Fly ash water washing water resource treatment method

Abstract

The application discloses a fly ash washing water resource treatment method, realizes zero discharge of decalcification sludge and evaporation mother liquor through precipitation process optimization and mother liquor closed circuit reuse, significantly reduces investment and operation cost, and simplifies operation management process. The fly ash washing water treatment adopts the evaporation and salt separation process, and the problems of high equipment investment, high operation energy consumption, complicated sludge management, high cost of evaporation mother liquor hazardous waste discharge and great environmental risk are solved.

Description

(I) Technical Field

[0001] This invention belongs to the field of waste incineration fly ash resource utilization technology, specifically relating to a method for fly ash washing water resource utilization. (II) Background Technology

[0002] Waste incineration fly ash is a lightweight, small-particle-size powdery substance separated from the flue gas dust removal system during waste incineration, and it is classified as hazardous waste. Currently, cement kiln co-processing technology is commonly used to reduce, render harmless, and recycle waste incineration fly ash. However, soluble substances such as potassium, sodium, and chloride contained in fly ash can affect the quality of cement products from cement kilns. Therefore, before co-processing, water washing is usually used to dissolve soluble substances (such as potassium ions, sodium ions, chloride ions, calcium ions, organic matter, and heavy metals) in the fly ash.

[0003] Existing fly ash wash water treatment typically employs the following process: calcium ions in the wash water are converted into calcium sulfate or calcium carbonate by adding sodium sulfate and sodium carbonate, and the resulting decalcified sludge is filtered and recovered using a mechanical filter press; heavy metals are removed by adding sodium sulfide or trisodium trithiocyanate (TMT); potassium, sodium, and chloride ions are separated into potassium chloride and sodium chloride industrial salt products by MVR (mechanical vapor recompression) evaporation and salt separation technology. After a certain evaporation cycle, due to the enrichment of impurities, the evaporation mother liquor is periodically discharged in small quantities for external disposal.

[0004] However, the aforementioned existing technologies have the following obvious limitations and defects: 1. Mechanical filtration (such as plate and frame filter presses) is used to filter decalcified sludge, requiring high-pressure feed pumps and high-pressure pressing pumps with a head of over 80 meters. This not only results in large equipment investments and extremely high energy consumption, but also requires regular manual assistance during filter press operation (such as replacing filter cloth and unloading filter cake), increasing the management difficulty and labor costs of sludge transportation. 2. Evaporation mother liquor, due to its high concentration of impurities and organic matter, is classified as hazardous waste. Regular external discharge and disposal will lead to high hazardous waste treatment costs and increase the environmental management risks for enterprises. (III) Summary of the Invention

[0005] The purpose of this invention is to provide a method for the resource-based treatment of fly ash wash water. By optimizing the sedimentation process and reusing the mother liquor in a closed loop, it achieves zero discharge of decalcified sludge and evaporation mother liquor, significantly reducing investment and operating costs and simplifying the operation and management process. This method overcomes the shortcomings of existing fly ash wash water treatment processes that rely on evaporation and salt separation, which suffer from high equipment investment, high energy consumption, cumbersome sludge management, high costs and environmental risks associated with the hazardous discharge of evaporation mother liquor.

[0006] The technical solution adopted in this invention is: This invention provides a method for the resource-based treatment of fly ash wash water. The method is carried out using a resource-based system, which includes a water washing unit, an equalization tank unit, a first reaction tank unit, a first sedimentation tank unit, a second reaction tank unit, a second sedimentation tank unit, a neutralization filtration unit, and an evaporation and desalination unit connected in sequence. The method includes the following steps: (1) Washing process: The fly ash from the waste incineration is sent to the washing unit, tap water is introduced, and the fly ash is washed and desalinated using a countercurrent washing method. The desalinated fly ash filter cake and high-salt fly ash washing water are separated. The high-salt fly ash washing water is pumped into the regulating tank unit through a closed pipeline, and the filter cake is sent to the washing fly ash temporary storage bin through a closed pipeline. The subsequent treatment is carried out in a cement kiln. (2) Two-stage decalcification and heavy metal removal process: The effluent from the equalization tank is pumped through a closed pipeline into the first-stage reaction sedimentation unit consisting of the first reaction tank unit and the first sedimentation tank unit, and the second-stage reaction sedimentation unit consisting of the second reaction tank unit and the second sedimentation tank unit. Chemical agents are added in the first reaction tank unit to remove most of the calcium ions in the water, and chemical agents are added in the second reaction tank unit to remove the remaining calcium ions and heavy metal ions. The decalcified sludge produced by the first sedimentation tank unit and the second sedimentation tank unit is returned to the water washing unit in step (1) through a sludge pump. Both the first sedimentation tank unit and the second sedimentation tank unit adopt vertical flow sedimentation tanks. (3) Evaporation and salt separation and closed-loop reuse of mother liquor: The supernatant of the second sedimentation tank unit enters the neutralization and filtration unit through a closed pipeline and is then pumped into the evaporation and salt separation unit through a closed pipeline for evaporation, crystallization and salt separation, respectively obtaining sodium chloride industrial salt products and potassium chloride industrial salt products; the evaporation mother liquor generated by the evaporation and salt separation unit is continuously returned to the water washing unit in step (1) through a closed pipeline, using the adsorption effect of fly ash particles to intercept impurities in the mother liquor and maintain the dynamic balance of impurity concentration in the water washing system; the evaporation condensate generated by the evaporation and salt separation unit is returned to the water washing unit through a closed pipeline to replace part of the tap water and reduce the amount of tap water used.

[0007] Furthermore, in step (1), the water washing unit preferably adopts a three-stage countercurrent washing process, and can also adopt more stages of countercurrent washing according to the requirements of fly ash desalination depth. The evaporation mother liquor generated by the evaporation and salt separation unit is continuously returned to the first stage water washing process of the water washing unit in step (1) through a closed pipeline. The feed flow rate of fly ash is 1~15 t / h (preferably 5 t / h), and the mass ratio of fly ash to tap water is 1:2-5 (preferably 1:3).

[0008] Further, in step (1), the fly ash from the waste incineration plant is collected from the flue gas purification system and sent to the fly ash silo for temporary storage via a closed conveying device, and then continuously sent to the washing unit via a screw conveyor. The washing unit uses a multi-stage countercurrent washing process to wash and desalinate the fly ash, fully dissolving the soluble chloride salts and alkali metal ions in the fly ash. After washing, solid-liquid separation is performed, and the desalinated fly ash filter cake is sent to the washing fly ash temporary storage silo for subsequent cement kiln co-processing. The high-salt fly ash washing water separated is sent to the regulating tank unit. The regulating tank is equipped with a low-speed stirring device with a stirring speed of 20~50 rpm to prevent suspended particles in the water from settling and caking, and to ensure uniform effluent quality.

[0009] Further, in step (2), sodium sulfate is continuously added to the first reaction tank unit to remove most of the calcium ions in the water. The total amount of sodium sulfate added is calculated based on the influent flow rate of the washing water and the molar concentration of calcium ions therein. That is, the molar amount of sodium sulfate added is 0.8 to 0.9 times the molar flow rate of calcium ions in the influent, preferably 0.85 times, so as to ensure the precipitation efficiency of calcium sulfate while avoiding excessive introduction of sulfate ions. Sodium carbonate and sodium sulfide are added to the second reaction tank unit to remove the remaining calcium ions and heavy metal ions, respectively. The calculation method for sodium carbonate and sodium sulfide dosage is the same as that for sodium sulfate dosage in the first reaction tank unit. The dosage of sodium carbonate is 1.0 to 1.2 times the molar flow rate of residual calcium ions in the effluent of the first-stage sedimentation tank unit, preferably 1.1 times, so that the final effluent calcium ion concentration meets the scale prevention requirements of MVR (≤100 mg / L). The dosage of sodium sulfide is 0.9 to 1.2 times the total molar flow rate of target heavy metals (Pb, Cd, Hg, etc.) in the effluent of the first-stage sedimentation tank unit, preferably 1.0 to 1.1 times, so that the total heavy metal concentration in the effluent meets the water quality requirements of evaporation and desalination influent (≤0.1 mg / L). This can be verified by small-scale titration.

[0010] Preferably, sodium sulfate, sodium carbonate, and sodium sulfide are all added in the form of an aqueous solution with a mass concentration of 10-20%; the first reaction tank and the second reaction tank are both stirred at room temperature (25±2 ℃) using a low-speed mechanical stirrer at a speed of 200 rpm for 30 minutes.

[0011] Furthermore, the vertical flow sedimentation tank consists of a tank body and a conical sludge hopper located at the lower end of the tank body. An overflow weir and a drain outlet are provided around the top of the tank body. The conical sludge hopper is connected to a sludge discharge pipe. The tank body is circular in plan. Water enters the tank from top to bottom through an inlet pipe into a central pipe located at the center of the tank. A funnel-shaped opening and a reflector plate are provided at the lower end of the central pipe, allowing the wastewater to be evenly distributed in the tank before slowly rising along the entire cross-section. Suspended solids settle into the conical sludge hopper at the bottom of the tank, and clarified water flows out from the perimeter of the tank along the overflow weir. The tank diameter is 4.0~7.0 m, with a maximum of ≤10 m; the effective water depth is 2.0~4.0 m, and the diameter-to-depth ratio is ≤3:1; the upward flow velocity in the tank is 0.2~0.5 mm / s; the sedimentation time is 1.5~4.0 h; and the flow velocity in the central pipe is no greater than 30 m / s. The flow rate is 1.35 times the diameter of the central tube, the diameter of the reflector plate is 1.3 times the diameter of the flared mouth, and the angle between the reflector plate surface and the horizontal plane is 17°; the gap height between the lower edge of the flared mouth and the reflector plate surface is 0.3~0.5 m, and the gap flow velocity is ≤30 mm / s; the bottom of the reflector plate is at least 0.3 m from the mud surface; the inclination angle of the conical sedimentation hopper is 55°~60°, and the diameter of the sludge discharge pipe is not less than 200 mm; a buffer layer of 0.3 m is set under the reflector plate, and the freeboard above the water surface of the pool is 0.3~0.5 m.

[0012] Furthermore, in step (2), both the first sedimentation tank unit and the second sedimentation tank unit are equipped with a central drive sludge scraper (preferably with a rotation speed of 2~3 rpm), which is driven by a central drive shaft set in the center of the tank to prevent local sludge deposition and hardening, and to ensure sludge fluidity; the concentrated sludge at the bottom of the sedimentation tank is continuously transported to the washing unit by a sludge pump, and after being washed with fly ash, it is discharged from the system with the desalination fly ash filter cake.

[0013] Furthermore, in step (2), the effluent from the equalization tank undergoes deep purification treatment sequentially through a two-stage reaction-sedimentation system according to the following steps: ① First-stage decalcification and heavy metal removal: The effluent from the equalization tank is first pumped into the first reaction tank unit, where sodium sulfate is continuously added as the first decalcification agent. Sodium sulfate reacts with calcium ions in the water to form slightly soluble calcium sulfate precipitate, which can remove more than 50% of the calcium ions in the water, significantly reducing the cost of agents for subsequent deep decalcification. The added sodium sulfate agent is prepared as a 10%~20% (w / w) aqueous solution and sent into the reaction tank by a metering pump. The specific addition rate is calculated according to the specific molar flow rate of calcium ions in the water. The mixture after the reaction is pumped into the first sedimentation tank unit for solid-liquid separation. ② Second-stage decalcification and heavy metal removal: The supernatant from the first sedimentation tank unit is pumped into the second reaction tank unit. Sodium carbonate is continuously added to the tank as a second decalcification agent, reacting with the remaining calcium ions in the water to form insoluble calcium carbonate precipitate, achieving deep removal of calcium ions and ensuring the scale prevention requirements of the subsequent evaporation system. The sodium carbonate is prepared as a 10%~20% (w / w) aqueous solution and continuously fed into the second reaction tank unit through a metering pump. The specific addition rate is calculated based on the specific calcium ion molar flow rate in the water. Simultaneously, sodium sulfide is added to the second reaction tank unit to remove dissolved heavy metal ions in the water through precipitation. The sodium sulfide is prepared as a 10%~15% (w / w) aqueous solution. A % aqueous solution is continuously fed into the second reaction tank unit through a metering pump. The specific addition rate is calculated according to the molar flow rate of heavy metal ions in the water. The mixed liquid after the reaction is pumped into the second sedimentation tank unit for solid-liquid separation. The concentrated decalcified sludge at the bottom of the first sedimentation tank unit and the second sedimentation tank unit is continuously transported back to the water washing unit in step (1) through a regular sludge pump. It enters the washing process together with the fresh fly ash and is finally discharged from the system along with the desalination fly ash filter cake. There is no need to set up a separate mechanical filter press dewatering equipment, nor is there a need for sludge transfer and disposal.

[0014] Further, in step (3), the neutralization filtration process involves first adjusting the pH to 7-8, followed by filtration. The filtration can be performed using any one of sand filtration, precision filtration, or nanofiltration membrane filtration, selected according to the effluent quality requirements. More preferably, a multi-media filter is used, followed by filtration of the filtrate using a security filter (with a built-in 5 μm PP melt-blown filter element). The filter media of the multi-media filter, from top to bottom, consist of ceramsite (particle size 1-2 mm) and quartz sand (particle size 0.5-0.8 mm), with a ceramsite to quartz sand height ratio of 1:1.2, a total filter layer thickness ≥1.6 m, and a filtration rate of 6-8 m / s. 3 / h.

[0015] Furthermore, in step (3), the flow rate of the evaporated mother liquor returned to the water washing unit is 0.5~5 m³. 3 The continuous reuse rate of evaporation mother liquor is 5%~20% of the total water used for washing, which can be adjusted according to the fly ash treatment volume and the enrichment level of the mother liquor. The flow rate of evaporation condensate returned to the washing unit is 10.5~11.5 m³ / h. 3 / h, the reuse rate is 70%~76% of the total water used for washing.

[0016] Furthermore, in step (3), the evaporation and salt separation unit adopts the MVR process; the evaporation temperature is 80~100℃, the single-stage temperature rise of the centrifugal compressor is 20℃, the flow rate in the forced circulation tube is 2.5 m / s, the high temperature is 85~95℃ to precipitate NaCl, and the low temperature is 30-40℃ to precipitate KCl.

[0017] Further, in step (3), the evaporation and salt separation and mother liquor closed-loop reuse steps are as follows: the supernatant of the second sedimentation tank unit is first pumped into the neutralization and filtration unit, the pH is adjusted to neutral by adding hydrochloric acid, and then the residual suspended particles are removed by filtration; the filtered water is pumped into the evaporation and salt separation unit through a closed pipeline, and sodium chloride industrial salt products and potassium chloride industrial salt products are obtained through evaporation concentration, cooling crystallization and centrifugal salt separation processes, respectively; the condensate generated by evaporation is reused in the water washing unit as tap water replenishment; the enriched evaporation mother liquor generated during the operation of the evaporation and salt separation unit is continuously used for... The water is returned to the first-stage washing process of the washing unit in step (1) in a small volume manner. Since all the impurities in the evaporation mother liquor come from the slightly soluble components in the fly ash, the solubility of the impurities remains constant under the temperature and salinity conditions of the washing system. At the same time, the fly ash particles have a well-developed pore structure and strong adsorption performance. The organic matter and trace impurities brought in by the reflux mother liquor can be adsorbed and intercepted by the fly ash particles and discharged from the system along with the desalination fly ash filter cake. Therefore, the concentration of impurities in the washing water can maintain a dynamic balance and will not be continuously enriched as the mother liquor is continuously reused, thus completely avoiding the discharge of the evaporation mother liquor.

[0018] Compared with the prior art, the present invention has the following significant technical effects and economic advantages: 1. Significantly reduced equipment investment. This invention uses a vertical flow sedimentation tank combined with a sludge scraper and a common sludge pump to replace the traditional plate and frame filter press and its supporting high-pressure feed pump and pressing pump system. Equipment investment can be reduced by more than 98%, significantly reducing the initial investment of the project.

[0019] 2. Significantly reduced operating energy consumption. Traditional filter press systems require high-lift feed pumps and high-pressure pressing pumps, resulting in extremely high energy consumption; this process only requires low-lift ordinary sludge pumps and low-speed agitators, reducing energy consumption in the decalcification sludge treatment stage by more than 98%, significantly reducing power operating costs.

[0020] 3. Reduced operating costs. On the one hand, the power consumption of the sedimentation system is much lower than that of the mechanical filter press system; on the other hand, the mother liquor from evaporation is fully recycled in a closed loop, eliminating the need for outsourcing its disposal as hazardous waste and saving significant hazardous waste disposal costs.

[0021] 4. Operation and management are greatly simplified. This process uses closed-loop pipeline transportation throughout, with a high degree of automation. It eliminates the need for manual operations such as filter press unloading, filter cloth replacement, and sludge transfer, as well as management procedures such as approval and supervision of hazardous waste transfer of evaporation mother liquor, significantly reducing labor costs and management difficulty.

[0022] 5. Closed-loop circulation, low environmental risk. All decalcified sludge and evaporation mother liquor are recycled to the water washing system. The fly ash itself adsorbs organic matter and trace impurities from the evaporation mother liquor, achieving complete closed-loop reuse of the evaporation mother liquor without the need for outsourced hazardous waste disposal. The sludge then enters the subsequent cement kiln co-processing stage along with the fly ash. The entire water treatment system has no external discharge of decalcified sludge or evaporation mother liquor; both are circulated in a closed loop through the water washing unit, eliminating the environmental risks associated with hazardous waste transfer and disposal.

[0023] 6. Stable and controllable water quality. Relying on the adsorption properties of fly ash itself, the TOC and other impurity indicators in the washing water after the mother liquor is reused will not continue to rise, and can maintain dynamic stability, ensuring the long-term stable operation of the subsequent evaporation and salt separation system. (iv) Description of the attached drawings

[0024] Figure 1 This is a process flow diagram of the resource utilization scheme for fly ash washing water treatment evaporation and salt separation according to the present invention.

[0025] Figure 2 This is a schematic diagram of a vertical flow sedimentation tank. (V) Detailed Implementation Methods

[0026] The present invention will be further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto: Example 1 1. Experimental Materials Fly ash from a waste incineration plant in Jiaxing was taken, and the original evaporation mother liquor from the evaporation and salt separation unit of the process of this invention was taken. The TOC of the original evaporation mother liquor was measured to be 4025.51 mg / L.

[0027] 2. Experimental Procedure

[0028] Reference Figure 1 The process involves the resource-based treatment of fly ash wash water, following these steps: (1) Water washing process: The fly ash from the waste incineration is fed into the water washing unit at a feed flow rate of 5 t / h. The fly ash to tap water is washed and desalinated using a three-stage countercurrent washing method with a mass ratio of 1:3. The desalinated fly ash filter cake and high-salt fly ash wash water (calcium ion molar concentration 1584.35 mg / L (calcium ion molar concentration 1584.35 mg / L)) are separated to obtain the desalinated fly ash filter cake and the high-salt fly ash wash water (calcium ion molar concentration 1584.35 mg / L ... 2+ (Calculated), total molar concentration of heavy metals 12.68 mg / L), high salt fly ash wash water is pumped into the equalization tank unit through a closed pipeline for temporary storage. The equalization tank is equipped with a low-speed mechanical stirring device that runs continuously at 30 rpm. (2) Two-stage decalcification and degravimetric process: The effluent from the equalization tank unit is pumped through a closed pipeline into the first-stage reaction sedimentation unit consisting of the first reaction tank unit and the first sedimentation tank unit, and the second-stage reaction sedimentation unit consisting of the second reaction tank unit and the second sedimentation tank unit; both the first sedimentation tank unit and the second sedimentation tank unit are vertical flow sedimentation tanks. Figure 2 As shown in the figure, its geometric structure and hydraulic parameters are as follows: The vertical flow sedimentation tank consists of a tank body and a conical sludge hopper located at the lower end of the tank body. An overflow weir and a drain outlet are set around the top of the tank body. The conical sludge hopper is connected to a sludge discharge pipe. The tank body is circular in plan. Water enters the tank from top to bottom through the inlet pipe into the central pipe located in the center of the tank. A bell mouth and a reflector plate are set at the lower end of the central pipe, so that the wastewater is evenly distributed in the tank and then slowly rises along the entire cross-section. Suspended solids settle into the conical sludge hopper at the bottom of the tank, and clarified water flows out from the perimeter of the tank along the overflow weir. The tank diameter is 4.0 m, the effective water depth is 3.0 m, the upward flow velocity in the tank is 0.33 mm / s, the sedimentation time is 2.5 h, and the flow velocity in the central pipe is 25. The flow rate is mm / s, the diameter and height of the bell mouth are both 1.35 times the diameter of the central tube, the diameter of the reflector plate is 1.3 times the diameter of the bell mouth, and the inclination angle of the reflector plate surface to the horizontal plane is 17°; the gap height between the lower edge of the bell mouth and the reflector plate surface is 0.3 m; the bottom of the reflector plate is 0.3 m from the mud surface; the inclination angle of the conical sedimentation hopper is 60°, and the diameter of the sludge discharge pipe is 250 mm; a buffer layer of 0.3 m is set at the bottom of the pool (below the reflector plate), and the top of the pool above the water surface is 0.3 m high. Both the first and second sedimentation tanks are equipped with centrally driven sludge scrapers (3 rpm), driven by a central drive shaft located in the center of the tank. Sodium sulfate is added to the first reaction tank to remove most of the calcium ions in the water. The sodium sulfate is added as a 15% (w / w) aqueous solution, and the dosage is 0.85 times the initial calcium ion molar concentration in the high-salt washing water of step (1), i.e., the 15% sodium sulfate aqueous solution addition rate is approximately 480 L / h. Sodium carbonate and sodium sulfide are continuously added to the second reaction tank to remove the remaining calcium ions and heavy metal ions. Sodium carbonate and sodium sulfide are added as 15% (w / w) aqueous solutions. The dosage of sodium carbonate is based on the remaining calcium ions in the effluent of the first sedimentation tank (calcium ion molar concentration 554.52 mg / L). 2+The sodium carbonate solution was added at a rate of approximately 169 L / h, which is 1.15 times the molar concentration of the target heavy metals (Pb, Cd, Hg, etc.) in the high-salt washing water of step (1), so that the final calcium ion concentration of the effluent met the scale prevention requirements of MVR (≤100 mg / L). The sodium sulfide solution was added at a rate of approximately 1.05 times the total molar concentration of the target heavy metals (Pb, Cd, Hg, etc.) in the high-salt washing water of step (1), which is 1.6 L / h, so that the total heavy metal concentration of the effluent met the water quality requirements of the evaporation desalination influent (≤0.1 mg / L). The first and second reaction tank units were both stirred at 200 rpm for 30 minutes at room temperature (25±2 ℃) using a low-speed mechanical stirring device. The decalcified sludge produced by the first and second sedimentation tank units was returned to the water washing unit of step (1) through a sludge pump. (3) Evaporation, salt separation, and closed-loop mother liquor reuse process: The supernatant from the second sedimentation tank unit enters the neutralization and filtration unit through a closed pipeline and a pump. The pH is adjusted to 6-8 with hydrochloric acid. The effluent after neutralization is filtered by a multi-media filter (the filter media from top to bottom are quartz sand (particle size 0.5-0.8 mm) and ceramsite (particle size 1-2 mm), with a height ratio of ceramsite to quartz sand of 1:1.2, a total filter layer thickness of 1.6 m, and a filtration rate of 6-8 m / s). 3 / h) filtration, the filtrate is then filtered again by a security filter (built-in 5 μm PP melt-blown filter element), and then pumped into the evaporation and salt separation unit through a closed pipeline for MVR (evaporation temperature 80~100℃, centrifugal compressor single-stage temperature rise 20℃, forced circulation pipe flow rate 2.5 m / s, high temperature 85~95℃ to precipitate NaCl, low temperature 30-40℃ to precipitate KCl), to obtain sodium chloride industrial salt products and potassium chloride industrial salt products respectively; the evaporation mother liquor generated by the evaporation and salt separation unit is continuously refluxed to the first stage water washing process of the water washing unit in step (1), and the impurities in the mother liquor are intercepted by the adsorption effect of fly ash particles to maintain the dynamic balance of impurity concentration in the water washing system. Five experimental groups were set up respectively, in which the volume of evaporation mother liquor reflux accounted for 0%, 5%, 10%, 20% and 30% of the total volume of water washing water, and the remaining volume was made up by tap water and evaporation condensate, that is, the evaporation mother liquor reflux rate was 0m 3 / h, 0.75 m 3 / h, 1.5 m 3 / h, 3.0 m 3 / h, 4.5 m 3 / h. The evaporative condensate from the evaporation and salt separation unit is returned to the water washing unit, with a flow rate of 11.0 m³ / h. 3 / h, the reuse rate is 73% of the total water used for washing.

[0029] The TOC value of the fly ash wash water after the fly ash washing unit in step (1) was determined using a TOC-5000TOC analyzer to investigate the effect of different reuse ratios of the evaporation mother liquor on the TOC of the fly ash wash water after the three-stage countercurrent washing of fly ash. Three parallel samples were set up for each group of experiments, and the average value of the results was taken.

[0030] 3. Experimental Results

[0031] The TOC values ​​of fly ash wash water under different evaporation mother liquor reuse ratios are shown in Table 1.

[0032] Table 1. TOC values ​​of fly ash wash water under different proportions of evaporation mother liquor in Jiaxing ash.

[0033] 4. Results Analysis

[0034] As shown in Table 1, when the reuse rate of the mother liquor increased from 0% to 20%, the actual TOC of the fly ash wash water increased from 96.0 mg / L to 105.2 mg / L, with a maximum relative change of only 9.6%. The results indicate that fly ash can effectively adsorb the organic matter carried in by the mother liquor, keeping the organic matter content in the wash water basically stable.

[0035] When the reuse rate increased to 30%, the TOC in the wash water rose sharply to 140.6 mg / L, with a relative change of 46.5%, indicating that the 30% reuse rate exceeded the effective adsorption capacity of fly ash for organic matter and should not be adopted.

[0036] Example 2

[0037] 1. Experimental Materials

[0038] The fly ash was taken from a waste incineration plant in Changxing, and the evaporation mother liquor was taken from the evaporation and salt separation unit of the process of this invention. The TOC of the mother liquor was measured to be 4185.24 mg / L.

[0039] 2. Experimental Procedure

[0040] Same as Example 1.

[0041] 3. Experimental Results

[0042] The TOC values ​​of fly ash wash water under different evaporation mother liquor reuse ratios are shown in Table 2.

[0043] Table 2. TOC values ​​of fly ash wash water under different proportions of evaporating mother liquor in Changxing fly ash production.

[0044] 4. Results Analysis

[0045] As shown in Table 2, when the reuse rate of the mother liquor increased from 0% to 20%, the actual TOC of the fly ash wash water increased from 110.62 mg / L to 120.24 mg / L, with a maximum relative change of only 8.7%. The results are consistent with those in Example 1, verifying the effective adsorption of organic matter in the mother liquor by fly ash.

[0046] When the reuse rate increased to 30%, the TOC of the wash water rose sharply to 163.61 mg / L, with a relative change of 47.9%, further confirming that a 30% reuse rate was not feasible.

[0047] Example 3

[0048] 1. Experimental Materials

[0049] The fly ash was taken from fly ash (China Energy Conservation Ash) from a waste incineration plant in Changxing. The evaporation mother liquor was taken from the original evaporation mother liquor of the evaporation and salt separation unit of the treatment process of this invention. The TOC of the original liquor was measured to be 3997.67 mg / L.

[0050] 2. Experimental Procedure

[0051] Same as Example 1.

[0052] 3. Experimental Results

[0053] The TOC values ​​of fly ash wash water under different evaporation mother liquor reuse ratios are shown in Table 3.

[0054] Table 3. TOC values ​​of fly ash wash water under different proportions of evaporation mother liquor in Zhongneng ash.

[0055] 4. Results Analysis: As shown in Table 3, when the proportion of mother liquor reused from 0% to 20%, the actual TOC of fly ash wash water increased from 136.50 mg / L to 148.79 mg / L, with a maximum relative change of only 9.0%.

[0056] When the reuse rate increased to 30%, the TOC of the wash water increased sharply to 194.65 mg / L, with a relative change of 42.6%, which is consistent with the results of Examples 1 and 2.

[0057] Comprehensive Analysis of Three Examples

[0058] As shown in Tables 1, 2, and 3, the experimental results for fly ash from three different sources all indicate that: (1) When the reuse rate is ≤20%, the TOC of the washing water remains stable, with a maximum relative change of 8.7%~9.6%, all of which are controlled within 10%; (2) When the reuse rate reaches 30%, the TOC of the washing liquid increases sharply, with a relative change of 42.6% to 47.9%.

[0059] This indicates that a 30% reuse rate exceeds the effective adsorption capacity of fly ash for organic matter, resulting in a significant accumulation of organic matter in the washing liquid. Therefore, the reuse rate of the evaporation mother liquor in this invention should be controlled within 20%, preferably 5% to 20%.

[0060] The TOC data of the 30% reuse ratio group in Examples 1-3 were compared with those of the 20% reuse ratio group, as shown in Table 5. This demonstrates that when the reuse ratio of the evaporation mother liquor exceeds 20% (i.e. 30%), it will lead to a significant accumulation of organic matter in the washing liquid, which highlights the rationality and criticality of the reuse ratio range (5%~20%) of the present invention.

[0061] Table 4. Comparison of TOC under 20% and 30% reuse ratios

[0062] Comparative Example 1

[0063] 1. Purpose of comparison

[0064] To demonstrate the superiority of using a vertical flow sedimentation tank instead of a plate and frame filter press in terms of investment and energy consumption in this invention.

[0065] 2. Comparison of Schemes

[0066] ① Experimental materials

[0067] The fly ash was taken from Jiaxing in Example 1 above.

[0068] ② Experimental steps

[0069] Comparing the two processing methods: Group A (Traditional Plate and Frame Filter Press Route): Decalcified sludge is filtered using a plate and frame filter press, requiring a high-pressure feed pump and a high-pressure pressing pump with a head of over 80 meters. Specific conditions are as follows: ① The plate and frame filter press has a filtration area of ​​50 m², and the filter cloth is made of polypropylene with a unit area mass of 550 g / m². ② Feeding stage: Start the high-pressure feed pump (head ≥80 m, 65SYB25-80 type, flow rate 25 m³ / h, power 15 kW) to pump the decalcified sludge into the filter chamber of the plate and frame filter press. Control the feed pressure at 0.6~0.8 MPa and the feed time at 20~60 min until the filter chamber is full and the feed pressure rises to 0.8 MPa; ③ Pressing stage: Start the high-pressure pressing pump (with high-pressure water pressure station) and inject high-pressure water into the diaphragm plate cavity. The pressing pressure is controlled at 1.2~1.6 MPa and held for 10~30 min. ④ Drying stage: Introduce compressed air to dry the filter cake for 5-10 minutes; ⑤ Unloading: Automatic plate unloading reduces the moisture content of the filter cake to 30%~50 wt%. Manual assistance is required for the transfer of the filter cake. ⑥ A complete filter press cycle takes about 40 to 110 minutes, and the energy consumption for processing a unit mass of sludge is about 50 kW·h / ton of sludge; ⑦ Equipment investment is approximately RMB 800,000 (including plate and frame filter press, high-pressure feed pump, high-pressure pressing pump and supporting pipelines).

[0070] Group B (processing route of the present invention): The proportion of mother liquor reused in Example 1 is fixed at 20%, and other operations are the same.

[0071] 3. Comparison Results

[0072] The energy consumption required to treat a unit mass of sludge is shown in Table 5.

[0073] Table 5 Comparison of Equipment Investment and Energy Consumption

[0074] 4. Comparative Analysis

[0075] The results show that the present invention uses a vertical flow sedimentation tank to replace the plate and frame filter press, which significantly reduces equipment investment and operating energy consumption, simplifies the operation process, eliminates the need for manual assistance in unloading and replacing filter cloth, and avoids the management problems of sludge transfer.

Claims

1. A method for the resource-based treatment of fly ash washing water, characterized in that, The method employs a resource recovery system, which includes a water washing unit, an equalization tank unit, a first reaction tank unit, a first sedimentation tank unit, a second reaction tank unit, a second sedimentation tank unit, a neutralization filtration unit, and an evaporation and salt separation unit connected in sequence. The method includes the following steps: (1) Washing process: The fly ash from the waste incineration is sent to the washing unit, tap water is introduced, and the fly ash is washed and desalinated using a countercurrent washing method. The desalinated fly ash filter cake and high-salt fly ash washing water are separated. The high-salt fly ash washing water is pumped into the regulating tank unit through a closed pipeline, and the filter cake is sent to the washing fly ash temporary storage bin through a closed pipeline. The subsequent treatment is carried out in a cement kiln. (2) Two-stage decalcification and heavy metal removal process: The effluent from the equalization tank is pumped through a closed pipeline into the first-stage reaction sedimentation unit consisting of the first reaction tank unit and the first sedimentation tank unit, and the second-stage reaction sedimentation unit consisting of the second reaction tank unit and the second sedimentation tank unit. Chemical agents are added in the first reaction tank unit to remove most of the calcium ions in the water, and chemical agents are added in the second reaction tank unit to remove the remaining calcium ions and heavy metal ions. The decalcified sludge produced by the first sedimentation tank unit and the second sedimentation tank unit is returned to the water washing unit in step (1) through a sludge pump. Both the first sedimentation tank unit and the second sedimentation tank unit adopt vertical flow sedimentation tanks. (3) Evaporation and salt separation and closed-loop reuse of mother liquor: The supernatant of the second sedimentation tank unit enters the neutralization and filtration unit through a closed pipeline and is then pumped into the evaporation and salt separation unit through a closed pipeline for evaporation, crystallization and salt separation, respectively obtaining sodium chloride industrial salt products and potassium chloride industrial salt products; the evaporation mother liquor generated by the evaporation and salt separation unit is continuously returned to the water washing unit in step (1) through a closed pipeline, using the adsorption effect of fly ash particles to intercept impurities in the mother liquor and maintain the dynamic balance of impurity concentration in the water washing system; the evaporation condensate generated by the evaporation and salt separation unit is returned to the water washing unit through a closed pipeline to replace part of the tap water and reduce the amount of tap water used.

2. The method as described in claim 1, characterized in that, In step (1), the water washing unit adopts a three-stage countercurrent washing process. The evaporation mother liquor generated by the evaporation and salt separation unit is continuously returned to the first-stage water washing process of the water washing unit in step (1) through a closed pipeline. The feed flow rate of fly ash is 1~15 t / h, and the mass ratio of fly ash to tap water is 1:2-5.

3. The method as described in claim 1, characterized in that, In step (1), a low-speed stirring device is installed in the regulating tank with a stirring speed of 20~50 rpm to prevent suspended particles in the water from settling and caking, and to ensure uniform effluent quality.

4. The method as described in claim 1, characterized in that, In step (2), sodium sulfate is continuously added to the first reaction tank unit to remove most of the calcium ions in the water. The molar dosage of sodium sulfate is 0.8 to 0.9 times the molar flow rate of calcium ions in the influent, ensuring the calcium sulfate precipitation efficiency while avoiding excessive introduction of sulfate ions. Sodium carbonate and sodium sulfide are added to the second reaction tank unit to remove the remaining calcium ions and heavy metal ions, respectively. The dosage of sodium carbonate is 1.0 to 1.2 times the molar flow rate of the remaining calcium ions in the effluent of the first sedimentation tank unit, so that the final effluent calcium ion concentration meets the scale prevention requirements of MVR. The dosage of sodium sulfide is 0.9 to 1.2 times the total molar flow rate of the target heavy metals in the effluent of the first sedimentation tank unit, controlling the total heavy metal concentration in the effluent to meet the water quality requirements of the evaporation salt separation influent.

5. The method as described in claim 4, characterized in that, Sodium sulfate, sodium carbonate, and sodium sulfide were all added in the form of a 10-20% aqueous solution. The first and second reaction tanks were both stirred at room temperature using a low-speed mechanical stirrer at 200 rpm for 30 minutes.

6. The method as described in claim 1, characterized in that, In step (2), both the first sedimentation tank unit and the second sedimentation tank unit are equipped with a central drive sludge scraping device to prevent local sludge deposition and hardening, and to ensure sludge fluidity.

7. The method as described in claim 6, characterized in that, The vertical flow sedimentation tank consists of a tank body and a conical sludge hopper located at the lower end of the tank body. An overflow weir and drainage outlet are located around the top of the tank body. The conical sludge hopper is connected to a sludge discharge pipe. The tank body is circular in plan. Water enters the tank from top to bottom through an inlet pipe into a central pipe located at the center of the tank. A funnel-shaped opening and a reflector plate are located at the lower end of the central pipe, allowing the wastewater to distribute evenly throughout the tank before slowly rising along the entire cross-section. Suspended solids settle into the conical sludge hopper at the bottom of the tank, and clarified water flows out from the perimeter of the tank along the overflow weir. The tank diameter is ≤10 m, the effective water depth is 2.0~4.0 m, and the diameter-to-depth ratio is ≤3:

1. The upward flow velocity within the tank is 0.2~0.5 mm / s; the sedimentation time is 1.5~4.0 h; and the flow velocity in the central pipe is no greater than 30 m / s. The flow rate is 1.35 times the diameter of the central tube, the diameter of the reflector plate is 1.3 times the diameter of the flared mouth, and the angle between the reflector plate surface and the horizontal plane is 17°; the gap height between the lower edge of the flared mouth and the reflector plate surface is 0.3~0.5 m, and the gap flow velocity is ≤30 mm / s; the bottom of the reflector plate is at least 0.3 m from the mud surface; the inclination angle of the conical sedimentation hopper is 55°~60°, and the diameter of the sludge discharge pipe is not less than 200 mm; a buffer layer of 0.3 m is set under the reflector plate, and the freeboard above the water surface of the pool is 0.3~0.5 m.

8. The method as described in claim 1, characterized in that, In step (3), the neutralization filtration process involves first adjusting the pH to 7-8, then filtering the solution using a multi-media filter, and finally filtering the filtrate using a security filter. The filter media of the multi-media filter consists of ceramsite and quartz sand from top to bottom, with a height ratio of ceramsite to quartz sand of 1:1.2, a total filter layer thickness of ≥1.6 m, and a filtration rate of 6-8 m / s². 3 / h; the ceramsite particle size is 1~2 mm, and the quartz sand particle size is 0.5~0.8 mm.

9. The method as described in claim 1, characterized in that, In step (3), the flow rate of the evaporated mother liquor returned to the water washing unit is 0.5~5 m³. 3 The continuous reuse rate of the evaporation mother liquor is 5%~20% of the total water used for washing; the flow rate of the evaporation condensate returned to the washing unit is 10.5~11.5 m³ / h. 3 / h, the reuse rate is 70%~76% of the total water used for washing.

10. The method as described in claim 1, characterized in that, In step (3), the evaporation and salt separation unit adopts the MVR process; the evaporation temperature is 80~100℃, the single-stage temperature rise of the centrifugal compressor is 20℃, the flow rate in the forced circulation tube is 2.5 m / s, the NaCl is precipitated at a high temperature of 85~95℃, and the KCl is precipitated at a low temperature of 30-40℃.

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