Treatment process for comprehensive recycling of fly ash

Abstract

The invention belongs to the technical field of fly ash treatment, and particularly relates to a treatment process for comprehensive recycling of fly ash, which specifically comprises the following steps: S1, collecting, accurately metering, washing and extracting fly ash, and respectively feeding generated mother liquor and filter residues into a concentration unit and a low-temperature thermal decomposition unit for treatment; s2, adding a pH regulator and a heavy supplement agent into the mother liquor in the concentration unit, and filtering to remove metal sludge to obtain calcium chloride mother liquor; evaporating the calcium chloride mother liquor to obtain a calcium chloride solution and sodium potassium waste salt; and S3, heating the filter residue to a pyrolysis desorption temperature for dechlorination decomposition, cooling the desorbed fly ash for resource recovery, carrying out cloth bag dust removal on the flue gas generated by desorption, carrying out secondary combustion decomposition, carrying out desulfurization, activated carbon adsorption and denitration treatment in sequence, and discharging the flue gas. The problems of low fly ash treatment efficiency and low resource utilization rate in the existing fly ash treatment process are solved, various products generated in the fly ash treatment process can be subjected to resource utilization, and the resource utilization rate of fly ash treatment is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of fly ash treatment, and in particular relates to a treatment process for comprehensive resource utilization of fly ash. Background Art

[0002] Fly ash from waste incineration contains easily leached heavy metals and trace amounts of persistent organic pollutants such as dioxins. my country has included fly ash in the National List of Hazardous Wastes. In order to prevent and control environmental pollution, improve the quality of the ecological environment, and regulate and guide the environmental management of fly ash from the incineration of domestic waste, the Ministry of Ecology and Environment of China has issued the "Technical Specifications for Pollution Control of Fly Ash from Incineration of Domestic Waste" (HJ1 134-2020), which has formulated more detailed specifications and standards for the current disposal of fly ash from waste incineration. Among them, fly ash treatment processes such as low-temperature thermal decomposition, high-temperature sintering and high-temperature melting should meet the following requirements: the total amount of dioxin residues in the fly ash treatment product should be controlled to not exceed 50ng-TEQ / kg (based on the dry weight of fly ash); the heavy metal leaching concentration should not exceed the maximum allowable emission concentration value specified in GB 8978; the soluble chlorine content should not exceed 2%, preferably not more than 1%.

[0003] The harmless disposal technology of fly ash is divided into thermal disposal technology and non-thermal disposal technology. Among them, thermal disposal technology mainly includes sintering, melt vitrification, low-temperature thermal disposal, hydrothermal disposal and supercritical water oxidation; non-thermal disposal methods include cement solidification, agent stabilization, biological / chemical leaching and mechanochemical disposal. The non-thermal disposal technology of fly ash solidifies heavy metals by adding agents, but the added agents have no degradation effect on dioxins. The low-temperature thermal disposal technology of fly ash is considered to be one of the best ways to degrade dioxins in fly ash. In an inert atmosphere, the fly ash can be treated at 300°C for 2 hours to achieve a degradation rate of 90% for dioxins. However, the low-temperature thermal disposal technology lacks control over heavy metals. The fly ash after low-temperature thermal treatment needs to be added with agents, combined with mechanochemical disposal, cement solidification and other technologies to meet the hazardous waste landfill standards.

[0004] In the prior art, a Chinese patent later disclosed as CN1 05126606A discloses a method for treating volatile organic matter in incineration fly ash by low-temperature pyrolysis-catalytic degradation, wherein the fly ash is transported to a low-temperature pyrolysis device for pyrolysis at 100-350°C for 10-60 minutes in a non-oxidizing atmosphere to produce a pyrolysis mixture. The mixture is transported to a catalytic degradation device, and the catalyst mainly contains titanium, tungsten or vanadium, and is degraded at 100-400°C for 300 seconds in an oxidizing atmosphere. However, the above-mentioned prior art lacks means for resource utilization of various substances in fly ash treatment, and only plays a role in degradation, and the fly ash treatment cost is high and the efficiency is low. Summary of the invention

[0005] In response to the problems of low fly ash treatment efficiency and low resource utilization in the existing fly ash treatment processes mentioned in the above background technology, the present invention provides a treatment process for comprehensive resource utilization of fly ash. Through deep water washing technology and low-temperature thermal decomposition technology, various products generated in the fly ash treatment process can be utilized as resources, thereby improving the resource utilization rate of fly ash treatment.

[0006] The specific scheme of the present invention:

[0007] A treatment process for comprehensive resource utilization of fly ash, characterized by comprising the following steps:

[0008] S1. Collect the fly ash and store it in the fly ash silo. After accurate measurement, seal and transport it to the reduction water washing unit for water washing and leaching. Send the generated mother liquor and filter residue to the concentration unit and low-temperature thermal decomposition unit for treatment respectively;

[0009] S2. Adding pH regulator and refilling agent to the mother liquor in the concentration unit, filtering and removing metal sludge to obtain calcium chloride mother liquor, and outsourcing the metal sludge; then evaporating the calcium chloride mother liquor to obtain calcium chloride solution and sodium-potassium waste salt, recovering the calcium chloride solution for use, and the sodium-potassium waste salt enters the refining system for refining;

[0010] S3. The filter residue entering the low-temperature thermal decomposition unit is heated to the thermal desorption temperature for dechlorination and decomposition. The fly ash after desorption is quickly cooled and recycled. The flue gas generated by desorption is first bag-filtered and then subjected to secondary combustion and decomposition, and then discharged after desulfurization, activated carbon adsorption and denitrification treatment.

[0011] Furthermore, the water washing and leaching in step S1 includes water washing and acid leaching, and the mass ratio of fly ash to water washing solution in the water washing is 1:1.5-2.5; the acid leaching solution is hydrochloric acid, the mass ratio of the water-washed fly ash to hydrochloric acid is 1:0.8-1.1, the acid leaching pH is 2-3, and the acid leaching time is 60-90 minutes.

[0012] Furthermore, in step S1, the moisture content of the filter residue is 25-35%, and the mass of the filter residue is 45-55% of the mass of the fly ash.

[0013] Furthermore, the adding of pH adjusting agent and refilling agent in step S2 comprises the following steps: adding pH adjusting agent to the mother liquor to adjust the pH of the mother liquor to 5.5-7.5, continuously stirring for 20-30 minutes and removing metal sludge, then adding refilling agent thereto, stirring and then adding pH adjusting agent thereto to adjust the pH to 10, continuously stirring for 20-30 minutes and removing metal sludge again to obtain calcium chloride mother liquor.

[0014] Furthermore, the evaporation of the calcium chloride mother liquor in step S2 comprises the following steps: evaporating the calcium chloride mother liquor to concentrate the calcium chloride concentration to 30wt%-35wt%, controlling the evaporation and concentration temperature at 110-115°C, centrifuging to obtain sodium chloride salt and a liquid phase, cooling the liquid phase at 0-10°C for crystallization to obtain potassium chloride salt and a calcium chloride solution, recycling the calcium chloride solution, and recycling the sodium chloride salt and the potassium chloride salt after being evaporated and refined in a secondary evaporator.

[0015] Furthermore, the low-temperature thermal decomposition treatment of the filter residue in step S3 includes the following steps: preheating, crushing and drying the filter residue at 110° C., and drying the filter residue to a moisture content of less than 1% to obtain dry fly ash; and rapidly heating the dry fly ash to 350° C. to 450° C. to perform dechlorination decomposition, and the dechlorination decomposition time is 60 to 90 minutes.

[0016] Furthermore, the fly ash rapid cooling and resource recovery in step S3 includes using the recovered fly ash for any one of cement admixture, concrete admixture and ceramsite raw material.

[0017] Furthermore, in step S3, the secondary combustion temperature is 1100-1200°C.

[0018] Beneficial effects of the present invention:

[0019] 1. The "deep reduction water washing" technology is used to detoxify heavy metals in fly ash by changing the occurrence form of heavy metals and utilizing the law of migration and transformation, thereby improving the fly ash treatment effect. At the same time, compared with the traditional water washing process, the wet slag of fly ash is reduced by more than 50%, with obvious effects, which greatly reduces the back-end treatment and disposal load. The "low-temperature thermal decomposition" technology is used to actively respond to the policy slogan of "energy conservation and carbon reduction". The detoxification of dioxins in fly ash is completed in a lower temperature range. Compared with high-temperature melting, high-temperature sintering and other technologies, it can greatly reduce energy consumption while ensuring that the dioxins in fly ash are treated to meet the standards.

[0020] 2. The solid phase residue of fly ash after comprehensive detoxification (heavy metal and dioxin detoxification) can meet the basic requirements of building materials resource utilization. Under the background of the "dual carbon" policy, it can get rid of the dependence of traditional processes on cement kiln co-disposal. The metal sludge produced in the reduction water washing can also be directly used for resource utilization. For example, magnesium hydroxide sludge can be used as a flame retardant or raw material for the preparation of magnesium oxide, and iron metal sludge and aluminum metal sludge can be used as neutralizers for acidic mine wastewater. After the by-products sodium chloride, potassium chloride, and calcium chloride are refined and meet the relevant product quality standards, the by-product salt can be directly utilized as a resource. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 The present invention is a schematic flow diagram of a treatment process for comprehensive resource utilization of fly ash. DETAILED DESCRIPTION

[0022] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0023] Example

[0024] As attached Figure 1 As shown, this embodiment provides a processing process for comprehensive resource utilization of fly ash, including the following steps:

[0025] S1. Collect the fly ash and store it in the fly ash silo. After accurate measurement, seal and transport it to the reduction water washing unit for water washing and leaching. Send the generated mother liquor and filter residue to the concentration unit and low-temperature thermal decomposition unit for treatment respectively;

[0026] Specifically, the fly ash generated in industrial production is collected, loaded into a special sealed tank truck and transported to the treatment site, and vacuum suction is used to suck the fly ash into the fly ash silo for storage. After accurate measurement in the ash silo, water is added to the measured fly ash to wash the fly ash, and the amount of water added is twice the mass of the fly ash. After the fly ash is fully washed with water, the hydrochloric acid solution is slowly stirred and added to the water washing slurry. When the pH of the water washing slurry reaches 2, the addition of hydrochloric acid is stopped. At this time, the mass ratio of hydrochloric acid addition to water washing slurry is 1:1. After fully stirring and acid leaching for 60 minutes, the mother liquor and filter residue are obtained by plate filter press. The moisture content of the filter residue produced by the filter press is controlled to be 30%. At this time, the mass of the filter residue is about 50% of the mass of the fly ash. The generated mother liquor is sent to the concentration unit to recover metal sludge and calcium chloride solution, and the filter residue is sent to the low-temperature thermal decomposition unit to remove impurities such as dioxins and then recycled.

[0027] S2. Adding pH regulator and refilling agent to the mother liquor in the concentration unit, filtering and removing metal sludge to obtain calcium chloride mother liquor, and outsourcing the metal sludge; then evaporating the calcium chloride mother liquor to obtain calcium chloride solution and sodium-potassium waste salt, recovering the calcium chloride solution for use, and the sodium-potassium waste salt enters the refining system for refining;

[0028] Specifically, a pH regulator is added to the mother liquor obtained by the S1 treatment to adjust the pH of the mother liquor to 6. In this embodiment, calcium hydroxide is used as the pH regulator. After mixing and stirring for 20 minutes, metal sludge is obtained. The metal sludge produced here is formed by precipitation of iron ions, aluminum ions and a small amount of calcium ions contained in the mother liquor in the form of hydroxide. The metal sludge obtained in this embodiment can be collected and outsourced for treatment.

[0029] After filtering and removing the sludge, a heavy supplement agent is added to the mother liquor and stirred for 10 minutes. In this embodiment, sodium sulfide is used as the heavy supplement agent. After stirring and reacting, the suspended impurities are filtered to remove the pH of the mother liquor, and then a pH adjuster is added to the mother liquor to adjust the pH to 10, at which time the magnesium ions present in the mother liquor can be precipitated. The magnesium sludge is filtered again to remove the metal magnesium sludge to obtain a calcium chloride mother liquor.

[0030] The calcium chloride mother liquor is evaporated and concentrated to a calcium chloride concentration of 30wt%, the evaporation temperature is controlled to be 110°C, the sodium chloride precipitate is separated by centrifugation under heat preservation, the liquid phase produced by centrifugation enters a cooling device and is cooled to 0°C, the potassium chloride precipitate is cooled and separated, and the calcium chloride solution is obtained by filtration and separation. The obtained calcium chloride solution can be directly used as an industrial raw material, and the sodium chloride precipitate and the potassium chloride precipitate are respectively recrystallized and refined to obtain refined salt.

[0031] S3. The filter residue entering the low-temperature thermal decomposition unit is rapidly heated to the thermal desorption temperature for dechlorination and decomposition. The fly ash after desorption is rapidly cooled and recycled. The flue gas generated by desorption is first bag-filtered and then decomposed through secondary combustion. It is then discharged after desulfurization, activated carbon adsorption and denitrification treatment.

[0032] Specifically, the filter residue obtained by S1 treatment is put into a drying device for low-temperature crushing and drying, and the drying temperature is 110°C. When the filter residue is dried to a moisture content of less than or equal to 1%, the drying is completed to obtain dry fly ash. The dry fly ash is transported to a pyrolysis reaction device, and nitrogen is introduced into the pyrolysis reaction device as a protective gas and oxygen is excluded therein to ensure that the oxygen content in the pyrolysis reaction device is less than 1% during the reaction. A dechlorination additive of 10% of the mass of the dry fly ash is added to the pyrolysis reaction device. In this embodiment, calcium oxide and calcium sulfate are used as dechlorination additives, and the mass ratio of calcium oxide to calcium sulfate is 1:1. Rapidly heat to 400°C and react for 60 minutes to remove dioxins in the dry fly ash. After the reaction is completed, the fly ash is cooled and can be directly used for resource utilization, such as for any one of cement admixtures, concrete admixtures and ceramsite raw materials.

[0033] The tail gas produced by the pyrolysis reaction is first cooled by a heat exchange device, and then introduced into a bag filter for dust removal. The tail gas after dust removal is introduced into a high-temperature combustion device for high-temperature combustion, and the dioxins remaining in the tail gas are decomposed into non-toxic substances such as carbon dioxide and water at a high temperature of 1100°C. The tail gas after high-temperature combustion is cooled by heat exchange again, and then enters the spray desulfurization device, activated carbon adsorption device and denitrification device in turn for treatment and then meets the emission standards.

[0034] In summary, the present invention adopts the "deep reduction water washing" technology, which detoxifies the heavy metals in the fly ash by changing the occurrence form of heavy metals and utilizing the migration and transformation law, thereby improving the fly ash treatment effect. At the same time, compared with the traditional water washing process, the wet slag of fly ash is reduced by more than 50%, with obvious effects, which greatly reduces the back-end processing and disposal load. The "low-temperature thermal decomposition" technology is adopted to actively respond to the policy slogan of "energy conservation and carbon reduction". The detoxification of dioxins in fly ash is completed in a lower temperature range. Compared with high-temperature melting, high-temperature sintering and other technologies, energy consumption can be greatly reduced while ensuring that the dioxin treatment in fly ash meets the standards.

[0035] At the same time, the solid phase residue of fly ash after comprehensive detoxification (heavy metal and dioxin detoxification) can meet the basic requirements of building materials resource utilization. Under the background of the "dual carbon" policy, it can get rid of the dependence of traditional processes on cement kiln co-disposal. The metal sludge produced in the reduction water washing can also be directly used for resource utilization. For example, magnesium hydroxide sludge can be used as a flame retardant or raw material for the preparation of magnesium oxide, and iron metal sludge and aluminum metal sludge can be used as neutralizers for acidic mine wastewater. After the by-products sodium chloride, potassium chloride, and calcium chloride are refined and meet the relevant product quality standards, the by-product salt can be directly utilized as a resource.

Claims

1. A treatment process for comprehensive resource utilization of fly ash, characterized in that: The following steps are involved: S1. Collect the fly ash and store it in the fly ash silo. After accurate measurement, seal and transport it to the reduction water washing unit for water washing and leaching. Send the generated mother liquor and filter residue to the concentration unit and low-temperature thermal decomposition unit for treatment respectively; S2. Adding pH regulator and refilling agent to the mother liquor in the concentration unit, filtering and removing metal sludge to obtain calcium chloride mother liquor, and outsourcing the metal sludge; then evaporating the calcium chloride mother liquor to obtain calcium chloride solution and sodium-potassium waste salt, recovering the calcium chloride solution for use, and the sodium-potassium waste salt enters the refining system for refining; S3. The filter residue entering the low-temperature thermal decomposition unit is heated to the thermal desorption temperature for dechlorination and decomposition. The fly ash after desorption is quickly cooled and recycled. The flue gas generated by desorption is first bag-filtered and then subjected to secondary combustion and decomposition, and then discharged after desulfurization, activated carbon adsorption and denitrification treatment.

2. According to the processing technology for comprehensive resource utilization of fly ash as described in claim 1, it is characterized in that: The water washing and leaching in step S1 includes water washing and acid leaching, wherein the mass ratio of fly ash to water washing solution is 1:1.5-2.5; the acid leaching solution is hydrochloric acid, the mass ratio of water-washed fly ash to hydrochloric acid is 1:0.8-1.1, the acid leaching pH is 2-3, and the acid leaching time is 60-90 minutes.

3. According to the processing technology for comprehensive resource utilization of fly ash as described in claim 2, it is characterized in that: The moisture content of the filter residue in step S1 is 25-35%, and the mass of the filter residue is 45-55% of the mass of the fly ash.

4. According to the processing technology for comprehensive resource utilization of fly ash as described in claim 1, it is characterized in that: The step S2 of adding the pH regulator and the refilling agent comprises the following steps: A pH regulator is added to the mother liquor to adjust the pH of the mother liquor to 5.5-7.5, and the metal sludge is removed after continuous stirring for 20-30 minutes. A heavy replenisher is added thereto, and after stirring, a pH regulator is added thereto to adjust the pH to 10. The mother liquor is obtained by continuous stirring for 20-30 minutes and the metal sludge is removed again to obtain a calcium chloride mother liquor.

5. A treatment process for comprehensive resource utilization of fly ash according to claim 4, characterized in that: The evaporation of calcium chloride mother liquor in step S2 comprises the following steps: evaporating the calcium chloride mother liquor to concentrate the calcium chloride concentration to 30wt%-35wt%, controlling the evaporation concentration temperature at 110-115°C, centrifuging to obtain sodium chloride salt and liquid phase, cooling and crystallizing the liquid phase at 0-10°C to obtain potassium chloride salt and calcium chloride solution, recycling the calcium chloride solution, and recycling the sodium chloride salt and potassium chloride salt after being evaporated and refined in a secondary evaporator.

6. According to the processing technology for comprehensive resource utilization of fly ash as described in claim 1, it is characterized in that: The low-temperature thermal decomposition treatment of the filter residue in step S3 comprises the following steps: preheating the filter residue at 110° C., crushing and drying the filter residue, and drying the filter residue to a moisture content of less than 1% to obtain dry fly ash; and rapidly heating the dry fly ash to 350° C. to 450° C. to perform dechlorination decomposition, and the dechlorination decomposition time is 60 to 90 minutes.

7. A treatment process for comprehensive resource utilization of fly ash according to claim 6, characterized in that: The fly ash is rapidly cooled and recycled in step S3, including using the recycled fly ash for any one of cement admixture, concrete admixture and ceramsite raw material.

8. A treatment process for comprehensive resource utilization of fly ash according to claim 7, characterized in that: The secondary combustion temperature in step S3 is 1100-1200°C.

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