A fly ash washing system and a fly ash treatment system containing the same.

Abstract

This application provides a fly ash washing system, including a multi-stage countercurrent washing device, a filtrate treatment device, and a biochemical system. Using this fly ash washing system, fly ash undergoes more thorough dechlorination before high-temperature calcination; the wastewater from the washing process produces recyclable crystalline salts after filtrate treatment, and the remaining mother liquor and condensate are treated by the biochemical system and reintroduced into the multi-stage countercurrent washing device as supplementary water for washing and dewatering, rather than being discharged as wastewater into the fly ash washing system, truly achieving zero discharge of washing wastewater with low energy consumption and no pollution. This application also provides a fly ash treatment system including the above-mentioned fly ash washing system, where heavy metals in the fly ash are completely solidified in the cement clinker lattice after high-temperature melting, resulting in thorough treatment without any future problems; dioxins are completely decomposed, eliminating the conditions for secondary synthesis.

Description

[0001] This application claims priority, application number 202120729264.6, filed on April 9, 2021, with China as the country of acceptance. Technical Field

[0002] This application relates to the field of hazardous waste treatment, specifically to a fly ash washing system and a fly ash treatment system including the fly ash washing system. Background Technology

[0003] Fly ash is a residual substance produced after waste incineration. It is a lightweight, fine-particle powder collected in flue gas ducts, separators, and dust collectors during the incineration process. Fly ash accounts for approximately 0.5% to 3% of the total incinerated waste. Fly ash contains not only large amounts of heavy metals such as Cd, Cr, Cu, Ni, Pb, and Zn, but also high concentrations of highly toxic dioxins and other organic carcinogens. It is classified as hazardous waste in the National Hazardous Waste List, and improper disposal will inevitably cause irreparable damage to our ecological environment.

[0004] Traditional fly ash treatment involves pre-treating the fly ash with a solidifying stabilizer before landfilling. However, due to the scarcity of national land resources and the environmental pollution caused by the leaching of heavy metals during landfilling, it is imperative to use new methods to treat fly ash generated from waste incineration and achieve its resource utilization. Summary of the Invention

[0005] The high soluble chloride content in fly ash from waste incineration in my country makes the melting and sintering process difficult to control, easily leading to the release of hydrogen chloride gas and causing secondary pollution. Current direct injection methods into cement kilns are only suitable for fly ash with a chloride ion content of less than 3%, and poor control of the feed rate can cause crusting inside the kiln, corroding equipment and pipelines. Furthermore, the high-chlorine content material released through bypass ventilation is also a challenge to handle.

[0006] To address the aforementioned problems, the primary objective of this application is to provide a fly ash washing system for more thorough dechlorination of fly ash before high-temperature calcination. This fly ash washing system includes a multi-stage countercurrent washing device, a filtrate treatment device, and a biochemical system.

[0007] The multi-stage countercurrent washing device comprises n washing units, where n ≥ 3. Each washing unit includes a washing tank and a sludge dewatering machine. Each washing tank includes a mud-water outlet. Specifically, the washing tank of the first-stage washing unit also has a fly ash inlet, while the second to nth-stage washing units do not. The washing tank of the nth-stage washing unit also has an initial rinse water inlet, while the first to n-1th-stage washing units do not. After the fly ash is washed in the washing tank, mud-water is produced. This mud-water is separated into sludge and filtrate by the sludge dewatering machine. Therefore, the sludge dewatering machine includes a mud-water inlet, a sludge outlet, and a filtrate outlet. In other words, fly ash enters the system from the first-stage washing unit, undergoes washing, and continuously enters the next-stage washing unit as sludge. Clean rinse water enters the system from the fifth-stage washing unit, washes away the sludge, and continuously flows into the previous-stage washing unit as filtrate.

[0008] In the aforementioned multi-stage countercurrent washing device, the sludge outlets of washing units 1 to n-1 are connected to the washing tanks of the next-stage washing unit to feed the sludge into the washing tanks of the next-stage washing unit. The sludge outlet of the nth-stage washing unit (i.e., the last-stage washing unit) is connected to a sludge conveying device to send the sludge into the next stage of fly ash treatment unit, such as a drying unit or a high-temperature melting unit. The filtrate outlets of washing units 2 to n are connected to the washing tanks of the previous-stage washing unit to guide the filtrate into the washing tanks of the previous-stage washing unit.

[0009] The filtrate treatment device is used to obtain crystalline salt and residual mother liquor. The filtrate treatment device includes a filtrate pretreatment device and a salt production system.

[0010] The inlet of the filtrate pretreatment device is connected to the filtrate outlet of the sludge dewatering machine in the primary washing unit. This means that the filtrate obtained from the separation of sludge and water from the primary washing unit by the sludge dewatering machine enters the filtrate pretreatment device for pretreatment. The filtrate pretreatment device includes a concentrated liquid outlet and a brine outlet. The concentrated liquid outlet is connected to the washing tank of the primary washing unit, allowing the concentrated liquid from the filtrate pretreatment device to mix with fly ash for washing. The liquid discharged from the brine outlet enters the salt production system for salt formation.

[0011] The inlet of the salt production system is connected to the brine outlet of the filtrate pretreatment unit. The salt production system includes a liquid outlet, which is used to transport the condensate and residual mother liquor generated during the salt production process.

[0012] The inlet of the biochemical system is connected to the liquid outlet of the salt production system, and the outlet of the biochemical system is connected to the washing tank of the nth-stage washing unit. In other words, the condensate and residual mother liquor produced by the salt production system are used to dilute the residual mother liquor. The diluted residual mother liquor enters the biochemical system, and the effluent from the biochemical system returns to the multi-stage counter-current washing system to be combined with the initial rinsing water, serving as washing water for recycling. The excess condensate after diluting the residual mother liquor can also bypass the biochemical system and be directly fed into the washing tank of the 5th-stage washing unit.

[0013] my country generates 10 million tons of fly ash annually. After dechlorination treatment using the aforementioned technology, only one-tenth of the domestic cement clinker production capacity is needed in cement kilns to convert all the fly ash into qualified cement clinker, saving raw materials and realizing the resource utilization of fly ash. The multi-stage countercurrent washing technology achieves excellent dealkali and dechlorination effects without dust generation. Because the washing environment is alkaline, the transfer rate of heavy metals and dioxins is low, and secondary capture and recovery of heavy metals are possible. Furthermore, the filtrate treatment device of this application produces crystalline salts from the ash washing wastewater, and the remaining mother liquor is treated by a biochemical system and reintroduced into the multi-stage countercurrent water washing device as a supplementary water source for the washing process, rather than being discharged as waste liquid into the fly ash washing system. This truly achieves zero discharge of ash washing wastewater, low energy consumption, and no pollution. The condensate can be used to dilute the remaining mother liquor or directly enter the multi-stage countercurrent water washing device to be combined into washing water, further conserving water resources.

[0014] Furthermore, in the multi-stage countercurrent water washing device, n=5. That is, the multi-stage countercurrent water washing device has 5 washing units. Using this technical solution can achieve a dechlorination percentage >95% with appropriate water consumption. If more than 5 washing units are used, the dechlorination effect will not be significantly improved, and the amount of water removed will increase, leading to higher water treatment costs.

[0015] Furthermore, the salt production system includes a nanofiltration salt separation unit, an ozone oxidation unit, a falling film concentration unit, and an evaporation crystallization system connected in sequence.

[0016] Furthermore, the nanofiltration desalination device can separate the liquid received from the filtrate pretreatment unit into a product water side and a concentrate side. The concentrate side is connected to the washing tank of the first-stage washing unit, while the product water side is connected to the ozone oxidation unit. The concentrate side is then combined into muddy water, while the product water side proceeds to the subsequent salt production steps. This technical solution achieves an overall salt recovery rate of over 90%. The final sodium chloride product meets the requirements of Grade 1 in Table 1 of the "Industrial Salt" standard (GB5462-2015), and the potassium chloride product meets the requirements of Class 1 Grade 1 in the "Potassium Chloride" standard (GB 6549-2011), achieving the goal of complete harmlessness and resource utilization. The evaporation mother liquor, after being treated by the biochemical system, can be used together with the condensate as a supplementary source for washing and dewatering, without being discharged externally.

[0017] Furthermore, the salt production system may also include an electric boiler, which is mainly used to provide heat energy. The steam generated by the electric boiler is used partly as a heat source for the falling film concentration device and the evaporation crystallization system, and partly as a heat source for the dryer to dry the crystallized salt.

[0018] Furthermore, the filtrate pretreatment device includes a coagulation sedimentation tank, a sand filter, an ultrafiltration device, and a resin adsorption device connected in sequence. By adding chemicals to the coagulation sedimentation tank, commonly used softening agents such as lime, soda ash, caustic soda flakes, and sodium sulfate are used to remove scale-forming ions such as calcium, magnesium, fluorine, and silicon. After treatment by this filtrate pretreatment device, it can ensure that the total hardness of the liquid entering the salt production system is ≤2.5 mg / L, fluoride ≤0.5 mg / L, and total silicon ≤0.05 mg / L; the turbidity of the ultrafiltration effluent is ≤2 NTU, the effluent SS is ≤5 ppm, and the effluent SDI is ≤5.

[0019] Furthermore, the rinsing water, concentrate, and resin regeneration liquid generated by the sand filter, ultrafiltration tank, and resin adsorption device can enter the washing tank of the primary water washing unit through the concentrate outlet, where they combine with fly ash to form mud water for further cleaning.

[0020] Furthermore, the coagulation sedimentation tank includes a primary coagulation sedimentation tank and a secondary coagulation sedimentation tank. The sludge outlet of the primary coagulation sedimentation tank is connected to a sludge dewatering device, the sludge produced by this device entering the washing tank of the primary washing unit; the filtrate produced by the dewatering device enters the secondary coagulation sedimentation tank, and the sludge produced by the secondary coagulation sedimentation tank enters the washing tank of the primary washing unit. The "sludge dewatering device" of this application can employ a sludge dewatering machine similar to that used in multi-stage counter-current washing devices.

[0021] Another objective of this application is to provide a fly ash treatment system, including a high-temperature melting unit and the fly ash washing system described in any of the above technical solutions. The high-temperature melting unit is used to calcine the sludge washed by the fly ash washing system at high temperatures. The high-temperature melting unit includes, but is not limited to, a cement kiln. Using this technical solution, heavy metals in the fly ash are completely solidified in the cement clinker lattice after high-temperature melting, resulting in thorough treatment without any future problems. The cement kiln system reaches temperatures above 1400℃, with long calcine times and complete combustion. Furthermore, the alkaline environment inside the kiln efficiently decomposes dioxins, preventing them from undergoing secondary synthesis.

[0022] Furthermore, a sludge drying device is included between the fly ash washing system and the high-temperature melting unit. This sludge drying device is connected to the high-temperature melting unit to utilize the waste heat from the high-temperature melting unit to dry the cement. This technical solution reduces the interference of the moisture content of the fly ash entering the kiln on the high-temperature melting unit, improves the processing capacity of the high-temperature melting unit, and effectively utilizes waste heat from production.

[0023] The beneficial effects of this application are as follows:

[0024] It avoids the long-term risks associated with fly ash solidification and landfill; it solves the problems of fly ash causing scaling inside the kiln and corrosion of equipment / pipelines in existing technologies, and fully realizes the reduction, resource utilization and harmlessness of fly ash disposal from waste incineration. Attached Figure Description

[0025] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments:

[0026] Figure 1 This is a schematic diagram of a fly ash washing system according to an embodiment of the present invention.

[0027] Component designation explanation

[0028] 10: Multi-stage counter-current water washing device;

[0029] 11: Level 1 washing unit; 12: Level 2 washing unit; 13: Level 3 washing unit; 14: Level 4 washing unit; 15: Level 5 washing unit;

[0030] 20. Filtrate treatment device; 21. Filtrate pretreatment device; 22. Salt production system;

[0031] 30. Biochemical systems; Detailed Implementation

[0032] The following specific embodiments illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. Although the description of the present invention is presented in conjunction with preferred embodiments, this does not mean that the features of the invention are limited to these embodiments. On the contrary, the purpose of describing the invention in conjunction with embodiments is to cover other options or modifications that may be derived based on the claims of the present invention. To provide a deep understanding of the invention, many specific details will be included in the following description. The invention may also be implemented without using these details. Furthermore, to avoid confusion or obscuring the focus of the invention, some specific details will be omitted in the description. It should be noted that, unless otherwise specified, the embodiments and features in the embodiments of the present invention can be combined with each other.

[0033] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0034] Figure 1 The present application illustrates a fly ash washing system according to an embodiment of the present application, including a multi-stage countercurrent washing device 10, a filtrate treatment device 20, and a biochemical system 30.

[0035] Specifically, in this embodiment, the multi-stage countercurrent washing device 10 includes five washing units, each equipped with a washing tank and a sludge dewatering machine. The first-stage washing unit 11 has a fly ash inlet; when using this fly ash washing system, fly ash enters the washing tank of the first-stage washing unit 11 through this inlet. The sludge-water generated in the washing tank enters the sludge dewatering machine through the sludge-water inlet, where sludge and filtrate are separated. Subsequently, the sludge enters the washing tank of the second-stage washing unit 12 through the sludge outlet, and so on, with sludge continuously entering the washing tank of the next stage washing unit until it is discharged from the sludge outlet of the fifth-stage washing unit 15, resulting in sludge with a moisture content of approximately 40%. The sludge outlet of the fifth-stage washing unit 15 is connected to a sludge conveying device to send the sludge to the next stage of fly ash treatment, such as a drying unit or a high-temperature melting unit.

[0036] The 5-stage washing unit 15 is equipped with an initial rinsing water inlet. When the fly ash washing system is working, the initial rinsing water enters the washing tank of the 5-stage washing unit through the rinsing water inlet. The filtrate obtained by separating the muddy water in the 5-stage washing unit 15 from the sludge dewatering machine is transported to the washing tank of the 4-stage washing unit 14 through the filtrate outlet, and so on. The filtrate continuously enters the washing tank of the previous stage washing unit until it is discharged from the filtrate outlet of the 1-stage washing unit 11 and enters the filtrate pretreatment device 21.

[0037] In this embodiment, the residual chloride ion concentration of the fly ash after multi-stage countercurrent elution is <10000 mg / kg, the alkalinity is <100 mg / kg, and there is no dust generation. In this alkaline elution environment, the transfer rates of heavy metals and dioxins are low, and secondary capture and recovery of heavy metals are possible.

[0038] The filtrate treatment apparatus 20 includes a filtrate pretreatment apparatus 21 and a salt production system 22. Figure 1 In the illustrated embodiment, the filtrate pretreatment device 21 includes a coagulation sedimentation tank, a sand filter, an ultrafiltration device, and a resin adsorption device connected in sequence. Specifically, the coagulation sedimentation tank includes a primary coagulation sedimentation tank and a secondary coagulation sedimentation tank. The sludge outlet of the primary coagulation sedimentation tank is connected to a sludge dewatering device, and the sludge produced by the sludge dewatering device can enter the washing tank of the primary washing unit 11; the filtrate produced by the sludge dewatering device can enter the secondary coagulation sedimentation tank, and the sludge produced by the secondary coagulation sedimentation tank also enters the washing tank of the primary washing unit 11. The liquid produced by the secondary sedimentation tank enters the sand filter, ultrafiltration device, and resin adsorption device. After treatment, the rinsing water, concentrate, and resin regeneration liquid leave the filtrate pretreatment device 21 through the concentrate outlet and enter the washing tank of the primary washing unit 11; the remaining liquid is used as brine and leaves the filtrate pretreatment device 21 through the brine outlet and enters the salt production system 22.

[0039] In this embodiment, the salt production system 22 includes a nanofiltration salt separation device, an ozone oxidation device, a falling film concentration device, and an evaporation crystallization system connected in sequence. Specifically, the salt production system in this embodiment also includes an electric boiler, the heat generated by which is supplied to the falling film concentration device for evaporation concentration, the evaporation crystallization system for crystallization salt precipitation, and the drying of the crystallized salt; and the nanofiltration salt separation device is, for example, but not limited to, the two-stage nanofiltration membrane system (two-stage NF membrane system) in this embodiment. The liquid is separated into a product water side and a concentrate side after passing through the nanofiltration salt separation device, wherein the concentrate side is connected to the water washing tank of the first-stage water washing unit to inject the concentrate into the first-stage water washing unit, and the product water side is connected to the ozone oxidation device for subsequent salt production steps; the evaporation crystallization system is, for example, but not limited to, the MVR evaporation crystallization system in this embodiment. During the evaporation crystallization process, KCl and NaCl crystallized salts, other mixed salts, residual mother liquor, and condensate can be generated. Other mixed salts do not meet the latest landfill standards, so they are returned to the nanofiltration salt separation device for continuous filtration and salt separation.

[0040] The inlet of the biochemical system 30 is connected to the liquid outlet of the salt production system 22, enabling it to receive residual mother liquor and condensate from the salt production system 22. The residual mother liquor can be diluted with condensate, and the diluted residual mother liquor is then processed by the biochemical system 30 before entering the washing tank of the 5-stage washing unit; the excess condensate from diluting the residual mother liquor can directly enter the washing tank of the 5-stage washing unit 15. Figure 1 As shown, the outlet of the biochemical system 30 is connected to the washing tank of the 5-stage washing unit 15. The effluent treated by the biochemical system 30 is then returned to the multi-stage countercurrent washing system. At the same time, the condensate can be directly returned to the multi-stage countercurrent washing system without going through the biochemical system, and combined with the initial rinsing water to serve as washing and dewatering water, truly achieving zero waste liquid discharge and reducing the amount of initial rinsing water used.

[0041] In this embodiment, fly ash enters the fly ash washing system at a rate of approximately 25 t / h. Based on an annual fly ash production of 10 million tons, after being washed and dechlorinated by the fly ash washing system, only one-tenth of the domestic cement clinker production capacity of cement kilns is needed to convert all the fly ash into qualified cement clinker, saving raw materials and realizing the resource utilization of fly ash.

[0042] This application also provides an embodiment of a fly ash treatment system, including the fly ash washing system shown in the above embodiments and a high-temperature melting unit. In this embodiment, the high-temperature melting unit is a cement kiln. After the heavy metals in the fly ash are melted at high temperature in the cement kiln, they are completely solidified in the cement clinker lattice, resulting in thorough treatment without any future problems. The cement kiln system has a temperature of over 1400℃, a long calcination time, and complete combustion. Furthermore, the kiln has an alkaline environment, which efficiently decomposes dioxins, preventing them from undergoing secondary synthesis.

[0043] In any embodiment of the fly ash treatment system of this application, a sludge drying device is included between the fly ash washing system and the high-temperature melting unit. The sludge drying device is connected to the high-temperature melting unit to utilize the waste heat of the high-temperature melting unit to dry the sludge. This can reduce the interference of the moisture content of the fly ash entering the kiln on the cement kiln, improve the processing capacity of the cement kiln, and effectively utilize the waste heat from production.

[0044] While the present invention has been illustrated and described with reference to certain preferred embodiments, those skilled in the art should understand that the above description is a further detailed explanation of the invention in conjunction with specific embodiments, and should not be construed as limiting the specific implementation of the invention to these descriptions. Various changes in form and detail can be made by those skilled in the art, including several simple deductions or substitutions, without departing from the spirit and scope of the invention.

Claims

1. A fly ash washing system, characterized in that, include: A multi-stage countercurrent water washing device includes n washing units, where n ≥ 3, and each washing unit includes: The washing tank has a mud and water outlet; and the washing tank of the first-stage washing unit has a fly ash inlet, while the washing tank of the nth-stage washing unit has an initial rinse water inlet; and, A sludge dewatering machine is used to separate sludge and filtrate from sludge and water after washing in the washing tank. The sludge dewatering machine includes a sludge-water inlet, a sludge outlet, and a filtrate outlet. The sludge outlet of the washing units from level 1 to level n-1 is connected to the washing tank of the next washing unit, and the sludge outlet of the nth washing unit is connected to a sludge conveying device. The filtrate outlet of the washing units from level 2 to level n is connected to the washing tank of the previous washing unit. A filtrate treatment apparatus for obtaining crystalline salt and residual mother liquor includes: A filtrate pretreatment device, wherein the inlet of the filtrate pretreatment device is connected to the filtrate outlet of the sludge dewatering machine of the primary washing unit, the filtrate pretreatment device includes a concentrated liquid outlet and a brine outlet, the concentrated liquid outlet being connected to the washing tank of the primary washing unit; and, A salt-making system is provided, wherein the inlet of the salt-making system is connected to the brine outlet of the filtrate pretreatment device, the salt-making system includes a liquid outlet for conveying condensate and residual mother liquor generated during the salt-making process, and the salt-making system includes a nanofiltration salt-separating device, an ozone oxidation device, a falling film concentration device, and an evaporation crystallization system connected in sequence. The nanofiltration salt-separating device can separate the liquid received from the filtrate pretreatment device into a product water side and a concentrate side. The concentrate side is connected to the washing tank of the first-stage washing unit for injecting concentrate into the first-stage washing unit. The product water side is connected to the ozone oxidation device. The evaporation crystallization system is used to generate KCl and NaCl crystalline salts, other mixed salts, residual mother liquor, and condensate. The other mixed salts are returned to the nanofiltration salt-separating device for continuous filtration and salt separation. The biochemical system has an inlet connected to the liquid outlet of the salt production system for receiving the remaining mother liquor and the condensate from the salt production system. The remaining mother liquor is diluted with the condensate. The outlet of the biochemical system is connected to the washing tank of the n-stage washing unit for returning the treated water from the biochemical system to the multi-stage countercurrent washing device.

2. The fly ash washing system as described in claim 1, characterized in that, In the multi-stage countercurrent water washing device, n = 5.

3. The fly ash washing system as described in claim 1, characterized in that, The salt production system includes an electric boiler. Part of the heat energy generated by the electric boiler is used as the heat source for the falling film concentration device and the evaporation crystallization system, and the other part is used as the heat source for drying the crystallized salt.

4. The fly ash washing system as described in claim 1, characterized in that, The filtrate pretreatment device includes a coagulation sedimentation tank, a sand filter, an ultrafiltration device, and a resin adsorption device connected in sequence.

5. The fly ash washing system as described in claim 4, characterized in that, The rinsing water, concentrate, and resin regeneration liquid generated by the sand filter, ultrafiltration tank, and resin adsorption device can enter the washing tank of the first-stage washing unit through the concentrate outlet.

6. The fly ash washing system as described in claim 4, characterized in that, The coagulation sedimentation tank includes: A primary coagulation sedimentation tank, wherein the sludge outlet of the primary coagulation sedimentation tank is connected to a sludge dewatering device; the sludge produced by the sludge dewatering device can enter the washing tank of the primary washing unit. The filtrate produced by the sludge dewatering device can enter the secondary coagulation sedimentation tank, and the sludge water produced by the secondary coagulation sedimentation tank can enter the washing tank of the primary washing unit.

7. A fly ash treatment system, characterized in that, include The fly ash washing system as described in any one of claims 1 to 6; and, The high-temperature melting unit is used for high-temperature calcination of sludge washed by the fly ash washing system.

8. The fly ash treatment system as described in claim 7, characterized in that, A sludge drying device is included between the fly ash washing system and the high-temperature melting unit. The sludge drying device is connected to the high-temperature melting unit and uses the waste heat of the high-temperature melting unit to dry the sludge.

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