Defluorination system suitable for zero discharge treatment of coal gas wastewater

Abstract

The utility model provides a defluorination system suitable for zero discharge treatment of coal gas wastewater. Comprising a two-stage defluorination reaction sedimentation tank, a softening reaction sedimentation tank, a multi-medium filter, a catalytic ozonation tank, a biochemical reaction unit, an ultrafiltration filter, a cation exchange softener, a decarburization device, an intermediate water production tank, an RO device, a reuse water tank, an RO concentrated water tank, a chelating resin softener, a chelating resin defluorination device and an evaporative crystallization system. The defluorination reaction sedimentation tank adopts a serial connection structure and respectively performs high-speed reaction, medium-speed reaction and low-speed reaction and sedimentation action, so that precipitates generated by defluorination chemical sedimentation reaction can form larger particles through coagulation and flocculation reaction and are separated and removed in the sedimentation tank, and the two-stage defluorination reaction sedimentation tank ensures that fluorine ions are effectively removed. The RO concentrated water is subjected to fluorine removal by adopting metal-chelated fluorine removal resin, so that the RO concentrated water has better selective adsorbability, and waste liquid generated by resin regeneration is conveyed to a first-stage fluorine removal reaction sedimentation tank for recycling, so that the consumption of medicaments is reduced.

Description

Technical Field

[0001] The technical field related to the present utility model is wastewater treatment, especially fluoride removal in zero liquid discharge of wastewater. Background Art

[0002] Fluorine is one of the most active elements among all elements and can react with various chemical substances. Fluorine in water mainly comes from natural sources such as surface water and groundwater, as well as artificial sources such as industrial wastewater. Many industries, including metallurgy, coking, electroplating, electronics, glass, chemical fertilizer, pesticides, etc., use fluorine-containing raw materials in their production processes, resulting in wastewater containing a high concentration of fluorine. A trace amount of fluorine in drinking water is beneficial to the human body, but if the concentration of fluoride ions in water is too high, such as exceeding 1 mg / L, long-term drinking will cause harm to health, leading to dental fluorosis and bone diseases. In addition, in wastewater, fluorine will combine with calcium ions to form calcium fluoride precipitates, causing scaling of filtration equipment and affecting its use function. Especially in zero liquid discharge projects, wastewater needs to go through evaporation and crystallization treatment steps, and the presence of fluorine will cause serious corrosion of these equipment. Therefore, in the conventional treatment of wastewater, especially in zero liquid discharge treatment projects, it is often necessary to remove fluorine from wastewater.

[0003] At present, the known methods for fluoride removal from wastewater mainly include chemical precipitation method, coagulation method, adsorption method, ion exchange method, etc. The chemical precipitation method mainly makes fluoride ions react with lime or calcium salts to form calcium fluoride that is insoluble in water to remove fluorine. However, calcium fluoride will cover the surface of lime particles, making the lime not fully utilized. Therefore, the dosage of chemicals is large, the sludge sedimentation property is poor, the amount of sludge produced is large, and it is difficult to dewater. The fluoride ion concentration in the effluent is generally above 20 mg / L. The coagulation method mainly uses hydroxide hydrated ions formed by iron salts or aluminum salts in water to adsorb fluoride ions in water and makes the colloid form a coagulant to remove fluorine. However, this method is affected by many factors, the removal effect is unstable, and the treatment cost is relatively high. It is generally used in combination with the chemical precipitation method. The adsorption method mainly uses materials such as activated alumina, zeolite, resin, etc. to adsorb fluoride ions on the solid surface to remove fluorine. The adsorption effects include electrostatic interaction, covalent bonding, coordination, metal chelation, etc. This method often has a small adsorption capacity of the adsorbent for fluorine, is easily interfered by the presence of other ions, requires a long hydraulic retention time for adsorption, and has a poor regeneration effect after adsorption saturation, and the repeated use effect is not good. The ion exchange method uses anion resin to remove fluoride ions, and the hydroxide radicals on the surface of the anion resin enter the water. After the resin fails, it needs to be regenerated, and the exchange capacity recovers well after regeneration. However, this method is also easily interfered by other anions in water because the anion resin has selectivity for the adsorption of different anions, and the order of ion exchange strength is SO4 2- >I - >NO3 - >CRO4 2- >Br- >CN - >Cl - >F - It has poor selectivity for fluoride ions, and as a result of the competition, the removal effect of fluoride ions is poor.

[0004] CN 112811669 B discloses a treatment system and method for fluorine-containing industrial wastewater. The process includes: a primary defluorination coagulation sedimentation reaction tank, a secondary defluorination coagulation sedimentation reaction tank, a mechanical agitation clarifier, a resin defluorination tank, and sludge treatment. Both the primary defluorination coagulation sedimentation reaction tank and the secondary defluorination coagulation reaction tank use a three-tank structure composed of aeration, agitation, and sedimentation, and a soluble calcium salt is added as a defluorination agent, and an alkali agent is used to adjust the pH to 11; a flocculant is also added in the secondary defluorination coagulation reaction tank; a flocculant is also added in the mechanical agitation clarifier; activated carbon, iron sand filter material, rare earth filter material, and special defluorination resin are layered and filled in the defluorination resin tank. Although the defluorination treatment method described in this invention can make the effluent of high-concentration fluorine-containing wastewater stable after treatment and can meet the discharge standard of less than 10 mg / L. However, this system is only applicable to fluorine-containing wastewater with relatively simple components, requires the use of excessive calcium salts, and for wastewater with a high fluorine concentration, it is necessary to pre-adjust the acidity to convert fluoride ions into hydrofluoric acid for stripping treatment. The defluorination resin tank uses a combination of various filter materials, which is not conducive to backwashing and regeneration of the adsorption filter materials.

[0005] CN 113620477 A discloses a defluorination system and method for high-salt wastewater, including a defluorination reaction system, a tubular microfiltration circulation system, and a resin adsorption system. The defluorination reaction system is used for the first treatment of fluorine-containing wastewater to achieve flocculation. The tubular microfiltration circulation system conducts the second treatment on the wastewater output by the defluorination reaction system to achieve tubular microfiltration. The resin adsorption system is used for the third treatment of the wastewater output by the tubular microfiltration circulation system to achieve resin adsorption. The defluorination reaction system adopts a reaction, neutralization, and circulation triple reaction tank, and each cell is equipped with a stirring device to realize the steps of coagulation reaction and sedimentation for defluorination. This patent does not disclose what kind of defluorination agent is used. In its embodiment, it mentions A1 in the defluorination agent 3+ and F -There is a complexing effect. "The amorphous A1(OH) flocs produced during the hydrolysis of aluminum perform ion exchange, adsorption, and sweep-up on F-, generating NaA1F6, A1F3, NaF, etc., to achieve the removal of fluoride ions in fluoride-containing wastewater". It can be speculated that the defluorinating agent used is an aluminum-based coagulant. This patent also does not disclose the type of resin used, but from the resin regeneration method mentioned in the examples, it can be inferred that an anion exchange resin is used. Although this patent can achieve a relatively high fluoride removal rate and does not increase calcium and magnesium ions in the effluent, using tubular microfiltration requires backwashing and replacement. Additionally, when using an anion exchange resin, the selectivity for fluoride ions is poor, and its regeneration requires the use of concentrated acids and alkalis.

[0006] CN 113666561 B discloses a treatment process for high-salt sulfur- and fluoride-containing wastewater. The high-salt sulfur- and fluoride-containing wastewater is subjected to forced oxidation to oxidize sulfite to sulfate, and then the pH is adjusted to below 4 to remove carbonate ions in the wastewater. Secondly, after adjusting the pH of the wastewater back to 5 - 10, a defluorinating agent is added to remove fluoride ions in the solution. The defluorinating agent used is CaCl2. The generated suspension is separated by a ceramic membrane to remove solid impurities. Finally, the wastewater after solid removal is further subjected to calcium and magnesium ion exchange resin adsorption to remove calcium and magnesium ions in the wastewater. The wastewater generated during the regeneration of the ion exchange resin is returned to the defluorination reaction kettle as a defluorinating agent, and the wastewater after decalcification enters MVR to recover crude salt. This invention uses a primary defluorination chemical precipitation reaction, and the defluorination effect is poor; using ceramic membrane separation also requires frequent backwashing, which is rather troublesome in operation. Using calcium and magnesium ion adsorption resin, the selectivity for fluoride ions is poor, and its regeneration requires the use of acids and alkalis.

[0007] CN 113896357 A provides a treatment method for fluoride-containing wastewater. The cation resin regeneration waste liquid is mixed with the fluoride-containing wastewater at a first ratio value, and its pH is adjusted to 7 - 9; then a flocculant solution is added to produce flocs; the flocs are separated to obtain a clear liquid. The cation resin regeneration waste liquid mainly contains CaCl2, MgCl2, and hydrochloric acid. The flocculant used is PAM or polyaluminum chloride or polyaluminum sulfate. This invention utilizes the cation resin regeneration waste liquid to treat fluoride-containing wastewater, achieving the reuse of the cation resin regeneration waste liquid and significantly reducing the usage amount of defluorination agents, and even being able to achieve no use of defluorination agents, reducing the treatment cost of fluoride-containing wastewater. However, this invention is mainly suitable for fluoride-containing wastewater with a single composition, and there are problems such as the removal effect being affected by the composition of the waste liquid and the removal effect not being guaranteed.

[0008] CN 116375277 A discloses a treatment method and system for coking high-salt wastewater, which utilizes unit technologies such as two-stage integrated defluorination, hardness removal, and silicon removal pretreatment, high-density precipitation, low-temperature and low-pressure wet oxidation, multi-media filtration, tubular ultrafiltration, membrane salt separation, alloy membrane electrodialysis for high-concentration, evaporation, and freeze crystallization. It pre-removes bacteria, refractory organic pollutants, particulate suspended solids, colloids, inorganic pollutants, etc. in coking high-salt wastewater, and then uses a membrane system for salt separation, evaporation, and freeze crystallization for purification to obtain product salts. Each stage of the integrated defluorination, hardness removal, and silicon removal pretreatment equipment has 4 reactors arranged in series, and calcium compounds, aluminum compounds, hydroxides, and carbonates or bicarbonates are added respectively. The calcium compounds are selected from one or more of calcium hydroxide and calcium chloride, and the aluminum compounds are selected from one or more of aluminum chloride and aluminum sulfate. The defluorination system of this invention mainly utilizes two-stage integrated defluorination, hardness removal, and silicon removal reaction devices, but the four reactions in the integrated reaction device will inevitably interfere with each other, resulting in problems such as waste of chemicals and poor precipitation effect. After the wastewater is highly concentrated by subsequent electrodialysis, fluoride ions and calcium and magnesium ions will be concentrated again, leading to problems in the use of subsequent equipment.

[0009] CN 116477790 A discloses a method for zero-emission defluorination and silicon removal of steelmaking wastewater. Polyaluminum and sodium meta-aluminate are added to the concentrated brine and quickly mixed to remove fluoride and silicon respectively; after adjusting the pH value, a flocculant is added for flocculation and solid-liquid separation, and the produced clear liquid enters subsequent concentration, evaporation, and crystallization treatment without problems such as blockage and corrosion. Since the removal method of this patent uses polyaluminum for coagulation and adsorption reaction of fluoride ions, the removal effect of fluoride ions is affected by various factors, and there is a problem of unstable removal effect.

[0010] CN 117819754 A discloses a method, system, and application for water reuse treatment of semiconductor fluoride-containing wastewater. According to the fluoride ion concentration of the wastewater to be treated, calcium salt defluorination is carried out through a primary regulating tank, reaction tank, and sedimentation tank, and after chemical precipitation, it enters a deep defluorination resin for further adsorption and removal of fluoride ions to obtain low-concentration fluoride-containing wastewater, reducing the usage amount of reagents. At the same time, the fluoride ions adsorbed by the deep defluorination resin are further eluted by a regenerant, and the eluted regenerated waste liquid is returned to the upstream reaction tank for treatment to realize water reuse of fluoride-containing wastewater and reduce the usage amount of reagents. The defluorination resin uses zirconium-type / aluminum-type ion exchange resin, and the regenerant is such as 4% sodium hydroxide or 10% aluminum chloride / aluminum sulfate. The eluted regenerated waste liquid is returned to the upstream reaction tank for treatment to realize water reuse of fluoride-containing wastewater. This invention can achieve wastewater reuse for the defluorination of semiconductor fluoride-containing wastewater. However, the applicable wastewater composition is relatively single, and the salt content concentration is not very high.

[0011] CN 210030233 U discloses an acidic fluoride-containing wastewater treatment system, adopting a process of double calcium fluoride removal + coagulation precipitation + weak acid cation calcium removal + fluoride ion exchange.

[0012] In summary, most of the currently disclosed industrial wastewater fluoride removal systems adopt chemical precipitation (lime or calcium salt) and flocculation reaction, resin adsorption, ion exchange or a combined process of these methods. The chemical precipitation method mainly removes fluoride by reacting fluoride ions with lime or calcium salt to form calcium fluoride that is insoluble in water. However, calcium fluoride will cover the surface of lime particles, preventing the dissolution of Ca(OH)2 and thus preventing Ca ions from entering the water to react with fluoride ions, resulting in insufficient utilization of lime. At the same time, in order to increase the fluoride ion removal rate and reduce the fluoride ion concentration in the effluent, it is necessary to excessively add fluoride removal agents, often requiring calcium salts several times more than the fluoride removal amount. Therefore, the reagent consumption is large, the sludge sedimentation property is poor, the sludge production is large, and dehydration is difficult. The fluoride ion concentration in the effluent is generally above 20 mg / L. In order to reduce the operating cost of the chemical precipitation method, some processes use the regeneration liquid of the cation resin bed as a fluoride removal agent (CN 113896357 A), or use the regeneration liquid of the subsequent anion fluoride removal resin after calcium precipitation treatment and causticization reaction as a fluoride removal agent (CN 117819754 A). In addition, in order to reduce the lime dosage and improve the fluoride removal effect, a double-alkali method of lime + CaCl2 is used for fluoride removal (CN 210030233 U). Although using calcium chloride to replace part of the lime can avoid the deposition of calcium fluoride on the lime surface, reduce the lime usage, and reduce the sludge volume, these methods are still based on calcium fluoride precipitation, and since CaCl2 is soluble in water, the calcium fluoride particles formed with fluoride are small and not easy to precipitate.

[0013] The coagulation method uses the cationic hydrated ions formed by iron salts or aluminum salts in water to adsorb fluoride ions in water, and makes the colloid form flocs to be removed. However, this method is affected by factors such as temperature, pH, the concentration of negatively charged colloids in water, and stirring intensity, and the removal effect is unstable.

[0014] The adsorption method mainly uses materials such as activated alumina, zeolite, and resin to adsorb fluoride ions on the solid surface to remove fluoride. Its functions include electrostatic action, covalent bonding, coordination, metal chelation, etc. For this method, the adsorbent often has a small adsorption capacity for fluoride, poor selectivity for fluoride ions, is easily interfered by the presence of other ions, requires a long adsorption time, has a poor regeneration effect after adsorption saturation, and the repeated use effect is often not good. Some resins are modified with metal chelating agents such as zirconium or aluminum to improve the selective adsorption of fluoride by the resin. In order to extend the regeneration cycle and reduce the cost increased by regeneration, the adsorption method is generally applicable to occasions with a low fluoride concentration.

[0015] The ion exchange method uses an anion resin to remove fluoride ions through ion exchange. The hydroxide ions on the surface of the anion resin then enter the water. After the resin becomes ineffective, it is regenerated, and the exchange capacity recovers well after regeneration. However, this method is also easily interfered by other anions in the water because the anion resin has selectivity in adsorbing different anions, and the order of ion exchange strength is SO4 2- >I - >NO3 - >CRO4 2- >Br - >CN - >Cl - >F - , and its selectivity for fluoride ions is relatively poor. The result of the competition is that the removal effect of fluoride ions is poor. For wastewater with a relatively high fluoride concentration, pretreatment is required.

[0016] In summary, the current defluorination system is not yet perfect. Especially for the treatment of concentrated water for zero discharge, the ion concentration is often high, there are many interference factors for the defluorination chemical precipitation reaction, and the defluorination effect is poor. In order not to significantly increase the salt concentration in the water during the defluorination process, a process with a small dosage of defluorinating agent needs to be adopted. Therefore, in reality, a more efficient defluorination system is needed to overcome the shortcomings of the existing technology. Utility Model Content

[0017] The purpose of the present utility model is to provide an efficient defluorination system for solving the above technical problems and for the zero-discharge treatment of coal gasification wastewater.

[0018] To achieve the above purpose, the present utility model adopts the following technical solutions:

[0019] A defluorination system suitable for the zero-discharge treatment of coal gasification wastewater, comprising an RO (reverse osmosis) fluoride-containing concentrated brine pool, two-stage defluorination reaction sedimentation tanks, softening reaction sedimentation tanks, multi-media filters, ozone catalytic oxidation pools, biochemical reaction units, ultrafiltration filters, cation exchange softeners, decarbonators, intermediate product water pools, and RO devices connected in sequence; the precipitated sludge, backwash sludge, or sludge concentrate generated by the two-stage defluorination reaction sedimentation tanks, softening reaction sedimentation tanks, multi-media filters, ozone catalytic oxidation pools, and ultrafiltration filters are partially refluxed to the RO fluoride-containing concentrated brine pool and the sludge treatment system for reuse or treatment and solid-liquid separation; the regeneration waste liquid of the cation exchange softener is refluxed to the softening reaction sedimentation tank for the reuse of the regeneration waste liquid; the product water of the RO device is connected to the recycled water pool, the concentrated water of the RO device is connected to the RO concentrated water pool, and the RO concentrated water pool is connected to a chelating resin softener, a chelating resin defluorinator, and an evaporation crystallization system through pumps for deep hardening removal and defluorination respectively, and then enters the subsequent evaporation crystallization system for treatment.

[0020] Preferably, the two-stage defluorination reaction sedimentation tank comprises a first defluorination reaction sedimentation tank and a second defluorination reaction sedimentation tank with the same structure, both of which include three groups of reaction chambers, a sedimentation tank and a communication area; the three groups of reaction chambers include a high-speed reaction chamber, a medium-speed reaction chamber and a low-speed reaction chamber, and stirring mechanisms are arranged in the high-speed reaction chamber, the medium-speed reaction chamber and the low-speed reaction chamber and are connected in series with each other; a water inlet pipe, an alkali liquor adding pipeline and a defluorinating agent adding pipeline are connected to the high-speed reaction chamber; a coagulant adding pipeline is connected to the medium-speed reaction chamber; a flocculant adding pipeline is connected to the low-speed reaction chamber; the low-speed reaction chamber is communicated with the sedimentation tank through the communication area; an inlet water area, a clear water area and a sedimentation area are arranged in the sedimentation tank; the clear water area is located above the inlet water area and is used for collecting clear liquid, and the clear water area is connected with a water outlet pipe for discharging the clear liquid; the sedimentation area is located between the clear water area and the inlet water area and is used for sedimenting flocs; a sludge discharge port is arranged at the bottom of the inlet water area and is connected with a sludge discharge branch pipe through a sludge discharge pump by using a sludge discharge pipe; wherein, the stirring mechanisms in the high-speed reaction chamber, the medium-speed reaction chamber and the low-speed reaction chamber are respectively externally connected with a driving unit, and the stirring speed of the stirring mechanisms is controlled from high to low through a gearbox.

[0021] Preferably, the sludge discharge pump is connected with the low-speed reaction chamber and the sludge discharge branch pipe respectively by using a sludge discharge return pipe.

[0022] Preferably, a water outlet channel is arranged at the upper section of the clear water area, and the water outlet channel is connected with the water outlet pipe for guiding the clear water in the clear water area to flow out through the water outlet pipe; the sedimentation area comprises a plurality of sedimentation inclined tubes laid between the clear water area and the inlet water area, and the waste water with flocs enters the plurality of sedimentation inclined tubes through the inlet water area to sediment the flocs.

[0023] Preferably, a sludge scraper is arranged at the bottom of the sedimentation tank, and the sludge scraper is externally connected with a driving mechanism for scraping the mud hanging on the bottom wall of the sedimentation tank.

[0024] Preferably, a pH probe is arranged in the high-speed reaction chamber for detecting the pH value in the high-speed reaction chamber.

[0025] Preferably, the stirring mechanisms in the three groups of reaction chambers are all arranged vertically, and the stirring mechanism comprises a stirring rod and stirring blades, the two ends of the stirring rod are movably arranged in the reactor, and one end of the stirring rod is externally connected with a driving unit through a gearbox; the stirring blades are symmetrically arranged as a group of stirring paddles, and at least two groups of stirring paddles are arranged on the stirring rod.

[0026] Preferably, the sludge hopper arranged in the center of the inlet water area is in an inverted conical or columnar structure, and the sludge discharge port is arranged at the bottom of the sludge hopper.

[0027] Preferably, the high-speed reaction chamber, the medium-speed reaction chamber, and the low-speed reaction chamber are separated by partition walls, and a high-to-medium communication port is provided between the high-speed reaction chamber and the medium-speed reaction chamber for connecting the high-speed reaction chamber and the medium-speed reaction chamber in series; a medium-to-low communication port is provided between the medium-speed reaction chamber and the low-speed reaction chamber for connecting the medium-speed reaction chamber and the low-speed reaction chamber in series.

[0028] Compared with the prior art, the present utility model has the following beneficial effects:

[0029] (1) After being treated by the two-stage defluorination reaction sedimentation tank, the softening reaction sedimentation tank, the multi-media filter, the ozone catalytic oxidation tank, the biochemical reaction unit, the ultrafiltration filter, the cation exchange softener, the decarbonator, the RO device, the chelating resin softener, and the chelating resin defluorinator, the fluoride ions and hardness in the wastewater are effectively removed, and the wastewater can enter the subsequent evaporation crystallization for further evaporation crystallization treatment.

[0030] (2) The defluorination reaction sedimentation tank in the present utility model adopts a series-connected four-tank structure, which respectively performs rapid, medium-speed, slow reactions and precipitation, so that the precipitates generated by the defluorination chemical precipitation reaction can form larger particles through coagulation and flocculation reactions and be separated and removed in the sedimentation tank. The two-stage defluorination reaction sedimentation tanks respectively use soluble calcium salts and magnesium salts as defluorinating agents, which can not only save the cost of the agents but also ensure the effective removal of fluoride ions. The generated RO concentrated water is defluorinated by using metal chelating defluorination resin, which has good selective adsorption. The waste liquid generated by resin regeneration is sent to the first-stage defluorination reaction sedimentation tank for reuse, which can further reduce the consumption of the agents.

[0031] (3) The present utility model can provide an efficient, reliable, and economical defluorination system and device for fluorine-containing concentrated brine. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 FIG. 1 is a schematic flow chart of a defluorination system applicable to zero-discharge treatment of coal gasification wastewater provided by an embodiment of the present utility model;

[0033] Figure 2 FIG. 2 is a schematic diagram of the batching structure in the two-stage defluorination reaction sedimentation tank and the softening reaction sedimentation tank of a defluorination system applicable to zero-discharge treatment of coal gasification wastewater provided by an embodiment of the present utility model;

[0034] Figure 3 FIG. 3 is a schematic flow chart of a chelating resin softener and a chelating resin defluorinator in a defluorination system applicable to zero-discharge treatment of coal gasification wastewater provided by an embodiment of the present utility model;

[0035] Figure 4 FIG. 4 is a schematic diagram of the structure of a reaction sedimentation tank in a defluorination system applicable to zero-discharge treatment of coal gasification wastewater provided by an embodiment of the present utility model.

[0036] The serial numbers in the figure are as follows:

[0037] 101, sludge treatment system; 102, RO fluorine-containing concentrated brine tank; 103, No. 1 defluorination reaction sedimentation tank; 104, No. 2 defluorination reaction sedimentation tank; 105, softening reaction sedimentation tank; 106, multi-media filter; 107, ozone catalytic oxidation tank; 108, biochemical reaction unit; 109, ultrafiltration filter; 110, cation exchange softener; 111, decarbonator; 112, intermediate product water tank; 113, RO device; 114, recycled water tank; 115, RO concentrated brine tank; 116, chelating resin softener; 117, chelating resin defluorinator; 118, evaporation crystallization system; 1, high-speed reaction chamber; 2, medium-speed reaction chamber; 3, low-speed reaction chamber; 4, sedimentation tank; 5, stirring mechanism; 6, inclined sedimentation tube; 7, water inlet area; 8, clear water area; 9, water outlet channel; 10, sludge scraper; 11, water inlet pipe; 12, high-to-medium communication hole; 13, medium-to-low-speed communication hole; 14, communication area; 15, water outlet pipe; 16, sludge discharge port; 17, sludge discharge pump; 18, sludge inlet pipe; 19, sludge discharge return pipe; 20, sludge discharge branch pipe; 21, alkali liquid addition pipeline; 22, defluorinating agent addition pipeline; 23, coagulant addition pipeline; 24, flocculant addition pipeline; 25, pH probe. Specific embodiments

[0038] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments.

[0039] As Figure 1 shown, a defluorination system suitable for zero-discharge treatment of coal gasification wastewater disclosed by the present invention includes an RO fluorine-containing concentrated brine tank 102, two-stage defluorination reaction sedimentation tanks, a softening reaction sedimentation tank 105, a multi-media filter 106, an ozone catalytic oxidation tank 107, a biochemical reaction unit 108, an ultrafiltration filter 109, a cation exchange softener 110, a decarbonator 111, an intermediate product water tank 112, and an RO device 113, which are connected in sequence.

[0040] The sediment sludge, backwash sludge or sludge concentrate generated by the two-stage defluorination reaction sedimentation tanks, the softening reaction sedimentation tank 105, the multi-media filter 106, the ozone catalytic oxidation tank 107, and the ultrafiltration filter 109 are partially refluxed to the RO fluorine-containing concentrated brine tank 102 and the sludge treatment system 101 for reuse or treatment and solid-liquid separation. The regeneration waste liquid of the cation exchange softener 110 is refluxed to the softening reaction sedimentation tank 105 for reuse of the regeneration waste liquid.

[0041] The product water of the RO device 113 is connected to the reused water tank 114, and the concentrated water of the RO device 113 is connected to the RO concentrated water tank 115. The RO concentrated water tank 115 is sequentially connected to a chelating resin softener 116, a chelating resin defluorinator 117, and an evaporation crystallization system 118 through a pump, for deep hardness removal and defluorination respectively, and then enters the subsequent evaporation crystallization system for treatment.

[0042] In this embodiment, the two-stage defluorination reaction sedimentation tank includes a first defluorination reaction sedimentation tank 103 and a second defluorination reaction sedimentation tank 104 with the same structure. The fluorine-containing concentrated brine in the RO fluorine-containing concentrated brine tank 102 generated by the RO device of the wastewater reuse system is lifted by a lift pump and passes through the first defluorination reaction sedimentation tank 103, the second defluorination reaction sedimentation tank 104, the softening reaction sedimentation tank 105, the multi-media filter 106, the ozone catalytic oxidation tank 107, the biochemical reaction unit 108, the ultrafiltration filter 109, the cation exchange softener 110, and the decarbonator 111 respectively, and then enters the intermediate product water tank 112. Then the water in the intermediate product water tank 112 enters the RO device 113 through a lift pump. The product water of the RO device 113 enters the reused water tank 114, and the concentrated water of the RO device 113 enters the RO concentrated water tank 115, and then is pumped into the chelating resin softener 116 and the chelating resin defluorinator 117 for deep hardness removal and defluorination respectively, and then enters the subsequent evaporation crystallization system 118 for further treatment.

[0043] An appropriate amount of alkali, defluorinating agent 1, coagulant, and flocculant are added to the first defluorination reaction sedimentation tank 103; an appropriate amount of alkali, defluorinating agent 2, coagulant, and flocculant are added to the second defluorination reaction sedimentation tank 104; alkali, softening agent, coagulant, flocculant, and acid are added to the softening reaction sedimentation tank 105; powdered activated carbon is added to the biochemical reaction unit 108. The sediment sludge, backwash sludge, or sludge concentrate generated by the first defluorination reaction sedimentation tank 103, the second defluorination reaction sedimentation tank 104, the softening reaction sedimentation tank 105, the multi-media filter 106, the ozone catalytic oxidation tank 107, and the ultrafiltration filter 109 are partially refluxed to the RO fluorine-containing concentrated brine tank 102 for reuse or treatment, and the remaining part is discharged into the sludge treatment system 101 as surplus sludge for solid-liquid separation; the regeneration waste liquid generated by the cation exchange softener 110 enters the softening reaction sedimentation tank 105 for reuse; the regeneration waste liquids generated by the chelating resin softener 116 and the chelating resin defluorinator 117 are sent to the softening reaction sedimentation tank 105 and the first defluorination reaction sedimentation tank 103 respectively for reuse. After the above treatment, the fluoride ion concentration in the wastewater entering the evaporation crystallization system 118 can reach below 1 mg / L.

[0044] Among the chemicals added to the first defluorination reaction sedimentation tank 103, the alkali mainly uses NaOH to adjust the pH required for the defluorination reaction. The first defluorinating agent uses calcium salts that are soluble or easily soluble in water, with CaCl2 being the best because soluble calcium salts are cheaper than magnesium salts, and the calcium fluoride precipitate produced is more likely to form larger flocs through the processes of coagulation and flocculation, facilitating sedimentation and separation. To avoid increasing the salt concentration in the wastewater, the first defluorinating agent is added according to a molar ratio of fluoride ions to calcium ions of 2:1, so that the added calcium ions can react completely with the fluoride ions. The coagulant uses iron salt coagulants, with polyferric chloride and polyferric sulfate being the best. The use of polyiron salts can not only cause the formed calcium fluoride to undergo a coagulation reaction, but also the positively charged sites on the polyiron salts can adsorb a part of the fluoride ions. Compared with aluminum-based coagulants such as polyaluminum chloride and polyaluminum sulfate, iron-based coagulants are not likely to clog the subsequent membrane filtration device. The flocculant mainly uses anionic polyacrylamide (PAM) to facilitate the flocculation reaction of the positively charged coagulation particles. The flocculation effect makes the floc particles formed by the coagulation reaction become larger, thus facilitating better precipitation. To enable the precipitation reaction to proceed quickly, and at the same time the calcium fluoride precipitate can grow into larger floc particles and can precipitate well in the sedimentation area.

[0045] The first defluorination reaction sedimentation tank 103 adopts an integrated reaction device and a four-tank structure in series, with a high-speed, medium-speed, and slow-speed reaction zone and a sedimentation zone set respectively. Since the solubility of CaF2 in water is poorly soluble, with a solubility of 87.57 mg / L, generally the F ion concentration in its effluent is still around 15 mg / L. Therefore, it is necessary to enter the second defluorination reaction sedimentation tank 104 for further defluorination.

[0046] Among the chemicals added to the second defluorination reaction sedimentation tank 104, the alkali agent, coagulant, and flocculant are the same as those used in the first defluorination reaction sedimentation tank 103. The second defluorinating agent uses magnesium salts that are soluble or easily soluble in water, with magnesium sulfate or magnesium chloride being the best. Although the water solubility of magnesium fluoride produced by the magnesium salt defluorinating agent and fluoride ions is slightly higher than that of calcium fluoride, Mg(OH)2 formed under alkaline conditions has an adsorptive effect on fluoride ions, so that the fluoride ion concentration after the reaction can be lower, reaching a concentration lower than 10 mg / L. To avoid increasing the salt concentration in the wastewater due to the addition of the defluorinating agent, the second defluorinating agent is added according to a molar ratio of fluoride ions (calculated based on the inlet concentration of this reaction device) to magnesium ions of 2:1, so that the added magnesium ions can react completely with the fluoride ions. To enable the precipitation reaction to proceed quickly, and at the same time the magnesium fluoride precipitate can grow into larger floc particles and can precipitate well in the sedimentation area, the second defluorination reaction sedimentation tank 104 adopts an integrated reaction device with the same structure as the first defluorination reaction sedimentation tank 103.

[0047] As an important part of the defluorination system, the chelating resin defluorinator 117 adopts the setting of a conventional ion exchange tank, and is filled with metal chelating defluorination resin inside. The metal chelating defluorination resin is a metal chelating agent that loads fluoride ions on the surface of macroporous resin.

[0048] Among the chemicals (alkali, softening agent, coagulant, flocculant, acid) added to the softening reaction sedimentation tank 105, the alkali and acid are used to adjust and callback the pH. The softening agent uses Na2CO3 and is used to react with calcium and magnesium ions in the water to form precipitation. The functions of the coagulant and flocculant are to assist precipitation; the multi-media filter is filled with manganese sand and quartz sand to remove iron and manganese in the water; the ozone catalytic oxidation tank 107 adopts a fixed-bed catalytic reaction device and is filled with a supported granular ozone reaction catalyst; the biochemical reaction unit 108 consists of an anoxic reaction tank and a contact oxidation tank, and powdered activated carbon is added to the contact oxidation tank to improve the organic matter removal effect of the biochemical treatment system; the ultrafiltration filter 109 adopts a submerged ultrafiltration membrane filter; the ion exchange softener 110 is filled with cation exchange resin to remove the remaining calcium and magnesium ions in the water; the decarbonator 111 adopts a packed tower decarbonator; the RO device (reverse osmosis device) 113 adopts a conventional reverse osmosis membrane filtration device; the chelating resin softener 116 adopts the setting of a conventional ion exchange tank and is filled with a chelating agent with calcium and magnesium ions loaded on the surface of macroporous resin.

[0049] In this embodiment, the first defluorination reaction sedimentation tank and the second defluorination reaction sedimentation tank have the same structure, which is composed of a high-speed reaction chamber 1, a medium-speed reaction chamber 2, a low-speed reaction chamber 3, a sedimentation tank 4, and a sludge pump 17. Stirring mechanisms 5 are arranged inside the three reaction chambers, and the speed of the stirring mechanisms is controlled by the gearboxes on the stirring mechanisms to be fast, medium, or slow. A sedimentation inclined tube 6 is arranged in the middle of the sedimentation tank 4. Below the sedimentation inclined tube 6 is the water inlet area 7, and above the sedimentation inclined tube 6 is the clear water area 8. A clear water channel 9 is arranged in the upper part of the clear water area 8. A sludge scraper 10 is arranged at the bottom of the sedimentation tank 4, and a sludge hopper is arranged at the bottom center. A sludge outlet 16 is arranged in the sludge hopper. The high-speed reaction chamber 1 is provided with a water inlet 11, a lye addition pipeline 21, a defluorinating agent addition pipeline 22, and a pH probe 25 at the top. The medium-speed reaction chamber 2 is provided with a coagulant addition pipeline 23 at the top. The low-speed reaction chamber 3 is provided with a flocculant addition pipeline 24 and a sludge return pipeline at the top. Partition walls are arranged between the high-speed reaction chamber 1 and the medium-speed reaction chamber 2 and between the medium-speed reaction chamber 2 and the low-speed reaction chamber 3. A high-to-medium communication hole 12 and a medium-to-low communication hole 13 are respectively arranged on the partition walls. A communication area 14 is arranged between the low-speed reaction chamber 3 and the sedimentation tank 4. Through the arrangement of the communication area 14, the reaction liquid can flow out from the bottom opening of the low-speed reaction chamber 3 and be evenly distributed horizontally in the sedimentation tank and slowly enter the water inlet area 7 of the sedimentation tank 4. A water outlet pipe 15 is arranged in the clear water area 8 of the sedimentation tank, and the water outlet pipe 15 is connected to the clear water channel 9 through a pipeline or a channel. The sludge outlet 16 is connected to the sludge pump 17 through a sludge inlet pipe 18. The outlet of the sludge pump 17 is connected to the top of the low-speed reaction chamber 3 through a sludge return pipe 19, and a sludge discharge branch pipe 20 is connected to the sludge return pipe 19.

[0050] The fluorine-containing concentrated brine generated from the RO device of the wastewater reuse system is lifted by a lift pump and first enters the first defluorination reaction sedimentation tank 103 from the water inlet 11 of the first defluorination reaction sedimentation tank 103. After the wastewater enters the first defluorination reaction sedimentation tank 103, it first enters the high-speed reaction chamber 1, where the pH is adjusted to 8-9, and a rapid reaction occurs with the added first defluorinating agent (with CaCl2 being the optimal one). Under suitable alkaline conditions, the fluoride ions in the water react with the first defluorinating agent to form CaF2 precipitate; the addition amount of the first defluorinating agent is added according to the molar ratio of calcium ions to fluoride ions being close to or greater than 1:2. Then, the wastewater enters the medium-speed reaction sedimentation chamber 2, where CaF2 undergoes a medium-speed reaction with the added coagulant to form visible flocs. The medium-speed reaction can create suitable hydraulic conditions to enable the effective formation and growth of the flocs. Then, the wastewater with flocs enters the low-speed reaction chamber 3, where the wastewater reacts with the added flocculant to generate larger and more easily precipitated flocs. Then, the wastewater with flocs is evenly distributed on the cross-section of the water inlet of the sedimentation tank through the connection area 14 and enters the water inlet area 7 of the sedimentation tank 4. Through a number of inclined sedimentation tubes 6, the flocs are precipitated in the inclined sedimentation tubes 6, and the clear liquid enters the clear water area 8 and then enters the clear water channel 9. Under the guidance of the clear water channel 9, the clear water is collected into the outlet pipe 15 through a connecting pipe or connecting channel and enters the second defluorination reaction sedimentation tank 104 for further treatment. The sludge precipitated in the inclined sedimentation tubes 6 of the sedimentation tank slides down under the action of gravity to the bottom of the sedimentation tank, and the scraping machine 10 causes the precipitated sludge to be collected into the sludge hopper at the center of the bottom of the sedimentation tank and discharged through the sludge discharge outlet 16 of the sludge hopper. Through the sludge pump 17, a part of it is recycled to the low-speed reaction chamber 3, and a part is sent as surplus sludge to the sludge dewatering device through the sludge discharge branch pipe 20 for dewatering and external transportation.

[0051] The clear liquid discharged from the outlet pipe 15 enters the second defluorination reaction sedimentation tank 104 for further defluorination, then enters the softening reaction sedimentation tank 105 for hardness removal, then enters the multi-media filter 106 to further remove suspended solids, and then enters the ozone catalytic oxidation tank 107, the biochemical reaction unit 108, and the ultrafiltration filter 109 respectively to remove the organic matter and generated suspended solids in the wastewater. Then, it enters the cation exchange softener 110 to further remove the hardness (calcium and magnesium ions) in the water, then enters the decarbonator 111 to remove the carbonate ions in the water, then enters the intermediate product water tank 112 and is pumped into the RO device 113 through a lift pump for desalination. The product water of the RO device 113 enters the reused water tank for reuse, and the concentrated water of the RO device 113 enters the RO concentrated water tank 115, and then is pumped into the chelating resin softener 116 and the chelating resin defluorinator 117 for deep hardness removal and defluorination respectively. The product water of the defluorinator enters the subsequent evaporation crystallization system 118 for further treatment.

[0052] The defluorination process adopts a two-stage chemical precipitation reaction. In the first stage, CaCl2 with better solubility is used as the defluorinating agent, together with polyferric coagulant and PAM flocculant. In the second stage, magnesium salts (magnesium chloride or magnesium sulfate) with better solubility are used as the defluorinating agent. Since the solubility of these magnesium salts is higher, although the solubility of the formed magnesium fluoride precipitate is slightly higher, Mg(OH)2 can adsorb fluoride ions, so a lower effluent fluoride ion concentration can be obtained.

[0053] Since the price of calcium salts is lower than that of magnesium salts, using soluble calcium salts and magnesium salts in the first-stage and second-stage chemical precipitation reactions respectively can also reduce the required chemical agent cost.

[0054] Using a two-stage chemical reaction of calcium salts and magnesium salts for defluorination, and in each stage, the defluorinating agent can be added according to the stoichiometric relationship based on the actual fluoride ion concentration of the wastewater entering this stage, without the need to add an excessive amount of the defluorinating agent. This can reduce the chemicals added to the wastewater and also reduce the salt concentration increased due to chemical defluorination, reducing the load on subsequent concentration, evaporation, and crystallization devices.

[0055] In the defluorination reaction sedimentation tank and softening reaction sedimentation tank of the two-stage process, iron-based polymeric coagulants such as polyferric chloride and polyferric sulfate are used as the coagulants, rather than aluminum-based polymeric coagulants, which can prevent the aluminum-containing flocs remaining in the aluminum-based polymeric coagulants from clogging the membrane filtration equipment and affecting their normal use.

[0056] The fluoride ion concentration in the concentrated brine generated by the RO filtration system will increase again, and re-defluorination is required. A resin adsorption device is selected, which is small in volume and simple to operate. The macroporous resin loaded with a fluoride ion metal chelating agent has good selective adsorption for fluoride ions, and a very low fluoride ion concentration can be obtained. At the same time, the resin can be regenerated by adding a regenerant after saturation.

[0057] The overall system consists of many units for defluorination, hardness removal, and organic matter (COD) removal, but they are interrelated and not completely independent. For example, the defluorination reaction sedimentation unit can also remove a part of the hardness, and a part of the fluoride ions can also be removed during the softening process. Adding activated carbon in the wastewater biochemical treatment section can also adsorb a small amount of fluoride ions onto the activated carbon.

[0058] The regeneration waste liquids from the chelating resin defluorinator 117 and the chelating resin softener 116 are respectively sent to the first defluorination reaction sedimentation tank 103 and the softening reaction sedimentation tank 105 for reuse, which can reduce the usage amount of the defluorinating agent and the softening agent and save the chemical agent cost.

[0059] Furthermore, in the present embodiment, the stirring mechanism 5 is vertically arranged, and the stirring mechanism 5 includes a stirring rod and stirring blades, both ends of the stirring rod are movably arranged in the reactor, and one end of the stirring rod is connected to an external driving unit through a gearbox; the stirring blades are symmetrically arranged as a group of stirring paddles, and at least two groups of stirring paddles are provided on the stirring rod.

[0060] The working principle of the utility model is as follows:

[0061] The RO fluorine-containing concentrated brine produced by the RO device of the coal gasification wastewater reuse system is lifted by a lifting pump and enters the No. 1 defluorination reaction sedimentation tank from the water inlet 11 of the No. 1 defluorination reaction sedimentation tank. After entering the No. 1 defluorination reaction sedimentation tank, it first enters the high-speed reaction chamber 1, where the pH is adjusted to 8-9, and reacts quickly with the added defluorination agent (CaCl2). Under suitable alkaline conditions, the fluoride ions in the water react with CaCl2 to form CaF2 precipitation; the amount of defluorination agent added is close to or greater than 1:2 according to the molar ratio of calcium ions to fluoride ions. Then, the wastewater enters the medium-speed reaction chamber 2, where CaF2 and the added coagulant (using polyferric chloride) react at a medium speed to form a coagulant visible to the naked eye. The medium-speed reaction can create suitable hydraulic conditions so that the coagulant can be effectively formed and grown. Next, the wastewater with coagulants enters the low-speed reaction chamber 3, where the wastewater reacts with the added flocculant (using polyacrylamide) to generate larger flocs with larger particles and easier precipitation. The wastewater with flocs is evenly distributed on the cross section through the connecting area 14 and slowly enters the water inlet area 7 of the sedimentation tank 4. Through a number of sedimentation inclined tubes 6, the flocs are precipitated in the sedimentation inclined tubes, and the clear liquid enters the clean water area 8 and enters the clean water channel 9. Under the guidance of the clean water channel 9, the clean water is collected to the outlet pipe 15 through the connecting pipe and enters the No. 2 defluorination reaction sedimentation tank. The sludge precipitated in the sedimentation inclined tube of the sedimentation tank slides to the bottom of the sedimentation tank under the action of gravity, and the precipitated sludge is collected to the sludge hopper at the center of the bottom of the sedimentation tank through the scraper 10, and discharged through the sludge outlet 16 of the sludge hopper, and through the sludge pump 17, part of it flows back to the low-speed reaction chamber 3, and part of it is sent to the sludge dewatering device as residual sludge through the sludge discharge branch pipe 20 for dehydration and transportation.

[0062] The clear liquid discharged from the water outlet pipe 15 of the first defluorination reaction sedimentation tank 103 enters the second defluorination reaction sedimentation tank 104 for further defluorination, then enters the softening reaction sedimentation tank 105 for hardness removal, then enters the multi-media filter 106 to further remove suspended solids, and then enters the ozone catalytic oxidation tank 107, the biochemical reaction unit 108, and the ultrafiltration filter 109 respectively to remove the organic matter and the generated suspended solids in the wastewater. Then it enters the cation exchange softener 110 to further remove the hardness (calcium and magnesium ions) in the water, then enters the decarbonator 111 to remove the carbonate ions in the water, then enters the intermediate product water tank 112 and is pumped into the RO device 113 through a lift pump for desalination. The water produced by the RO device 113 enters the recycled water tank 114, and the concentrated water of the RO device 113 enters the RO concentrated water tank 115. Then, after being pumped into the chelating resin softener 116 and the chelating defluorination resin defluorinator 117 for deep hardness removal and defluorination respectively, the wastewater enters the subsequent evaporation crystallization system 118 for further treatment.

[0063] The water quality of the influent, the effluent of the pre-reactor and the main reactor in this embodiment is shown in Table 1.

[0064] Table 1 Concentration indexes of fluoride ions in the influent and effluent of the defluorination system in this embodiment

[0065] COD (mg / L) TDS (mg / L) <![CDATA[F - (mg / L)]]> Influent 242 10184 31 Effluent from the first defluorination reaction sedimentation tank 242 10340 15 Effluent from the second defluorination reaction sedimentation tank 242 10340 6 Ozone catalytic oxidation tank 126 10564 6 Biochemical treatment unit 22 10558 5 Cation exchanger 22 10557 5 Decarbonator 22 10557 5 RO product water 2.2 316 0.1 RO concentrate 66 33374 15.9 Effluent from the metal chelating resin softener 65 34978 15.9 Effluent from the metal chelating resin defluorinator 60 34958 0.3

[0066] In the description of the present invention, it should be understood that the orientation or positional relationship indicated by the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", etc. is based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation to the present invention.

[0067] In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features.

Claims

1. A defluorination system applicable to zero - discharge treatment of coal - gasification wastewater, characterized in that, It includes a RO fluorine-containing concentrated brine tank (102), a two-stage defluorination reaction sedimentation tank, a softening reaction sedimentation tank (105), a multi-media filter (106), an ozone catalytic oxidation tank (107), a biochemical reaction unit (108), an ultrafiltration filter (109), a cation exchange softener (110), a decarbonator (111), an intermediate product water tank (112) and a RO device (113) connected in sequence; The sediment sludge, backwash sludge or sludge concentrate generated by the two-stage defluorination reaction sedimentation tank, the softening reaction sedimentation tank (105), the multi-media filter (106), the ozone catalytic oxidation tank (107) and the ultrafiltration filter (109) are partially refluxed to the RO fluorine-containing concentrated brine tank (102) and the sludge treatment system (101) for reuse or treatment and solid-liquid separation; Soluble calcium salts and magnesium salts are added as defluorinating agents in the two-stage defluorination reaction sedimentation tank; The regeneration waste liquid in the cation exchange softener (110) is refluxed to the softening reaction sedimentation tank (105) for reuse of the regeneration waste liquid; The product water of the RO device (113) is connected to the recycled water tank (114), the concentrated water of the RO device (113) is connected to the RO concentrated water tank (115), and the RO concentrated water tank (115) is connected to a chelating resin softener, a chelating resin defluorinator and an evaporation crystallization system in sequence by a pump for deep hardness removal and defluorination respectively, and enters the subsequent evaporation crystallization system for treatment.

2. The defluorination system applicable to zero-discharge treatment of coal gasification wastewater according to claim 1, wherein, The two-stage defluorination reaction sedimentation tank includes a first defluorination reaction sedimentation tank (103) and a second defluorination reaction sedimentation tank (104) with the same structure, both of which include three groups of reaction chambers, a sedimentation tank (4) and a communication area (14); The three groups of reaction chambers include a high-speed reaction chamber (1), a medium-speed reaction chamber (2), and a low-speed reaction chamber (3). Stirring mechanisms (5) are provided in the high-speed reaction chamber (1), the medium-speed reaction chamber (2) and the low-speed reaction chamber (3) and are connected in series with each other; an inlet pipe (11), an alkali liquid addition pipeline (21) and a defluorinating agent addition pipeline (22) are connected to the high-speed reaction chamber (1); a coagulant addition pipeline (23) is connected to the medium-speed reaction chamber (2); a flocculant addition pipeline (21) is connected to the low-speed reaction chamber (3); The low-speed reaction chamber (3) communicates with the sedimentation tank (4) through the communication area (14); an inlet area (7), a clear water area (8) and a sedimentation area are provided in the sedimentation tank (4); the clear water area (8) is located above the inlet area (7) for collecting clear liquid, and the clear water area (8) is connected to an outlet pipe (15) for discharging clear liquid; the sedimentation area is located between the clear water area (8) and the inlet area (7) for sedimenting flocs; a sludge discharge port (16) is provided at the bottom of the inlet area (7) and is connected to a sludge discharge branch pipe (20) through a sludge discharge pump (17); Among them, the stirring mechanisms (5) in the high-speed reaction chamber (1), the medium-speed reaction chamber (2) and the low-speed reaction chamber (3) are respectively externally connected to a driving unit, and the stirring speed of the stirring mechanisms (5) is controlled from high to low through a gearbox.

3. The defluorination system applicable to zero - discharge treatment of coal - gasification wastewater according to claim 2, wherein, The sludge discharge pump (17) is connected to the low-speed reaction chamber (3) and the sludge discharge branch pipe (20) respectively by a sludge discharge return pipe (19).

4. A defluorination system applicable to zero - discharge treatment of coal - gasification wastewater according to claim 2, characterized in that, An upper section of the clear water area (8) is provided with a water outlet channel (9), and the water outlet channel (9) is connected to a water outlet pipe (15) for guiding the clear water in the clear water area (8) to flow out through the water outlet pipe (15). The sedimentation area includes a number of sedimentation inclined tubes (6) laid between the clear water area (8) and the water inlet area (7). The wastewater with flocs enters the number of sedimentation inclined tubes (6) through the water inlet area (7) to sediment the flocs.

5. The defluorination system applicable to zero-emission treatment of coal gasification wastewater according to claim 2, characterized in that, A sludge scraper (10) is provided at the bottom of the sedimentation tank (4). The sludge scraper (10) is externally connected to a driving mechanism for scraping the sludge adhering to the bottom wall of the sedimentation tank (4).

6. The defluorination system applicable to zero - discharge treatment of coal - gasification wastewater according to claim 2, wherein, A pH probe (25) is provided in the high-speed reaction chamber (1) for detecting the pH value in the high-speed reaction chamber (1).

7. The defluorination system applicable to zero - discharge treatment of coal - gasification wastewater according to claim 2, wherein, The stirring mechanisms (5) in the three reaction chambers are all vertically arranged. The stirring mechanism (5) includes a stirring rod and stirring blades. Both ends of the stirring rod are movably arranged in the reaction chamber, and one end of the stirring rod is externally connected to a driving unit through a gearbox. The stirring blades are symmetrically arranged as a set of stirring paddles, and at least two sets of stirring paddles are provided on the stirring rod.

8. The defluorination system applicable to zero - discharge treatment of coal - gasification wastewater according to claim 2, wherein, A sludge hopper with an inverted conical or columnar structure is provided at the center of the water inlet area (7), and the sludge discharge port (16) is arranged at the bottom of the sludge hopper.

9. The defluorination system applicable to zero - discharge treatment of coal - gasification wastewater according to claim 2, wherein, The high-speed reaction chamber (1), the medium-speed reaction chamber (2) and the low-speed reaction chamber (3) are separated by partition walls. A high-to-medium communication port (12) is provided between the high-speed reaction chamber (1) and the medium-speed reaction chamber (2) for connecting the high-speed reaction chamber (1) and the medium-speed reaction chamber (2) in series. A medium-to-low communication port (13) is provided between the medium-speed reaction chamber (2) and the low-speed reaction chamber (3) for connecting the medium-speed reaction chamber (2) and the low-speed reaction chamber (3) in series.

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