperature range and add alkaline and oxidizing solid additives to the fly ash to chemically reset the halogen source and metal catalyst species in the fly ash. The additives include at least one of calcium oxide, calcium hydroxide and calcium peroxide. After the additives are added, continue to heat the system to enter the first temperature range for mercury removal treatment. The additive is used to deactivate and solidify non-volatile metals, eliminate the precursor basis of dioxin formation by destroying the heterogeneous catalytic active sites of dioxin synthesis, and volatilize and separate volatile metals in a chlorination environment. Step S3: In the first temperature range, mercury in fly ash is preferentially volatilized, and mercury-containing gas is extracted for first condensation and enrichment; Step S4: At a second temperature range higher than the first temperature range, the target heavy metals in the fly ash are volatilized and dioxin-like pollutants are decomposed, and the generated heavy metal-containing gas is discharged for a second condensation enrichment; the target heavy metals include, but are not limited to, Hg, Pb, Cd, Zn, etc. Step S5: The high-temperature gas generated in step S4 is rapidly cooled to quickly cross the temperature range of 200°C to 500°C. The slight negative pressure in step S1 is used to ensure unidirectional gas outflow during the treatment process and to prevent pollutant leakage; the stirring and agitation in step S1 is used to achieve isothermal heating conditions where the temperature difference between the reactor inner wall and the fly ash pile does not exceed 15°C. The fly ash pile temperature is the core temperature or multi-point average temperature measured by a temperature sensor installed inside the stirring shaft, and the temperature difference ΔT is the difference between the representative point temperature of the reactor wall and the representative point temperature of the pile.

[0025] In step S1, the range of the micro-negative pressure is -10 Pa to -200 Pa. Preferably, the range of the micro-negative pressure is -50 Pa to -150 Pa.

[0026] The stirring and agitation ensures that the temperature difference between the inner wall of the heating device and the fly ash pile does not exceed 15°C.

[0027] In step S2, the amount of alkaline and oxidizing solid additives added is 1% to 20% of the fly ash mass.

[0028] In step S5, the rapid cooling process is achieved by spray cooling or heat exchange cooling, so that the temperature of the high-temperature gas drops to below 200°C within 5 seconds.

[0029] The target temperature range is 100℃~220℃, the first temperature range is 220℃~350℃, and the second temperature range is 600℃~1050℃.

[0030] In step S2, the auxiliary agent is an alkaline compound containing calcium and / or magnesium, used to capture / neutralize free halogen sources, reduce catalytic active centers such as Cu / Fe, and reduce the leaching migration of some residual heavy metals, thereby promoting the stabilization / reduction of leaching of metals Cu and Fe.

[0031] Step S3 is performed under inert or slightly oxygenated atmosphere conditions.

[0032] The fly ash harm reduction method based on closed isothermal segmented thermal response and reset coupling also includes real-time monitoring and closed-loop control of the pressure in step S1, the temperature and temperature difference in steps S1 and S2, and the stirring speed.

[0033] like Figure 2 As shown, the fly ash hazard reduction system based on closed isothermal segmented thermal response and reset coupling includes: A sealed heating vessel is used to contain fly ash and apply heat to it. The micro negative pressure control unit, including a blower, a pressure sensor and a controller, is used to establish and maintain a micro negative pressure inside the sealed heating vessel. A stirring and turning device is installed inside the sealed heating vessel to turn the material to achieve isothermal heating; A chemical additive dosing device is connected to the sealed heating vessel and is used to add the alkaline and oxidizing solid additives; The first condensation enrichment module and the second condensation enrichment module are connected to the exhaust port of the sealed heating vessel through parallel pipelines, and each pipeline is equipped with a controlled valve. A rapid cooling device, connected to the outlet of the second condensation enrichment module, is used to rapidly cool high-temperature gas to below 200°C; An exhaust gas purification device is connected to the outlet of the quenching device; The central control unit is electrically connected to the pressure sensor, the temperature sensor of the sealed heating vessel, the controlled valve, the stirring and agitating device, and the heating unit, respectively. The central control device is used to maintain a target slight negative pressure by adjusting the opening of the induced draft fan and the inlet / outlet valves according to the feedback signal of the pressure sensor; the central control device is used to adjust the heating power or stirring speed according to the temperature of the inner wall of the vessel and the material temperature fed back by the temperature sensor to control the temperature difference to not exceed 15°C; the central control device is used to control the opening and closing of the controlled valves according to the temperature signal of the sealed heating vessel to guide the gas in different temperature ranges to the first condensation enrichment module or the second condensation enrichment module respectively.

[0034] The stirring and turning device includes a stirring shaft and blades disposed on the stirring shaft. The blades are provided with lifting plates. The stirring shaft passes through the wall of the sealed heating vessel and is provided with a sealing structure at the penetration point.

[0035] The stirring shaft has a hollow structure, and its interior is equipped with a temperature sensor for directly measuring the material temperature and / or an inert gas delivery channel.

[0036] The first condensation enrichment module operates in a temperature range of 0℃ to 80℃; the second condensation enrichment module operates in a temperature range of 150℃ to 300℃. The second condensation enrichment module may include a ceramic honeycomb structure, a porous carrier, or a filter deposition structure.

[0037] The additive is used to deactivate and solidify the subsequent non-volatile metals such as Cu and Fe. By destroying the heterogeneous catalytic active sites of dioxin synthesis, it eliminates the precursor basis of dioxin generation from the source, and volatilizes and separates volatile metals such as Hg, Pb, Cd, and Zn in a chlorination environment. The fly ash reduction system based on the closed isothermal segmented thermal response and reset coupling also includes a high-temperature pyrolysis chamber connected between the closed heating vessel and the second condensation enrichment module.

[0038] The micro-negative pressure control unit monitors the pressure inside the vessel in real time through the pressure sensor and transmits the signal to the central control device. The central control device forms a closed-loop interlock with the induced draft fan inverter, feed valve, discharge valve, and exhaust valve through a PID algorithm. When the pressure exceeds the upper limit of the set range, the induced draft fan power is increased or the exhaust valve is opened wider; when the pressure falls below the lower limit of the set range, it is adjusted accordingly, thereby stabilizing the pressure within the preferred range of -50Pa to -150Pa and ensuring that any possible leakage is inward leakage, achieving directional flow of exhaust gas and zero dust escape. The micro-negative pressure control unit includes an induced draft fan, a high-precision pressure sensor, and a programmable logic controller. The pressure sensor monitors the pressure inside the sealed heating vessel in real time and feeds the signal back to the central control device. The central control device dynamically adjusts the inverter speed of the induced draft fan according to the deviation between the set pressure value and the measured value through a PID algorithm, while simultaneously interlocking with the feed valve, discharge valve, and exhaust valve. For example, when the pressure exceeds the set upper limit, the induced draft fan power is automatically increased or the exhaust valve is opened wider; when the pressure falls below the set lower limit, the power is reduced accordingly. This closed-loop control ensures that the system always operates stably under the target slight negative pressure, achieving directional and quantitative collection of exhaust gas and preventing any pollutant leakage.

[0039] The rapid cooling process is crucial for preventing dioxin resynthesis in this process. Through high-pressure two-fluid atomizing spray or a high-efficiency plate heat exchanger, the flue gas exiting the second condensation enrichment module, with a temperature of approximately 300-500°C, is cooled to below 200°C within an extremely short time of 5 seconds. This rapidly crosses the 200-500°C temperature window, the most likely temperature for de novo dioxin synthesis, effectively inhibiting its regeneration from a reaction kinetics perspective.

[0040] The added alkaline and oxidizing solid additives, such as CaO, Ca(OH)2, CaO2, or MgO, have multiple synergistic effects: First, they react with free halogen sources such as HCl and Cl2 in fly ash to generate stable CaCl2 or MgCl2, achieving chlorine fixation; second, the active oxygen generated by the decomposition of CaO2 can oxidize Cu... 2+ Fe 2+ The oxidation of low-valence metal ions to high-valence states, such as CuO and Fe2O3, significantly weakens their catalytic activity. Secondly, these alkaline substances can neutralize the acidic components in fly ash and increase the alkalinity of the system. This not only inhibits the volatilization and corrosion of chlorides at low temperatures, but also promotes the transformation of some heavy metals into more stable oxide or silicate forms, achieving chemical stabilization and reducing the tendency of materials to adhere to and coke on the vessel wall.

[0041] A fly ash toxicity reduction method based on closed-loop isothermal segmented thermal response and reset coupling involves heating fly ash under closed and slightly negative pressure conditions, and adding alkaline and oxidizing solid additives, such as CaO and CaO2, when the temperature reaches the range of 100℃ to 220℃. The additives preferentially react with halogen sources such as HCl / Cl2 in the fly ash to form stable salts, such as CaCl2. Simultaneously, the active oxygen generated by the decomposition of oxidizing additives such as CaO2 can oxidize typical metal catalytic species in the fly ash that promote dioxin synthesis, especially transition metal elements such as copper and iron existing in the form of chlorides or oxides, into higher valence states or more stable oxides, such as CuO and Fe2O3, thereby weakening their catalytic activity. This method resets and disrupts the reaction environment required for dioxin formation at its source.

[0042] Simultaneously, utilizing the differences in volatility among different heavy metals, mercury is selectively separated and recovered in a lower temperature range of 220–350℃. Then, in a high temperature range of 600–1050℃, heavy metals such as lead, cadmium, and zinc are volatilized, and residual dioxins are completely decomposed. Finally, the high-temperature flue gas is rapidly cooled to quickly cross the dioxin resynthesis sensitive temperature range of 200–500℃, and then purified before being discharged.

[0043] Preferably, the fly ash is stirred and turned over throughout the heating process to achieve a basically uniform temperature field inside the reactor, such as a temperature difference between the inner wall and the material of ≤15℃, to ensure the uniformity of the chemical reaction and mass transfer process and prevent local overheating or condensation.

[0044] A fly ash harm reduction system based on a closed isothermal segmented thermal response and reset coupling comprises a closed heating vessel providing a closed reaction environment; a device for adding chemical additives into the vessel; a stirring and agitating device for achieving uniform mixing and heat transfer of materials; first and second condensation and enrichment modules connected to the vessel's exhaust port via parallel pipelines and equipped with controlled valves for condensing and recovering mercury and other heavy metals respectively; a quenching device for rapidly cooling flue gas to prevent dioxin resynthesis; and a purification device to ensure that the exhaust gas meets standards. This closed isothermal segmented thermal response and reset coupling fly ash harm reduction system maintains operation at -50 to -200 Pa through a micro-negative pressure control unit to prevent pollutant leakage. The central processing unit automatically switches the gas flow path based on the vessel's internal temperature signal and adjusts heating or stirring according to the temperature difference signal to maintain an isothermal environment.

[0045] A preferred embodiment of the present invention discloses a fly ash reduction system based on a closed isothermal segmented thermal response and reset coupling, comprising a closed heating vessel, a stirring and agitating device, a chemical additive dosing device, a first condensation enrichment module, a second condensation enrichment module, a high-temperature pyrolysis chamber, a quenching device, and a tail gas purification device. The various devices of the closed isothermal segmented thermal response and reset coupled fly ash reduction system are connected via pipes and valves. The first and second condensation enrichment modules are connected to the exhaust port of the closed heating vessel via parallel pipes. Each pipe is equipped with a controlled valve, such as a solenoid valve or a pneumatic valve, the opening and closing of which is automatically executed by a central processing unit based on feedback signals from the temperature sensor inside the vessel.

[0046] The sealed heating vessel body adopts a cylindrical design, with an inner lining of corrosion-resistant and refractory material and an outer heating jacket for providing a heat source.

[0047] The stirring and agitating device includes a central shaft penetrating the sealed heating vessel, on which multiple layers of spiral stirring blades and a wall scraper are mounted. The stirring shaft extends through a sealed cavity at the end of the sealed heating vessel. This sealed cavity preferably employs a double-layer mechanical seal and is purged with inert gas to form an air curtain, ensuring dynamic sealing under slight negative pressure conditions and preventing bearing corrosion. The stirring shaft has multiple layers of stirring blades. Preferably, the blades may also be equipped with lifting plates or scraper structures to effectively lift and scatter the material at the bottom, achieving more thorough radial and axial mixing, ensuring uniform heat and mass transfer, and achieving isothermal heating with a temperature difference ≤15℃.

[0048] The stirring shaft has a hollow structure, with thermocouples installed inside to directly measure the core temperature of the fly ash pile. It also serves as a distribution pipe for trace amounts of inert gas. The function of the stirring and agitating device is to break down the static thermal conduction barriers between fly ash particles through forced convection, allowing heat to be transferred rapidly and evenly from the reactor wall to the interior of the material, thus achieving an isothermal effect, i.e., controlling the temperature difference between the reactor wall and the material to be ≤15℃. Without this active stirring, a significant temperature gradient would inevitably form in low thermal conductivity powders like fly ash.

[0049] This invention discloses a fly ash harm reduction method based on closed isothermal segmented thermal response and reset coupling, the specific operation steps of which are as follows: S1: The fly ash to be treated is fed into the sealed heating vessel via a closed conveying system. The system is started, and a closed-loop system consisting of an induced draft fan and a pressure sensor establishes and maintains a slight negative pressure of -50 to -200 Pa within the system. This pressure range ensures that any possible minor leaks are internal, preventing the escape of toxic and harmful gases and dust into the environment during processing, while also avoiding excessively high negative pressure that could cause unnecessary air infiltration and affect the reaction atmosphere. The stirring and agitating device is started at a low speed to initially loosen the material.

[0050] S2: Turn on the heating system and raise the temperature at a preset controllable rate. When the temperature reaches the range of 100℃~220℃, uniformly add alkaline and oxidizing solid additives at a ratio of 1%-20% of the fly ash mass using the chemical additive dosing device. Under stirring, the additives and fly ash are thoroughly mixed. During subsequent heating, the main reactions occur, such as: CaO+2HCl→CaCl2+H2O; CaO+Cl2→CaCl2+1 / 2O2, Calcium peroxide (CaO2) decomposes upon heating, releasing reactive oxygen species. These reactive oxygen species oxidize typical metal catalytic species in fly ash that promote dioxin synthesis, especially transition metals such as copper and iron in the form of chlorides or oxides, into higher valence states or more stable oxides, thus weakening the catalytic ability of the metals.

[0051] Meanwhile, the central processing unit monitors the vessel wall temperature and the fly ash temperature measured by thermocouples inside the stirring shaft in real time. Through a PID algorithm, the heating power and stirring speed are dynamically adjusted to control the temperature difference between the vessel wall and fly ash temperatures within 10℃, and not exceeding 15℃.

[0052] S3: When the temperature reaches and stabilizes at 220–350℃, a large amount of elemental mercury and easily decomposable mercury compounds in the fly ash volatilize. The central processing unit receives the temperature signal and automatically opens the valve leading to the first condensation and enrichment module while simultaneously closing the valve leading to the second condensation and enrichment module. The gas generated in this temperature range is then directed separately to the first condensation and enrichment module. The first condensation and enrichment module maintains a low temperature of 0–80℃, causing the mercury vapor to condense into liquid metallic mercury and be collected, achieving separate recovery of mercury. The atmosphere during this stage should ideally be controlled to be inert or slightly oxygenated.

[0053] S4: After low-temperature mercury removal, the system continues to heat up. When the temperature exceeds 350℃ and reaches the target range of 600–1050℃, the central processing unit automatically switches valves and opens the pipeline to the second condensation enrichment module. Within this temperature range and after holding for a certain period, the vapor pressure of chlorides of heavy metals such as lead, cadmium, and zinc increases significantly, and a large amount volatilizes into the gas phase. Simultaneously, any dioxin-like organic matter remaining in the fly ash is completely oxidized and decomposed at this high temperature. The gas produced in this stage is guided to the second condensation enrichment module. The second condensation enrichment module is temperature-controlled at 150–300℃, and heavy metal vapors condense and deposit on the surface of the ceramic honeycomb or porous carrier within the module. To further ensure complete dioxin destruction, the gas can optionally pass through a high-temperature pyrolysis chamber maintained at 850–1100℃.

[0054] S5: The flue gas exiting the high-temperature section immediately enters the quenching device. The quenching device can employ direct contact cooling via a high-efficiency two-fluid atomizing spray tower or indirect cooling via a modular plate heat exchanger. By precisely controlling the flow rate, pressure, and temperature of the cooling medium, the high-temperature flue gas is rapidly cooled, allowing it to quickly cross the sensitive temperature range of 200–500°C for dioxin resynthesis, effectively blocking the DeNovo synthesis reaction from a kinetic perspective.

[0055] S6: After rapid cooling, the flue gas enters the exhaust gas purification device, where it undergoes multiple stages of purification treatment, including an alkaline scrubbing tower to remove acidic gases such as HCl and SOx, an activated carbon adsorption tower to capture trace amounts of heavy metal vapors and organic matter that may escape, and a bag filter to remove particulate matter, ensuring that the final emission gas meets the relevant national standards.

[0056] After the above treatment, the total amount of heavy metals and leaching toxicity of fly ash residue are significantly reduced, and the dioxin toxicity equivalent is extremely low. It can be safely disposed of as general industrial solid waste or after simple stabilization, or it can be used as a resource for building materials.

[0057] Example 1

[0058] Treat fly ash from typical municipal solid waste incineration.

[0059] Process parameters: throughput 10kg; slight negative pressure -120Pa; addition of 8wt%CaO; heating to 280℃ with the stirring mechanism running continuously at 5-15rpm, the temperature difference ΔT is always <15℃ during the process, and mercury removal is carried out after holding at this temperature for 45 minutes; heating to 880℃ and holding for 20 minutes; using a two-fluid spray quench tower, the measured time for flue gas to drop from 650℃ to 180℃ is approximately 1.3 seconds.

[0060] The test results are shown in the table below:

[0061] Example 2 Treatment of fly ash from high-mercury hazardous waste incineration Process parameters: Add 6wt%CaO + 2wt%CaO2; slight negative pressure -150Pa; temperature difference ΔT < 15℃ under stirring; mercury removal at 300℃ for 60 minutes; high temperature treatment at 900℃ for 25 minutes; rapid cooling using a plate heat exchanger.

[0062] The test results are shown in the table below:

[0063] It has met the stringent control standards for solid waste and exhaust gas.

[0064] Comparative Example 1 The same heat treatment temperature, time, and stirring conditions as in Example 1 were used, but without the addition of any alkaline or oxidizing solid additives CaO / CaO2.

[0065] The test results are shown in the table below:

[0066] The above data clearly shows: The method of this invention can efficiently remove >95% of mercury from fly ash and significantly reduce the content of other heavy metals and dioxin toxicity >98%. The comparison between Comparative Example 1 and Example 1 strongly demonstrates that source chemical repositioning elements are indispensable for achieving deep dioxin removal and mercury fixation. Without the addition of additives, relying solely on the same heat treatment, the dioxin removal rate drops sharply, and the mercury fixation effect also deteriorates, indicating that source chemical intervention is indispensable for achieving deep harm reduction. In the examples, a uniform temperature field with a temperature difference ΔT <15℃ was achieved through stirring and active control, ensuring the chemical reaction and the staged volatilization of heavy metals. The measured quenching time of the quenching device was approximately 1.3 seconds, far below the 5-second upper limit, ensuring that the flue gas quickly crosses the dioxin regeneration temperature zone, verifying the effectiveness of the process-directed blocking elements, effectively achieving rapid cooling of the flue gas, and combined with source control, ensuring the dioxin treatment effect.

[0067] The process flow of this invention is clear and easy to automate. It is applicable to the technical upgrading or new construction projects of fly ash treatment lines in existing municipal solid waste incineration plants and hazardous waste disposal centers. The treated fly ash meets the requirements for waste entry into municipal solid waste landfills, as stipulated in the "Pollution Control Standard for Municipal Solid Waste Landfills" (GB16889), and has good prospects for industrial application and promotion value.

[0068] This invention provides a fully enclosed, slightly negative-pressure environment throughout the process, and achieves isothermal heating of materials within the reactor through a built-in stirring and agitation device, with a temperature difference ≤15℃, ensuring uniform heat and mass transfer and preventing localized overheating and coking. Simultaneously, alkaline and oxidizing solid additives containing calcium and magnesium are added to the fly ash within a specific low-temperature window of 100–220℃ to neutralize acidic chlorides in the fly ash, fix halogens, oxidize and deactivate metal catalytic species, and promote the stabilization of heavy metals. Based on the differences in the volatility of heavy metals, this invention performs segmented thermal response and condensation enrichment, and rapidly quenches the high-temperature product flue gas, reducing it from above 600℃ to below 200℃ within 5 seconds, quickly crossing the 200–500℃ sensitive temperature range for dioxin resynthesis, thus kinetically blocking the de novo synthesis of dioxins.

[0069] This invention utilizes a fully closed-loop, slightly negative-pressure operation, enabling directional and quantitative collection of exhaust gases. This significantly reduces the amount of ineffective gases and lowers the processing load and energy consumption of subsequent purification systems. By chemically resetting and destroying the preconditions for dioxin formation at the source, combined with rapid cooling during directional process interruption, a dual mechanism ensures the efficient elimination of dioxins and prevents their further synthesis, resulting in more thorough treatment. Isothermal stirring ensures uniform heating of materials, avoiding melting and sintering caused by localized high temperatures. Simultaneously, the addition of alkaline additives neutralizes acidic components, further inhibiting the formation and adhesion of low-temperature eutectic compounds, ensuring long-term stable system operation. This invention achieves segmented resource recovery of heavy metals, improves the stability of treated products, and constructs a complete pollution control chain from source to end, resulting in significant comprehensive environmental and economic benefits.

[0070] The above description illustrates preferred embodiments of the present invention and helps those skilled in the art to more fully understand the technical solution of the present invention. However, these embodiments are merely illustrative and should not be construed as limiting the specific implementation of the present invention to these embodiments. For those skilled in the art, several simple deductions and modifications can be made without departing from the inventive concept, and all such modifications should be considered within the protection scope of the present invention.

Claims

1. A fly ash harm reduction method based on closed isothermal segmented thermal response and reset coupling, characterized in that, Includes the following steps: Step S1: Under the closed and slightly negative pressure conditions controlled by the pressure sensor and controller, heat energy is applied to the fly ash, and the fly ash is stirred and turned at the same time to enhance heat and mass transfer. Step S2: Heat the system to the target temperature range and add alkaline and oxidizing solid additives to the fly ash to chemically reset the halogen source and metal catalyst species in the fly ash. The additives include at least one of calcium oxide, calcium hydroxide and calcium peroxide. After the additives are added, continue to heat the system to enter the first temperature range for mercury removal treatment. Step S3: In the first temperature range, mercury in fly ash is preferentially volatilized, and mercury-containing gas is extracted for first condensation and enrichment; Step S4: At a second temperature range higher than the first temperature range, the target heavy metals in the fly ash are volatilized and dioxin-like pollutants are decomposed, and the generated heavy metal-containing gas is discharged for second condensation enrichment. Step S5: The high-temperature gas generated in step S4 is rapidly cooled to quickly cross the temperature range of 200°C to 500°C. The slight negative pressure in step S1 is used to ensure that the gas flows out in one direction during the treatment process and to prevent the pollutants from leaking out; the stirring and turning in step S1 is used to achieve isothermal heating conditions where the temperature difference between the inner wall of the reactor and the fly ash pile does not exceed 15°C.

2. The fly ash harm reduction method based on closed isothermal segmented thermal response and reset coupling according to claim 1, characterized in that, In step S1, the range of the micro-negative pressure is -10 Pa to -200 Pa.

3. The fly ash harm reduction method based on closed isothermal segmented thermal response and reset coupling according to claim 2, characterized in that, The range of the micro-negative pressure is further limited to -50Pa to -150Pa.

4. The fly ash harm reduction method based on closed isothermal segmented thermal response and reset coupling according to claim 1, characterized in that, The stirring and agitation ensures that the temperature difference between the inner wall of the heating device and the fly ash pile does not exceed 15°C.

5. The fly ash harm reduction method based on closed isothermal segmented thermal response and reset coupling according to claim 1, characterized in that, In step S2, the amount of the additive added is 1% to 20% of the fly ash mass; the additive is used to deactivate and solidify non-volatile metals, eliminate the precursor basis of dioxin generation by destroying the heterogeneous catalytic active sites of dioxin synthesis, and volatilize and separate volatile metals in conjunction with the chlorination environment.

6. The fly ash harm reduction method based on closed isothermal segmented thermal response and reset coupling according to claim 1, characterized in that, In step S5, the rapid cooling process is achieved by spray cooling or heat exchange cooling, so that the temperature of the high-temperature gas drops to below 200°C within 5 seconds.

7. The fly ash harm reduction method based on closed isothermal segmented thermal response and reset coupling according to claim 1, characterized in that, The target temperature range is 100℃~220℃, the first temperature range is 220℃~350℃, and the second temperature range is 600℃~1050℃.

8. The fly ash harm reduction method based on closed isothermal segmented thermal response and reset coupling according to claim 1, characterized in that, In step S2, the auxiliary agent is an alkaline compound containing calcium and / or magnesium, used to capture / neutralize free halogen sources, reduce catalytic active centers such as Cu / Fe, and reduce the leaching migration of some residual heavy metals, thereby promoting the stabilization / reduction of leaching of metals Cu and Fe.

9. The fly ash harm reduction method based on closed isothermal segmented thermal response and reset coupling according to claim 1, characterized in that, Step S3 is performed under inert or slightly oxygenated atmosphere conditions.

10. The fly ash harm reduction method based on closed isothermal segmented thermal response and reset coupling according to claim 1, characterized in that, It also includes real-time monitoring and closed-loop control of the pressure in step S1, the temperature and temperature difference between steps S1 and S2, and the stirring speed.

11. A fly ash reduction system based on closed isothermal segmented thermal response and reset coupling, used to implement the fly ash reduction method based on closed isothermal segmented thermal response and reset coupling as described in any one of claims 1-10, characterized in that, include: A sealed heating vessel is used to contain fly ash and apply heat to it. The micro negative pressure control unit, including a blower, a pressure sensor and a controller, is used to establish and maintain a micro negative pressure inside the sealed heating vessel. A stirring and turning device is installed inside the sealed heating vessel to turn the material to achieve isothermal heating; A chemical additive dosing device is connected to the sealed heating vessel and is used to add the alkaline and oxidizing solid additives; The first condensation enrichment module and the second condensation enrichment module are connected to the exhaust port of the sealed heating vessel through parallel pipelines, and each pipeline is equipped with a controlled valve. A rapid cooling device, connected to the outlet of the second condensation enrichment module, is used to rapidly cool high-temperature gas to below 200°C; An exhaust gas purification device is connected to the outlet of the quenching device; The central control unit is electrically connected to the pressure sensor, the temperature sensor of the sealed heating vessel, the controlled valve, the stirring and agitating device, and the heating unit, respectively. The central control device is used to maintain a target slight negative pressure by adjusting the opening of the induced draft fan and the inlet / outlet valves according to the feedback signal of the pressure sensor; the central control device is used to adjust the heating power or stirring speed according to the temperature of the inner wall of the vessel and the material temperature fed back by the temperature sensor to control the temperature difference to not exceed 15°C; the central control device is used to control the opening and closing of the controlled valves according to the temperature signal of the sealed heating vessel to guide the gas in different temperature ranges to the first condensation enrichment module or the second condensation enrichment module respectively.

12. The fly ash reduction system based on closed isothermal segmented thermal response and reset coupling according to claim 11, characterized in that, The stirring and turning device includes a stirring shaft and blades disposed on the stirring shaft. The blades are provided with lifting plates. The stirring shaft passes through the wall of the sealed heating vessel and is provided with a sealing structure at the penetration point.

13. The fly ash reduction system based on closed isothermal segmented thermal response and reset coupling according to claim 12, characterized in that, The stirring shaft has a hollow structure, and its interior is equipped with a temperature sensor for directly measuring the material temperature and / or an inert gas delivery channel.

14. The fly ash harm reduction system based on closed isothermal segmented thermal response and reset coupling according to claim 11, characterized in that, The first condensation enrichment module operates in a temperature range of 0℃ to 80℃; the second condensation enrichment module operates in a temperature range of 150℃ to 300℃.

15. The fly ash reduction system based on closed isothermal segmented thermal response and reset coupling according to claim 11, characterized in that, It also includes a high-temperature pyrolysis chamber connected between the sealed heating vessel and the second condensation enrichment module.

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