A method and system for synergistic treatment of solid waste incineration and perchlorate crystallization

Abstract

The application provides a kind of solid waste incineration and perchlorate crystallization synergistic treatment method and system, dry solid waste and filter wet material are sent into double screw stirring mixer, secondary steam generated by evaporation crystallization is introduced to carry out jacket heat exchange preheating at the same time.Mixed material after pretreatment is sent into rotary kiln to carry out primary incineration, and the flue gas at the outlet of rotary kiln enters two combustion chambers.High-temperature flue gas in two combustion chambers generates steam through waste heat boiler, and is distributed to rotary kiln insulation, evaporation crystallization heating and waste water preheating according to pressure grade.Waste water is separated into solid and liquid through precision filter, wet material is returned to mixing machine, and clarified liquid enters evaporation crystallization unit to carry out concentration crystallization.Secondary steam generated by evaporation crystallization is returned to pretreatment unit to heat mixed material.The application realizes uniform heating of evaporation crystallization, continuous operation stability and efficient salt recovery, improves waste heat and water resource utilization rate, reduces system energy consumption and operation cost, and improves disposal safety.

Description

Technical Field

[0001] This invention relates to the field of hazardous waste treatment and resource utilization technology, and in particular to a method and system for the synergistic treatment of solid waste incineration and perchlorate crystallization. Background Technology

[0002] With the development of pyrotechnics manufacturing and the defense industry, the safe disposal and resource utilization of hazardous solid waste containing nitrates, such as waste explosives and fuse residues, as well as associated wastewater containing nitrates / high salinity, has become an important engineering issue. Hazardous solid waste containing nitrates is highly sensitive, and pretreatment to reduce sensitivity and stable feed control before entering the furnace are crucial for safe production. At the same time, conventional treatment of high salinity wastewater has cost and cycle issues, while evaporation and crystallization can achieve salt recovery, but it is easily affected by scaling and other factors during operation, which increases energy consumption and maintenance costs.

[0003] Currently, incineration is the most common method used in the industry to dispose of such waste. For example, Chinese patent CN104033910A discloses an incineration device that can co-process waste explosives and organic waste liquid, relying on combustion organization within the furnace for harmless disposal. However, the safety control of this solution mainly focuses on the explosion-proof structure inside the furnace, lacking a systematic method for the synergistic desensitization and passivation of "dry solid waste - filtered wet material" before entering the furnace and for stabilizing the feed, making it difficult to reduce the feeding risks caused by fluctuations in material sensitivity from the source.

[0004] Regarding waste heat recovery, Chinese patent CN204421018U discloses a hazardous waste incineration and waste heat utilization system, which is equipped with a waste heat boiler to produce steam and uses steam in multiple branches to improve waste heat utilization efficiency. However, when the system simultaneously has multiple temperature-level heat demands such as rotary kiln insulation, evaporation crystallization drive, and wastewater preheating, it is difficult to implement the principle of "using energy according to quality" and achieve optimal overall energy efficiency if a steam cascade distribution strategy matching the temperature level is lacking.

[0005] Regarding the resource recovery of high-salt / nitrate wastewater, literature indicates that commonly used methods for wastewater containing perchlorate include adsorption, ion exchange, chemical reduction, and biological methods. However, engineering applications still face challenges in terms of economic viability and adaptability. Meanwhile, although evaporation and crystallization can achieve salt recovery, they are susceptible to scaling during operation, leading to deposits on the heating pipe walls, increased maintenance costs, and higher system energy consumption, which has become a key challenge in the treatment of high-salt wastewater.

[0006] Correspondingly, Chinese patent CN104445788A discloses an integrated process for zero-discharge treatment and reuse of high-salinity wastewater, and CN212800022U discloses a system for zero-discharge and salt-separation resource utilization of high-concentration brine. However, these systems mostly operate as relatively independent units at the wastewater end, typically relying on external heat sources. They lack unified coupling and utilization with waste heat from front-end incineration and closed-loop design for secondary steam / condensate recirculation, making it difficult to further improve the overall energy efficiency and water resource recycling level.

[0007] In summary, existing technologies generally suffer from the following problems: insufficient pre-furnace synergistic desensitization and passivation, unstable feed safety window; lack of steam cascade distribution for multi-temperature loads in waste heat utilization; weak coupling between wastewater resource recovery unit and incineration unit, insufficient reuse of secondary steam and condensate; and easy scaling during evaporation and crystallization. Summary of the Invention

[0008] The purpose of this invention is to provide a method and system for the synergistic treatment of solid waste incineration and perchlorate crystallization. The pretreatment method, employing "dry solid waste – synergistic passivation of wet material through filtration + steam preheating to reduce sensitivity," significantly reduces the sensitivity fluctuations of the feed material. Simultaneously, the waste heat from incineration is converted into steam and distributed in stages according to grade, achieving energy level matching between rotary kiln insulation, evaporation crystallization drive, and wastewater preheating. Furthermore, a closed-loop water circulation system is constructed through the recovery, purification, and reuse of secondary steam and condensate, thereby reducing overall system energy consumption and operating costs, and improving disposal safety. In the evaporation crystallization and wastewater preheating stages, the system utilizes steam in stages and temperature control design to ensure more uniform heating of the liquid within the evaporation crystallization unit, reducing the risk of localized overheating, localized dry walls, and salt crystal deposition, thus mitigating scaling tendencies during the evaporation crystallization process. Simultaneously, by controlling steam pressure, steam flow rate, liquid circulation velocity, and wastewater preheating temperature, the evaporation intensity and liquid supersaturation are adjusted, resulting in more stable crystal growth and improved system continuous operation stability and salt recovery efficiency.

[0009] To achieve the above objectives, the present invention provides a co-treatment system for solid waste incineration and perchlorate crystallization, comprising: The twin-screw mixer is used to receive dry hazardous solid waste containing nitrate and wet material returned from the filter, and to stir, crush and mix the two to obtain a mixture. The rotary kiln incinerator, secondary combustion chamber, waste heat boiler, quench tower and flue gas treatment unit are connected in sequence; the mixture is initially incinerated in the rotary kiln incinerator, and the resulting flue gas enters the secondary combustion chamber for secondary combustion. The high-temperature flue gas after secondary combustion enters the waste heat boiler for waste heat recovery and generates high-grade steam. The flue gas at the outlet of the waste heat boiler enters the quench tower for rapid cooling. The cooled flue gas then enters the flue gas treatment unit for purification and is discharged in compliance with standards. High-grade steam is introduced into the rotary kiln incinerator for heat preservation or thermal compensation; another part of the steam is de-cooled and depressurized to form medium-grade steam, which is used to heat the evaporation and crystallization unit; the residual heat of the condensate after heat exchange of medium-grade steam or the low-grade steam formed by flash evaporation is used to preheat the wastewater pool. Medium-grade steam is introduced into the evaporation and crystallization unit as a heat source to drive the filtration of the clarified liquid to evaporate and concentrate, and precipitate salt crystals containing perchlorate to obtain the salt product. Low-grade steam is introduced into the wastewater tank to preheat and keep the wastewater warm, so as to reduce the heat load of subsequent filtration and evaporation crystallization. Wastewater undergoes solid-liquid separation via a filter, with the wet material being returned to a twin-screw mixer as a co-passivation medium, while the clarified liquid enters the evaporation and crystallization unit for concentration and crystallization. The secondary steam generated by evaporation and crystallization is introduced into a twin-screw mixer to preheat the dry and wet mixture, reduce the sensitivity of the material entering the furnace, and improve the stability of the feed.

[0010] Preferably, the process condensate in the system is collected in a condensate recovery tank, purified, and reused to replenish the waste heat boiler and quench tower, thus realizing a closed-loop water resource circulation.

[0011] Preferably, the twin-screw mixer has a co-rotating or counter-rotating twin-screw structure and is equipped with a crushing section, a mixing section and a conveying section. Dry and wet materials are mixed, crushed and homogenized in the twin-screw mixer and then continuously or intermittently conveyed to the rotary kiln incinerator.

[0012] Preferably, high-grade steam, medium-grade steam, and low-grade steam are supplied in stages through a desuperheating and pressure-reducing valve group or a steam distribution manifold, and the steam supply targets correspond to rotary kiln insulation, evaporation crystallization drive, and wastewater preheating, respectively.

[0013] Preferably, the evaporation crystallization unit adopts multi-effect evaporation, forced circulation evaporation, or MVR evaporation crystallization.

[0014] Preferably, it also includes a water treatment system, which is equipped with filtration and reverse osmosis functions to purify and reuse condensate water, reducing the amount of fresh water added.

[0015] Preferably, the salt product crystallized from the evaporation crystallization unit is a salt product containing perchlorate.

[0016] A method for the co-treatment of solid waste by incineration and perchlorate crystallization includes the following steps: S1. Synergistic passivation pretreatment: Dry nitrate-containing hazardous solid waste is fed into a twin-screw mixer, while wet material from the filtration unit is returned to the twin-screw mixer for synergistic mixing, crushing, and homogenization with the dry material to obtain a mixture; auxiliary steam can be used for preheating during system startup; after the system is running stably, secondary steam generated by the evaporation and crystallization unit is introduced into the twin-screw mixer to preheat and reduce sensitivity of the mixture; S2. Staged incineration for harmlessness: The mixture is fed into a rotary kiln incinerator for primary incineration. The flue gas from the rotary kiln outlet enters the secondary combustion chamber for secondary combustion, achieving complete oxidation and decomposition of organic components and generating high-temperature flue gas. S3. Waste heat recovery and steam cascade utilization: The high-temperature flue gas is sent to a waste heat boiler for waste heat recovery to generate steam, and the steam is divided into high-grade steam, medium-grade steam and low-grade steam; the high-grade steam is introduced into a rotary kiln incinerator for heat preservation / heat compensation, the medium-grade steam is introduced into an evaporation crystallization unit as a heating source, and the low-grade steam is introduced into a wastewater pool for wastewater preheating / heat preservation; S4. Flue gas purification and emission: The flue gas from the waste heat boiler outlet is sent to the quench tower for rapid cooling, and then sent to the flue gas treatment system for purification treatment. After meeting the standards, harmless waste gas is discharged. S5. Wastewater Treatment and Salt Resource Utilization: High-salt, nitrate-containing wastewater containing perchlorate or quenched wastewater from a quench tower is sent to a wastewater tank. Low-grade steam is used to preheat and maintain the temperature of the wastewater. The preheated wastewater undergoes solid-liquid separation through a filter. The resulting wet material is returned to a twin-screw mixer, and the resulting clarified liquid enters an evaporation and crystallization unit. Medium-grade steam is used to drive the evaporation and crystallization unit to evaporate and concentrate the clarified liquid, precipitating salt crystals to obtain crude salt product. S6. Closed-loop water resource recycling: The process condensate from the entire system is collected in the condensate recovery tank, purified by the water treatment system, and then reused in the waste heat boiler and quench tower to achieve closed-loop water resource recycling.

[0017] Therefore, the present invention employs the above-mentioned synergistic treatment method and system for solid waste incineration and perchlorate crystallization, and the technical effects are as follows: Safety Enhancement: By synergistic passivation of dry solid waste and filtered wet material in a twin-screw mixer, and the addition of steam preheating to reduce sensitivity, the sensitivity of the material entering the furnace is reduced and fluctuations are suppressed, thereby improving the safety of the feeding and pretreatment processes.

[0018] Energy efficiency improvement: By utilizing waste heat boilers to generate steam and distributing it according to grade levels, energy level matching is achieved across multiple heat-using ends, such as rotary kiln insulation, evaporation crystallization drive, and wastewater preheating. This improves the overall efficiency of waste heat utilization and reduces the overall energy consumption of the system. Simultaneously, it helps alleviate scaling problems during the evaporation crystallization process and improves the stability of continuous operation.

[0019] Resource recovery and closed-loop circulation: the wet filter material is returned to participate in passivation, the salt produced by evaporation and crystallization is utilized as a resource, and the steam condensate is purified and reused in the waste heat boiler and quench tower, thereby improving the system's water resource recycling rate and reducing the need for external discharge and fresh water replenishment.

[0020] Enhanced system coupling: Through the coordinated construction of energy cascade utilization and closed-loop water resource circulation, the system-level integrated utilization of thermal energy and water resources is realized. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of a synergistic treatment system for solid waste incineration and perchlorate crystallization according to the present invention. Detailed Implementation

[0022] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0023] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning as understood by one of ordinary skill in the art to which this invention pertains.

[0024] Example 1 like Figure 1 As shown, in the incineration subsystem, dry hazardous solid waste containing nitrates enters a twin-screw mixer, where it is co-mixed, pulverized, and homogenized with the filtered wet material from the crystallization subsystem. The twin-screw mixer jacket introduces secondary steam generated by the crystallization subsystem for heat exchange, utilizing the latent heat of the steam to preheat and reduce sensitivity of the mixture. The pretreated mixture enters a rotary kiln incinerator for primary incineration. The resulting flue gas undergoes further complete oxidation and decomposition in the secondary combustion chamber before entering a waste heat boiler for waste heat recovery. High-grade steam generated by the waste heat boiler is preferentially led to the rotary kiln incinerator via a steam distribution pipeline for insulation or thermal compensation. The flue gas exiting the waste heat boiler is cooled by a quench tower before being sent to the flue gas treatment system for purification and emission.

[0025] In the perchlorate crystallization subsystem, the high-salt, nitrate-containing wastewater in the wastewater tank undergoes solid-liquid separation via a filter. The separated wet material is returned to the twin-screw mixer in the incineration subsystem via a return pipeline as a co-passivation medium; the separated clear liquid enters the evaporation crystallization unit. Medium-grade steam from the incineration subsystem's heat exchange utilization is introduced into the evaporation crystallization unit as a heating source, driving the clear liquid to evaporate, concentrate, and precipitate perchlorate-containing salt products. Through wastewater preheating and steam cascade utilization, the evaporation crystallization process achieves uniform heating, helping to alleviate scaling, extend operating cycles, and improve salt recovery efficiency. Low-grade steam or its condensate from the cascade utilization provides preheating heat to the wastewater tank via indirect heat exchange, reducing the heat load on subsequent processes. Wastewater preheating further improves scaling conditions and enhances the continuous operational stability of the evaporation crystallization unit. The secondary steam generated by the evaporation crystallization unit is introduced into the twin-screw mixer for heat exchange and condensation, and then collected with condensate from other processes within the system in a condensate recovery tank. The condensate is purified by the water treatment system and then reused as purified makeup water for the waste heat boiler and quench tower, thus creating a closed-loop water resource circulation system.

[0026] This embodiment describes the operation process of a co-treatment system for solid waste incineration and perchlorate crystallization. The specific parameters and steps are as follows: (1) First, the dry solid waste containing nitrate to be treated is fed into a twin-screw mixer, while the wet material separated by the filter is introduced at the same time. Secondary saturated steam with an absolute pressure of 0.12–0.32 MPa and a temperature of 110℃–135℃ is introduced into the jacket of the mixer for preheating. Through the synergistic mixing of dry and wet materials, the sensitivity of the mixture is reduced to the safe range for furnace entry, and the latent heat of steam is used to preheat the material to 60℃–80℃.

[0027] (2) The passivated mixture is continuously fed into the rotary kiln incinerator for primary combustion. The flue gas generated by combustion enters the secondary combustion chamber. By adjusting the burner power, the temperature of the high-temperature section of the secondary combustion chamber (based on the 5-minute average value of the temperature monitoring points) is maintained between 1100℃ and 1200℃, and the flue gas residence time is not less than 2.0 s. The high-temperature flue gas then enters the waste heat boiler, where heat exchange generates high-pressure saturated steam with a pressure of 0.6–1.0 MPa. The flue gas outlet temperature is controlled at 500℃ ± 20℃. The flue gas from the waste heat boiler outlet enters the quench tower for rapid cooling to ≤200℃ before entering the flue gas treatment system for purification and emission to meet standards.

[0028] (3) Steam cascade distribution and utilization: High-level utilization: The 0.6–1.0MPa high-pressure steam produced by the waste heat boiler is introduced to the steam jacket of the rotary kiln incinerator to maintain the temperature of the outer wall of the rotary kiln and reduce heat loss. Mid-level utilization: The steam obtained after high-level steam use is introduced into the heating chamber of the evaporation and crystallization unit to drive the wastewater to undergo multi-effect evaporation. At this time, the steam pressure is maintained at 0.2–0.4 MPa. Low-level utilization: The low-grade steam and / or the residual heat of its condensate obtained after the intermediate-level steam use are introduced to the wastewater tank to preheat the wastewater in the tank to 40℃–55℃.

[0029] The preheated wastewater in the wastewater tank is treated by a precision filter, and the filtered wet material is returned to the twin-screw mixer for passivation. The clarified liquid is heated, evaporated, concentrated, and crystallized in the evaporation and crystallization unit to precipitate salts containing perchlorate. The crystallized salt is dehydrated by centrifugation / filtration to produce crude salt byproducts with a moisture content of ≤5%; the salt recovery rate is over 95% based on dissolved inorganic salts in the wastewater. The secondary steam generated during the evaporation process is returned to the twin-screw mixer as preheating power.

[0030] (4) All process condensate in the system is collected in a condensate recovery tank, treated by a water treatment and purification device for reuse. The water treatment and purification device includes an RO reverse osmosis device, and preferably also includes a deep desalination unit such as ion exchange / electrodeionization and a deoxygenation device. The purified water obtained is used as makeup water for the waste heat boiler and makeup water for the quench tower. The condensate reuse rate of the entire system reaches more than 85%, realizing the water balance within the system and zero discharge of wastewater.

[0031] Therefore, the present invention adopts the above-mentioned method and system for the synergistic treatment of solid waste incineration and perchlorate crystallization. Through synergistic passivation, steam cascade utilization and secondary steam reflux, it achieves uniform heating of evaporation crystallization, stable continuous operation and efficient salt recovery, while improving the utilization rate of waste heat and water resources, reducing system energy consumption and operating costs, and improving disposal safety.

[0032] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A co-treatment system for solid waste incineration and perchlorate crystallization, characterized in that, include: The twin-screw mixer is used to receive dry materials of hazardous solid waste containing nitrate and wet materials returned from the filter, and to stir, crush and mix the two to obtain a mixture. The rotary kiln incinerator, secondary combustion chamber, waste heat boiler, quench tower and flue gas treatment unit are connected in sequence; the mixture is initially incinerated in the rotary kiln incinerator, and the resulting flue gas enters the secondary combustion chamber for secondary combustion. The high-temperature flue gas after secondary combustion enters the waste heat boiler for waste heat recovery and generates high-grade steam. The flue gas at the outlet of the waste heat boiler enters the quench tower for rapid cooling. The cooled flue gas then enters the flue gas treatment unit for purification and is discharged in compliance with standards. High-grade steam is introduced into the rotary kiln incinerator for heat preservation or thermal compensation; another part of the steam is de-cooled and depressurized to form medium-grade steam, which is used to heat the evaporation and crystallization unit; the residual heat of the condensate after heat exchange of medium-grade steam or the low-grade steam formed by flash evaporation is used to preheat the wastewater pool. Medium-grade steam is introduced into the evaporation and crystallization unit as a heat source to drive the filtration of the clarified liquid to evaporate and concentrate, and precipitate salt crystals containing perchlorate to obtain the salt product. Low-grade steam is introduced into the wastewater tank to preheat and keep the wastewater warm, so as to reduce the heat load of subsequent filtration and evaporation crystallization. Wastewater undergoes solid-liquid separation via a filter, with the wet material being returned to a twin-screw mixer as a co-passivation medium, while the clarified liquid enters the evaporation and crystallization unit for concentration and crystallization. The secondary steam generated by evaporation and crystallization is introduced into a twin-screw mixer to preheat the dry and wet mixture, reduce the sensitivity of the material entering the furnace, and improve the stability of the feed.

2. The co-treatment system for solid waste incineration and perchlorate crystallization according to claim 1, characterized in that, The process condensate in the system is collected in a condensate recovery tank, purified, and reused to replenish the waste heat boiler and quench tower, thus realizing a closed-loop water resource cycle.

3. The co-treatment system for solid waste incineration and perchlorate crystallization according to claim 1, characterized in that, The twin-screw mixer has a co-rotating or counter-rotating twin-screw structure and is equipped with a crushing section, a mixing section and a conveying section. Dry and wet materials are mixed, crushed and homogenized in the twin-screw mixer and then continuously or intermittently conveyed to the rotary kiln incinerator.

4. The co-treatment system for solid waste incineration and perchlorate crystallization according to claim 1, characterized in that, High-grade steam, medium-grade steam, and low-grade steam are supplied in stages through desuperheating and pressure-reducing valve groups or steam distribution drums, and the steam supply targets correspond to rotary kiln insulation, evaporation crystallization drive, and wastewater preheating, respectively.

5. The co-treatment system for solid waste incineration and perchlorate crystallization according to claim 1, characterized in that, The evaporation crystallization unit adopts multi-effect evaporation, forced circulation evaporation, or MVR evaporation crystallization.

6. The co-treatment system for solid waste incineration and perchlorate crystallization according to claim 1, characterized in that, It also includes a water treatment system, which is equipped with filtration and reverse osmosis functions to purify and reuse condensate water, reducing the amount of fresh water added.

7. The co-treatment system for solid waste incineration and perchlorate crystallization according to claim 1, characterized in that, The salt product crystallized from the evaporation crystallization unit is a salt product containing perchlorate.

8. A method for the co-treatment of solid waste incineration and perchlorate crystallization, characterized in that, The system described in claim 1 is used to perform the following steps: S1. Synergistic passivation pretreatment: Dry nitrate-containing hazardous solid waste is fed into a twin-screw mixer, while wet material from the filtration unit is returned to the twin-screw mixer for synergistic mixing, crushing, and homogenization with the dry material to obtain a mixture; auxiliary steam can be used for preheating during system startup; after the system is running stably, secondary steam generated by the evaporation and crystallization unit is introduced into the twin-screw mixer to preheat and reduce sensitivity of the mixture; S2. Staged incineration for harmlessness: The mixture is fed into a rotary kiln incinerator for primary incineration. The flue gas from the rotary kiln outlet enters the secondary combustion chamber for secondary combustion, achieving complete oxidation and decomposition of organic components and generating high-temperature flue gas. S3. Waste heat recovery and steam cascade utilization: The high-temperature flue gas is sent to a waste heat boiler for waste heat recovery to generate steam, and the steam is divided into high-grade steam, medium-grade steam and low-grade steam; the high-grade steam is introduced into a rotary kiln incinerator for heat preservation / heat compensation, the medium-grade steam is introduced into an evaporation crystallization unit as a heating source, and the low-grade steam is introduced into a wastewater pool for wastewater preheating / heat preservation; S4. Flue gas purification and emission: The flue gas from the waste heat boiler outlet is sent to the quench tower for rapid cooling, and then sent to the flue gas treatment system for purification treatment. After meeting the standards, harmless waste gas is discharged. S5. Wastewater Treatment and Salt Resource Utilization: High-salt, nitrate-containing wastewater containing perchlorate or quenched wastewater from a quench tower is sent to a wastewater tank. Low-grade steam is used to preheat and maintain the temperature of the wastewater. The preheated wastewater undergoes solid-liquid separation through a filter. The resulting wet material is returned to a twin-screw mixer, and the resulting clarified liquid enters an evaporation and crystallization unit. Medium-grade steam is used to drive the evaporation and crystallization unit to evaporate and concentrate the clarified liquid, precipitating salt crystals to obtain crude salt product. S6. Closed-loop water resource recycling: The process condensate from the entire system is collected in the condensate recovery tank, purified by the water treatment system, and then reused in the waste heat boiler and quench tower to achieve closed-loop water resource recycling.

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