A method for synergistic thermal treatment of household garbage incineration fly ash and deacidification tower scattered ash

Abstract

This invention relates to a method for the synergistic thermal treatment of fly ash generated during municipal solid waste incineration and ash from the desulfurization tower generated by the flue gas purification system. The method includes the following steps: Step S1, drying and crushing the ash from the desulfurization tower; Step S2, mixing the ash from the desulfurization tower with the incineration fly ash; Step S3, pyrolysis: feeding the mixture into a pyrolysis furnace and carrying out a pyrolysis reaction within a temperature range of 200°C to 550°C. The pyrolysis process is divided into three stages: low-temperature drying preheating, high-temperature pyrolysis detoxification, and medium-temperature re-detoxification. During this process, nitrogen gas is continuously introduced to provide an oxygen-deficient environment, and pyrolysis gas is continuously discharged; Step S4, cooling and washing: cooling and washing the ash after pyrolysis to obtain fly ash and chloride salts. This invention synergistically treats municipal solid waste incineration fly ash and ash from the desulfurization tower, improving treatment efficiency while saving equipment investment. The ash after pyrolysis has extremely low dioxin content, creating favorable conditions for subsequent resource utilization.

Description

Technical Field

[0001] This invention relates to the field of solid waste thermal treatment and resource utilization technology, specifically to a method for synergistic thermal treatment of fly ash generated during municipal solid waste incineration and ash from the deacidification tower generated by the flue gas purification system, in order to achieve efficient removal of dioxins. Background Technology

[0002] In thermal treatment processes such as municipal solid waste incineration and pyrolysis, a deacidification step is often included to remove acidic gases from the flue gas. This results in the simultaneous generation of two types of ash with different properties in the same production facility: one is fly ash collected by devices such as bag filters, which is powdery, lightweight, fine-grained, and has a low moisture content; the other is loose ash from the deacidification tower obtained by cleaning the inner wall of the deacidification tower, which is lumpy or muddy, hard in texture or highly viscous, and extremely hygroscopic.

[0003] Currently, the industry generally adopts separate collection, treatment or disposal methods for these two types of ash, resulting in the following problems with existing technologies: (1) High treatment cost: separate treatment lines need to be built or operated for the two types of ash, resulting in high equipment investment and operating energy consumption. (2) Lack of synergistic utilization of resources: the physicochemical properties (such as dryness, wetness, particle size, composition) of the two types of ash have significant differences and complementarity, but existing technologies have failed to effectively utilize this complementarity. (3) Limited treatment effect: when fly ash is treated alone, its high chlorine content affects subsequent utilization; when blocky and sticky desulfurization tower ash is thermally treated alone, there are problems such as material layer caking, uneven heat and mass transfer, and incomplete dioxin degradation, which makes it difficult for the dioxin toxicity equivalent and soluble chlorine content of the final solid residue to stably meet strict environmental protection standards.

[0004] On the other hand, utilizing the co-processing of two types of waste to achieve waste-to-waste treatment is becoming a problem-solving approach. Chinese patent document CN109226175A discloses a co-processing technology for waste acid in the resource-based refining of municipal solid waste incineration fly ash. Large amounts of waste acid are generated in industries such as chemical, dye, petroleum, and pharmaceuticals. This application utilizes a large amount of waste acid to dissolve fly ash, and through multiple rinsing, dioxins, heavy metals, and salts in the fly ash can be dissolved into the filtrate. The filtrate is then treated to reduce the content of dioxins, heavy metals, and salts, while simultaneously separating sodium chloride and potassium chloride salts, achieving comprehensive resource utilization of waste acid and fly ash. Chinese patent document CN1134581275A discloses a method for the co-processing of municipal solid waste incineration fly ash and pyrite tailings. This method involves mixing pyrite tailings sand with fly ash to form a slurry, and then placing the slurry in a reactor to sequentially pass through a hydrothermal reaction stage, a transition stage, and a supercritical oxidation reaction stage. Ferrous ions in pyrite tailings can generate magnetite during hydrothermal reactions, and magnetite can catalyze the oxidation of dioxins in the presence of ozone. Chinese patent document CN117164257A also discloses a method for co-treating solid waste and fly ash from waste incineration. This method involves compounding fly ash from waste incineration with alkaline solid waste, utilizing the alkaline compounds in the alkaline solid waste as a dechlorination active medium to inhibit the secondary synthesis reaction of dioxins during fly ash pyrolysis. After low-temperature pyrolysis to degrade dioxins in the fly ash, the resulting primary residue is washed with water to remove chloride salts, yielding secondary residue. This secondary residue is then pretreated and compounded with one or more bulk solid wastes, and further processed by adjusting the calcium-silicon ratio for high-value utilization in building materials. Summary of the Invention

[0005] This invention aims to solve the technical problems of high cost and lack of resource synergy caused by separate treatment of incineration fly ash and desulfurization tower ash in the prior art. By co-processing two ashes with complementary physical properties in a specific ratio and process, the dioxin removal efficiency is improved while co-processing.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows: A method for the synergistic thermal treatment of fly ash from municipal solid waste incineration and ash from a desulfurization tower includes the following steps: Step S1, Drying and crushing of loose ash from the deacidification tower: The loose ash from the deacidification tower is dried to control its moisture content between 15% and 30%, and then mechanically crushed. Step S2, Mixing of desulfurization tower ash and incineration fly ash: Mix the crushed desulfurization tower ash and municipal solid waste incineration fly ash at a mass ratio of 1:1-3, and stir to ensure that the two are evenly mixed. Step S3, thermal decomposition: The mixture is fed into a pyrolysis furnace and thermal decomposition reaction is carried out in the temperature range of 200°C to 550°C. During this process, nitrogen is continuously introduced to provide an oxygen-deficient environment, and pyrolysis gas is continuously discharged. Step S4, Cooling and washing: The ash after thermal pyrolysis is cooled and washed with water to obtain fly ash and chloride salts.

[0007] The inventive concept of this invention lies in utilizing the complementary physical properties and chemical composition of powdered, low-moisture dry fly ash and high-viscosity, calcium-based desulfurization tower ash. Through synergistic optimization of steps such as crushing, mixing, drying, and thermal decomposition, a reaction system with good permeability and uniform heat transfer is constructed. Simultaneously, the abundant calcium-based substances in the desulfurization tower ash capture the chlorine released during the thermal decomposition of fly ash, generating stable chlorides and fixing the chlorine in the residue, which is beneficial for inhibiting the low-temperature resynthesis of dioxins. Furthermore, the residual carbon or activated carbon entrained in the desulfurization tower ash can catalyze the hydrodechlorination reaction of dioxins, reducing the decomposition activation energy and enabling deep degradation under relatively mild conditions, thereby achieving a synergistic effect of "1+1>2".

[0008] As a further improvement, in step S1, the loose ash from the deacidification tower is crushed to a particle size of less than 20mm. The crushed loose ash from the deacidification tower is conducive to being mixed evenly with the incineration fly ash, increasing the permeability of the material.

[0009] As a further improvement, in step S3, the pyrolysis process is divided into three stages: low-temperature drying and preheating, high-temperature pyrolysis and detoxification, and medium-temperature re-detoxification. In the low-temperature drying and preheating stage, the mixture is dried and preheated at 200-250℃ for 10-30 minutes; in the high-temperature pyrolysis and detoxification stage, the mixture is pyrolyzed at 450-550℃ for 10-30 minutes; and in the medium-temperature re-detoxification stage, the mixture is pyrolyzed at 400-450℃ for 10-30 minutes. Unlike the traditional gradient heating method where the temperature increases from low to high, this application moves the high-temperature stage to the middle position. 250-400℃ is a sensitive temperature range for dioxin resynthesis, meaning that the removal efficiency of dioxins is relatively low within this temperature range. In this application, the material directly enters the high-temperature range from the drying temperature, shortening the material's heating time. This means the material has a shorter residence time within the sensitive temperature range for dioxin resynthesis, which helps to improve the removal efficiency of dioxins. After the high-temperature stage, most of the dioxins are decomposed into CO2, H2O, and small-molecule hydrocarbons, which are then discharged with the pyrolysis gases. The remaining portion continues to decompose at a temperature not lower than 400°C. Secondly, the relatively low temperature of the third stage also facilitates the cooling of the ash after pyrolysis, reducing the amount of cooling medium required.

[0010] As a further improvement, the mixture in the low-temperature drying preheating stage is dried at 250℃ for 20 minutes, the mixture in the high-temperature pyrolysis detoxification stage is pyrolyzed at 500℃ for 20 minutes, and the mixture in the medium-temperature re-detoxification stage is pyrolyzed at 400℃ for 20 minutes. Tests conducted in the laboratory using these heat treatment parameters yielded satisfactory results.

[0011] As a further improvement, the pyrolysis furnace adopts a two-layer spiral furnace, which divides the total length of the spiral furnace into three equal sections. Each section is electrically heated to precisely control the heat treatment temperature of that section.

[0012] As a further improvement, the pyrolysis gas generated during the pyrolysis process is exited from a single pyrolysis gas outlet located in the high-temperature pyrolysis detoxification section. This means that the pyrolysis gas generated in the intermediate-temperature re-detoxification stage needs to be heated in the high-temperature pyrolysis detoxification section before being exited, resulting in a relatively low probability of dioxin resynthesis from the pyrolysis gas generated in the intermediate-temperature re-detoxification stage. In contrast, in the traditional gradient heating mode, the pyrolysis gas generated in the highest temperature stage needs to flow through the intermediate-temperature section before exiting the pyrolysis furnace, leading to a relatively high probability of dioxin resynthesis in the intermediate-temperature section.

[0013] As a further improvement, in step S4, the ash after thermal decomposition is rapidly cooled to prevent the resynthesis of dioxins.

[0014] In summary, this invention co-processes fly ash from municipal solid waste incineration with loose ash from desulfurization towers, which improves processing efficiency while saving equipment investment. The ash after pyrolysis has extremely low dioxin content, creating favorable conditions for subsequent resource utilization. Attached Figure Description

[0015] Figure 1 This is a flow chart of the co-heat treatment process of incineration fly ash and deacidification tower ash of the present invention. Figure 2 This is a schematic diagram of the pyrolysis furnace of the present invention.

[0016] In the diagram: 10, feed inlet; 20, discharge outlet; 30, pyrolysis gas outlet. Detailed Implementation Example 1

[0017] 1. Raw material preparation Fly ash from municipal solid waste incineration and ash from the deacidification tower were obtained from a municipal solid waste incineration plant in Ningbo. The fly ash was collected in a baghouse dust collector. To adsorb dioxins and heavy metals from the flue gas, an activated carbon injection point was installed before the baghouse dust collector. The fly ash collected in the baghouse dust collector contained activated carbon and had the following properties: powdery, with a moisture content of <1%. The ash from the deacidification tower was collected as lumpy ash cleaned from the deacidification tower. Its properties were as follows: partially lumpy, partially muddy, with a viscosity of 3000~4000 mPa·s and a moisture content of approximately 35%. Because calcium hydroxide slurry was injected into the deacidification tower to neutralize acidic gases, the ash from the deacidification tower had a certain calcium content (16~23%).

[0018] 2. Synergistic heat treatment The synergistic heat treatment experiment was conducted at the Zhejiang Provincial Key Laboratory of Pyrolysis Disposal Technology and Intelligent Equipment for Industrial Solid Waste at Huzhou University. The specific treatment process is as follows: Figure 1As shown.

[0019] Step S1: Drying and Crushing of Deacidification Tower Ash: The deacidification tower ash with a moisture content of approximately 35% is dried to control the moisture content between 15% and 25%. Then, the ash is fed into a twin-shaft shear crusher for coarse crushing, controlling the output particle size to be less than 15mm.

[0020] Step S2, Mixing the loose ash from the deacidification tower with the fly ash from the incineration: Add the crushed loose ash from the deacidification tower and the fly ash from the municipal solid waste incineration into a double spiral mixer at a mass ratio of 1:1, and mix for 15 minutes until the color and texture of the materials are basically uniform when observed by the naked eye.

[0021] Step S3, pyrolysis: The mixture is fed into a pyrolysis furnace, such as... Figure 2 As shown, the pyrolysis furnace adopts a two-layer spiral furnace, with its total length divided into three sections: a low-temperature drying and preheating section, a high-temperature pyrolysis and detoxification section, and a medium-temperature re-detoxification section. The high-temperature pyrolysis and detoxification section spans both layers. The mixture is fed into the pyrolysis furnace through inlet 10. It undergoes drying and preheating at 250°C for 20 minutes in the low-temperature drying and preheating section, pyrolysis at 500°C for 20 minutes in the high-temperature pyrolysis and detoxification section, and finally pyrolysis at 400°C for 20 minutes in the medium-temperature re-detoxification section. The pyrolyzed mixture is then discharged from the pyrolysis furnace through outlet 20. The low-temperature drying and preheating section, the high-temperature pyrolysis and detoxification section, and the medium-temperature re-detoxification section all utilize electric heating to precisely control the heat treatment temperature of each section. Nitrogen gas is continuously introduced at a rate of 1–2 L / min to provide an oxygen-deficient environment. The nitrogen pipeline configuration is based on existing technology and does not... Figure 2 The pyrolysis gas is continuously discharged from pyrolysis gas outlet 30, which is located in the high-temperature pyrolysis detoxification section. The pyrolysis gas generated in the intermediate-temperature re-detoxification section needs to pass through the high-temperature pyrolysis detoxification section before being discharged from the pyrolysis furnace. Therefore, the probability of the gas generated in the intermediate-temperature re-detoxification section resynthesizing dioxins is low. After high-temperature dust removal, the pyrolysis gas enters the indirect condenser for cooling. The indirect condenser recovers water vapor and ammonia salt solution from the pyrolysis gas. The indirect condenser adopts a shell-and-tube indirect heat exchange form. The cooled pyrolysis gas then enters the activated carbon box for dioxin and heavy metal adsorption treatment. The treated waste gas is finally discharged after high-temperature combustion.

[0022] Step S4, Cooling and Washing: The ash from thermal pyrolysis is rapidly cooled to below 200°C to prevent the resynthesis of dioxins. A post-washing process is then performed; this is an existing technique and can be multi-stage, ultimately yielding fly ash and chloride salts.

[0023] 3. Results Detection and Discussion The ash from the uniformly mixed sample in step S2 and the ash from the pyrolysis sample in step S3 were taken and their dioxin toxicity equivalents were determined using high-resolution gas chromatography-mass spectrometry (HRGC / HRMS). The values ​​obtained were 260 ng TEQ / kg and 5 ng TEQ / kg, respectively, with a removal rate of 98.1%.

[0024] This embodiment demonstrates that by co-treating municipal solid waste incineration fly ash and desulfurization tower ash, and by combining these with improvements in the heat treatment process, two ash residues with vastly different properties can be successfully transformed into solid residues with extremely low environmental risk, thus verifying the effectiveness of the co-treatment scheme. Example 2

[0025] Example 2 investigated the effect of the mixing ratio of desulfurization tower ash to incineration fly ash on dioxin treatment efficiency. Example 2 was conducted in two trials, with mixing ratios of 1:2 and 1:3 for both trials. Other parameters were the same as in Example 1. The product detection results were as follows: dioxin toxicity equivalents were 22 ng TEQ / kg and 41 ng TEQ / kg, respectively. This indicates that the dioxin removal efficiency increases with the increase of the content of desulfurization tower ash. Under the above pyrolysis conditions, a mixing ratio of 1:3 for desulfurization tower ash and incineration fly ash can achieve an environmental standard of <50 ng TEQ / kg.

[0026] Comparative Example 1 Comparative Example 1 primarily verifies the effect of swapping the heating temperatures of the second and third stages on the dioxin treatment efficiency. Other experimental parameters were the same as in Example 1. The product detection results are as follows: the dioxin toxicity equivalent was 8.1 ng TEQ / kg. Although the results are not significantly different from those of the examples, the lower discharge temperature compared to Example 1 helps to save on the consumption of subsequent condensing media.

[0027] Comparative Example 2 Comparative Example 2 directly replaced the mixed materials with incinerator fly ash and introduced it into a pyrolysis furnace for pyrolysis. Other experimental parameters were the same as in Example 1. The product detection results are as follows: the dioxin toxicity equivalent was 47 ng TEQ / kg. It is evident that the mixed pyrolysis of incinerator fly ash and desulfurization tower ash has a significant advantage in dioxin removal.

Claims

1. A method for the synergistic thermal treatment of fly ash from municipal solid waste incineration and ash from desulfurization towers, characterized in that, Includes the following steps: Step S1, Drying and crushing of loose ash from the deacidification tower: The loose ash from the deacidification tower is dried to control its moisture content between 15% and 30%, and then mechanically crushed. Step S2, Mixing of desulfurization tower ash and incineration fly ash: Mix the crushed desulfurization tower ash and municipal solid waste incineration fly ash at a mass ratio of 1:1-3, and stir to ensure that the two are evenly mixed. Step S3, thermal decomposition: The mixture is fed into a pyrolysis furnace and thermal decomposition reaction is carried out in the temperature range of 200°C to 550°C. During this process, nitrogen is continuously introduced to provide an oxygen-deficient environment, and pyrolysis gas is continuously discharged. Step S4, Cooling and washing: The ash after thermal pyrolysis is cooled and washed with water to obtain fly ash and chloride salts.

2. The method for synergistic thermal treatment of fly ash from municipal solid waste incineration and ash from desulfurization towers as described in claim 1, characterized in that: In step S1, the loose ash from the deacidification tower is crushed to a particle size of less than 20 mm.

3. The method for synergistic thermal treatment of fly ash from municipal solid waste incineration and ash from desulfurization towers as described in claim 1, characterized in that: In step S3, the pyrolysis process is divided into three stages: low-temperature drying and preheating, high-temperature pyrolysis and detoxification, and medium-temperature re-detoxification. In the low-temperature drying and preheating stage, the mixture is dried and preheated at 200-250℃ for 10-30 minutes. In the high-temperature pyrolysis and detoxification stage, the mixture is pyrolyzed at 450-550℃ for 10-30 minutes. In the medium-temperature re-detoxification stage, the mixture is pyrolyzed at 400-450℃ for 10-30 minutes.

4. The method for synergistic thermal treatment of fly ash from municipal solid waste incineration and ash from deacidification towers as described in claim 3, characterized in that: The mixture in the low-temperature drying and preheating stage is dried at 250°C for 20 minutes, the mixture in the high-temperature pyrolysis and detoxification stage is pyrolyzed at 500°C for 20 minutes, and the mixture in the medium-temperature re-detoxification stage is pyrolyzed at 400°C for 20 minutes.

5. The method for synergistic thermal treatment of fly ash from municipal solid waste incineration and ash from desulfurization towers as described in claim 3, characterized in that: The pyrolysis furnace is a two-layer spiral furnace, which divides the total length of the spiral furnace into three equal sections. Each section is heated by electricity to precisely control the heat treatment temperature of that section.

6. The method for synergistic thermal treatment of fly ash from municipal solid waste incineration and ash from desulfurization towers as described in claim 3, characterized in that: The pyrolysis gas generated during the pyrolysis process is discharged from the same pyrolysis gas outlet, which is located in the high-temperature pyrolysis detoxification section. This means that the pyrolysis gas generated in the intermediate-temperature re-detoxification stage needs to be heated in the high-temperature pyrolysis detoxification section before being discharged.

7. The method for synergistic thermal treatment of fly ash from municipal solid waste incineration and ash from desulfurization towers as described in claim 1, characterized in that: In step S4, the ash after thermal decomposition is rapidly cooled to prevent the resynthesis of dioxins.

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