CN221644722U - Waste incineration fly ash washing filtrate processing system - Google Patents

Abstract

The application discloses a waste incineration fly ash washing filtrate treatment system which comprises a pretreatment unit, a decalcification unit and a fine treatment unit, wherein the decalcification unit comprises at least two stages of decalcification devices, and sodium sulfate is used as a decalcification agent in the first stage of decalcification devices. The garbage incineration fly ash water washing filtrate treatment system converts most of calcium ions in the filtrate into calcium sulfate precipitates, so that the hardness removal cost is reduced, and the generated calcium sulfate precipitates can be reused, thereby realizing the maximum utilization of resources.

Description

Waste incineration fly ash washing filtrate treatment system

Technical Field

The present application relates to the technical field of wastewater treatment, and in particular to a waste incineration fly ash washing filtrate treatment system.

Background Art

Fly ash is a hazardous waste with both heavy metal hazard characteristics and environmental persistent organic toxicity hazard characteristics. In the traditional process, fly ash is washed and separated, and the resulting filtrate is evaporated and crystallized to obtain crystalline salt. The calcium ion concentration in the fly ash washing filtrate reaches 2% to 3%, and hardness removal treatment is required to meet the water inlet requirements of the subsequent evaporation and crystallization process.

The traditional fly ash washing filtrate hardness removal process adds a large amount of sodium carbonate solution and sodium hydroxide solution to the filtrate to precipitate the calcium ions in the filtrate wastewater in the form of calcium carbonate. The calcium ion concentration of the treated filtrate can be reduced to 200ppm, achieving the purpose of reducing the hardness of the filtrate wastewater.

However, the consumption of sodium carbonate in the traditional process is relatively large, which makes the cost of removing hardness from the filtrate wastewater too high, and the calcium carbonate precipitate produced has basically no usable value, and even needs to be treated again to be harmless, which consumes additional manpower and financial resources. In addition, the amount of calcium ions that can be precipitated by sodium carbonate and sodium hydroxide in the traditional process is limited, resulting in a large amount of calcium ions entering the subsequent process after the precipitation is completed, which has a great impact on the subsequent process.

Summary of the invention

The purpose of this application is to reduce the operating cost of a waste incineration fly ash washing filtrate treatment system.

To achieve the above objectives, the technical solution adopted in the present application is: to provide a waste incineration fly ash washing filtrate treatment system, including a pretreatment unit, a decalcification unit and a fine treatment unit, wherein the decalcification unit includes at least two-stage decalcification devices, wherein the first-stage decalcification device uses sodium sulfate as a decalcification agent.

As a preferred embodiment, the decalcification unit includes a decalcification reaction tank and a decalcification sedimentation tank, the filtrate treated by the pretreatment unit enters the decalcification reaction tank, the filtrate flowing out of the decalcification sedimentation tank enters the fine treatment unit, the decalcification reaction tank uses sodium sulfate as a decalcification agent, and the decalcification sedimentation tank uses sodium carbonate as a decalcification agent.

As another preferred embodiment, the decalcification reaction tank reduces the calcium ion concentration in the filtrate to below 1200 ppm, and the decalcification precipitation tank reduces the calcium ion concentration in the filtrate to below 50 ppm.

As another preferred embodiment, the decalcification unit also includes a first solid-liquid separator, the water outlet of the decalcification reaction tank is connected to the first solid-liquid separator, the water outlet of the first solid-liquid separator is connected to a decalcification sedimentation tank, and the first solid-liquid separator is used to separate the gypsum precipitate formed in the decalcification reaction tank.

As another preferred embodiment, the decalcification unit also includes a gypsum washing tank and a second solid-liquid separation tank. The gypsum precipitate enters the gypsum washing tank and is rinsed with water. The outlet of the gypsum washing tank is connected to the second solid-liquid separator. The second solid-liquid separator separates the solid for external transportation as gypsum, and the second solid-liquid separator separates the liquid which enters the decalcification precipitation tank.

As another preference, the decalcification unit further comprises a third solid-liquid separator, and the precipitate generated in the decalcification sedimentation tank enters the third solid-liquid separator.

As another preference, the decalcification reaction in the decalcification reaction tank lasts for more than 10 minutes.

As another preferred embodiment, the decalcification reaction tanks are arranged in series in a plurality of units.

As another preferred embodiment, the fine treatment unit includes a plurality of filtering devices, and the concentrated water separated by the filtering devices is returned to the water inlet of the decalcification unit for further decalcification.

Further preferably, the fine treatment unit comprises a second filter, an ultrafiltration device, a third filter, an ion exchanger and a nanofiltration device connected in sequence, the filtrate flowing out of the decalcification unit enters the second filter, and the concentrated water flowing out of the nanofiltration unit enters the decalcification unit.

Compared with the prior art, the beneficial effects of this application are:

(1) The present application uses a multi-stage decalcification process and a decalcification agent mainly composed of sodium sulfate, which reduces the consumption of sodium carbonate and can also obtain calcium sulfate dihydrate with certain economic value, thereby reducing the operating cost of the waste incineration fly ash washing filtrate treatment system;

(2) The present application sets up a nanofiltration device to recover the remaining sulfate ions in the decalcification agent, so an excess of sodium sulfate can be added to the decalcification unit to convert calcium ions into calcium sulfate precipitates as much as possible.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a flow chart of an embodiment of the present application;

FIG2 is a schematic diagram of a sedimentation tank according to an embodiment of the present application;

FIG3 is a schematic diagram of a decalcification reaction tank according to an embodiment of the present application;

In the figure: 1. pretreatment unit; 11. sedimentation tank; 12. first filter; 2. decalcification unit; 21. decalcification reaction tank; 22. decalcification sedimentation tank; 23. first solid-liquid separator; 24. gypsum washing tank; 25. second solid-liquid separator; 26. third solid-liquid separator; 3. fine treatment unit; 31. second filter; 32. ultrafiltration device; 33. third filter; 34. ion exchange device; 35. nanofiltration device.

DETAILED DESCRIPTION

Below, the present application is further described in conjunction with 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.

In the description of the present application, it should be noted that directional words, such as the terms "center", "lateral", "longitudinal", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", etc., indicating directions and positional relationships are based on the directions or positional relationships shown in the accompanying drawings, which are only for the convenience of narrating the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and cannot be understood as limiting the specific scope of protection of the present application.

It should be noted that the terms "first", "second", etc. in the description and claims of the present application are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence.

The terms "including" and "having" and any variations thereof in the specification and claims of this application are intended to cover non-exclusive inclusions. For example, a process, method, system, product or apparatus comprising a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to these processes, methods, products or apparatuses.

As shown in Figure 1, the waste incineration fly ash washing filtrate treatment system of the present application includes a pretreatment unit 1, a decalcification unit 2 and a fine treatment unit 3, wherein the decalcification unit 2 includes at least two-stage decalcification devices, and the first-stage decalcification device uses sodium sulfate as a decalcification agent to convert most of the calcium ions in the filtrate into calcium sulfate precipitates, which can reduce the hardness removal cost while the calcium sulfate precipitates produced can be reused to maximize resource utilization.

In some embodiments, the pretreatment unit 1 includes a sedimentation tank 11 and a first filter 12. The waste incineration fly ash washing filtrate first enters the sedimentation tank 11, where the fly ash particles in the filtrate are removed by gravity sedimentation. After passing through the sedimentation tank 11, the washing filtrate continues to flow into the first filter 12, and the first filter 12 further removes fine fly ash particles in the filtrate to ensure the stability of subsequent processes. The sludge generated in the sedimentation tank 11 enters the water washing system.

In some embodiments, as shown in Fig. 2, the sedimentation tank 11 is in the form of a vertical flow sedimentation tank, with facilities such as inclined pipes and scrapers inside, and no chemicals are added, and the fly ash particles in the filtrate are precipitated by gravity. The first filter 12 can be a multi-media filter.

In other embodiments, the sedimentation tank 11 may also be in the form of a horizontal flow type, a radial flow type, or other types of sedimentation tanks, and a sludge scraper may not be provided.

In some embodiments, the decalcification unit 2 includes a decalcification reaction tank 21 and a decalcification sedimentation tank 22. The filtrate treated by the pretreatment unit 1 enters the decalcification reaction tank 21, and the filtrate flowing out of the decalcification sedimentation tank 22 enters the fine treatment unit 3. The decalcification reaction tank 21 uses sodium sulfate as a decalcification agent, and the decalcification sedimentation tank 22 uses sodium carbonate as a decalcification agent.

The present application sets up at least two-stage decalcification process. The first-stage decalcification device uses sodium sulfate as the decalcification agent. The unit price of sodium sulfate is much lower than that of sodium carbonate, which effectively reduces the usage of sodium carbonate and reduces the operating cost of the waste incineration fly ash washing filtrate treatment system. It is estimated that the cost will drop by more than 70%.

In addition, sodium sulfate has a fast decalcification reaction rate, solid-liquid separation can be performed without long precipitation, the equipment is small in size, occupies a small area, and has low equipment investment cost. In some specific embodiments, sodium sulfate can be industrial by-product sodium sulfate such as sodium sulfate decahydrate, which further reduces the operating cost of the filtrate treatment system and realizes the rational use of resources.

In some embodiments, the decalcification reaction tank 21 reduces the calcium ion concentration in the filtrate to below 1200 ppm, and the decalcification sedimentation tank 22 reduces the calcium ion concentration in the filtrate to below 50 ppm.

In some embodiments, the suspended matter in the filtrate after the washing filtrate is treated by the pretreatment unit 1 is ≤3 ml/L, and then the filtrate enters the decalcification reaction tank 21, and sodium sulfate solution is simultaneously added to the decalcification reaction tank 21, and is fully stirred to allow the calcium ions in the filtrate to fully react with sodium sulfate to generate gypsum, the main component of which is dihydrate gypsum, i.e., _CaSO4 · _2H2O .

In some embodiments, as shown in FIG. 3 , a plurality of evenly distributed baffles are provided inside the decalcification reaction tank 21 , and a multi-layer blade is provided in the mixer to enhance the axial and radial tumbling and collision of the gypsum particles in the reaction tank, thereby improving the decalcification reaction efficiency and increasing the particle size of the gypsum particles.

In other embodiments, the decalcification reaction tank 21 may also be in the form of a concrete reaction tank.

In some embodiments, the reaction time in the decalcification reaction tank 21 is more than 10 minutes, which can achieve a good calcium ion precipitation effect. Preferably, the decalcification reaction tank 21 can be set to at least 2 units, which are operated alternately to reduce the loss of the machine service life and maintain the reaction effect. In other embodiments, two decalcification reaction tanks 21 can be used in series to improve the precipitation effect of calcium ions.

The amount of sodium sulfate added to the decalcification reaction tank 21 can be calculated using the following formula:

Q ₁ =3.55a×b÷c÷d×k

Q ₁ : sodium sulfate solution flow rate, m ³ /h;

a: water washing filtrate flow rate, m ³ /h;

b: calcium ion concentration in the filtrate, calculated as Ca ²⁺ , ppm;

c: sodium sulfate solution concentration, 20%;

d: specific gravity of sodium sulfate solution, 1.18;

k: Excess coefficient.

In some preferred embodiments, the decalcification reaction tank 21 system is equipped with an online hardness meter to monitor the hardness of the incoming water and automatically calculate the dosage. After a single water inlet, dosage, and reaction, the hardness of the filtrate is checked. If the filtrate hardness is lower than 1200ppm, it can enter the subsequent second-stage decalcification device; if the filtrate calcium ion concentration is still higher than 1200ppm, automatic dosage is performed again, and then the first-stage decalcification reaction is carried out to reduce the subsequent sodium carbonate consumption.

In some embodiments, the decalcification precipitation tank 22 automatically adds sodium carbonate and sodium hydroxide according to the calcium ion concentration data in the filtrate flowing out of the decalcification reaction tank 21. After the second precipitation in the decalcification precipitation tank 22, the calcium ion concentration in the filtrate can be reduced to less than 50 ppm, which is conducive to the stable operation of the subsequent process equipment.

The amount of sodium carbonate added to the decalcification sedimentation tank 22 can be calculated using the following formula:

_Q2 ＝2.65a×b÷e÷f×k

Q ₂ : sodium carbonate solution flow rate, m ³ /h;

a: water washing filtrate flow rate, m ³ /h;

b: calcium ion concentration in the filtrate, expressed as Ca ² + , ppm;

e: sodium carbonate solution concentration, 10%;

f: specific gravity of sodium carbonate solution, 1.1;

k: Excess coefficient.

In some embodiments, the decalcification sedimentation tank 22 completes feeding and other controls through an automatic program without manual intervention.

In some embodiments, the decalcification unit 2 is provided with a plurality of solid-liquid separators to improve the decalcification effect. The decalcification unit 2 further comprises a first solid-liquid separator 23, a gypsum washing tank 24, a second solid-liquid separator 25 and a third solid-liquid separator 26. The filtrate flowing out of the decalcification reaction tank 21 enters the first solid-liquid separator 23, the filtrate flowing out of the first solid-liquid separator 23 enters the decalcification precipitation tank 22, and the solid phase of the first solid-liquid separator 23 enters the gypsum washing tank 24. Fresh water is added to the gypsum washing tank 24 at a certain water-solid ratio for flushing to reduce the content of chloride ions in the solid precipitate, and then the solid-liquid mixed phase obtained enters the second solid-liquid separator 25 for separation.

The second solid-liquid separator 25 separates the solid precipitate again to obtain a precipitate mainly composed of calcium sulfate, which is transported as a finished gypsum. The filtrate produced by the second solid-liquid separator 25 enters the decalcification sedimentation tank 22 for the next decalcification reaction.

The finished gypsum shipped after being processed by the gypsum washing tank 24 and the second solid-liquid separator 25 has a chloride ion content of less than 0.5%, and can be used as an additive for cement plants. This method converts most of the calcium carbonate that originally required additional processing into calcium sulfate dihydrate with a certain economic value, which can further reduce the operating cost of the system.

The filtrate flowing out of the decalcification sedimentation tank 22 enters the fine treatment unit 3, and the produced sludge enters the third solid-liquid separator 26 for further separation. The sludge obtained by the third solid-liquid separator 26 mainly contains calcium carbonate.

In some embodiments, the first solid-liquid separator 23, the second solid-liquid separator 25 and the third solid-liquid separator 26 can be various solid-liquid separation equipment such as centrifuges, vacuum filters, belt filters, plate and frame filter presses, etc.

The fine treatment unit 3 includes multiple filtering devices to remove small particles, organic matter, and residual chlorine contained in the filtrate to meet the water quality requirements. The fine treatment unit 3 includes a second filter 31, an ultrafiltration device 32, a third filter 33, an ion exchange device 34, and a nanofiltration device 35 connected in sequence. The water-washed filtrate flows out of the decalcification unit 2, enters the second filter 31, and flows out of the nanofiltration device 35 after completing the fine treatment unit 3 to obtain produced water.

In some embodiments, the second filter 31 is a multi-media filter, the third filter 33 is an activated carbon filter, and the membrane pore size of the ultrafiltration device 32 is ≤50um. Through a series of filtration and adsorption, various impurities in the water are removed to meet the water intake requirements of subsequent processes. The ultrafiltration device 32 can also use filtering facilities such as microfiltration.

In other embodiments, the first filter 12, the second filter 31 and the third filter 33 may also be various mechanical filters such as laminated filters and filter element filters.

In order to prevent residual calcium ions in the water from scaling on the surface of the nanofiltration membrane and ensure a higher recovery rate in the nanofiltration section, an ion exchange device 34 is set before the nanofiltration process. Through resin adsorption, the calcium ion concentration of the filtrate after two-stage decalcification is reduced from 50ppm to less than 1ppm, thereby achieving complete hardness removal of the filtrate.

The operation range of the nanofiltration device 35 is between ultrafiltration and reverse osmosis. The removal rate of high-valent anion salt solution is higher than that of low-valent anion salt solution. The removal rate of sodium sulfate can reach more than 98%, ensuring that the nanofiltration water production is mainly monovalent salt, reducing the difficulty of subsequent crystallization salt separation, and thus ensuring the quality of subsequent salt separation.

In some embodiments, the concentrated water outlet of the nanofiltration device 35 is connected to the decalcification reaction tank 21. The recovery rate of the nanofiltration device 35 is about 70% to 80%, and the concentrated water produced can be reused as sodium sulfate preparation water to improve the reuse rate of system water while avoiding the waste of sodium sulfate.

When using the nanofiltration device 35 to recover sulfate ions in the filtrate treatment system, an excess of sodium sulfate decalcification agent can be added to the decalcification reaction tank 21 to convert calcium ions into calcium sulfate precipitates as much as possible, thereby reducing the subsequent consumption of sodium carbonate decalcification agent and thus reducing the operating cost of the treatment system.

In order to improve the quality of salt out of evaporation and crystallization and avoid the adverse effect of sulfate ions introduced in the first stage decalcification process on the subsequent evaporation and crystallization process, the utility model arranges an "ultrafiltration + nanofiltration" double membrane treatment process after the decalcification unit 2, which is used to separate the divalent ions from the monovalent ions in the filtrate, and intercept the sulfate remaining in the first stage decalcification reaction, and reuse it to the front end of the process as water for the preparation of sodium sulfate solution, thereby improving the reuse rate of system water and avoiding the waste of sodium sulfate, further reducing the project operation cost.

The present application adopts a multi-stage decalcification device to reduce the hardness of the filtrate outlet water to less than 1ppm, and the filtrate is mainly composed of monovalent ions, which is conducive to maintaining the stable operation of the subsequent evaporation and crystallization system, reducing the difficulty of crystallization and salt separation, and thus ensuring the quality of subsequent salt separation.

In some embodiments, the waste incineration fly ash washing filtrate treatment system of the present application realizes fully automatic control through various online instruments and program algorithms, without the need for human intervention, freeing up manpower, reducing operating costs and ensuring the hardness removal effect of the filtrate.

The above describes the basic principles, main features and advantages of the present application. Those skilled in the art should understand that the present application is not limited by the above embodiments. The above embodiments and the specification only describe the principles of the present application. The present application may have various changes and improvements without departing from the spirit and scope of the present application. These changes and improvements fall within the scope of the present application for which protection is sought. The scope of protection claimed by the present application is defined by the attached claims and their equivalents.

Claims (8)

1. The garbage incineration fly ash water washing filtrate treatment system is characterized by comprising a pretreatment unit, a decalcification unit and a fine treatment unit, wherein the decalcification unit comprises at least two stages of decalcification devices, and sodium sulfate is used as a decalcification agent by the first decalcification device; the decalcification unit comprises a decalcification reaction tank and a decalcification sedimentation tank, the filtrate treated by the pretreatment unit enters the decalcification reaction tank, the filtrate flowing out of the decalcification sedimentation tank enters the fine treatment unit, the decalcification reaction tank uses sodium sulfate as a decalcification agent, and the decalcification sedimentation tank uses sodium carbonate as a decalcification agent; the decalcification reaction tank reduces the concentration of calcium ions in the filtrate to below 1200ppm, and the decalcification sedimentation tank reduces the concentration of calcium ions in the filtrate to below 50 ppm.

2. The system for treating waste incineration fly ash washing filtrate according to claim 1, wherein the decalcification unit further comprises a first solid-liquid separator, wherein the outlet water of the decalcification reaction tank is connected with the first solid-liquid separator, the outlet water of the first solid-liquid separator is connected with a decalcification sedimentation tank, and the first solid-liquid separator is used for separating gypsum sediment formed by the decalcification reaction tank.

3. The system for treating waste incineration fly ash washing filtrate according to claim 2, wherein the decalcification unit further comprises a gypsum washing tank and a second solid-liquid separator, wherein gypsum precipitate enters the gypsum washing tank and is washed by adding water, an outlet of the gypsum washing tank is connected with the second solid-liquid separator, solids obtained by separation of the second solid-liquid separator are transported outside as gypsum, and liquid obtained by separation of the second solid-liquid separator enters the decalcification sedimentation tank.

4. A waste incineration fly ash washing filtrate treatment system according to claim 3, wherein the decalcification unit further comprises a third solid-liquid separator, and the precipitate generated by the decalcification sedimentation tank enters the third solid-liquid separator.

5. The waste incineration fly ash washing filtrate treatment system according to claim 1, wherein the decalcification reaction duration in the decalcification reaction tank is more than 10 min.

6. The waste incineration fly ash washing filtrate treatment system according to claim 1, wherein the decalcification reaction tanks are arranged in series.

7. The system for treating the waste incineration fly ash washing filtrate according to claim 1, wherein the fine treatment unit comprises a plurality of filtering devices, and concentrated water separated by the filtering devices flows back to the water inlet of the decalcification unit for decalcification treatment again.

8. The system for treating waste incineration fly ash washing filtrate according to claim 7, wherein the fine treatment unit comprises a second filter, an ultrafiltration device, a third filter, an ion exchanger and a nanofiltration device which are connected in sequence, wherein filtrate flowing out of the decalcification unit enters the second filter, and concentrated water flowing out of the nanofiltration device enters the decalcification unit.