Dioxin low-temperature pyrolysis system

Abstract

The invention discloses a dioxin low-temperature pyrolysis system which comprises a fly ash pretreatment unit, a primary pyrolysis reactor, a gas-solid separator, a secondary catalytic reactor, a quench tower, an alkaline tower, an adsorption tower and a gas circulation unit which are connected in sequence. According to the system, anaerobic pyrolysis of fly ash is realized through a first-stage pyrolysis reactor, a fly ash return pipe is arranged at the bottom of a gas-solid separator, a second-stage catalytic reactor is filled with a catalytic layer and is provided with an electric heat tracing jacket, and a gas circulation unit forms a closed circulation gas path. The method realizes efficient degradation of dioxin and comprehensive utilization of energy, and has the advantages of high treatment efficiency and low operation cost.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of dioxin treatment, in particular to a dioxin low-temperature pyrolysis system. BACKGROUND

[0002] Municipal solid waste incineration fly ash, as a hazardous waste, contains high concentrations of dioxins and heavy metals, and its harmless disposal has become a problem that needs to be solved in the environmental protection field. The fly ash low-temperature pyrolysis dioxin removal technology has attracted widespread attention due to its low energy consumption, high treatment efficiency, and suitability for continuous large-scale treatment. The key to this technology is to achieve an oxygen-free environment during the reaction process. Currently, nitrogen gas is continuously introduced into the reaction system as a protective gas. However, as the fly ash treatment scale expands, the nitrogen consumption increases dramatically, leading to high electricity consumption of the nitrogen generator unit and a significant increase in operating costs, which restricts the further promotion and application of this technology.

[0003] Although a variety of fly ash pyrolysis treatment devices have been proposed, most of them still rely on a large amount of externally supplied nitrogen to maintain the system atmosphere, and have not effectively achieved gas medium recycling and energy comprehensive utilization. Although some devices have pyrolysis, purification, and cooling functions, they lack mechanisms for recycling and reusing useful carriers in the reaction tail gas, resulting in resource waste and high energy consumption. The applicant's prior patent application document CN117680477A provides a fly ash low-temperature pyrolysis device that can achieve carrier gas recycling, reduce nitrogen consumption, and improve system thermal efficiency. However, there is still room for improvement in terms of pyrolysis efficiency and other aspects. SUMMARY

[0004] The present application aims to overcome at least one of the technical problems mentioned in the background art.

[0005] To achieve the above-mentioned purpose, the technical solutions provided by the present application are as follows.

[0006] A dioxin low-temperature pyrolysis system, comprising a fly ash pretreatment unit, a primary pyrolysis reactor, a gas-solid separator, a secondary catalytic reactor, a quench tower, an alkali washing tower, an adsorption tower, and a gas circulation unit connected in sequence through pipelines and valves; the fly ash pretreatment unit comprises a storage bin and a dryer, and the outlet of the storage bin is connected to the feed inlet at the top of the primary pyrolysis reactor through a screw feeder.

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

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

[0009] As a preferred technical scheme, the gas-solid separator adopts a cyclone separator or a ceramic filter, and a fly ash backflow pipeline is arranged at a bottom of the gas-solid separator and is connected to a middle upper portion of the primary pyrolysis reactor through a discharge valve.

[0010] As a preferred technical scheme, the secondary catalytic reactor is internally filled with a catalytic layer taking cordierite honeycomb ceramic as a carrier, and an electric heating jacket is wrapped outside the secondary catalytic reactor.

[0011] As a preferred technical scheme, a nozzle is arranged in the quenching tower, and the nozzle sprays atomized cooling water into the quenching tower; a packing layer is arranged in the caustic washing tower, and caustic liquor is sprayed through a circulating pump.

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

[0013] As a preferred technical scheme, the gas circulation unit comprises a circulating fan and a gas heater connected in sequence, and constitutes a closed loop circulating gas path.

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

[0015] As a preferred technical scheme, the quenching tower and the caustic washing tower are both provided with a liquid discharge pipeline, and the liquid discharge pipeline is sequentially and communicatively connected with a condensate collecting tank and a pH adjusting pool.

[0016] The application has the advantages and beneficial effects that: by constructing a cascade reaction system of primary pyrolysis-gas-solid separation-secondary catalysis, in the primary pyrolysis stage, the organic matters in the fly ash are decomposed under low-temperature anaerobic conditions, and the secondary synthesis of dioxin is effectively avoided; after the gas phase product is separated from the fly ash, the unreacted fly ash particles entrained in the gas phase can flow back to the reactor for continuous reaction, and the utilization rate of raw materials is improved; after the separation, the gas phase enters the secondary reactor provided with a catalyst, and catalytic oxidation reaction occurs on the surface of the catalyst, so that the incomplete decomposition products (dioxin precursors) and residual dioxin molecules generated in the primary pyrolysis are completely degraded into CO2 and H2O, and the final removal efficiency of the system is improved.

[0017] The system shown in the present application also integrates multi-stage purification units such as quenching, alkali washing and adsorption, and reduces external nitrogen consumption and system comprehensive energy consumption through gas circulation and multi-stage waste heat recovery structure, and has the advantages of complete treatment, low operation cost and environmental friendliness. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 is a layout diagram of the dioxin low-temperature pyrolysis system shown in the present application.

[0019] Reference signs: 1 - storage bin, 2 - dryer, 3 - screw feeder, 4 - first-stage pyrolysis reactor, 5 - gas-solid separator, 6 - fly ash return pipe, 7 - bypass pipeline, 8 - air supplement branch pipe, 9 - second-stage catalytic reactor, 10 - quenching tower, 11 - alkali washing tower, 12 - adsorption tower, 13 - circulating fan, 14 - gas heater, 15 - heat medium circulation pipeline, 16 - liquid discharge pipe, 17 - condensate collection tank, 18 - pH adjustment pool. DETAILED DESCRIPTION

[0020] In order to make the above-mentioned purposes, features and advantages of the present application more obvious and easy to understand, the specific embodiments of the present application will be described in detail below with reference to the drawings. It can be understood that the specific embodiments described herein are only used to explain the present application, but not to limit the present application. In addition, it should be noted that only the parts related to the present application are shown in the drawings for convenience of description, not all the structures. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0021] The terms "comprising" and "having" and any variations thereof in the present application are intended to cover non-exclusive inclusion. For example, a process, method, system, product or device comprising a series of steps or units is not limited to the listed steps or units, but optionally further comprises steps or units not listed, or optionally further comprises other steps or units inherent to these processes, methods, products or devices.

[0022] In this paper, the term "embodiment" means that the specific features, structures or characteristics described in conjunction with the embodiment can be included in at least one embodiment of the present application. The phrase appears at various places in the specification does not necessarily refer to the same embodiment, nor is it independent or alternative to other embodiments. Those skilled in the art explicitly or implicitly understand that the embodiments described herein can be combined with other embodiments.

[0023] Please refer to Figure 1, in order to realize the efficient, low temperature, low energy consumption degradation of dioxin in household garbage incineration fly ash, and overcome the problems of relying on a large number of external nitrogen supply, high energy consumption, incomplete tail gas treatment and other problems in the prior art, the embodiment provides a dioxin low-temperature pyrolysis system, which comprises a fly ash pretreatment unit, a first pyrolysis reactor 4, a gas-solid separator 5, a secondary catalytic reactor 9, a quenching tower 10, an alkali washing tower 11, an adsorption tower 12 and a gas circulation unit connected in turn through pipelines and valves; the fly ash pretreatment unit comprises a storage bin 1 and a dryer 2, and the outlet thereof is connected to the feed inlet at the top of the first pyrolysis reactor 4 through a screw feeder 3.

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

[0025] In order to realize low-temperature anaerobic decomposition of organic matter in fly ash in the first pyrolysis stage and prevent secondary synthesis of dioxin, the technical scheme provided by the embodiment comprises that the first pyrolysis reactor 4 is a vertical cylindrical structure and is indirectly heated by an external electric heating furnace; the top of the first pyrolysis reactor 4 is provided with a gas phase outlet, and the bottom is provided with a slag discharge port; the gas phase outlet is connected to the inlet of the gas-solid separator 5 through a heat preservation pipeline. The external electric heating furnace heats the reactor wall through radiation heat transfer, so that the fly ash inside the reactor occurs pyrolysis reaction under the condition of 300-400℃, effectively destroys the molecular structure of dioxin and inhibits the regeneration of dioxin.

[0026] In order to realize effective separation and reflux of fly ash particles before the gas phase product enters the secondary catalytic reaction, and improve the utilization rate of raw materials, the technical scheme provided by the embodiment comprises that the gas-solid separator 5 adopts a cyclone separator or a ceramic filter; the bottom of the gas-solid separator 5 is provided with a fly ash reflux pipe 6, and the fly ash reflux pipe 6 is connected to the middle-upper part of the first pyrolysis reactor 4 through a discharge valve. The unreacted fly ash particles carried by the gas phase are captured in the gas-solid separator 5 and then returned to the reactor through the reflux pipe 6 to continue to participate in the reaction, forming an internal circulation and improving the degradation rate of organic matter in the fly ash.

[0027] In order to realize deep catalytic oxidation of the gaseous product generated in the first pyrolysis, and completely decompose the residual dioxin and precursors, the technical scheme provided by the embodiment comprises that the secondary catalytic reactor 9 is internally filled with a catalytic layer taking cordierite honeycomb ceramic as a carrier; and the secondary catalytic reactor 9 is externally wrapped with an electric heating jacket. The catalytic layer promotes the catalytic oxidation reaction of gaseous organic matter under the condition of 200-300℃, generates CO2 and H2O, and realizes complete degradation of dioxin.

[0028] Specifically, the catalytic layer can adopt a variety of transition metal oxide catalysts including V2O5 (vanadium pentoxide), WO3 (tungsten oxide), TiO2 (titanium dioxide).

[0029] In order to quickly cool the high-temperature gas after reaction, prevent the re-synthesis of dioxin, and achieve the neutralization and purification of the acid gas, the technical scheme provided in the embodiment includes that a nozzle for spraying atomized cooling water is arranged in the quench tower 10; a packing layer is arranged in the alkali washing tower 11, and an alkali liquor is sprayed through a circulating pump. The quench tower 10 reduces the gas from 300 DEG C to below 80 DEG C within 1 second, thereby inhibiting the secondary generation of dioxin; the alkali washing tower 11 removes the acid components in the gas through the circulation and spraying of the alkali liquor.

[0030] Specifically, the quench tower 10 adopts a nozzle, atomized water is mixed with compressed air to form micron-sized water droplets, the heat exchange area is increased, and the cooling efficiency is improved. The packing in the alkali washing tower 11 is a polypropylene Pall ring, which can enhance the gas-liquid mass transfer effect.

[0031] In order to realize the final purification of the tail gas and the recycling of the carrier gas, and reduce the nitrogen consumption, the technical scheme provided in the embodiment includes that the gas circulation unit includes a circulating fan 13 and a gas heater 14 connected in sequence, and constitutes a closed loop gas circuit connected between the outlet of the adsorption tower 12 and the carrier gas inlet at the bottom of the first pyrolysis reactor 4. The gas purified through the adsorption tower 12 is delivered to the gas heater 14 by the circulating fan 13, is preheated, and then reenters the first pyrolysis reactor 4 as a carrier gas, thereby forming a closed loop circulation and reducing the amount of external nitrogen supplement.

[0032] Specifically, the gas heater 14 adopts a shell-and-tube structure, the heat medium inlet thereof is connected with the flue gas discharge pipeline of the external electric heating furnace of the first pyrolysis reactor 4, and the waste heat of the flue gas is used to preheat the circulating gas, thereby realizing the step-by-step utilization of energy.

[0033] In order to further improve the thermal efficiency of the system and realize the comprehensive utilization of waste heat, the technical scheme provided in the embodiment includes that the system further has a heat medium circulation pipeline 15, which introduces part of the waste heat generated by the electric heating jacket of the second catalytic reactor 9 to the jacket of the screw feeder 3 or the dryer 2 of the fly ash pretreatment unit. By recycling the waste heat of the heating jacket of the second catalytic reactor 9, the fly ash is preheated or dried, and the energy consumption of the pretreatment unit is reduced.

[0034] Specifically, the temperature of the heat conducting oil flowing in the heat medium circulation pipeline 15 is maintained at 150-200 DEG C, and the heat conducting oil is subjected to heat exchange 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 the traditional system.

[0035] In order to collect and treat the waste water generated in the quenching and alkali washing process, and realize the standard discharge of liquid waste, the technical scheme provided by the embodiment comprises that the bottom of the quenching tower 10 and the alkali washing tower 11 is provided with a liquid discharge pipe 16, the liquid discharge pipe 16 is sequentially communicated with a condensate collection tank 17 and a pH adjusting tank 18. After the waste water is collected, it enters the pH adjusting tank 18 for neutralization treatment, and is discharged or reused after reaching the discharge standard.

[0036] Specifically, the pH adjusting tank 18 is provided with a stirring device and an online pH monitor, and acid or alkali solution can be automatically added according to the pH value of the inlet water, so as to ensure that the outlet water pH is stable between 6-9.

[0037] The working principle of the application is that: after the fly ash is pretreated and dried, it is sent into the first pyrolysis reactor 4 by the screw feeder 3, and low-temperature pyrolysis is carried out under anaerobic conditions, so that dioxin is decomposed into small-molecule gaseous products; the pyrolysis gas carrying unreacted fly ash enters the gas-solid separator 5, the fly ash particles return to the reactor through the reflux pipe 6 for continuous reaction, and the gas enters the second catalytic reactor 9 and is completely oxidized to carbon dioxide and water under the action of the catalyst; the purified gas is subjected to multi-stage treatment such as quenching, alkali washing and adsorption, and the acidic gas and trace pollutants are removed, and finally it is sent back to the system by the circulating fan 13 as a carrier gas for repeated use. Through closed-loop gas circulation, fly ash reflux and multi-stage waste heat recovery, the system realizes efficient degradation of dioxin, comprehensive utilization of energy and effective control of operation cost, and has the advantages of complete treatment, low energy consumption and environmental friendliness.

[0038] The above-described embodiments only express several embodiments of the application, which are described in detail and in detail, but should not be understood as limiting the scope of the patent. It should be noted that for ordinary skilled in the art, without departing from the concept of the application, a number of modifications and improvements can be made, which are within the scope of protection of the application. Therefore, the protection scope of the patent of the application should be subject to the appended claims.

Claims

1. A dioxin low temperature pyrolysis system characterized by, The system comprises a fly ash pretreatment unit, a first pyrolysis reactor (4), a gas-solid separator (5), a second catalytic reactor (9), a quench tower (10), an alkali washing tower (11), an adsorption tower (12) and a gas circulation unit connected in sequence through pipelines; the fly ash pretreatment unit comprises a storage bin (1) and a dryer (2), and the outlet of the storage bin (1) is connected to the feed inlet at the top of the first pyrolysis reactor (4) through a screw feeder (3).

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

3. A dioxin low temperature pyrolysis system according to claim 2, wherein A bypass pipeline (7) is arranged in parallel between the connecting pipeline between the gas phase outlet of the first 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 second catalytic reactor (9); a three-way valve is arranged on the bypass pipeline (7), and a gas supplement branch pipeline (8) is connected to the three-way valve.

4. The dioxin low temperature pyrolysis system of claim 1, wherein, 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 backflow pipeline (6) which is connected to the middle upper part of the first pyrolysis reactor (4) through a discharge valve.

5. The dioxin low temperature pyrolysis system of claim 1, wherein, The second catalytic reactor (9) is filled with a catalytic layer with cordierite honeycomb ceramic as a carrier; the second catalytic reactor (9) is wrapped with an electric heating jacket.

6. A dioxin low temperature pyrolysis system according to claim 1, wherein A nozzle for spraying atomized cooling water is arranged in the quench tower (10); the alkali washing tower (11) is provided with a filler layer, and alkali liquor is sprayed through a circulating pump.

7. The dioxin low temperature pyrolysis system of claim 1, wherein, The top gas phase outlet of the alkali washing tower (11) is connected to the adsorption tower (12), and the adsorption tower (12) is filled with an adsorption layer of activated carbon or zeolite.

8. The dioxin low temperature pyrolysis system of claim 1, wherein, The gas circulation unit comprises a circulating fan (13) and a gas heater (14) connected in sequence, forming a closed loop gas circuit connected between the outlet of the adsorption tower (12) and the carrier gas inlet at the bottom of the first pyrolysis reactor (4).

9. A dioxin low temperature pyrolysis system according to claim 8, wherein 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 first 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 second catalytic reactor (9) to the jacket of the screw feeder (3) or the dryer (2) of the fly ash pretreatment unit.

10. The dioxin low temperature pyrolysis system of claim 1, wherein, The bottoms of the quench tower (10) and the alkali washing tower (11) are provided with drain pipes (16), and the drain pipes (16) are sequentially connected to a condensate collection tank (17) and a pH adjusting tank (18).

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