A device and method for self-sustaining smoldering treatment of dioxins in waste incineration fly ash

Abstract

The present invention discloses a device and method for self-sustaining smoldering treatment of dioxins in fly ash from waste incineration, including fly ash pellets and biomass waste mixing and conveying units, air supply units, smoldering reaction units, tail gas treatment units, monitoring units and control units. The smoldering treatment technology has the advantages of green, low-carbon, and controllable process, wherein biomass solid wastes such as waste wood chips and rice husks are used as energy sources, and fly ash pellets are used as porous media to provide the chemical reaction required for smoldering treatment, and can store heat and heat to transfer heat to ignite the downstream area, realize self-sustaining reaction, and maintain a peak temperature range of 400-850°C, and can fully remove organic pollutants such as dioxins in fly ash without the need to introduce additional energy. The present invention can realize continuous smoldering treatment of fly ash, with stable tail gas components, controllable secondary pollution, low investment and operating costs, and provides new ideas for the current situation of high energy consumption disposal in the field of waste, with considerable promotion value.

Description

Technical Field

[0001] The present invention relates to the field of harmless disposal of waste incineration fly ash, and in particular to a device and method for self-sustaining smoldering disposal of dioxins in waste incineration fly ash. Background Art

[0002] Municipal solid waste incineration power generation technology has become the mainstream technology for domestic waste disposal in my country. As of 2022, the annual disposal capacity of municipal solid waste incineration is approximately 190 million tons, accounting for 79% of the national municipal solid waste collection volume. Furthermore, fly ash generated by incineration accounts for 3-15% of the total municipal solid waste disposal volume, exceeding 10 million tons annually. Due to its high concentration of highly toxic substances such as dioxins, persistent organic compounds, and heavy metals, fly ash has been listed on my country's list of hazardous wastes (HW18).

[0003] Landfill is still the primary method of disposal for fly ash from municipal solid waste incineration in my country. Due to limited land resources and the hazardous nature of the waste, land and economic resources are insufficient in most regions to meet landfill requirements. The "Technical Specifications for Pollution Control of Municipal Solid Waste Incineration Fly Ash (Trial)" (HJ 1134-2020) issued by the Ministry of Ecology and Environment regulates the harmless disposal of fly ash and sets basic prerequisites for its resource utilization. Hazardous substance content must meet the following requirements: a chlorine content ≤ 2%, a heavy metal leaching risk that meets GB 8978, and a dioxin toxicity equivalent concentration (TEQ) below 50 ng TEQ / kg. Currently, a number of fly ash harmless disposal and resource utilization technologies have been developed and demonstrated both domestically and internationally. Dioxins, due to their large molecular weight, high thermal stability, complex chemical structure, and trace levels, are difficult to remove and degrade, making them a key challenge for nearly all fly ash harmless disposal and resource utilization technologies. Comparative analysis shows that non-thermal treatment technologies are extremely limited in their effectiveness at removing dioxins. Among thermal treatment technologies, high-temperature sintering and high-temperature melting processes can effectively degrade dioxins in fly ash, but these processes are energy-intensive and costly. While fly ash co-treatment in cement kilns has been used to some extent, the amount of co-combustion is limited, specific requirements for incoming fly ash are imposed, and the process is subject to other constraints, such as cement production. While low-temperature thermal decomposition processes meet the energy-saving needs of "low-carbon emission reduction," existing technologies place high demands on a reducing atmosphere and tight sealing during the treatment process. Furthermore, the process requires temperatures exceeding 400°C, resulting in high energy consumption, reaching approximately 1500 MJ per ton of fly ash treated. In particular, the lack of a high-temperature stage prevents consistent and complete decomposition of dioxins in fly ash with variable properties. Therefore, the reliability and suitability of these technologies need to be improved.

[0004] The smoldering combustion method (hereinafter referred to as smoldering technology) achieves objectives such as volume reduction and degradation of organic pollutants in the disposal target through a slow, flameless, heterogeneous, exothermic oxidation reaction occurring on the surface of a porous medium. Heat is provided by calorific substances condensed on the surface of the porous medium or intermixed within the porous medium through an exothermic oxidation reaction. Except for the initial stage of the smoldering process, which requires external heat, all subsequent heat required for disposal is provided by the disposal material itself. This significantly reduces energy costs and provides a new approach to addressing the key bottleneck of fly ash disposal in the current waste incineration industry. Summary of the Invention

[0005] The present invention aims to address the deficiencies of the prior art and to provide a device and method for treating dioxins in waste incineration fly ash by self-sustaining smoldering.

[0006] The object of the present invention is achieved by the following technical solutions: a self-sustaining smoldering device for treating dioxins in fly ash from waste incineration, comprising a conveying unit for mixing fly ash pellets and biomass waste and a smoldering reaction unit;

[0007] The fly ash pellet and biomass waste mixing and conveying unit is used to prepare fly ash particles into fly ash pellets according to the smoldering self-sustaining conditions, fly ash particle size and dioxin content, adjust the blending ratio of fly ash pellets and biomass waste, mix them homogeneously, and then convey them to the smoldering reaction unit;

[0008] The smoldering reaction unit is used to control the loading and unloading and ignition processes. The fly ash pellets serve as porous media to provide the required activated reaction surface for the smoldering reaction of biomass waste, and accumulate the heat generated by the smoldering inside the smoldering reaction chamber to ignite the materials in the downstream area, thereby achieving self-sustaining of the smoldering disposal process. Compared with incineration, the smoldering reaction area and the exhaust gas generated have a slightly reducing atmosphere, which inhibits the regeneration of dioxins and plays a reducing / detoxifying role on high-valent and highly toxic heavy metals in fly ash.

[0009] Furthermore, the fly ash pellets are prepared by classifying fly ash particles according to their particle size into pellets of 3-10 mm, and the proportion of biomass waste added is regulated according to the type and calorific value of the biomass used and the required smoldering self-sustaining conditions.

[0010] Furthermore, in the smoldering reaction unit, the peak temperature is maintained at 400-850°C, achieving desorption or degradation of dioxins in the fly ash pellets; at the same time, the reducing atmosphere such as CO in the tail gas helps to inhibit the regeneration of dioxins and reduce high-valent heavy metals.

[0011] Furthermore, in the smoldering reaction unit, the smoldering reaction temperature of the material is monitored in real time by a thermocouple, and the smoldering self-sustaining is ensured by regulating the loading and unloading and ignition processes or promptly starting the resistance heating ignition device.

[0012] Furthermore, based on the rule that fly ash particle size is inversely proportional to dioxin content, fly ashes of different particle sizes were screened. Fly ash with a particle size greater than 20 μm was directly prepared into fly ash pellets of 3-10 mm after washing, while fly ash with a particle size less than 20 μm was prepared into fly ash pellets after washing with water and adding 5-10% by mass of CaO. The fly ash pellets of different particle sizes were smoldered, and the smoldering peak temperature and residence time required for fly ash treatment were adjusted.

[0013] Furthermore, the smoldering reaction unit includes a smoldering reaction chamber wind chamber cover. When the thermocouple at the bottom end of the smoldering reaction tube reaches the ignition temperature, air is transported to the smoldering reaction chamber wind chamber cover; the wind chamber cover is equipped with an inert porous medium to support the material in the reaction tube and uniform the wind chamber airflow.

[0014] On the other hand, the present invention also provides a method for treating dioxins in waste incineration fly ash by self-sustaining smoldering, the specific steps of the method are:

[0015] (1) Based on the smoldering self-sustaining conditions and the relationship between fly ash particle size and dioxin content, the washed fly ash particles were prepared into fly ash pellets and 5-10% CaO was added to the fly ash pellets with a particle size of less than 20 μm; the mixing ratio of fly ash pellets and biomass waste was adjusted;

[0016] (2) Regulate the loading and unloading and ignition process of the smoldering reaction. The fly ash pellets, as the porous medium in the smoldering reaction, not only provide the required activation reaction surface for the smoldering of biomass waste, but also store the heat generated by the smoldering and ignite the downstream materials, thus achieving self-sustaining smoldering disposal.

[0017] (3) The peak temperature reaches 400-850 ℃, which can ensure the desorption or degradation of dioxins in fly ash. At the same time, the slightly hypoxic state in the smoldering reaction zone and the reducing atmosphere in the tail gas inhibit the regeneration of dioxins and reduce the high-valent toxic heavy metals in the fly ash.

[0018] The beneficial effects of the present invention are:

[0019] 1. Adding 6-15% by mass of waste wood chips, waste rice husks and other biomass waste can achieve a smoldering peak temperature of the fly ash pellets at 400-850 °C, and maintain the residence time of the mixture at the high temperature point of 850 °C for not less than 2 seconds, which provides a guarantee for the efficient removal of dioxins inside the fly ash pellets.

[0020] 2. Except for the startup phase, all heat during the smoldering process is provided by the exothermic oxidation reaction of the biomass waste mixed in the porous medium. This ensures low energy consumption and low costs for the smoldering process. Furthermore, the co-treatment of biomass waste does not increase carbon emissions, resulting in significant carbon reduction benefits compared to other technologies. Furthermore, the resistance heating plate built into the bottom of each reactor can be activated at any time in the event of an unexpected non-self-sustaining event, such as a smoldering reaction interruption, fully ensuring that all materials in the reactor undergo smoldering treatment, ensuring the reliability and stability of the treatment.

[0021] 3. In smoldering technology, exhaust gases cool during the preheating of the raw materials, typically maintaining exhaust temperatures below 200°C, avoiding the low-temperature regeneration range for dioxins. Furthermore, the high- and low-temperature physical regions of the smoldering process correspond to high- and low-oxygen atmospheres, respectively, providing ideal temperature and atmosphere conditions for dioxin thermal decomposition.

[0022] 4. After condensation and dehydration, the smoldering exhaust gas is adsorbed by activated carbon and then discharged, ensuring the removal of polluting non-condensable gases and ensuring the cleanliness and safety of the exhaust gas. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0024] Figure 1 A schematic diagram of a self-sustaining smoldering device for treating dioxins in waste incineration fly ash according to the present invention;

[0025] Figure 2 It is a cross-sectional schematic diagram of the smoldering reaction chamber of the present invention.

[0026] Figure 3 It is a longitudinal cross-sectional schematic diagram of the discharge component of the fly ash pellets after treatment of the present invention.

[0027] Figure markings: 1. Fly ash pellet loader / conveyor; 2. Biomass waste loader / conveyor; 3. Electric mixer; 4. Mixed material conveyor; 5. Smoldering reaction chamber exhaust hood; 6. Smoldering reaction chamber hood cylinder; 7. Resistance heating ignition device; 8. I-shaped electric turntable; 9. Smoldering reaction chamber wind chamber hood; 10. Hopper; 11. Blower; 12. Condenser; 13. Activated carbon adsorption bin; 14. Induced draft fan; 15. Post-smoldering reaction material conveyor; 16. Hopper; 17. Smoldering reaction cylinder; 17-1. Loading cylinder; 17-2. Discharging cylinder; 18. First-stage thermocouple; 19. Final-stage thermocouple. DETAILED DESCRIPTION

[0028] In order to clarify the implementation objectives, technical solutions and advantages of the present invention, the present invention is further described in detail below with reference to the accompanying drawings and implementation methods. It should be pointed out that for ordinary method personnel in this field, several modifications and improvements can be made without departing from the principles of the present invention, and these are also considered to fall within the scope of protection of the present invention.

[0029] like Figure 1 、 Figure 2 and Figure 3 As shown, the present invention provides a self-sustaining smoldering device for the treatment of dioxins in waste incineration fly ash. By adding biomass solid waste such as sawdust and rice husks as an energy source, external energy and air are introduced to ignite the smoldering, flameless, and exothermic oxidation reaction. Before the smoldering reaction, the fly ash is washed to reduce its chlorine content for the subsequent reaction to prepare building material aggregates. The fly ash is then graded according to particle size to produce pellets ranging from 3 to 10 mm. During the smoldering reaction, the fly ash pellets act as a porous medium, providing the activated reaction surface required for the smoldering reaction. They also store and transfer heat to ignite downstream areas, achieving a self-sustaining reaction with a peak temperature of 400-850°C. Furthermore, the peak temperature region is slightly anoxic, and the exhaust gas contains reducing atmospheres such as CO, which not only inhibits dioxin regeneration but also effectively reduces high-valent, highly toxic heavy metals such as hexavalent chromium in the fly ash. The smoldering flue gas is then condensed to remove water and then adsorbed on activated carbon before meeting emission standards. The smoldering reaction temperature of the material is monitored in real time using thermocouples. By controlling the loading and unloading process and ignition, or by promptly activating the resistance heating ignition device, the smoldering reaction is self-sustaining. This solution achieves low-carbon, high-efficiency removal of dioxins from fly ash, with low disposal energy consumption and simple equipment installation and commissioning.

[0030] The present invention provides a device for treating dioxins in fly ash from waste incineration by self-sustaining smoldering, which comprises a conveying unit for mixing fly ash pellets and biomass waste, a smoldering reaction unit and an air supply unit.

[0031] The conveying unit for mixing fly ash pellets and biomass waste includes a connected fly ash pellet loader / conveyor 1, a biomass waste loader / conveyor 2, and an electric mixer 3, which respectively convey the fly ash pellets and biomass waste to the electric mixer 3. According to the rule that the fly ash particle size is inversely proportional to the dioxin content, fly ashes of different particle sizes can be screened. Fly ash with a particle size greater than 20 μm is directly prepared into fly ash pellets of 3-10 mm after washing with water, while fly ash with a particle size less than 20 μm is prepared into fly ash pellets after washing with water and adding CaO with a mass fraction of 5-10%. Fly ash pellets of different particle sizes can be smoldered in batches, which facilitates adjustment of the smoldering peak temperature and residence time required for fly ash treatment. The particle size of the fly ash pellets is generally 3-10 mm, and the addition ratio of biomass waste such as waste wood chips and waste rice husks is 6-15% by mass. After being evenly stirred, the mixture is conveyed to the loading barrel 17-1 of the smoldering reaction unit through the mixed material conveyor 4. When the smoldering reaction barrel 17 is transferred from the unloading barrel 17-2 area to the loading barrel area, the mixed material is loaded.

[0032] After loading is completed, the smoldering reaction tubes 17 in the loading tube 17-1 area of ​​the smoldering reaction unit are driven by the I-shaped electric turntable 8 to the next smoldering reaction tube area. Ignition is initiated by the resistance heating ignition device 7. When the first-stage thermocouple 18 at the bottom of the smoldering reaction tube 17 reaches the ignition temperature, the blower 11 of the air supply unit is activated to deliver air to the smoldering reaction chamber plenum 9. The plenum plenum is filled with an inert porous medium such as quartz sand or gravel, which supports the material in the reaction tube and provides uniform airflow in the plenum. When the temperature of the first-stage thermocouple 19 reaches its peak temperature, the bottom heating device is turned off, and self-sustaining smoldering begins. The peak smoldering temperature of the fly ash pellets is maintained between 400°C and 850°C throughout the entire treatment process, with a peak propagation velocity of approximately 3-5 cm / min. When the temperature of the final-stage thermocouple 19 drops below 250°C, the electric turntable is activated to transfer the smoldering reaction tube to the unloading area. The treated material is then discharged into the hopper 16 via the material conveyor 15. After unloading, the empty drum enters the loading area for further loading, repeating the aforementioned loading, startup, reaction, and unloading process. Exhaust gas generated during the smoldering process is collected and transported centrally via the smoldering reaction chamber exhaust hood 5, which is connected to the exhaust gas treatment system. Hopper 10 is used to load inert porous media such as quartz sand or gravel, unloaded from the smoldering reaction chamber plenum hood 9, during overhaul or maintenance of the smoldering reaction unit.

[0033] The diameter of the smoldering reaction tube is 0.5-0.8 m, and the height is 1-1.5 m. The single-batch processing capacity of a single smoldering reaction tube is about 0.6-0.8 t, the processing time of each batch of fly ash pellets is about 2-3 h, and the daily processing capacity of the equipment is about 8-10 t. The size of the smoldering reaction tube can be adjusted according to the actual demand for fly ash processing volume. However, the diameter of the smoldering reaction tube is recommended to be less than 0.8 m to reduce radial heat dissipation loss and maintain a stable smoldering reaction. The height is recommended to be less than 1.5 m to control the bed material pressure loss and thus reduce the power consumption of the blower.

[0034] The smoldering reaction flue gas flow rate is about 100-300 Nm 3 / h, the flue gas is collected by the smoldering reaction chamber hood 6 and then transported to the tail gas purification unit, and then passes through the condenser 12 and the activated carbon adsorption chamber 13 in sequence to further remove possible non-condensable pollutants, and then discharged through the induced draft fan 14 and the chimney.

[0035] The smoldering treatment device for dioxins in fly ash includes six smoldering reaction cylinders. Each reaction cylinder is first loaded with materials in the loading cylinder area, and then a smoldering reaction occurs one by one in the four smoldering reaction cylinder areas, and finally the materials are unloaded in the unloading cylinder 17-2 area. The I-shaped electric turntable 8 realizes a semi-continuous smoldering reaction of the mixed materials in each reaction cylinder, which significantly improves the treatment efficiency of dioxins in fly ash.

[0036] The smoldering dioxin in fly ash treatment device also includes a temperature monitor and automated control system. The temperature monitor monitors the device's temperature in real time and feeds this data back to the automated control system, enabling automatic regulation of the power system. In exceptional circumstances, if the peak temperature of a non-final thermocouple in a smoldering reactor drops 100°C below a preset peak temperature, the resistance heating ignition device 7 is automatically activated to replenish heat and ensure successful smoldering treatment of the entire reactor.

[0037] On the other hand, corresponding to the aforementioned embodiment of a device for treating dioxins in waste incineration fly ash by self-sustaining smoldering, the present invention also provides a method for treating dioxins in waste incineration fly ash by self-sustaining smoldering, the specific steps of the method are:

[0038] Raw fly ash is first washed to remove chloride salts, eliminating the chlorine element required for dioxin regeneration during subsequent disposal. After washing, the fly ash is screened, and fly ash with a particle size of 20 μm or larger is directly pelletized. Fly ash with a particle size below 20 μm is then mixed with 5-10% by mass of CaO to form pellets. The particle size of the fly ash pellets is controlled to be within the porous media particle size range commonly used in smoldering technology, i.e., 3-10 mm. Subsequently, the fly ash pellets are mixed with biomass waste, such as sawdust and rice husks, and blended with an electric mixer until visually uniform. The biomass waste blend ratio can range from 6-15% by mass, depending on the calorific value of the biomass waste and the predetermined smoldering peak temperature. This mixture is then transported via conveyor equipment to the smoldering reactor located in the loading area. This reactor is temporarily referred to as the loading reactor to distinguish it from reactors in other areas. Each reactor rotating to this location serves as a loading reactor within the loading area. After loading is complete, the motorized turntable activates to transfer the reactor to the next area, and a resistance heating disk built into the bottom of the reactor activates to heat the reactor. The blower then sequentially activates and deactivates the heating disk based on temperature feedback from the reactor's thermocouples. Specifically, the blower activates when the first-stage thermocouple reaches ignition temperature, and deactivates when it reaches peak temperature. The reactor then utilizes the stored heat from the internal materials to initiate a self-sustaining smoldering chain reaction. When the temperature of the final thermocouple in the reactor drops below 250°C, the smoldering of all materials is complete, and the motorized turntable activates to move the materials into the discharge area. The materials then pass through a discharge pipe running through the bottom air chamber and into a conveying device, where they are transported to the bottom hopper for discharge. The resulting materials are fly ash pellets and bottom ash, which can be used directly or after brief screening as building materials. The plenum is filled with quartz sand or gravel, which supports the material in the reaction tube and allows air to pass through. A discharge pipe, located at the center of the plenum, is used to unload the quartz sand and other materials in rare circumstances, such as during overhaul or maintenance of the smoldering reaction unit. These discharge pipes are located on the sides of the top exhaust hood, and a flue gas discharge pipe is located at the center. The flue gas generated by the smoldering combustion is collected by the exhaust hood and then fed into exhaust treatment equipment such as the condenser and activated carbon adsorption chamber. After cleaning, the exhaust gas is exhausted by the induced draft fan.

[0039] This study investigated the smoldering treatment of dioxins in waste incineration fly ash. By adding 8% waste sawdust, the mixture achieved a peak smoldering temperature of approximately 650°C. The minimum energy density threshold for a self-sustaining smoldering reaction was approximately 0.68 MJ / kg of material, significantly lower than the energy consumption required for low-temperature thermal decomposition. Before smoldering treatment, the average dioxin toxicity equivalent concentration (TEQ) in the mixture was 356 ng TEQ / kg. After smoldering treatment, the average TEQ / kg was below 10 ng TEQ / kg, meeting the TEQ / kg requirement of less than 50 ng TEQ / kg in the "Technical Specification for Pollution Control of Municipal Waste Incineration Fly Ash (Trial Implementation)" (HJ 1134-2020). The TEQ / kg treatment rate exceeded 95%. These results demonstrate the feasibility of smoldering treatment for dioxin removal from fly ash.

[0040] Analysis of the fingerprint distribution characteristics of 17 2,3,7,8-PCDD / Fs toxic dioxin homologues in the gas and solid phases before and after smoldering treatment showed that the proportion of highly chlorinated dioxins in the solid phase decreased and the proportion of low-chlorinated dioxins increased after smoldering treatment, indicating that dioxins may have undergone degradation reactions from highly chlorinated to low-chlorinated during smoldering treatment.

[0041] The above is merely an embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations are possible. Any modifications, equivalent substitutions, and improvements within the spirit and principles of the present invention should be included within the scope of the claims of the present invention.

Claims

1. A self-sustaining smoldering device for treating dioxins in fly ash from waste incineration, characterized in that: It includes a conveying unit for mixing fly ash pellets and biomass waste, a smoldering reaction unit and an air supply unit; The conveying unit for mixing fly ash pellets and biomass waste comprises a fly ash pellet feeder / conveyor and a biomass waste feeder / conveyor connected to an electric mixer, and the fly ash pellets and the biomass waste are conveyed to the electric mixer respectively; the conveying unit for mixing fly ash pellets and biomass waste is used to prepare fly ash particles into fly ash pellets according to the smoldering self-sustaining conditions, the fly ash particle size and the dioxin content, specifically: according to the law that the fly ash particle size is inversely proportional to the dioxin content, fly ashes of different particle sizes are screened, and fly ashes with a particle size greater than 20 μm are directly prepared into fly ash pellets of 3-10 mm after washing, and fly ashes with a particle size less than 20 μm are prepared into fly ash pellets after washing with 5-10% by mass of CaO, and fly ash pellets of different particle sizes are smoldered in batches, and the smoldering peak temperature and residence time required for the fly ash treatment are adjusted; After the blending ratio of fly ash pellets and biomass waste is adjusted and mixed homogeneously, the mixed material is transported to the loading barrel of the smoldering reaction unit through the mixed material conveyor, and the mixed material is loaded when the smoldering reaction barrel is transferred from the unloading barrel area to the loading barrel area; The smoldering reaction unit is used to control the loading and unloading and ignition processes. The fly ash pellets serve as porous media to provide the required activation reaction surface for the smoldering reaction of biomass waste, and accumulate the heat generated by the smoldering in the smoldering reaction chamber to ignite the materials in the downstream area, thereby realizing the self-sustaining of the smoldering treatment process; the smoldering reaction unit includes 6 smoldering reaction cylinders. After the smoldering reaction cylinders in the loading cylinder area of ​​the smoldering reaction unit are loaded, they are driven by an I-shaped electric turntable to move to the next smoldering reaction cylinder area to cause smoldering reactions one by one. The I-shaped electric turntable is used to realize the semi-continuous smoldering reaction of the mixed materials in each reaction cylinder, and ignites under the heating of the resistance heating ignition device. When the first-stage thermocouple at the bottom of the smoldering reaction cylinder reaches the ignition temperature, the blower of the air supply unit is started to transport air to the wind chamber cover of the smoldering reaction chamber equipped with an inert porous medium; when the temperature of the first-stage thermocouple reaches the peak temperature, the bottom heating device is turned off to start self-sustaining smoldering. In the smoldering reaction unit, the peak temperature is maintained at 400-850 ℃, achieving the desorption or degradation of dioxins in the fly ash pellets; at the same time, the CO in the tail gas helps to inhibit the regeneration of dioxins and reduce high-valent heavy metals; Compared with incineration, the smoldering reaction area and the exhaust gas produced have a slightly reducing atmosphere, which inhibits the regeneration of dioxins and plays a reducing / detoxifying role on high-valent and highly toxic heavy metals in fly ash; when the temperature of the final thermocouple of the reaction tube drops below 250°C, the electric turntable is started to transfer it to the unloading area. After disposal, the material is discharged to the hopper through the material conveyor. After unloading, the empty barrel enters the loading area to continue loading, and the reaction process is cyclically carried out; the exhaust gas generated by the smoldering process is collected and uniformly transported through the exhaust hood of the smoldering reaction chamber connected to the exhaust gas treatment system.

2. A self-sustaining smoldering device for treating dioxins in fly ash from waste incineration according to claim 1, characterized in that: The fly ash pellets are prepared by classifying fly ash particles according to their particle sizes into pellets of 3-10 mm, and the proportion of biomass waste added is regulated according to the type and calorific value of the biomass used and the required smoldering self-sustaining conditions.

3. A self-sustaining smoldering device for treating dioxins in fly ash from waste incineration according to claim 1, characterized in that: In the smoldering reaction unit, the smoldering reaction temperature of the material is monitored in real time by a thermocouple, and the smoldering self-sustaining is ensured by regulating the material loading and unloading and ignition process or timely starting the resistance heating ignition device.

4. A self-sustaining smoldering device for treating dioxins in fly ash from waste incineration according to claim 1, characterized in that: The smoldering reaction unit comprises a smoldering reaction chamber wind chamber cover. When the thermocouple at the bottom end of the smoldering reaction tube reaches the ignition temperature, air is transported to the smoldering reaction chamber wind chamber cover. The wind chamber cover is equipped with an inert porous medium to support the material in the reaction tube and to uniformly flow the wind chamber air.

5. A method for treating dioxins in waste incineration fly ash by self-sustaining smoldering based on the device according to any one of claims 1 to 4, characterized in that: The specific steps of this method are: (1) According to the smoldering self-sustaining conditions and the relationship between fly ash particle size and dioxin content, the washed fly ash particles are prepared into fly ash pellets and 5-10% CaO is added in the preparation of fly ash pellets with a particle size less than 20 μm; Regulate the mixing ratio of fly ash pellets and biomass waste; (2) Regulate the loading and unloading and ignition process of the smoldering reaction. The fly ash pellets, as porous media in the smoldering reaction, not only provide the required activation reaction surface for the smoldering of biomass waste, but also store the heat generated by the smoldering and ignite the downstream materials, thus achieving self-sustaining smoldering treatment; (3) The peak temperature reaches 400-850 ℃, which can ensure the desorption or degradation of dioxins in fly ash. At the same time, the slightly hypoxic state in the smoldering reaction zone and the reducing atmosphere in the tail gas inhibit the regeneration of dioxins and reduce the high-valent toxic heavy metals in the fly ash.

Images