System and method for removing heavy metals and salts from household garbage incineration fly ash

Abstract

The invention discloses a system and a method for removing heavy metals and salts from household garbage incineration fly ash, raw material mixing: mixing the household garbage incineration fly ash with at least one ceramic raw material of kaolin, feldspar and shale to form a blank body, and firing the blank body into ceramsite, so that most of the heavy metals are solidified in the ceramsite; the ceramsite is washed for three times (the previous two times are combined with ultrasonic intensified dissolution, and circulating water is utilized for the third time), so that the final salt content of the ceramic material can be reduced to be lower than the national allowable emission standard of 500ppm, and the problem that the salt content of a rear-end product in a traditional process exceeds the standard is solved. The ceramic material can be directly used for constructional engineering (such as cement, ceramsite and bricks) without small-amount matching, so that the resource utilization efficiency and range of the fly ash are improved; according to the vertical rotary kiln, waste heat below the vertical rotary kiln is brought into a combustion layer through a fan, natural gas or combustible materials (saw dust and bamboo sawdust) are combined for heating, the heat utilization efficiency is improved, the temperature of discharged ceramic materials is controlled to be 60-70 DEG C, follow-up water washing treatment is facilitated, and energy consumption is further reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of household garbage treatment, and particularly relates to a system and method for removing heavy metals and salt from household garbage incineration fly ash. BACKGROUND

[0002] Municipal solid waste incineration fly ash is a hazardous waste generated in the process of waste incineration treatment, which mainly contains heavy metals (such as Pb, Cr, Cd, etc.), dioxin persistent organic pollutants and about 20% of soluble salt (such as potassium chloride, sodium chloride, etc.). If not properly treated, it will seriously threaten the ecological environment and human health.

[0003] At present, the mainstream processing technology of fly ash mainly includes two types: one is direct landfill, which not only needs to occupy a large amount of land resources, but also the toxic and harmful substances in fly ash are easy to leak due to the damage of the anti-seepage layer, causing groundwater pollution and serious environmental risk; the other is the "water washing + sintering" process, which aims to remove salt and part of heavy metals by water washing, and then destroy dioxin and realize residue resource through sintering, but this process has the following defects: 1. High cost of water and treatment: in order to reduce the salt content of fly ash to below 1%, more than 10 tons of water are added per ton of fly ash, and about 10 tons of wastewater containing excessive heavy metals and more than 2% of salt are generated, which need to be distilled to meet the discharge standard, and the cost of equipment and fuel is extremely high; 2. Large fuel consumption: the filter cake containing 50% water after water washing needs to be heated to remove dioxin, and the high water content leads to a large increase in fuel cost; 3. Unstable pollution control: the filter cake is easy to break into dust after dehydration in the rotary kiln, and the heavy metals and salt still do not meet the standard, which needs to be additionally invested in high-temperature bag dust removal, anti-seepage storage and other equipment to collect and store, increasing the cost and having limited effect; 4. Limited resource utilization at the back end: the salt content of the treated raw material is still about 1%, which is much higher than the national standard, and can only be used in a small amount, and the dioxin mixed with water cannot be decomposed in low-temperature vacuum state, and still exists in the remaining salt, which seriously restricts the efficient resource utilization of fly ash.

[0004] The above problems lead to low comprehensive utilization level of fly ash in China, which is difficult to meet the requirements of environmental protection policies such as "prohibition of landfill" and "waste-free city", and a fly ash treatment technology with low cost, high efficiency and pollution discharge standard is urgently needed. SUMMARY

[0005] In order to overcome the shortcomings of the prior art, one of the purposes of the present application is to provide a system and method for removing heavy metals and salt from household garbage incineration fly ash.

[0006] One of the purposes of the present application is achieved by adopting the following technical solutions: A method for removing heavy metals and salts from fly ash from incineration of domestic waste, comprising the following steps: S1: Raw material mixing: Mix fly ash from the incineration of domestic waste with at least one ceramic raw material selected from kaolin, feldspar, and shale, add water and stir until a thin slurry forms, then mix with the fly ash, and use a concrete mixer to extend the stirring time until the fly ash and the slurry are fully uniform to form a paste-like substance; S2: Embryo preparation: The paste obtained in step S1 is pressed into spherical embryos with a diameter of 3 cm using a ball press; S3: Pretreatment and firing: The spherical embryos are placed in the top chamber of the kiln and slowly heated and dehydrated. They are then fed into a vertical rotary kiln in batches via a positive pressure fan for firing. The vertical rotary kiln only has a rotary discharge device at the bottom, and the rest of the kiln body does not move, so the unfired embryos will not be damaged by the rotation of the kiln. During the firing process, the combustion layer has the highest temperature. The mixture of fly ash, the main component of which is silica, and raw materials such as kaolin and feldspar will be ceramicized at a specific temperature and sintered into ceramsite. Heavy metals are also solidified in the ceramic and cannot be precipitated. The temperature below gradually decreases, and air is injected into the combustion layer through a fan to bring heat into the combustion layer. After firing, a porous, ceramicized pottery is obtained, and the discharge temperature of the pottery is 60-70 degrees Celsius. S4: Multi-stage water washing and desalination: The ceramic material obtained in step S3 is washed at least three times, wherein the first two water washes include: adding an equal weight of water to the ceramic material, applying high-power ultrasonic waves for 10 minutes to allow soluble salts and a small amount of soluble heavy metals to enter the water to form brine; sending the brine to a vacuum low-temperature distillation and salt separation crystallization system for treatment, and dehydrating the ceramic material to a moisture content of less than 5% by high-speed centrifugal dehydrator; the third water wash uses recycled water from the first two water washes, which is then dehydrated by a high-speed centrifugal dehydrator. S5: Compliance test: After processing in step S4, the salt content of the ceramic material is ≤500ppm, and the heavy metal content is lower than the hazardous waste standard.

[0007] Furthermore, in step S3, the firing heating method is natural gas combustion heating, or at least one combustible material such as sawdust or bamboo chips is mixed into the ceramsite embryo for combustion heating. As the temperature gradually increases, the sawdust and bamboo chips are gradually converted into activated carbon with an adsorption effect, thereby reducing the emission of some harmful gases.

[0008] Furthermore, in step S4, after the first water washing, the ceramsite with a salt content of 20% is washed with the same mass of clean water for the first water washing, and the brine concentration is 20%, and the comprehensive salt content of the pottery with 5% residual brine is 1%; after the second washing with the same mass of clean water, the brine concentration is 1%, and the comprehensive salt content of the pottery with 5% residual brine is 0.05%; after the third water washing, the brine concentration is 0.05%, and the comprehensive salt content of the pottery with 5% residual brine is 0.0025%, that is, the theoretical value is 25ppm.

[0009] The system for removing heavy metals and salts from fly ash from municipal solid waste incineration includes: Raw material mixing device: a concrete mixer used to mix fly ash with ceramic raw materials and water to form a uniform paste; Embryo preparation device: a ball press connected to the raw material mixing device, used to press the paste into spherical embryos with a diameter of 3 cm; Pretreatment and firing device: including an overhead bin and a vertical rotary kiln. The overhead bin is used to slowly heat and dehydrate the spherical embryos. The vertical rotary kiln is connected to the overhead bin via a positive pressure fan. The bottom material is equipped with a rotary discharge device, and the rest of the kiln body is fixed. It is used to fire the spherical embryos to obtain ceramic pottery. Multi-stage water washing device: including a washing tank, an ultrasonic generator, a high-speed centrifugal dehydrator, and a vacuum low-temperature distillation and salt separation crystallization system; the washing tank is used to hold ceramic materials and water, the ultrasonic generator is located in the washing tank, and the ultrasonic power is 1 kilowatt per ton of ceramsite washed. The high-speed centrifugal dehydrator is connected to the washing tank to dehydrate the ceramic materials, and the vacuum low-temperature distillation and salt separation crystallization system is connected to the washing tank to treat the brine generated by the first two water washes; Water circulation device: connects the vacuum low-temperature distillation salt separation crystallization system with the cleaning tank, and is used to transport the distilled water to the cleaning tank for the third water wash.

[0010] Furthermore, the vertical rotary kiln also includes a heating device, which is a natural gas burner, or a combustion structure for combustible materials such as sawdust and bamboo chips mixed with the ceramsite embryo.

[0011] Furthermore, the dehydration capacity of the high-speed centrifugal dehydrator is such that the moisture content of the pottery is less than 5%.

[0012] Furthermore, a temperature control device is provided between the top bin and the vertical rotary kiln for controlling the dehydration progress of the spherical embryos when they enter the vertical rotary kiln from the top bin.

[0013] Furthermore, the combustion layer of the vertical rotary kiln is provided with a temperature monitoring module for real-time monitoring of the combustion layer temperature and feeding back the temperature to the fan to adjust the air intake.

[0014] Compared with the prior art, the present invention has the following beneficial effects: 1. Only 2 tons of water are required per ton of fly ash (20% of the traditional process). The brine produced by the first two water washes is treated by vacuum low-temperature distillation, reducing the amount of distilled water by 80%, significantly reducing equipment and fuel costs; 2. The embryo is slowly dehydrated in the overhead bin before firing, which reduces the moisture content entering the kiln and significantly reduces the removal of dioxins and fuel consumption during the firing process; while the existing technology cannot remove dioxins mixed with moisture.

[0015] 3. The use of a vertical rotary kiln (only the bottom material rotates, while the rest of the kiln body is fixed) avoids the breakage of the embryo during the firing process. After high-temperature firing, the ceramic material forms a porous ceramic structure, which can solidify most heavy metals inside the ceramic, reducing the risk of secondary release of heavy metals; 4. Through three water washes (the first two are combined with ultrasonic enhanced dissolution, and the third uses recycled water), the salt content of the final ceramic material can be reduced to below the national standard of 500ppm. This solves the problem of excessive salt content in the back-end products of traditional processes, allowing the ceramic material to be directly used in construction projects (such as cement, ceramsite, bricks, etc.) without the need for small amounts of additives, thereby improving the efficiency and scope of fly ash resource utilization. 5. The vertical rotary kiln uses a fan to introduce the residual heat from the bottom into the combustion layer, and combines it with natural gas or combustibles (sawdust, bamboo chips) for heating, which improves the heat utilization efficiency. The holes formed inside the ceramsite after combustion are conducive to the precipitation of salt, and the temperature of the discharged ceramsite is controlled at 60-70℃, which is convenient for subsequent water washing and further reduces energy consumption.

[0016] The above description is only an overview of the technical solution of the present invention. In order to more clearly understand the technical means of the present invention, it can be implemented in accordance with the contents of the specification. In order to make the above and other purposes, features and advantages of the present invention more obvious and easy to understand, the following preferred embodiments are specifically cited and described in detail with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a process step diagram of this embodiment. DETAILED DESCRIPTION

[0018] The present invention will be further described below in conjunction with the accompanying drawings and specific implementation methods. It should be noted that, under the premise of no conflict, the various embodiments or technical features described below can be arbitrarily combined to form new embodiments.

[0019] It should be noted that when a component is referred to as being "fixed to" another component, it may be directly on the other component or there may also be a central component. When a component is considered to be "connected to" another component, it may be directly connected to the other component or there may also be a central component. When a component is considered to be "set on" another component, it may be directly set on the other component or there may also be a central component. The terms "vertical", "horizontal", "left", "right" and similar expressions used herein are for illustrative purposes only.

[0020] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one skilled in the art to which this invention pertains. The terms used in this specification of the present invention are for the purpose of describing specific embodiments only and are not intended to limit the present invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0021] 1. Raw materials: Municipal solid waste incineration fly ash (taken from a waste incineration power plant, initial test data: salt content 20.3%, heavy metal content: Pb 520mg / kg, Cr 380mg / kg, Cd 15mg / kg, moisture content 8%); ceramic raw materials (kaolin 30%, feldspar 20%, shale 50%, all industrial grade); tap water; sawdust (combustible, calorific value 4000kcal / kg).

[0022] 2. Equipment: JS500 concrete mixer; Φ30mm pelletizing machine; vertical rotary kiln (4.8m in diameter, 9m in height, 163m³ effective volume, 500 tons of ceramsite sintered per day, bottom material with rotary discharge device); overhead silo (temperature control range 20-200°C); 100kW ultrasonic cleaning tank; high-speed centrifugal dehydrator (also known as horizontal screw dehydrator, processing capacity 30t / h); vacuum low-temperature distillation salt crystallization system (evaporation capacity 60t / h); inductively coupled plasma mass spectrometer (ICP-MS, heavy metal detection); ion chromatograph (salt detection).

[0023] Step 1: Mix the ingredients Take 700t of fly ash, add 300t of ceramic raw materials (60t of kaolin, 60t of feldspar, 180t of shale), first add 300t of water and 100t of sawdust to the ceramic raw materials and stir in a pre-homogenization tank until it becomes a thin mud (water content of about 30%), then put it into a concrete mixer and extend the stirring time to 3 minutes to form a uniform paste (water content of about 30%).

[0024] Step 2: Embryo body preparation The paste was fed into a ball press and pressed into spherical embryos with a diameter of 3 cm (the weight of a single ball was about 15 g). The embryos were placed in a naturally ventilated environment for 24 hours to harden.

[0025] Step 3: Pretreatment and Firing Pretreatment: Place the embryo into the top bin of the kiln, or set it as a side bin. By introducing the kiln exhaust gas, slowly raise the embryo temperature from room temperature to 75°C for 24 hours or longer, and dehydrate it to a moisture content of less than 5%.

[0026] Firing: The pre-treated embryos are fed into the vertical rotary kiln in batches through a positive pressure fan to prevent the gas in the kiln from escaping through the charging port. The temperature of the combustion layer in the kiln is controlled at 1200℃, and the temperature gradient above is 75℃→400℃→700℃→1000℃ from top to bottom; the gradual heating of the ceramsite is conducive to the gradual discharge of the moisture contained in it, without causing the embryo to burst due to the rapid heating of the embryo and the boiling of the water inside. The temperature gradient below the combustion layer is 1000℃→700℃→400℃→100℃, and the gradual cooling of the ceramsite is also conducive to keeping it from breaking. The firing time from entering the kiln to discharge is about 8 hours, that is, when firing day and night, 3 batches can be completely refined every 24 hours, with a total of about 490m 3 During the firing process, fans inject air to bring heat from below into the combustion layer. The final discharged pottery temperature is 65°C, and a total of 500 tons of pottery is obtained (loss is due to water evaporation and sawdust burning into ash).

[0027] Step 4: Multi-stage water washing and desalination First wash: 500 tons of tap water were added to 500 tons of pottery, and the mixture was placed in a 100kW ultrasonic cleaning tank for 10 minutes. The mixture was then separated and the pottery was sent to a high-speed centrifugal dehydrator to be dehydrated to a moisture content of 4.8%. 475 tons of brine was collected and tested to have a salt content of 20.1%.

[0028] Second wash: 500t of tap water was added to the dehydrated ceramics, and ultrasonic treatment and centrifugal dehydration were repeated. The ceramics had a moisture content of 4.5%. 481kg of brine was collected, with a salt content of 1.02%.

[0029] The third water washing: using 500t of recycled water from the first two water washings after vacuum low-temperature distillation, repeat the above operation, the moisture content of the ceramic material is 4.2%.

[0030] Step 5: Compliance testing, sampling and testing of the final pottery.

[0031] (1) Salt content change data during water washing process Washing times Brine weight (t) Salt content of brine Residual salt content in pottery (t) Moisture content of pottery initial - 20.3% 20.3 8% After the first time 475 20.1% 1.0 (500t of pottery) 4.8% After the second time 481 1.02% 0.051 4.5% After the third time 482 (circulating water) 0.025% 0.0021 4.2% The final salt content of the pottery is: 0.0021kg / 82kg≈0.00256%, or 25.6ppm (the actual measured value is 291ppm, slightly higher due to the trace salt content in natural water).

[0032] index The present invention "burn first and then wash" Traditional "wash first, then burn" Reduce the ratio Water consumption (tons / tons of fly ash) 2 10 80% Distillation water volume 1.9 tons (first 2 times) 9.5 tons 83% Fuel consumption (natural gas) 8m³ 25m³ 68%

[0033] 1. After being processed by the "burn first, then wash" process, the salt content of the ceramic material made from fly ash is 291ppm, which is lower than the national standard of 500ppm; the heavy metal content is lower than the hazardous waste identification standard and can be directly used in construction projects.

[0034] 2. Compared with traditional processes, water consumption is reduced by 80%, distillation costs are reduced by 83%, and fuel consumption is reduced by 68%, significantly improving the economy and feasibility of comprehensive utilization of fly ash.

[0035] (Note: The experimental data is derived from the average of three parallel experiments. The detection method complies with the requirements of the "Technical Specifications for Pollution Control of Fly Ash from the Incineration of Municipal Waste" (HJ1134-2020). The above embodiments are only preferred embodiments of the present invention and cannot be used to limit the scope of protection of the present invention. Any non-substantial changes and replacements made by technicians in this field on the basis of the present invention fall within the scope of protection required by the present invention.

Claims

1. A method for removing heavy metals and salts from fly ash from incineration of domestic waste, characterized in that: The following steps are involved: S1: Raw material mixing: Mix fly ash from the incineration of domestic waste with at least one ceramic raw material selected from kaolin, feldspar, and shale, add water and stir until a thin slurry forms, then mix with the fly ash, and use a concrete mixer to extend the stirring time until the fly ash and the slurry are fully uniform to form a paste-like substance; S2: Embryo preparation: The paste obtained in step S1 is pressed into spherical embryos with a diameter of 3 cm using a ball press; S3: Pretreatment and Firing: The spherical embryos are placed in the top chamber of the kiln, slowly heated and dehydrated, and then fed in batches into a vertical rotary kiln for firing via a positive pressure fan. The vertical rotary kiln only has a rotating discharge device at the bottom, while the rest of the kiln body remains stationary. During the firing process, the combustion layer has the highest temperature, while the temperature below gradually decreases. Air is injected into the combustion layer via a fan, bringing heat into the combustion layer. After firing, a porous, ceramicized pottery is obtained, and the discharge temperature of the pottery is 60-70 degrees Celsius. S4: Multi-stage water washing and desalination: The ceramic material obtained in step S3 is washed at least three times, wherein the first two water washes include: adding an equal weight of water to the ceramic material and applying ultrasonic waves for 10 minutes to allow soluble salts and a small amount of soluble heavy metals to enter the water to form brine; sending the brine to a vacuum low-temperature distillation and salt separation crystallization system for treatment, and dehydrating the ceramic material by a high-speed centrifugal dehydrator to a moisture content of less than 5%; the third water wash uses recycled water from the first two water washes, and the ceramic material is also dehydrated by a high-speed centrifugal dehydrator after the water wash; S5: Compliance test: After processing in step S4, the salt content of the ceramic material is ≤500ppm, and the heavy metal content is lower than the hazardous waste standard.

2. The method according to claim 1, characterized in that In step S3, the firing heating method is natural gas combustion heating, or at least one combustible material selected from sawdust and bamboo chips is mixed into the ceramsite embryo to be burned and heated.

3. The method according to claim 1, characterized in that In step S4, after the ceramsite with a salt content of 20% is washed for the first time with the same mass of clean water, the brine concentration is 20%, and the comprehensive salt content of the pottery with 5% residual brine is 1%; after the second washing with the same mass of clean water, the brine concentration is 1%, and the comprehensive salt content of the pottery with 5% residual brine is 0.05%; after the third washing, the brine concentration is 0.05%, and the comprehensive salt content of the pottery with 5% residual brine is 0.0025%, that is, the theoretical value is 25ppm.

4. A system for removing heavy metals and salts from fly ash from domestic waste incineration by implementing the method described in any one of claims 1 to 3, characterized in that: include: Raw material mixing device: a concrete mixer used to mix fly ash with ceramic raw materials and distillation end water containing excessive heavy metals to form a uniform paste; Embryo preparation device: a ball press connected to the raw material mixing device, used to press the paste into spherical embryos with a diameter of 3 cm; Pretreatment and firing device: including an overhead bin and a vertical rotary kiln. The overhead bin is used to slowly heat and dehydrate the spherical embryos. The vertical rotary kiln is connected to the overhead bin via a positive pressure fan. The bottom material is equipped with a rotary discharge device, and the rest of the kiln body is fixed. It is used to fire the spherical embryos to obtain ceramic pottery. Multi-stage water washing device: includes a washing tank, an ultrasonic generator, a high-speed centrifugal dehydrator, and a vacuum low-temperature distillation and salt separation crystallization system; the washing tank is used to hold pottery and water, the ultrasonic generator is located in the washing tank, and the power (kilowatt) matches the tonnage of each washing. The high-speed centrifugal dehydrator is connected to the washing tank to dehydrate the pottery, and the vacuum low-temperature distillation and salt separation crystallization system is connected to the washing tank to process the brine generated by the first two water washes; Water circulation device: connects the vacuum low-temperature distillation salt separation crystallization system with the cleaning tank, and is used to transport the distilled water to the cleaning tank for the third water wash.

5. The system according to claim 4, characterized in that The vertical rotary kiln further comprises a heating device, which is a natural gas burner or a combustion structure for combustible materials such as sawdust and bamboo chips mixed with the ceramsite embryo.

6. The system according to claim 4, characterized in that The dehydration capacity of the high-speed centrifugal dehydrator is to reduce the moisture content of the pottery to less than 5%.

7. The system according to claim 4, wherein: A temperature control device is provided between the top bin and the vertical rotary kiln for controlling the dehydration progress of the spherical embryos when they enter the vertical rotary kiln from the top bin.

8. The system according to claim 4, wherein: The combustion layer of the vertical rotary kiln is provided with a temperature monitoring module for real-time monitoring of the combustion layer temperature and feeding back to the fan to adjust the air intake.

Images