Emulsion-containing wastewater separation and recovery process

Abstract

The invention relates to the technical field of chemical wastewater separation and recovery production, in particular to an emulsion-containing wastewater separation and recovery process which comprises the following steps: S1, coarse filtration pretreatment: introducing VAE (Vinyl Acetate Ethylene)-containing emulsion wastewater into a pretreatment device, and sequentially carrying out sedimentation treatment and multi-stage filtration treatment; s2, membrane circulation separation treatment: introducing the VAE-containing wastewater into a membrane separation device, separating out clear water and a concentrated solution, carrying out production recycling on the clear water, and continuously introducing the concentrated solution and supplemented VAE-containing emulsion wastewater into the membrane separation device for circulation concentration; automatic backwashing treatment is carried out at regular time; and S3, limit concentration treatment: when the solid content of the VAE emulsion is increased to the threshold solid content, carrying out limit concentration by the membrane separation device, and discharging the VAE concentrated emulsion. The problem that the VAE emulsion is difficult to recycle in the prior art can be solved.

Description

Technical Field

[0001] The invention relates to the technical field of chemical wastewater separation and recovery, in particular to a process for separating and recovering wastewater containing emulsion. Background Art

[0002] Vinyl acetate-ethylene copolymer emulsion (hereinafter referred to as VAE emulsion) is a vinyl acetate-ethylene copolymer. It is a water-based adhesive that uses water as a dispersion medium. It is also green and environmentally friendly. It is an environmentally friendly adhesive and is widely used in adhesives, coatings, textile processing, paper processing, construction and other fields. In the production process of VAE emulsion, the emulsion may stick to the production line equipment. Therefore, after the production is completed, a large amount of clean water is usually required to clean the production line, and a large amount of VAE emulsion wastewater is generated. Since the wastewater containing VAE emulsion is in the form of a stable emulsion and a suspended liquid, it is not easy to separate and treat it. In addition, the chemical oxygen demand (COD) of the wastewater containing VAE emulsion is high, and it is difficult to meet the emission standards, and the wastewater treatment is difficult.

[0003] At present, the treatment process of VAE emulsion wastewater mainly uses flocculation sedimentation method, that is, flocculants are added to the VAE emulsion wastewater, and the emulsion colloidal particles suspended in the wastewater form flocs under the action of molecular forces. The generated flocs collide and condense with each other during the sedimentation process, and their size and mass continue to increase, thereby achieving the purpose of sedimentation separation and treatment of emulsion wastewater. However, this treatment process has the following problems:

[0004] 1. It is necessary to add multiple flocculants, which has high processing costs. At the same time, the waste residues produced by flocculation and precipitation of VAE emulsion can only be treated as solid waste and cannot be recycled, resulting in a waste of resources;

[0005] 2. The removal rate of suspended solids in wastewater containing VAE emulsion by flocculation sedimentation method is not high. Even if combined with demulsification process or flotation process, the turbidity of wastewater is still high, reaching more than 80NTU, which is difficult to meet higher emission standards. Summary of the invention

[0006] The invention provides a separation and recovery process for wastewater containing emulsion, which can solve the problem that it is difficult to recycle VAE emulsion in the prior art.

[0007] This application provides the following technical solutions:

[0008] A process for separating and recovering wastewater containing emulsion, comprising the following steps:

[0009] S1: Coarse filtration pretreatment: The wastewater containing VAE emulsion is passed into the pretreatment device for sedimentation treatment and filtration treatment in sequence, and then passed into the circulation tank;

[0010] S2: Membrane circulation separation treatment: The VAE-containing wastewater in the circulation tank is first filtered and then passed into the membrane separation device to separate clean water and concentrated liquid. The clean water is reused in production, and the concentrated liquid is returned to the circulation tank and continues to be passed into the membrane separation device with the supplemented VAE emulsion-containing wastewater for circulation and concentration; and automatic backwashing treatment is performed regularly;

[0011] S3: Extreme concentration treatment: When the solid content of VAE emulsion in the circulation tank reaches the threshold solid content, the pretreatment device stops adding VAE emulsion wastewater to the circulation tank, and the membrane separation device performs extreme concentration. When the solid content of VAE emulsion in the circulation tank reaches the rated solid content, the VAE concentrated emulsion in the circulation tank is discharged.

[0012] Before adopting the above technical solution, the inventors had considered designing other processes to recycle the wastewater containing VAE emulsion, but the effect was not significant.

[0013] The inventors first considered adopting an evaporation process and using a multiple-effect evaporator to recover the VAE emulsion. However, the inventors found that this technical solution had the following problems: the device had high energy consumption, the equipment occupied a large area, and the device was prone to crusting and clogging. The inventors then considered a centrifugal separation process to recover the VAE emulsion through a centrifuge, but the effect was not significant, and there were problems such as incomplete wastewater separation and difficulty in increasing the solid content of the concentrate.

[0014] Then, the inventors considered the membrane separation process, and separated the VAE emulsion wastewater into VAE emulsion and water through the separation and concentration of the membrane assembly. However, since the emulsion particles contained in the VAE emulsion are insoluble in water and are extremely easy to solidify or agglomerate during the treatment process, the membrane assembly is easily blocked and difficult to operate continuously and stably. This is also the reason why the predecessors did not consider using the membrane separation process to separate the VAE emulsion wastewater. The inventors conducted in-depth research on the membrane separation process and added a coarse filtration pretreatment before the membrane separation process. The coarse filtration pretreatment is used to remove larger solid particles and other impurities in the VAE emulsion wastewater to reduce the blockage of the membrane channel. However, the VAE emulsion wastewater that has been pretreated by coarse filtration is still prone to colloid agglomeration in the subsequent membrane circulation separation process, thereby blocking the membrane channel. Therefore, the inventors perform a timed automatic backwashing process in the membrane circulation separation process to promptly remove the blockage in the membrane channel, and each backwashing can restore the membrane flux to 60%-90% of the initial value.

[0015] Technical principle:

[0016] In this scheme, the wastewater containing VAE emulsion is first subjected to a coarse filtration pretreatment mainly based on sedimentation treatment and filtration treatment, so as to remove larger particles of slag and other impurities in the wastewater containing VAE emulsion, so as to reduce the blockage of the membrane channel in the subsequent membrane circulation separation treatment. Then, the wastewater containing VAE emulsion is passed into the circulation tank, and firstly subjected to filtration treatment to remove the slag newly generated due to the agglomeration of the colloid particles, and then flows into the membrane separation device for membrane circulation separation treatment to obtain clean water and concentrated liquid, wherein the separated clean water can be recycled and used as production water; the filtered concentrated liquid flows back to the circulation tank from the membrane separation device, and is passed into the membrane separation device again with the newly added wastewater containing VAE emulsion, so as to achieve the effect of circulation separation and gradual concentration. When the solid content of the VAE emulsion in the circulation tank is increased to the threshold solid content, the pretreatment device stops feeding into the circulation tank to achieve the effect of rapid separation and extreme concentration. When the solid content of the VAE emulsion in the circulation tank reaches the rated solid content, the VAE concentrated emulsion in the circulation tank can be discharged to obtain the product.

[0017] Beneficial effects:

[0018] 1. The VAE emulsion can be recycled and utilized: Compared with the prior art, VAE emulsion can only be treated as solid waste. This solution realizes the recycling separation and gradual concentration of VAE emulsion-containing wastewater through membrane circulation separation treatment and extreme concentration treatment, and obtains VAE concentrated emulsion and clean water with turbidity lower than 1NTU. The recovery rate of VAE emulsion can reach 100%. Since no chemical substances are added to the wastewater containing VAE emulsion in this solution, the concentrated VAE emulsion has a high purity and does not change the product performance of the VAE emulsion. In addition, since the solid content of VAE emulsion in wastewater is generally in the range of 0.5%-1%, the solid content is extremely low, and this solution can concentrate the solid content of VAE emulsion to the rated solid content, so that the VAE concentrated emulsion can be sold as a special product with high product utilization value.

[0019] 2. Realize the reuse of water resources: Compared with the existing technology, the turbidity of wastewater is generally higher than 80NTU. The turbidity of clean water produced by this solution is less than 1NTU, the COD removal rate is more than 94%, and the solid content removal rate is more than 91%. On the one hand, it is conducive to saving water resources. The produced clean water can be recycled and reused, reducing fresh water use and effectively reducing production costs. On the other hand, the produced clean water can also meet the requirements of other industrial water and can be used for other production, realizing the effective utilization of water resources and green development.

[0020] Furthermore, the automatic backwashing treatment includes backwashing of the clean water outlet and backwashing of the concentrated liquid outlet; the clean water outlet backwashing step is to backwash the clean water from the clean water outlet of the membrane separation device into the membrane channel of the membrane separation device, and flush the blockage on the membrane channel away from the membrane separation device; the concentrated liquid outlet backwashing step is to backwash the clean water from the concentrated liquid outlet of the membrane separation device into the membrane channel of the membrane separation device, and flush the large particles of residue on the inner wall of the membrane and the membrane port away from the membrane separation device.

[0021] Beneficial effect: This scheme uses automatic backwashing treatment to allow clean water to be backwashed into the membrane channel from the clear liquid outlet of the membrane separation device at regular intervals, thereby flushing out the blockages on the membrane micropores and surface, thereby ensuring the flux and filtration efficiency of the membrane. Generally, the membrane flux before production is 100%. During production, since the VAE emulsion wastewater is a suspension, the suspended particles will immediately block the membrane channel, making the membrane flux about 50%, and gradually decrease as the production proceeds. Through the backwashing of this scheme, the membrane flux can be restored to 60%-90% of the initial value at regular intervals to ensure the production efficiency. At the same time, since the pipeline pressure of the membrane separation circulation pipeline is relatively low after the membrane channel is blocked, when the high-pressure backwashing clean water flushes out the blockages on the membrane micropores and surface, the blockages can flow back to the circulation tank through the membrane separation circulation pipeline under the action of the pressure difference, thereby flushing the blockages on the membrane channel away from the membrane separation device to avoid being retained in the membrane separation device. At the same time, the backwash device can also backfill the concentrate outlet of the membrane separation device into the membrane channel, which can flush out the large particles of slag on the inner wall of the membrane and the membrane port, and merge the slag from the backwash circulation pipeline into the membrane separation circulation pipeline, preventing the membrane channel from being blocked and extending the operation cycle of the membrane separation device.

[0022] Furthermore, the method further includes step S4: cleaning treatment, wherein the cleaning treatment includes sequentially performing a first clean water replacement, a mixed chemical cleaning and a second clean water replacement, wherein the first clean water replacement is to use clean water to replace the VAE emulsion of the membrane separation device back into the circulation tank, and the mixed chemical cleaning is to use a mixed chemical cleaning solution to perform a circulating chemical cleaning on the membrane separation device; and the second clean water replacement is to use clean water to replace and drain the mixed chemical cleaning solution in the membrane separation device.

[0023] Beneficial effects: This solution can perform positive cleaning on the membrane separation device after production is completed through the first clean water replacement, and replace the VAE emulsion of the membrane separation device back into the circulation tank, which is beneficial to ensure the cleanliness of the membrane separation device and also reduces the loss of VAE emulsion. Next, this solution performs mixed chemical cleaning, using mixed chemical washing liquid to circulate and deeply clean the membrane separation system, so that the membrane flux is restored to more than 90% of the initial value, and the service life and filtration efficiency of the membrane assembly are improved. In addition, this solution replaces and drains the mixed chemical cleaning solution in the membrane separation device through the second clean water replacement to avoid the residual mixed chemical cleaning solution from adversely affecting the next production.

[0024] Furthermore, in step S3, the threshold solid content ranges from 10% to 20%, and the rated solid content ranges from 20% to 35%.

[0025] Beneficial effects: Since the solid content of VAE emulsion in wastewater is generally in the range of 0.5%-1%, and the solid content is extremely low, the threshold solid content is set at 10%-20% in this scheme. Fresh VAE emulsion-containing wastewater is continuously added to the circulation tank through the previous pretreatment device, so that the VAE emulsion in the circulation tank and the membrane separation device is sufficient, thereby increasing the output of VAE concentrated emulsion during one production; in addition, through the previous continuous circulation separation, the solid content of VAE emulsion has been increased to 10-40 times of the original, so as to achieve effective concentration of VAE emulsion-containing wastewater. At this time, through extreme concentration treatment, the concentration of VAE emulsion can be quickly achieved, so that it reaches a rated solid content of 20%-35%, and the produced VAE concentrated emulsion can be sold as a special product. The inventors found that when the threshold solid content is less than 10%, the extreme concentration time is long, which easily causes blockage of the membrane channel and low separation efficiency. At the same time, the output of one production is also small. When the threshold solid content is greater than 20%, the membrane circulation separation processing time is long, thereby reducing production efficiency. When the rated solid content is less than 20%, the solid content of the VAE emulsion in the product is low, the product performance is poor, and the sales volume will decrease. When the rated solid content is greater than 35%, the extreme concentration time is long, which easily causes blockage of the membrane channel, thereby reducing production efficiency.

[0026] Furthermore, in the automatic backwashing and clean water replacement, the clean water temperature ranges from 60 to 90°C; the temperature range of the mixed chemical cleaning solution is from 60 to 90°C.

[0027] Beneficial effect: Since VAE emulsion is easy to coagulate and stick to the membrane channel under low temperature conditions, and can reduce the adhesion and soften it under high temperature conditions, this solution controls the temperature of clean water and mixed chemical washing solution at 60-90°C, which is conducive to softening the VAE emulsion coagulant blocking the membrane channel, thereby helping to dredge the membrane channel. In addition, the inventor found that when the temperature of clean water and mixed chemical washing solution is lower than 60°C, the VAE emulsion coagulant is still relatively hard and difficult to separate from the membrane channel, and the removal effect is poor. When the temperature of clean water and mixed chemical washing solution exceeds 90°C, although the removal effect is slightly improved, the energy consumption is large and the production cost is significantly increased.

[0028] Furthermore, the membrane separation device comprises a plurality of membrane modules connected in parallel, wherein the membrane modules are inorganic membranes, and the pore size of the inorganic membranes is 20-100 nm.

[0029] Beneficial effects: This solution effectively improves the working efficiency of the membrane separation device by setting up several parallel membrane modules, thereby shortening the filtration processing time. In addition, compared with the prior art generally using organic membranes, this solution uses inorganic membranes for membrane modules. Inorganic membranes have the advantages of high temperature resistance, chemical corrosion resistance, high mechanical strength, strong antimicrobial ability, easy cleaning and recovery, etc., which are more conducive to automatic backwashing treatment and mixed chemical cleaning. In addition, the inorganic membrane with the above pore size not only has a large permeability, but also a narrow pore size distribution, and has high separation efficiency and separation accuracy.

[0030] Furthermore, the automatic backwashing time interval is 12-24 hours; each automatic backwashing time is 5-10 minutes; and the mixed chemical cleaning time is 1-3 hours.

[0031] Beneficial effect: This scheme is conducive to timely flushing the blockage on the membrane channel away from the membrane separation device through the setting of the above-mentioned automatic backwashing time interval and duration, thereby ensuring the flux and filtration efficiency of the membrane. The inventor found that when the automatic backwashing time interval is less than 12h, the addition of excessive cleaning water will over-dilute the milky VAE wastewater concentrate, so there will be a problem of slow increase in the solid content of the milky VAE wastewater. When the time interval is greater than 24h, the automatic backwashing is not timely, and the membrane circulation separation efficiency is low; when the automatic backwashing duration is less than 5min, the blockage removal effect is poor and the filtration efficiency is low. When the automatic backwashing duration is greater than 10min, the milky VAE wastewater concentrate will be over-diluted and the backwashing effect will not be significantly improved. In addition, when the above-mentioned mixed chemical cleaning time is adopted, it can not only ensure that the mixed chemical solution has sufficient reaction time with the blockage on the membrane channel, thereby ensuring the cleaning effect, but also avoid the problem of too long mixed chemical cleaning time, causing unnecessary waste of resources and reducing production efficiency.

[0032] Furthermore, the mixed chemical cleaning solution includes a mixed chemical solution of a sodium hypochlorite solution with a mass concentration of 1%-3%, a sodium hydroxide solution with a mass concentration of 1%-3%, and a citric acid solution with a mass concentration of 1%-3%.

[0033] Beneficial effects: Since VAE emulsion wastewater also contains other organic matter (such as PVA, vinyl acetate, ethylene, emulsifiers, bactericides, initiators, etc.), calcium and magnesium ions, and since VAE emulsion has dehydration film-forming properties, 1%-3% sodium hypochlorite solution can well remove scaling organic matter, 1%-3% sodium hydroxide solution can soften emulsion particles, and 1%-3% citric acid solution can remove calcium and magnesium ion scaling. Therefore, the mixed chemical solution made from the above solutions can effectively remove blockages on the membrane channel, making the cleaning effect better.

[0034] Furthermore, the pretreatment device includes a sedimentation tank and a filtration treatment system connected through an overflow pipe, and the filter mesh number of the filtration treatment system is 200-300 meshes.

[0035] Beneficial effects: This solution uses sedimentation treatment in a sedimentation tank to allow large particles of residue in the VAE emulsion wastewater to settle to the bottom due to their large specific gravity in water, thereby effectively removing them. In addition, this solution uses multi-stage filtration treatment of the filtration treatment system to allow the VAE emulsion wastewater overflowing the sedimentation tank to be filtered and effectively remove small particles of residue and other impurities, thereby effectively reducing the blockage of the membrane separation device in the subsequent membrane circulation separation treatment. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 This is a schematic structural diagram of an emulsion-containing wastewater separation and recovery device according to Example 1 of the present invention. DETAILED DESCRIPTION

[0037] The following is further described in detail through specific implementation methods:

[0038] The symbols in the drawings of the specification include: sedimentation tank 1, first filtration treatment system 2, circulation tank 3, membrane separation device 4, clean water tank 5, mixed chemical washing tank 6, liquid delivery pipeline 7, membrane separation circulation pipeline 8, water production pipeline 9, concentrate discharge pipeline 10, backwashing pipeline 11, positive washing pipeline 12, chemical washing circulation pipeline 13, sewage pipeline 14, overflow pipeline 15, membrane assembly 16, sampling channel 17, circulation pump 18, clean water pump 19, chemical washing pump 20, low-pressure steam heating pipeline 21, clean water pipeline 22, first flow meter 23, second flow meter 24, third flow meter 25, first pressure gauge 26, second pressure gauge 27, third pressure gauge 28, feed pipe 29, clean water reuse pipeline 30, second filtration treatment system 31, membrane assembly clean liquid outlet 32, membrane assembly concentrate outlet 33, backwashing circulation pipeline 34.

[0039] Example 1

[0040] like Figure 1 As shown, this embodiment discloses a separation and recovery device for emulsion-containing wastewater, including a pretreatment device, a circulation tank 3, a membrane separation device 4, a backwashing device and a mixed chemical washing device. The pretreatment device, the circulation tank 3, and the membrane separation device 4 are sequentially connected through a liquid delivery pipeline 7. Specifically, the pretreatment device includes a sedimentation tank 1 and a first filtration treatment system connected through an overflow pipeline 15, such as Figure 1 As shown, a feed pipe 29 is provided in the middle of the left side of the sedimentation tank 1, and the wastewater containing VAE emulsion can enter the sedimentation tank 1 from the feed pipe 29. In addition, an overflow port is provided in the upper right part of the sedimentation tank 1, and the overflow port is connected to the left end of the overflow pipe 15. The overflow pipe 15 is provided with a first flow meter 23 and a flow regulating valve to detect and control the flow of the overflow pipe 15. In this embodiment, the first filtering treatment system 2 includes two connected centrifugal filters with automatic slag removal function, the feed port of the centrifugal filter on the left is connected to the right end of the overflow pipe 15, and the discharge port of the centrifugal filter on the right is connected to the liquid delivery pipe 7. At the same time, the aperture of the filter screen of the right centrifugal filter is smaller than that of the filter screen of the left centrifugal filter, which can effectively separate small particles of slag and other impurities in the wastewater containing VAE emulsion. In this embodiment, the filter screen of the left centrifugal filter has a mesh number of 100, and the filter screen of the right centrifugal filter has a mesh number of 200.

[0041] In this embodiment, the circulation tank 3 is provided with four ports, namely, a first liquid inlet located in the middle of the left side of the circulation tank 3, a second liquid inlet located at the top of the circulation tank 3, a concentrate outlet located at the bottom of the circulation tank 3, and a liquid outlet located in the middle of the right side of the circulation tank 3. Specifically, the first liquid inlet of the circulation tank 3 is connected to the centrifugal filter on the right side of the first filtering treatment system 2 through a liquid delivery pipeline 7; the concentrate outlet of the circulation tank 3 is connected to a concentrate outlet pipeline 10, and a second flowmeter 24 and a flow regulating valve are arranged on the concentrate outlet pipeline 10; the liquid outlet of the circulation tank 3 is connected to the membrane separation device 4 through a liquid delivery pipeline 7. In addition, the liquid delivery pipeline 7 between the circulation tank 3 and the membrane separation device 4 is provided with a second filtering treatment system 31, a circulation pump 18 and a first pressure gauge 26 in sequence, wherein the second filtering treatment system 31 has the same structure as the first filtering treatment system 2, and will not be described in detail here. In addition, valves are provided at the liquid inlet and outlet of the circulation pump 18. At the same time, the circulation tank 3 is set as a high-level tank relative to the circulation pump 18. In this way, when the circulating water enters the circulation pump 18 from the high-level circulation tank 3, the pressure can be increased before the circulation pump 18, thereby reducing the energy consumption of the circulation pump 18.

[0042] The membrane separation device 4 includes a plurality of membrane assemblies 16 connected in parallel. The membrane assemblies 16 are inorganic membranes. The pore size of the inorganic membranes is in the range of 20-100 nm. In this embodiment, there are two membrane assemblies 16, and the membrane assemblies 16 are ceramic membranes. The pore size of the ceramic membranes is 20 nm. The membrane assemblies 16 include membranes including membrane tubes and inorganic ceramic membranes arranged in the membrane tubes, such as Figure 1 As shown, the membrane assembly 16 also includes a liquid inlet located at the top of the membrane tube, a membrane assembly concentrated liquid outlet 33 located at the bottom of the membrane tube, a membrane assembly clear liquid outlet 32 ​​located at the middle and lower part of the right side wall of the membrane tube, and a sampling port located at the middle and upper part of the left side of the membrane tube. Specifically, the liquid inlet of the membrane assembly 16 is connected to the liquid outlet of the circulation tank 3 through the liquid delivery pipeline 7; the membrane assembly clear liquid outlet 32 ​​is connected to the water production pipeline 9, and the water production pipeline 9 is provided with a valve; the membrane assembly concentrated liquid outlet 33 is connected to the membrane separation circulation pipeline 8, and the other end of the membrane separation circulation pipeline 8 is connected to the second liquid inlet at the top of the circulation tank 3, and the membrane separation circulation pipeline 8 is also provided with a valve; the sampling port of the membrane assembly 16 is connected to the sampling pipeline for sampling and analysis, and the sampling pipeline is provided with a valve. In addition, a second pressure gauge 27 is provided near the clear liquid outlet of the water production pipeline 9, and a third flow meter 25 is provided on the right side of the second pressure gauge 27; a third pressure gauge 28 is provided near the concentrated liquid outlet 33 of the membrane assembly of the membrane separation circulation pipeline 8. The first, second and third pressure gauges can be used to monitor the liquid inlet, concentrated liquid outlet and clear liquid outlet pressures of the membrane separation device 4, thereby adjusting the pressure difference. In this embodiment, the liquid inlet pressure of the membrane separation device 4 is controlled to be 0.25-0.5MPa, and the concentrated liquid outlet is controlled to be 0.1-0.3MPa.

[0043] The backwashing device includes a clean water tank 5, which includes a first inlet and a second inlet located at the middle upper left side of the tank body, and a liquid outlet located at the bottom right side of the tank body, wherein the first liquid inlet of the clean water tank 5 is connected to the clean water pipeline 22 to realize the replenishment of clean water; the second liquid inlet of the clean water tank 5 is connected to the low-pressure steam heating pipeline 21 to realize the heating of the clean water in the clean water tank 5, and valves are provided on the clean water pipeline 22 and the low-pressure steam heating pipeline 21; the liquid outlet of the clean water tank 5 is first connected to the liquid inlet of the clean water pump 19, and the liquid outlet of the clean water pump 19 is connected to two pipelines, namely, the positive and negative flushing pipelines, wherein the other end of the positive flushing pipeline 12 is connected to the liquid inlet of the membrane separation device 4 and is provided with a backwashing circulation pipeline 34 and is connected to the membrane separation circulation pipeline 8, and the backwashing circulation pipeline 34 is provided with a valve. The other end of the backwashing pipeline 11 is connected to the component clear liquid outlet 32 ​​and the membrane component concentrated liquid outlet 33, and valves are provided respectively. The liquid inlet and outlet of the clean water pump 19 and the positive and negative flushing pipelines are all provided with valves. In addition, the clean water tank 5 is also provided with an online thermometer.

[0044] The mixing chemical washing device includes a mixing chemical washing tank 6, which includes a first liquid inlet, a second liquid inlet, a feeding port, and a liquid outlet at the top of the tank body, wherein the first liquid inlet of the mixing chemical washing tank 6 is connected to a clean water pipeline 22 and a low-pressure steam heating pipeline 21 to achieve the purpose of replenishing clean water and heating the solution in the tank body, and valves are provided on the clean water pipeline 22 and the low-pressure steam heating pipeline 21; the liquid outlet of the mixing chemical washing tank 6 is respectively connected to a drain pipe and a chemical washing circulation pipeline 13, and valves are provided on the drain pipe and the chemical washing circulation pipeline 13. The drain pipe is used to empty the mixing chemical washing tank 6, and the chemical washing circulation pipeline 13 is first connected to a chemical washing pump 20, and then connected to the liquid inlet of the membrane separation device 4, and the inlet and outlet of the chemical washing pump 20 are both provided with valves; the second liquid inlet of the mixing chemical washing tank 6 is connected to the concentrated outlet of the membrane separation device 4 through the chemical washing circulation pipeline 13, and at the same time, Figure 1 As shown, the chemical washing circulation pipeline 13 located between the concentrated liquid outlet of the membrane separation device 4 and the liquid inlet of the mixed chemical washing device is also connected to the sewage pipeline 14, and a valve is also provided on the sewage pipeline 14 to discharge the mixed chemical washing liquid after chemical washing; the feeding port of the mixed chemical washing tank 6 is used to add the mixed chemical washing solution. At the same time, the water production pipeline 9 located on the right side of the third flowmeter 25 is connected to the clean water recycling pipeline 30, and the clean water recycling pipeline 30 is provided with a flow regulating valve. The other end of the clean water recycling pipeline 30 is connected to the chemical washing circulation pipeline 13 to achieve the purpose of replenishing clean water and facilitate the reuse of water resources. In addition, an online thermometer is also provided in the mixed chemical washing tank 6.

[0045] In addition, this embodiment also discloses a process for separating and recovering wastewater containing emulsion, comprising the following steps:

[0046] S1: Coarse filtration pretreatment: The wastewater containing VAE emulsion is passed into the pretreatment device for sedimentation treatment and filtration treatment in sequence, and then passed into the circulation tank 3;

[0047] Specifically, the solid content of the VAE emulsion wastewater is 0.5%-1%, and its temperature range is 30-50°C. In this embodiment, the specific temperature of the VAE emulsion wastewater is 30°C. The VAE emulsion wastewater flows into the sedimentation tank 1 from the feed pipe 29 of the sedimentation tank 1, and the large particles of slag in the VAE emulsion wastewater are settled to the bottom of the tank. The flow regulating valve on the overflow pipe 15 is opened, and the VAE emulsion wastewater after sedimentation treatment is transported to the centrifugal filter of the first filtration treatment system 2 through the overflow pipe 15, and is filtered to remove small particles of slag and other impurities. Then, the filtered VAE emulsion wastewater flows into the circulation tank 3 through the liquid delivery pipe 7.

[0048] S2: Membrane circulation separation treatment:

[0049] The VAE-containing wastewater in the circulation tank 3 is first filtered and then passed into the membrane separation device 4 to separate the clean water and the concentrated solution. The clean water is reused in production, and the concentrated solution is returned to the circulation tank 3 and continues to be passed into the membrane separation device 4 with the supplemented VAE emulsion-containing wastewater for circulation and concentration; and automatic backwashing treatment is performed regularly;

[0050] Specifically, when the liquid level of the circulation tank 3 is higher than the liquid outlet of the circulation tank 3, the circulation pump 18 is started, and the VAE emulsion wastewater is pumped into the liquid delivery pipeline 7 under the action of the circulation pump 18, and is filtered by the second filtration treatment system 31, and then enters each membrane module 16 of the membrane separation device 4 for filtration and separation, wherein the clean water produced after separation is discharged from the membrane module clean liquid outlet 32 ​​and enters the water production pipeline 9, and the water supply resources are reused, and the flow regulating valve of the clean water reuse pipeline 30 is adjusted to allow the clean water in the water production pipeline 9 to be discharged through the clean water return pipeline 30. The chemical washing circulation pipeline 13 is introduced by pipeline 30, and then replenished into the mixed chemical washing tank 6; the concentrated liquid produced after separation is discharged from the concentrated liquid outlet 33 of the membrane module, and flows into the membrane separation circulation pipeline 8, and then flows back to the circulation tank 3 from the second liquid inlet at the top of the circulation tank 3, and then continues the next circulation separation with the newly replenished VAE emulsion-containing wastewater. During this process, the flow regulating valve of the overflow pipeline 15 automatically adjusts the amount of liquid replenishment from the overflow pipeline 15 to the circulation tank 3 through the real-time flow displayed by the third flow meter 25 of the water production pipeline 9.

[0051] At the same time, the inlet and outlet valves of the clean water pump 19 and the valve of the backwash pipe 11 are opened regularly, and the clean water pump 19 is turned on regularly. Under the action of the clean water pump 19, the clean water in the clean water tank 5 is pumped into the backwash pipe 11 by the clean water pump 19, and then backwashed into the membrane channels of each membrane component 16 from the clean liquid outlet 32 ​​of the membrane component of the membrane separation device 4, thereby causing the blockages on the membrane channels to be flushed inward. After the membrane channels are blocked, the pressure in the membrane separation circulation pipe 8 is relatively low, and the blockages flow back into the circulation tank 3 under the action of the pressure difference, thereby realizing online backwashing. In addition, the blockages can be filtered out by the second filtration treatment system 31 the next time they flow from the circulation tank 3 into the liquid delivery pipe 7. In addition, the automatic liquid backwashing time interval is 12-24h, and the duration of each automatic backwashing is 5-10min, and the clean water temperature in the clean water tank ranges from 60-90°C. In this embodiment, the automatic backwashing time interval is specifically 12h, the duration of each automatic backwashing is specifically 5min, and the clean water temperature in the clean water tank is specifically 60°C.

[0052] In addition, the present embodiment also includes a timed opening of the membrane module concentrate outlet 33 for backwashing. When the membrane module concentrate outlet 33 is backwashed, the circulation pump 18 needs to be turned off first, and then the valve of the backwashing pipeline 11, the valve of the membrane module concentrate outlet 33, and the valve of the backwashing circulation pipeline 34 are opened in sequence. The clean water at 60°C in the clean water tank 5 is pumped into the backwashing pipeline 11 by the clean water pump 19, and then backwashed from the membrane module concentrate outlet 33 into the membrane separation device 4 and into the membrane channels of each membrane module 16, flushing away the large particles of slag blocking the inner wall of the membrane and the membrane port. The slag mixed flushing liquid is merged from the backwashing circulation pipeline 34 into the membrane separation circulation pipeline 8 and replaced back into the circulation tank 3. Among them, the automatic concentrate backwashing time interval is 12-24h, and the duration of each automatic backwashing is 5-10min, and the clean water temperature in the clean water tank ranges from 60-90°C. In this embodiment, the automatic backwashing time interval is specifically 12h, the duration of each automatic backwashing is specifically 5min, and the clean water temperature in the clean water tank is specifically 60°C.

[0053] S3: Extreme Concentration Processing:

[0054] When the solid content of the VAE emulsion in the circulation tank 3 is increased to a threshold solid content of 10%-20%, the pretreatment device stops adding VAE emulsion wastewater to the circulation tank 3, and the membrane separation device 4 performs extreme concentration. When the solid content of the VAE emulsion in the circulation tank 3 reaches a rated solid content of 20%-35%, the VAE concentrated emulsion in the circulation tank 3 is discharged.

[0055] Specifically, after the solid content of the VAE emulsion in the circulation tank 3 reaches a threshold solid content of 10%, the flow regulating valve on the overflow pipe 15 is closed, and the membrane separation device 4 starts to perform extreme concentration. When the solid content of the VAE emulsion in the circulation tank 3 reaches a rated solid content of 25%, the membrane separation device 4 is stopped, and the flow regulating valve of the concentrated emulsion discharge pipe 10 of the circulation tank 3 is opened, so that the circulation tank 3 is discharged through the concentrated emulsion discharge pipe 10, thereby obtaining a VAE concentrated emulsion product.

[0056] S4: Cleaning treatment:

[0057] The cleaning process includes a first clean water replacement, a mixed chemical cleaning and a second clean water replacement in sequence.

[0058] The first clean water replacement is to use clean water to replace the VAE emulsion of the membrane separation device 4 back into the circulation tank 3. Specifically, after the concentration is discharged, the inlet and outlet valves of the circulation pump 18 are closed, the inlet and outlet valves of the clean water pump 19 and the valve of the positive flushing pipeline 12 are opened, and the clean water pump 19 is started. The clean water at 60°C in the clean water tank 5 is pumped into the positive flushing pipeline 12 by the clean water pump 19, and then enters the membrane channel of each membrane component 16 from the liquid inlet of the membrane component 16 of the membrane separation device 4, and replaces the material in the membrane separation device 4 back into the circulation tank 3 through the membrane separation circulation pipeline 8.

[0059] Mixed chemical cleaning is to use a mixed chemical cleaning solution to perform cyclic chemical cleaning on the membrane separation device 4, and the mixed chemical cleaning solution includes a sodium hypochlorite solution with a concentration of 1%-3%, a sodium hydroxide solution with a concentration of 1%-3%, and a sodium citrate solution with a concentration of 1%-3%, and the temperature range of the mixed chemical cleaning solution is 60-90°C. Specifically, after the first clean water replacement is completed, the clean water pump 19 is stopped, the inlet and outlet valves of the clean water pump 19 are closed, the valve of the membrane separation circulation pipeline 8 is closed, the valve on the chemical washing circulation pipeline 13 and the inlet and outlet valves of the chemical washing pump 20 are opened, and then the chemical washing pump 20 is started. The mixed chemical cleaning solution in the mixed chemical washing tank 6 is pumped into the chemical washing circulation pipeline 13 by the chemical washing pump 20, and then enters the membrane channel of each membrane assembly 16 from the liquid inlet of the membrane assembly 16 of the membrane separation device 4, and circulates chemical washing, and the mixed chemical cleaning time is 1-3h. In this embodiment, the temperature of the mixed chemical cleaning solution in the mixed chemical washing tank 6 is specifically 60°C, and the mixed chemical cleaning time is specifically 3h.

[0060] The second clean water replacement is to use clean water to replace and drain the mixed chemical cleaning solution in the membrane separation device 4. Specifically, after the mixed chemical cleaning is completed, the chemical cleaning pump 20 is stopped, its inlet and outlet valves are closed, the inlet and outlet valves of the clean water pump 19, the valve of the positive flushing pipeline 12, and the valve of the sewage pipeline 14 are opened, and the clean water pump 19 is started again to replace the mixed chemical washing liquid in the membrane assembly 16, and the mixed chemical washing liquid is discharged from the sewage pipeline 14.

[0061] Example 2

[0062] The difference between this embodiment and the first embodiment is that the pore size of the inorganic membrane is 60nm, the temperature of the wastewater containing VAE emulsion is 40°C; in step S2, the automatic backwashing time interval is 18h, the duration of each automatic backwashing is specifically 7min, and the temperature of the clean water in the clean water tank 5 is 75°C; in step S3, the threshold solid content is 15%, and the rated solid content is 20%; in step S4, the temperature of the mixed chemical cleaning solution in the mixed chemical cleaning tank 6 is 75°C, and the mixed chemical cleaning time is 2h.

[0063] Example 3

[0064] The difference between this embodiment and the first embodiment is that the pore size of the inorganic membrane is 100 nm, the temperature of the wastewater containing VAE emulsion is 50° C.; in step S2, the automatic backwashing time interval is 24 hours, the duration of each automatic backwashing is specifically 10 minutes, and the temperature of the clean water in the clean water tank 5 is 90° C.; in step S3, the threshold solid content is 20%, and the rated solid content is 28%; in step S4, the temperature of the mixed chemical cleaning solution in the mixed chemical cleaning tank 6 is 90° C., and the mixed chemical cleaning time is 1 hour.

[0065] Comparative Example 1

[0066] The difference between this comparative example and Example 1 is that the temperature of the wastewater containing VAE emulsion is 25°C.

[0067] Comparative Example 2

[0068] The difference between this comparative example and the first embodiment is that the temperature of the clean water in the clean water tank 5 is 40°C, and the temperature of the mixed chemical cleaning solution in the mixed chemical cleaning tank 6 is 40°C.

[0069] Comparative Example 3

[0070] The difference between this comparative example and Example 1 is that the threshold solid content is 5%.

[0071] Comparative Example 4

[0072] The difference between this comparative example and Example 3 is that the threshold solid content is 25%.

[0073] Comparative Example 5

[0074] The difference between this comparative example and Example 3 is that the rated solid content is 36%.

[0075] Comparative Example 6

[0076] The difference between this comparative example and Example 2 is that no automatic backwashing process is performed.

[0077] Comparative Example 7

[0078] The difference between this comparative example and Example 3 is that the pore size of the inorganic membrane is 200 nm.

[0079] Comparative Example 8

[0080] The difference between this comparative example and Example 2 is that the mixed chemical cleaning solution is 1% sodium hypochlorite and 1% nitric acid. For easy reference, the parameter settings in Examples 1-3 and Comparative Examples 1-7 are summarized as follows, see Table 1 for details:

[0081] Table 1

[0082]

[0083]

[0084] Test Example 1

[0085] The turbidity, COD removal rate, solid content removal rate, and average yield of the clean water separated in the above Examples 1-3 and Comparative Examples 1-7 were measured; the stability of the VAE concentrated emulsion obtained by concentration was measured; and the membrane flux recovery rate and the total production time were measured.

[0086] The detection method is as follows:

[0087]

Clear water turbidity

[0088]

COD removal rate

[0089] [Solid content removal rate]: Tested according to the full solid determination method;

[0090] [Stability of VAE concentrated emulsion]: Test according to the method for determining the dilution stability of emulsion;

[0091]

Membrane flux recovery rate measurement

[0092] Where: J-membrane flux (L / m 2 ·h), V-sampling volume (L); T-sampling time (h); A-membrane effective area (m 2 );J 测 - membrane flux during measurement; J 初 - Initial membrane flux.

[0093]

Concentrated solid content

[0094] The test results are shown in Table 2:

[0095] Table 2 Test results

[0096]

[0097] It can be seen from Examples 1-3 that, by using this solution, the turbidity of clean water is less than 1NTU, and 100% recovery of VAE emulsion is basically achieved. The COD removal rate is more than 94.3% overall, and the solid content removal rate is more than 91.8%, which is much higher than the emission standard, and is conducive to the recycling and reuse of water resources; the clean water production efficiency is higher than 58Kg / h, which is conducive to saving water resources; the stability of VAE concentrated emulsion is less than 3.5%, and the product stability is high; the membrane flux recovery rate is more than 90%, which is conducive to extending the service life of the device; the concentrated liquid has a high solid content and can be concentrated to more than 20 times the original, and the total production time is less than 65 hours, which is conducive to improving production efficiency.

[0098] By comparing Comparative Example 1 with Example 1, it can be seen that the temperature of the VAE emulsion wastewater in Comparative Example 1 is relatively low, and the VAE emulsion wastewater is prone to colloid agglomeration, thereby blocking the membrane channel, resulting in a low clean water production efficiency. The clean water efficiency of Comparative Example 1 is 13.4% lower than that of Example 1;

[0099] From the comparison between Comparative Example 2 and Example 1, it can be seen that the temperature of the clean water and the temperature of the mixed chemical cleaning solution in Comparative Example 2 are relatively low, and it is difficult to soften the VAE emulsion coagulant blocking the membrane channel, thereby reducing the recovery rate of the membrane flux. The membrane flux recovery rate of Comparative Example 1 is only 85%;

[0100] By comparing Comparative Example 3 with Example 1, it can be seen that the threshold solid content of Comparative Example 3 is lower, so that the total production time is greatly shortened, and the clean water production efficiency is basically the same as that of Example 1, that is, the total output is greatly reduced;

[0101] By comparing Comparative Example 4 with Example 3, it can be seen that the threshold solid content of Comparative Example 4 is higher, which makes the membrane filtration separation stage time longer, thereby making the total production time longer than that of Example 3;

[0102] From the comparison between Comparative Example 5 and Example 3, it can be seen that the rated solid content of Comparative Example 5 is higher, which makes the limit concentration time longer, and the product concentration is higher, which is easy to block the membrane channel, making the total production time 17.4% longer than that of Example 3, and the stability of the VAE emulsion is not good, which is 4.3%;

[0103] From the comparison between Comparative Example 6 and Example 2, it can be seen that Comparative Example 6 does not perform backwashing, which easily blocks the membrane channel, resulting in low clean water production efficiency. The clean water production efficiency of Comparative Example 6 is 19.3% lower than that of Example 2, and the total production time is prolonged;

[0104] By comparing Comparative Example 7 with Example 3, it can be seen that the pore size of the inorganic membrane in Comparative Example 7 is larger, resulting in higher turbidity of the clean water, which is 30 times higher than that in Example 3, and the COD removal rate and solid content removal rate are both lower. In addition, since the pore size of the VAE emulsion particles is similar to that of the inorganic membrane in Comparative Example 7, more VAE emulsion particles are stuck in the pores of the inorganic membrane, thereby blocking the membrane channel, resulting in lower clean water production efficiency and longer total production time;

[0105] From the comparison between Comparative Example 8 and Example 2, it can be seen that the mixed chemical washing solution of Comparative Example 8 has a poor cleaning effect on the membrane, and the membrane flux recovery rate is only 80%.

[0106] The above are only embodiments of the present invention. The invention is not limited to the field involved in this implementation case. The common knowledge such as the known specific structure and characteristics in the scheme is not described in detail here. It should be pointed out that for those skilled in the art, several deformations and improvements can be made without departing from the structure of the present invention, which should also be regarded as the protection scope of the present invention, and these will not affect the effect of the implementation of the present invention and the practicality of the patent. The scope of protection required by this application shall be based on the content of its claims, and the specific implementation methods and other records in the specification can be used to interpret the content of the claims.

Claims

1. A process for separating and recovering wastewater containing emulsion, characterized in that: The following steps are involved: S1: Coarse filtration pretreatment: The wastewater containing VAE emulsion is passed into the pretreatment device for sedimentation treatment and filtration treatment in sequence, and then passed into the circulation tank; S2: Membrane circulation separation treatment: The VAE-containing wastewater in the circulation tank is first filtered and then passed into the membrane separation device to separate clean water and concentrated liquid. The clean water is reused in production, and the concentrated liquid is returned to the circulation tank and continues to be passed into the membrane separation device with the supplemented VAE emulsion-containing wastewater for circulation and concentration; and automatic backwashing treatment is performed regularly; S3: Extreme concentration treatment: When the solid content of VAE emulsion in the circulation tank reaches the threshold solid content, the pretreatment device stops adding VAE emulsion wastewater to the circulation tank, and the membrane separation device performs extreme concentration. When the solid content of VAE emulsion in the circulation tank reaches the rated solid content, the VAE concentrated emulsion in the circulation tank is discharged.

2. The process for separating and recovering emulsion-containing wastewater according to claim 1, characterized in that: The automatic backwashing treatment includes backwashing of the clean water outlet and backwashing of the concentrated liquid outlet; the clean water outlet backwashing step is to backwash the clean water from the clean water outlet of the membrane separation device into the membrane channel of the membrane separation device, and flush the blockage on the membrane channel away from the membrane separation device; the concentrated liquid outlet backwashing step is to backwash the clean water from the concentrated liquid outlet of the membrane separation device into the membrane channel of the membrane separation device, and flush the large particle residue on the membrane inner wall and the membrane port away from the membrane separation device.

3. A process for separating and recovering emulsion-containing wastewater according to claim 2, characterized in that: It also includes step S4: cleaning treatment, which includes performing a first clean water replacement, mixed chemical cleaning and a second clean water replacement in sequence. The first clean water replacement is to use clean water to replace the VAE emulsion of the membrane separation device back into the circulation tank, and the mixed chemical cleaning is to use a mixed chemical cleaning solution to perform circulating chemical cleaning on the membrane separation device; the second clean water replacement is to use clean water to replace and drain the mixed chemical cleaning solution in the membrane separation device.

4. The process for separating and recovering emulsion-containing wastewater according to claim 3, characterized in that: In the step S3, the threshold solid content ranges from 10% to 20%, and the rated solid content ranges from 20% to 35%.

5. A process for separating and recovering wastewater containing emulsion according to claim 4, characterized in that: In the automatic backwashing and clean water replacement, the clean water temperature ranges from 60 to 90°C; the temperature range of the mixed chemical cleaning solution is from 60 to 90°C.

6. A process for separating and recovering wastewater containing emulsion according to claim 5, characterized in that: The membrane separation device comprises a plurality of membrane components connected in parallel, wherein the membrane components are inorganic membranes, and the pore size of the inorganic membranes is 20-100 nm.

7. A process for separating and recovering wastewater containing emulsion according to claim 6, characterized in that: The automatic backwashing time interval is 12-24 hours; the duration of each automatic backwashing is 5-10 minutes; and the mixed chemical cleaning time is 1-3 hours.

8. The process for separating and recovering wastewater containing emulsion according to claim 7, characterized in that: The mixed chemical cleaning solution comprises a sodium hypochlorite solution with a mass concentration of 1%-3%, a sodium hydroxide solution with a mass concentration of 1%-3%, and a sodium citrate solution with a mass concentration of 1%-3%.

9. A process for separating and recovering wastewater containing emulsion according to claim 8, characterized in that: The pretreatment device comprises a sedimentation tank and a filtration treatment system which are connected through an overflow pipe, and the filter mesh number of the filtration treatment system is 200-300 meshes.

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