A dioxin low-temperature pyrolysis system

Abstract

The utility model discloses a dioxin low temperature pyrolysis system, including the fly ash pretreatment unit, primary pyrolysis reactor, gas -solid separator, two -stage catalytic reactor, quench tower, alkali washing tower, adsorption tower and gas circulation unit that connect gradually. The system realizes fly ash oxygen -free pyrolysis through primary pyrolysis reactor, and the bottom of gas -solid separator is equipped with fly ash backflow pipe, and two -stage catalytic reactor is loaded with catalytic layer and is equipped with electric heat -jacket, and gas circulation unit constitutes closed -circuit circulating gas path. The utility model realizes the efficient degradation and energy comprehensive utilization of dioxin, has the advantages of high processing efficiency, low operating cost.

Description

Technical Field

[0001] This utility model relates to the field of dioxin treatment technology, specifically to a dioxin low-temperature pyrolysis system. Background Technology

[0002] Municipal solid waste incineration fly ash, as hazardous waste containing high concentrations of dioxins and heavy metals, has become a pressing environmental issue requiring effective disposal. Low-temperature pyrolysis of fly ash for dioxin removal has attracted widespread attention due to its advantages such as low energy consumption, high processing efficiency, and adaptability to continuous large-scale processing. The key to this technology lies in achieving an oxygen-free environment during the reaction process, currently commonly achieved by continuously introducing nitrogen into the reaction system as a protective gas. However, with the expansion of fly ash treatment scale, nitrogen consumption increases dramatically, leading to high power consumption and significantly increased operating costs for nitrogen generators, thus hindering the further promotion and application of this technology.

[0003] While various fly ash pyrolysis treatment devices have been proposed, most still rely on large amounts of externally supplied nitrogen to maintain the system atmosphere, failing to effectively achieve gaseous medium circulation and comprehensive energy utilization. Although some devices possess pyrolysis, purification, and cooling functions, they lack mechanisms for recovering and reusing useful carriers in the reaction tail gas, resulting in resource waste and high energy consumption. The applicant's earlier patent application, CN117680477A, ​​provides a low-temperature fly ash pyrolysis device capable of achieving carrier gas recycling, reducing nitrogen consumption, and improving system thermal efficiency; however, it still has room for further improvement in pyrolysis efficiency and other aspects. Utility Model Content

[0004] The purpose of this utility model is to overcome at least one of the technical problems mentioned in the background art.

[0005] To achieve the above objectives, the technical solution provided by this utility model is as follows.

[0006] A dioxin low-temperature pyrolysis system includes a fly ash pretreatment unit, a primary pyrolysis reactor, a gas-solid separator, a secondary catalytic reactor, a quench tower, an alkaline washing tower, an adsorption tower, and a gas circulation unit, which are connected in sequence by pipelines and valves. The fly ash pretreatment unit includes a storage silo and a dryer. The outlet of the storage silo is connected to the feed inlet at the top of the primary pyrolysis reactor via a screw feeder.

[0007] As a preferred technical solution, the primary pyrolysis reactor is a vertical cylindrical structure, and is indirectly heated by an external electric heating furnace. The primary pyrolysis reactor is provided with a gas phase outlet at the top and a slag discharge port at the bottom. The gas phase outlet is connected to the inlet of the gas-solid separator through an insulated pipeline.

[0008] As a preferred technical solution, a bypass pipeline is provided in parallel on the connecting pipeline between the gas phase outlet of the primary pyrolysis reactor and the inlet of the gas-solid separator, and the outlet of the bypass pipeline is connected to the inlet of the secondary catalytic reactor; the bypass pipeline is connected to a make-up gas branch pipe through a three-way valve.

[0009] As a preferred technical solution, the gas-solid separator adopts a cyclone separator or a ceramic filter, and a fly ash return pipe is provided at the bottom of the gas-solid separator. The fly ash return pipe is connected back to the middle and upper part of the primary pyrolysis reactor through a discharge valve.

[0010] As a preferred technical solution, the secondary catalytic reactor is filled with a catalytic layer supported by cordierite honeycomb ceramic, and the secondary catalytic reactor is wrapped with an electric heat tracing jacket.

[0011] As a preferred technical solution, the quench tower is equipped with nozzles that spray atomized cooling water into the quench tower; the alkaline washing tower is equipped with a packing layer and is sprayed with alkaline solution by a circulating pump.

[0012] As a preferred technical solution, the top gas phase outlet of the alkaline washing tower is connected to an adsorption tower, and the adsorption tower is filled with an adsorption layer of activated carbon or zeolite.

[0013] As a preferred technical solution, the gas circulation unit includes a circulating fan and a gas heater connected in sequence, which constitute a closed-loop circulating gas path.

[0014] As a preferred technical solution, the heat medium inlet of the gas heater in the gas circulation unit is connected to the primary pyrolysis reactor; the system is also provided with a heat medium circulation pipeline, which leads part of the waste heat generated by the electric heating jacket of the secondary catalytic reactor to the jacket of the screw feeder or the dryer of the fly ash pretreatment unit.

[0015] As a preferred technical solution, both the quench tower and the alkaline washing tower are equipped with drain pipes, which are sequentially connected to a condensate collection tank and a pH adjustment tank.

[0016] The advantages and beneficial effects of this invention are as follows: By constructing a tiered reaction system of primary pyrolysis-gas-solid separation-secondary catalysis, in the primary pyrolysis stage, the organic matter in the fly ash decomposes under low-temperature and oxygen-free conditions, effectively avoiding the secondary synthesis of dioxins; after gas-solid separation, the unreacted fly ash particles entrained in the gas phase products can be returned to the reactor for further reaction, improving the utilization rate of raw materials. The separated gas phase enters the secondary reactor containing the catalyst, where a catalytic oxidation reaction occurs on the catalyst surface, which can completely degrade the incomplete decomposition products (dioxin precursors) and residual dioxin molecules generated by primary pyrolysis into CO2 and H2O, improving the final removal efficiency of the system.

[0017] The system shown in this utility model also integrates multi-stage purification units such as rapid cooling, alkaline washing, and adsorption. Through gas circulation and multi-stage waste heat recovery structure, it reduces external nitrogen consumption and overall system energy consumption, and has the advantages of thorough treatment, low operating cost, and environmental friendliness. Attached Figure Description

[0018] Figure 1 This is a layout diagram of the dioxin low-temperature pyrolysis system shown in this utility model.

[0019] Figure label: 1-Storage silo, 2-Dryer, 3-Screw feeder, 4-First-stage pyrolysis reactor, 5-Gas-solid separator, 6-Fly ash return pipe, 7-Bypass pipe, 8-Maintenance gas branch pipe, 9-Second-stage catalytic reactor, 10-Quick cooler tower, 11-Alkali washing tower, 12-Adsorption tower, 13-Circulating fan, 14-Gas heater, 15-Heat medium circulation pipe, 16-Drain pipe, 17-Condensate collection tank, 18-pH adjustment tank. Detailed Implementation

[0020] To make the above-mentioned objectives, features, and advantages of this application more apparent and understandable, the specific embodiments of this application will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the scope of this application. Furthermore, it should be noted that, for ease of description, only the parts relevant to this application are shown in the accompanying drawings, not the entire structure. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of this application.

[0021] The terms “comprising” and “having”, and any variations thereof, used in this application are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or apparatus that includes a series of steps or units is not limited to the steps or units listed, but may optionally include steps or units not listed, or may optionally include other steps or units inherent to such process, method, product, or apparatus.

[0022] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly or implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0023] Please see Figure 1In order to achieve efficient, low-temperature, and low-energy degradation of dioxins in municipal solid waste incineration fly ash, and to overcome the problems of existing technologies such as reliance on large amounts of externally supplied nitrogen, high energy consumption, and incomplete tail gas treatment, this embodiment provides a dioxin low-temperature pyrolysis system, including a fly ash pretreatment unit, a primary pyrolysis reactor 4, a gas-solid separator 5, a secondary catalytic reactor 9, a quench tower 10, an alkaline washing tower 11, an adsorption tower 12, and a gas circulation unit, which are connected in sequence through pipelines and valves; the fly ash pretreatment unit includes a storage silo 1 and a dryer 2, and its outlet is connected to the feed port at the top of the primary pyrolysis reactor 4 through a screw feeder 3.

[0024] Specifically, after the fly ash is removed from the storage silo 1 by the dryer 2, it is stably conveyed to the primary pyrolysis reactor 4 by the screw feeder 3. The screw feeder 3 can be controlled by a variable frequency motor, and the feeding speed can be adjusted according to the processing capacity to ensure uniform distribution of materials in the reactor.

[0025] To achieve low-temperature, oxygen-free decomposition of organic matter in fly ash during the primary pyrolysis stage and prevent secondary dioxin synthesis, the technical solution provided in this embodiment includes a vertical cylindrical primary pyrolysis reactor 4, indirectly heated by an external electric heater. The reactor 4 has a gas phase outlet at the top and a slag discharge port at the bottom. The gas phase outlet is connected to the inlet of a gas-solid separator 5 via an insulated pipeline. The external electric heater heats the reactor wall through radiant heat transfer, causing the internal fly ash to undergo a pyrolysis reaction at 300–400°C, effectively destroying the dioxin molecular structure and inhibiting its regeneration.

[0026] To effectively separate and reflux fly ash particles before the gaseous products enter the secondary catalytic reaction, thereby improving raw material utilization, the technical solution provided in this embodiment includes: a gas-solid separator 5 employing a cyclone separator or a ceramic filter; a fly ash reflux pipe 6 is installed at the bottom of the gas-solid separator 5, which is connected back to the upper middle part of the primary pyrolysis reactor 4 via a discharge valve. Unreacted fly ash particles carried in the gas phase are captured in the gas-solid separator 5 and returned to the reactor via the reflux pipe 6 to continue participating in the reaction, forming an internal circulation and improving the degradation rate of organic matter in the fly ash.

[0027] To achieve deep catalytic oxidation of the gaseous products generated from primary pyrolysis and thoroughly decompose residual dioxins and precursors, the technical solution provided in this embodiment includes a secondary catalytic reactor 9 internally filled with a catalytic layer supported by cordierite honeycomb ceramics; the secondary catalytic reactor 9 is externally encased in an electrically heated jacket. The catalytic layer promotes the catalytic oxidation of gaseous organic matter at 200–300°C, generating CO2 and H2O, thus achieving the complete degradation of dioxins.

[0028] Specifically, the catalyst layer can employ various transition metal oxide catalysts, including V2O5 (vanadium pentoxide), WO3 (tungsten oxide), and TiO2 (titanium dioxide).

[0029] To rapidly cool the high-temperature gas after the reaction, prevent the re-synthesis of dioxins, and neutralize and purify the acidic gas, the technical solution provided in this embodiment includes: a quench tower 10 equipped with nozzles for spraying atomized cooling water; and an alkaline scrubbing tower 11 equipped with a packing layer and sprayed with alkaline solution via a circulating pump. The quench tower 10 cools the gas from 300°C to below 80°C within 1 second, inhibiting the secondary formation of dioxins; while the alkaline scrubbing tower 11 removes acidic components from the gas through circulating alkaline solution spraying.

[0030] Specifically, the quench tower 10 uses nozzles to atomize water and mix it with compressed air to form micron-sized water droplets, increasing the heat exchange area and improving cooling efficiency. The packing material inside the alkali washing tower 11 is polypropylene Pall rings, which can enhance the gas-liquid mass transfer effect.

[0031] To achieve final purification of exhaust gas and recycling of carrier gas, thereby reducing nitrogen consumption, the technical solution provided in this embodiment includes a gas circulation unit comprising a circulating fan 13 and a gas heater 14 connected in sequence, forming a closed-loop circulation gas path connecting the outlet of the adsorption tower 12 and the carrier gas inlet at the bottom of the primary pyrolysis reactor 4. The gas purified by the adsorption tower 12 is transported by the circulating fan 13 to the gas heater 14 for preheating, and then re-enters the primary pyrolysis reactor 4 as carrier gas, forming a closed-loop circulation and reducing the amount of external nitrogen replenishment.

[0032] Specifically, the gas heater 14 adopts a shell-and-tube structure, and its heat medium inlet is connected to the flue gas emission pipeline of the external electric heating furnace of the first-stage pyrolysis reactor 4. It uses the waste heat of the flue gas to preheat the circulating gas and realize the cascade utilization of energy.

[0033] To further improve system thermal efficiency and achieve comprehensive utilization of waste heat, the technical solution provided in this embodiment includes a heat medium circulation pipeline 15. This pipeline 15 guides part of the waste heat generated by the electric heating jacket of the secondary catalytic reactor 9 to the jacket of the screw feeder 3 or the dryer 2 of the fly ash pretreatment unit. By recovering the heat tracing waste heat of the secondary catalytic reactor 9 for fly ash preheating or drying, the energy consumption of the pretreatment unit is reduced.

[0034] Specifically, the temperature of the heat transfer oil flowing in the heat medium circulation pipeline 15 is maintained between 150 and 200°C, and it exchanges heat with the jacket of the dryer 2 or the screw feeder 3 through a plate heat exchanger. This structure not only improves the overall thermal efficiency of the system, but also avoids the energy waste caused by the direct discharge of waste heat in traditional systems.

[0035] To collect and treat the wastewater generated during the quenching and alkaline washing processes, and to achieve compliant discharge of liquid waste, the technical solution provided in this embodiment includes drain pipes 16 installed at the bottom of both the quenching tower 10 and the alkaline washing tower 11. The drain pipes 16 are sequentially connected to a condensate collection tank 17 and a pH adjustment tank 18. After collection, the wastewater enters the pH adjustment tank 18 for neutralization treatment, and is then discharged or reused after meeting discharge standards.

[0036] Specifically, the pH adjustment tank 18 is equipped with a stirring device and an online pH monitor, which can automatically add acid or alkali solution according to the pH value of the influent to ensure that the pH of the effluent is stable between 6 and 9.

[0037] The working principle of this invention is as follows: After pretreatment and drying, fly ash is fed into the primary pyrolysis reactor 4 by a screw feeder 3, where it undergoes low-temperature pyrolysis under oxygen-free conditions, decomposing dioxins into small-molecule gaseous products. The pyrolysis gas carries unreacted fly ash into the gas-solid separator 5, where the fly ash particles return to the reactor via the return pipe 6 for further reaction. The gas then enters the secondary catalytic reactor 9, where it is completely oxidized into carbon dioxide and water under the action of a catalyst. The purified gas undergoes multiple stages of treatment, including rapid cooling, alkaline washing, and adsorption, to remove acidic gases and trace pollutants. Finally, it is returned to the system by a circulating fan 13 for reuse as carrier gas. Through closed-loop gas circulation, fly ash recirculation, and multi-stage waste heat recovery, the system achieves efficient dioxin degradation, comprehensive energy utilization, and effective control of operating costs, offering advantages such as thorough treatment, low energy consumption, and environmental friendliness.

[0038] The embodiments described above are merely illustrative of several implementations of this utility model, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the utility model patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this utility model, and these all fall within the protection scope of this utility model. Therefore, the protection scope of this utility model patent should be determined by the appended claims.

Claims

1. A dioxin low-temperature pyrolysis system, characterized in that, The system includes a fly ash pretreatment unit, a primary pyrolysis reactor (4), a gas-solid separator (5), a secondary catalytic reactor (9), a quench tower (10), an alkaline washing tower (11), an adsorption tower (12), and a gas circulation unit, all connected in sequence via pipelines and valves. The fly ash pretreatment unit includes a storage silo (1) and a dryer (2). The outlet of the storage silo (1) is connected to the feed inlet at the top of the primary pyrolysis reactor (4) via a screw feeder (3).

2. The dioxin low-temperature pyrolysis system according to claim 1, characterized in that, The primary pyrolysis reactor (4) is a vertical cylindrical structure and is indirectly heated by an external electric heating furnace. The primary pyrolysis reactor (4) has a gas phase outlet at the top and a slag discharge port at the bottom. The gas phase outlet is connected to the inlet of the gas-solid separator (5) through an insulated pipeline.

3. The dioxin low-temperature pyrolysis system according to claim 2, characterized in that, A bypass pipeline (7) is provided in parallel on the connecting pipeline between the gas phase outlet of the primary pyrolysis reactor (4) and the inlet of the gas-solid separator (5). The outlet of the bypass pipeline (7) is connected to the inlet of the secondary catalytic reactor (9). A three-way valve is provided on the bypass pipeline (7), and the three-way valve is connected to a gas supply branch pipe (8).

4. The dioxin low-temperature pyrolysis system according to claim 1, characterized in that, The gas-solid separator (5) is a cyclone separator or a ceramic filter; the bottom of the gas-solid separator (5) is provided with a fly ash return pipe (6), which is connected back to the upper middle part of the primary pyrolysis reactor (4) through a discharge valve.

5. A dioxin low-temperature pyrolysis system according to claim 1, characterized in that, The secondary catalytic reactor (9) is filled with a catalytic layer supported by cordierite honeycomb ceramics; the secondary catalytic reactor (9) is wrapped with an electric heat tracing jacket.

6. A dioxin low-temperature pyrolysis system according to claim 1, characterized in that, The quench tower (10) is equipped with nozzles for spraying atomized cooling water; the alkaline washing tower (11) is equipped with a packing layer and is sprayed with alkaline solution by a circulating pump.

7. A dioxin low-temperature pyrolysis system according to claim 1, characterized in that, The top gas phase outlet of the alkaline washing tower (11) is connected to the adsorption tower (12), which is filled with an adsorption layer of activated carbon or zeolite.

8. A dioxin low-temperature pyrolysis system according to claim 1, characterized in that, The gas circulation unit includes a circulating fan (13) and a gas heater (14) connected in sequence, forming a closed-loop circulating gas path between the outlet of the adsorption tower (12) and the bottom carrier gas inlet of the first-stage pyrolysis reactor (4).

9. A dioxin low-temperature pyrolysis system according to claim 8, characterized in that, The heat medium inlet of the gas heater (14) is connected to the flue gas discharge pipeline of the external electric heating furnace of the primary pyrolysis reactor (4) through a pipeline; the system is also provided with a heat medium circulation pipeline (15), which leads part of the waste heat generated by the electric heating jacket of the secondary catalytic reactor (9) to the jacket of the screw feeder (3) or the dryer (2) of the fly ash pretreatment unit.

10. A dioxin low-temperature pyrolysis system according to claim 1, characterized in that, Both the quench tower (10) and the alkaline washing tower (11) are equipped with a drain pipe (16) at the bottom, and the drain pipe (16) is connected in sequence to a condensate collection tank (17) and a pH adjustment tank (18).

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