Method and system for simply and efficiently treating fluorine-containing acidic wastewater in polycrystalline silicon production

Abstract

The invention discloses a method and a system for simply and efficiently treating fluorine-containing acidic wastewater in polycrystalline silicon production, and belongs to the technical field of wastewater treatment. The system comprises a wastewater treatment system and a sludge treatment system, the wastewater treatment system comprises a pretreatment stage, a neutralization treatment stage and a deep treatment stage, fluorine-containing acidic wastewater enters a neutralization reaction tank for precipitation after being subjected to physical filtration and homogenization treatment in an adjusting tank, and flocculation treatment is performed by adopting a clarification tank and an air flotation machine; sludge generated in the fluorine-containing acidic wastewater treatment process is subjected to dehydration treatment through a sludge dehydrator. According to the invention, a combined technological process of chemical precipitation, the inclined tube clarifier and the air flotation purifier is utilized, so that the fluorine-containing acidic wastewater is treated in a standard reaching manner, the cyclic utilization of the wastewater is realized, and the method has the advantages of remarkable reduction and resource utilization; the whole technical scheme provided by the invention is simple, the existing traditional process flow is shortened, the efficiency is improved, the treated sewage can reach the discharge standard, and the method is green and economical.

Description

Technical Field

[0001] The present invention belongs to the technical field of wastewater treatment, and in particular relates to a method and system for simply and efficiently treating fluorine-containing acidic wastewater in polysilicon production. Background Art

[0002] The polysilicon production industry is a high water consumption industry. The polysilicon production wastewater has a large amount of water, high suspended solids content, high organic matter concentration, complex components and is difficult to biodegrade. In addition, in its production process, a large amount of hydrofluoric acid and nitric acid are used for surface texturing and wet etching and other processes. Therefore, the wastewater generated in the polysilicon production process often contains high concentrations of fluoride ions, COD and total nitrogen. Therefore, if the polysilicon production wastewater is not effectively treated, it will cause serious harm to the natural environment.

[0003] According to the water quality of polysilicon production wastewater, it is mainly divided into two categories: acidic wastewater and fluoride-containing wastewater. Acidic wastewater mainly contains HCl, SiO 2 The components come from the tail gas washing device, cold hydrogenation device and slurry washing process. The fluoride-containing wastewater mainly contains HNO 3 , HF, H 2 O and other components come from the discharge water of wastewater storage tanks and waste acid storage tanks. At present, the main methods for treating polysilicon production wastewater at home and abroad include chemical precipitation, coagulation precipitation, adsorption, ion exchange, reverse osmosis, activated carbon defluorination, and electrocoagulation. Among these methods, activated carbon defluorination requires the use of activated carbon, and the treatment and operation costs are high; the ion exchange method has strict requirements on the quality of sewage and has high costs; the reverse osmosis method and electrocoagulation method consume a lot of electricity and the equipment is expensive, so they are not often used.

[0004] Chinese patent CN101941752B discloses a treatment and device for fluorine-containing wastewater, and introduces a fluidized bed crystallization reactor. Using the principle of induced crystallization, calcium fluoride precipitate with large particles and low water content can be recovered. However, due to the low solubility of calcium fluoride, the reaction needs to be controlled at a low supersaturation, which is not suitable for treating high-concentration fluorine-containing wastewater, and requires the addition of crystal seeds, which has high treatment costs. Therefore, considering the actual operability and economic factors, for industrial wastewater treatment with the main goal of meeting discharge standards, it is urgent to develop a method for efficiently treating fluorine-containing acidic wastewater in polysilicon production, so as to overcome the problems caused by traditional processes, such as the treated wastewater not meeting the standards, the pH value in the wastewater exceeding the standard, and the large waste of production costs. Summary of the invention

[0005] In view of the above-mentioned problems existing in the prior art, the technical problem to be solved by the present invention is to provide a method and system for simply and efficiently treating fluorine-containing acidic wastewater in polysilicon production, which solves the problems that the existing polysilicon production wastewater is difficult to treat and the treatment process is immature, the effluent is unstable in meeting the standards, and the process operation cost is high.

[0006] In order to solve the above problems, the technical solution adopted by the present invention is as follows:

[0007] A system for simply and efficiently treating fluorine-containing acidic wastewater in polysilicon production comprises a wastewater treatment system and a sludge treatment system. The wastewater treatment system comprises a pretreatment stage, a neutralization treatment stage and a deep treatment stage which are sequentially connected through pipelines. The neutralization treatment stage comprises a sewage lifting pump connected to a regulating tank and a neutralization reaction tank, an intermediate water tank and an integrated high-efficiency clarification tank which are sequentially connected. The deep treatment stage comprises an integrated high-efficiency flotation machine. The sludge generated during the treatment of fluorine-containing acidic wastewater is dehydrated by a sludge dehydrator.

[0008] Preferably, the pretreatment stage comprises a grid filter pool and a regulating pool which are connected in sequence, and is connected to the water inlet through the grid filter pool, and a plurality of layers of filter grids are arranged in the grid filter pool.

[0009] Preferably, the neutralization reaction tank is composed of a four-stage neutralization reaction tank, a four-stage neutralization mixer and a four-stage neutralization aeration device;

[0010] The integrated high-efficiency clarifier is composed of a two-stage stirring reaction zone and a clarification zone, and the clarification zone is composed of an inclined tube clarifier and an inclined tube clarifier.

[0011] Preferably, the bottom end of the integrated high-efficiency flotation machine is connected to the sludge storage tank through a sludge pump, and the sludge produced in the neutralization reaction tank and the integrated high-efficiency clarification tank is transported to the sludge treatment system through the sludge pump for centralized treatment until it meets the discharge standards.

[0012] A method for treating fluorine-containing acidic wastewater in polysilicon production using the system comprises the following steps:

[0013] (1) After filtering large suspended solids through a multi-layer screen, a certain fluorine-containing acidic wastewater flows directly into the regulating tank through a pipeline. After being homogenized and treated in the regulating tank for 12 hours, it enters the neutralization reaction tank through a sewage lift pump;

[0014] (2) Add lime milk and calcium chloride to the neutralization reaction tank, stir and neutralize to produce precipitate, the hydraulic retention time is not less than 1 hour, the neutralized wastewater flows into the intermediate water tank under gravity conditions, and then is pumped to the two-stage stirring reaction zone of the integrated high-efficiency clarification tank;

[0015] (3) When the wastewater is lifted to the two-stage stirring reaction zone, PAC and PAM are added. After the coagulation reaction, the wastewater enters the bottom of the inclined tube clarifier through the water distribution area. The wastewater is hydraulically retained in the inclined tube clarifier for 3 to 4 hours. The solid flocculants are gradually separated from the water. The sludge is gradually concentrated to the bottom under the action of gravity. The clean water flows upward into the supernatant collection tank and is lifted by the pump into the integrated high-efficiency flotation machine for deep treatment.

[0016] (4) The wastewater is mixed with the dissolved air water released by the integrated high-efficiency air flotation machine, the floating scum is collected and PAC and PAM are added to the integrated high-efficiency air flotation machine, the sludge scraped by air flotation is sent to the sludge storage tank, part of the clean water after air flotation is returned for dissolved air use, part of it enters the reuse water pool, part of the reuse water is sent to the elution tower for circulation elution, and part of it is sent to the calcium chloride wastewater evaporation system;

[0017] (5) The sludge generated in the neutralization reaction tank and the integrated high-efficiency clarification tank is transported to the sludge storage tank through the sludge pump. The sludge in the sludge storage tank is dehydrated and then transported out for treatment.

[0018] Preferably, in step 2), the dosage of lime milk and calcium chloride in the neutralization reaction tank is 0.7 g / L, and the mixture is stirred for neutralization and precipitation is produced, so that the pH value of the wastewater is 6-7.

[0019] Preferably, in step 3), the dosage of PAC is 1.1 g / L PAC, and the dosage of PAM is 0.02 g / L PAM.

[0020] Preferably, in step 4), 0.7 g / L PAC and 0.01 g / L PAM are added to the integrated high-efficiency air flotation machine.

[0021] Preferably, in step 4), the hydraulic retention time of the wastewater in the integrated high-efficiency air flotation machine is 5-6 min, and the operating pressure is 0.4-0.5 MPa.

[0022] Preferably, in step 5), the sludge dewatering machine is a box-type high-pressure diaphragm filter press, and after dehydration to below 85%, the sludge is transported out for treatment.

[0023] Beneficial effects: Compared with the prior art, the advantages of the present invention are:

[0024] (1) The present invention utilizes a combined process of chemical precipitation, inclined tube clarifier and flotation purifier to ensure that fluorine-containing acidic wastewater is treated up to standard, realizes the recycling of wastewater, and has significant advantages of wastewater reduction and resource utilization.

[0025] (2) The present invention uses baffles to separate the neutralization reaction tank stages, so that the wastewater is baffled and moved forward in the reaction tank to fully mix and react with the lime milk and calcium chloride. The neutralized wastewater flows into the intermediate water tank under gravity, thereby improving the utilization rate of calcium-containing alkaline substances;

[0026] (3) The entire technical scheme of the present invention is simple. The fluorine-containing acidic wastewater is physically filtered and homogenized in the regulating tank before entering the neutralization reaction tank for sedimentation. A clarification tank and an air flotation machine are used for flocculation treatment. The sludge generated during the treatment process is dehydrated by a sludge dewatering machine, which shortens the existing traditional process flow and improves efficiency. The treated wastewater can meet the discharge standards and is green and economical. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a schematic diagram of the process flow of the present invention. DETAILED DESCRIPTION

[0028] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with specific embodiments.

[0029] Example 1

[0030] This embodiment provides a simple and efficient system for treating fluorine-containing acidic wastewater in polysilicon production. Figure 1 As shown, it includes a wastewater treatment system and a sludge treatment system connected in sequence. The wastewater treatment system includes a pretreatment stage, a neutralization treatment stage and a deep treatment stage. The pretreatment stage includes a grid filter tank and a regulating tank connected in sequence, and is connected to the water inlet through the grid filter tank. A multi-layer filter grid is arranged in the grid filter tank. After the large suspended solids are filtered through the multi-layer grid, the fluorine-containing acidic wastewater directly flows into the regulating tank through a pipeline. After being homogenized and homogenized in the regulating tank, it enters the neutralization treatment stage through a sewage lift pump. The neutralization treatment stage includes a sewage lift pump connected to the regulating tank and a neutralization reaction tank, an intermediate water tank and an integrated high-efficiency clarification tank connected in sequence.

[0031] The neutralization reaction tank consists of a four-stage neutralization reaction tank, a four-stage neutralization mixer and a four-stage neutralization aeration device. The hydraulic retention time in the four-stage neutralization reaction tank is not less than 1h. The four-stage neutralization mixer is: the upper and lower layers are propeller mixers and the middle layer is a folding paddle to achieve efficient mixing and stirring effects. The reaction tank stages are separated by baffles, so that the wastewater is baffled and moved forward in the neutralization reaction tank, fully mixed and reacted with the lime milk, and the neutralized wastewater flows into the middle water tank under gravity conditions, and is then lifted to the integrated high-efficiency clarification tank by a pump.

[0032] The integrated high-efficiency clarifier consists of a two-stage stirring reaction zone and a clarification zone. When the wastewater is lifted to the two-stage stirring reaction zone, PAC and PAM are added to condense the tiny particles and increase the sedimentation rate; the clarification zone consists of an inclined tube clarifier and an inclined tube clarifier. In the inclined tube clarifier, under the sedimentation acceleration of the inclined tube, the solid flocculants are gradually separated from the water, and the sludge is gradually concentrated to the bottom of the inclined tube clarifier under the action of gravity. The clean water flows upward and enters the deep treatment stage from the upper part through the supernatant collection tank. The deep treatment stage includes an integrated high-efficiency air flotation machine. The wastewater is mixed with the dissolved air water released by the integrated high-efficiency air flotation machine, and the tiny bubbles are used as carriers to make the flocculants carrying tiny suspended particles in the wastewater adhere to the bubbles and float to the water surface with the bubbles to form scum. The purpose of separating impurities and further removing suspended matter is achieved by collecting the scum. The bottom of the integrated high-efficiency flotation machine is connected to the sludge storage tank through a sludge pump. The sludge generated in the neutralization reaction tank and the integrated high-efficiency clarification tank is transported to the sludge treatment system through the sludge pump for centralized treatment until it meets the discharge standards.

[0033] The sludge treatment system includes a sludge storage tank and a sludge dewatering machine connected in sequence. The sludge enters the sludge storage tank, is concentrated and then dehydrated by the sludge dewatering machine, and the dehydrated supernatant enters the reuse water pool. The residence time in the reuse water pool is 2 hours. Part of the reuse water is sent to the elution tower for circulating elution, and part is sent to the calcium chloride wastewater evaporation system. The dehydrated sludge is transported out for treatment and landfill.

[0034] In the integrated high-efficiency clarifier, wastewater enters the bottom of the inclined tube clarifier, and the flocculation reaction bridges the tiny particles, further increasing the particle size of the floccules and accelerating their precipitation. After the flocculation reaction, the sedimentation rate of the obtained floccules can be controlled within 0.3-0.5mm / s under the condition of proper pH adjustment. In order to reduce the investment cost, the integrated high-efficiency clarifier can be a steel concrete structure, and the internal support components are made of carbon steel anti-corrosion. In order to deal with the situation where the inclined tube is hung with mud, which eventually causes the inclined tube to collapse due to insufficient load, a thickened ethylene-propylene copolymer inclined plate filler with smooth surface treatment can be used. It is light in weight, has a long service life, a smooth surface, less wall hanging, high strength, and is not easy to collapse. The installation angle is adjusted from the conventional 60° to a 45° tilt angle, the pool is cleaned regularly, and the inclined tube is flushed with pressurized water to remove the wall hanging sludge to ensure the long-term stable operation of the equipment. The lime milk added to the neutralization reaction tank is made by the calcium carbide slag process.

[0035] Example 2

[0036] The treatment system of Example 1 is used to treat fluorine-containing acidic wastewater produced by a polysilicon plant. The fluorine-containing acidic wastewater contains a large amount of strong acid, COD, BOD, fluoride and suspended solids.

[0037] (1) The fluorine-containing acidic wastewater from a polysilicon plant flows directly into the regulating tank through a pipeline after filtering large suspended solids through a multi-layer grid. After being homogenized and treated in the regulating tank for 12 hours, it enters the neutralization reaction tank through a sewage lift pump, and the hydraulic retention time is not less than 1 hour;

[0038] (2) Add lime milk and calcium chloride to the neutralization reaction tank, where the dosage of lime milk and calcium chloride is 0.7 g / L, stir and neutralize to produce precipitate, so that the pH value of the wastewater is 7-8. The neutralized wastewater flows into the intermediate water tank under gravity conditions, and is then pumped to the two-stage stirring reaction zone of the integrated high-efficiency clarification tank;

[0039] (3) When the wastewater is lifted to the two-stage stirring reaction zone, 1.1 g / L PAC and 0.02 g / L PAM are added to cause the tiny particles to flocculate and increase the sedimentation rate. After the coagulation reaction, the wastewater enters the bottom of the inclined tube clarifier through the water distribution area. The flocculation reaction bridges the tiny particles, further increasing the particle size of the floccules and accelerating their sedimentation. After the flocculation reaction, when the pH is adjusted to 7.5~8.5, the sedimentation rate of the obtained floccules is controlled at 0.3mm / s. The solid floccules are gradually separated from the water after hydraulic retention in the inclined tube clarifier for 3~4 hours. The sludge is gradually concentrated to the bottom under the action of gravity. The clean water flows upward into the supernatant collection tank, and after being lifted by the pump, it enters the integrated high-efficiency flotation machine for deep treatment;

[0040] (4) The water in the dissolved air tank stays at a pressure of 0.5MPa for 10-15s, so that a large amount of air is dissolved in the water. The dissolved air efficiency can reach more than 99.8%. The wastewater is mixed with the dissolved air water released by the integrated high-efficiency air flotation machine, and the tiny bubbles are used as carriers to make the floccules carrying tiny suspended particles in the wastewater adhere to the bubbles and float to the water surface with the bubbles to form scum. The purpose of separating impurities and further removing suspended matter is achieved by collecting the scum. The hydraulic retention time of the integrated high-efficiency air flotation machine is 5-6min, and the operating pressure is 0.5MPa. 0.7 g / L PAC and 0.01 g / L PAM are added to the integrated high-efficiency air flotation machine. The sludge scraped by air flotation is sent to the sludge storage tank, and part of the clean water after air flotation is returned for dissolved air use, and part enters the reuse water pool. Part of the reuse water is sent to the elution tower for circulation elution, and part is sent to the calcium chloride wastewater evaporation system;

[0041] (5) The sludge generated in the neutralization reaction tank and the integrated high-efficiency clarification tank is transported to the sludge storage tank through a sludge pump. The sludge in the sludge storage tank is dehydrated to less than 85% by a box-type high-pressure diaphragm filter press and then transported out for treatment.

[0042] This scheme is actually applied in a polysilicon plant production wastewater treatment project. The operation data of the wastewater treatment system is monitored, and the treatment effect is shown in Table 1.

[0043] Table 1 Wastewater treatment effects of different treatment stages

[0044]

[0045] The discharged water and sludge can meet the standards after being treated by this scheme. The relevant data are shown in Table 2 (the designed wastewater inlet water quality of the plant is obtained by statistically analyzing the relevant test reports of the environmental testing station)

[0046] Table 2 Main pollutant indicators of influent and effluent water quality

[0047]

[0048] Example 3

[0049] The treatment method described in Example 2 is adopted. For the calcium ions and fluoride ions still existing in the integrated high-efficiency air flotation machine, this embodiment also includes adding an adsorption process to the deep treatment system, exchanging and adsorbing the calcium ions and fluoride ions in the wastewater in the ion exchange resin, and performing decalcification treatment. The adsorption device of this embodiment is arranged between the integrated high-efficiency air flotation machine and the reuse water pool. The adsorption device is a selective ion exchange resin and a cation exchange resin connected in series. The wastewater after deep treatment by the integrated high-efficiency air flotation machine first enters the selective ion exchange resin and then enters the cation exchange resin. The model of the ion exchange resin can be selected according to the amount of wastewater. In this embodiment, the selected selective ion exchange resin is Tulsion®CH-87 gel type, and the cation exchange resin is D113 weak acid cation exchange resin.

[0050] The above description is only a preferred embodiment of the present invention and is not any formal or substantial limitation of the present invention. It should be pointed out that a person skilled in the art may make several improvements and supplements without departing from the present invention, and these improvements and supplements should also be regarded as the protection scope of the present invention.

Claims

1. A simple and efficient system for treating fluorine-containing acidic wastewater in polysilicon production, comprising a wastewater treatment system and a sludge treatment system, characterized in that: The wastewater treatment system consists of a pretreatment stage, a neutralization treatment stage and a deep treatment stage connected in sequence by pipelines. The neutralization treatment stage includes a sewage lifting pump connected to the regulating tank and a neutralization reaction tank, an intermediate water tank, and an integrated high-efficiency clarification tank connected in sequence. The deep treatment stage includes an integrated high-efficiency flotation machine. The sludge generated during the treatment of fluorine-containing acidic wastewater is dehydrated by a sludge dehydrator.

2. The system for treating fluorine-containing acidic wastewater in polysilicon production in a simple and efficient manner according to claim 1 is characterized in that: The pretreatment stage includes a grid filter pool and a regulating pool which are connected in sequence, and is connected to the water inlet through the grid filter pool. Multiple layers of filter grids are arranged in the grid filter pool.

3. The system for treating fluorine-containing acidic wastewater in polysilicon production in a simple and efficient manner according to claim 1, characterized in that: The neutralization reaction tank is composed of a four-stage neutralization reaction tank, a four-stage neutralization mixer and a four-stage neutralization aeration device; The integrated high-efficiency clarifier is composed of a two-stage stirring reaction zone and a clarification zone, and the clarification zone is composed of an inclined tube clarifier and an inclined tube clarifier.

4. The system for treating fluorine-containing acidic wastewater in polysilicon production in a simple and efficient manner according to claim 1, characterized in that: The bottom end of the integrated high-efficiency flotation machine is connected to the sludge storage tank through a sludge pump, and the sludge generated in the neutralization reaction tank and the integrated high-efficiency clarification tank is transported to the sludge treatment system through the sludge pump for centralized treatment until it meets the discharge standard.

5. A method for treating fluorine-containing acidic wastewater in polysilicon production using the system according to claim 1, characterized in that: The following steps are involved: (1) After filtering large suspended solids through a multi-layer screen, a certain fluorine-containing acidic wastewater flows directly into the regulating tank through a pipeline. After being homogenized and treated in the regulating tank for 12 hours, it enters the neutralization reaction tank through a sewage lift pump; (2) Add lime milk and calcium chloride to the neutralization reaction tank, stir and neutralize to produce precipitate, the hydraulic retention time is not less than 1 hour, the neutralized wastewater flows into the intermediate water tank under gravity conditions, and then is pumped to the two-stage stirring reaction zone of the integrated high-efficiency clarification tank; (3) When the wastewater is lifted to the two-stage stirring reaction zone, PAC and PAM are added. After the coagulation reaction, the wastewater enters the bottom of the inclined tube clarifier through the water distribution area. The wastewater is hydraulically retained in the inclined tube clarifier for 3 to 4 hours. The solid flocculants are gradually separated from the water. The sludge is gradually concentrated to the bottom under the action of gravity. The clean water flows upward into the supernatant collection tank and is lifted by the pump into the integrated high-efficiency flotation machine for deep treatment. (4) The wastewater is mixed with the dissolved air water released by the integrated high-efficiency air flotation machine, the floating scum is collected and PAC and PAM are added to the integrated high-efficiency air flotation machine, the sludge scraped by air flotation is sent to the sludge storage tank, part of the clean water after air flotation is returned for dissolved air use, part of it enters the reuse water pool, part of the reuse water is sent to the elution tower for circulation elution, and part of it is sent to the calcium chloride wastewater evaporation system; (5) The sludge generated in the neutralization reaction tank and the integrated high-efficiency clarification tank is transported to the sludge storage tank through the sludge pump. The sludge in the sludge storage tank is dehydrated and then transported out for treatment.

6. The method for treating fluorine-containing acidic wastewater in polysilicon production according to claim 5, characterized in that: In the step 2), the dosage of lime milk and calcium chloride in the neutralization reaction tank is 0.7 g / L, and the mixture is stirred to neutralize and produce precipitate, so that the pH value of the wastewater is 6-7.

7. The method for treating fluorine-containing acidic wastewater in polysilicon production according to claim 5, characterized in that: In the step 3), the dosage of PAC is 1.1 g / L PAC, and the dosage of PAM is 0.02 g / L PAM.

8. The method for treating fluorine-containing acidic wastewater in polysilicon production according to claim 5, characterized in that: In the step 4), 0.7 g / L PAC and 0.01 g / L PAM are added to the integrated high-efficiency air flotation machine.

9. The method for treating fluorine-containing acidic wastewater in polysilicon production according to claim 5, characterized in that: In the step 4), the hydraulic retention time of the wastewater in the integrated high-efficiency air flotation machine is 5-6 minutes, and the operating pressure is 0.4-0.5 MPa.

10. The method for treating fluorine-containing acidic wastewater in polysilicon production according to claim 5, characterized in that: In the step 5), the sludge dewatering machine is a box-type high-pressure diaphragm filter press, and after dehydration to below 85%, the sludge is transported out for treatment.

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