Membrane-making DMF (Dimethyl Formamide) wastewater quality-divided treatment method

Abstract

The invention belongs to the field of water treatment, and particularly relates to a quality-divided treatment method of membrane-making DMF (Dimethyl Formamide) wastewater, which comprises the following processes: treating DMF wastewater with different concentrations generated in a membrane production process by using different membrane device systems; concentrated and produced water backflow is arranged between the membrane systems; and the energy recovery device is used for recovering and reusing the residual energy in the operation process of the membrane system. According to the invention, multiple sets of membrane systems are adopted to receive and treat membrane-making wastewater in a quality-divided manner, and concentrated and produced water backflow is arranged between the sets of membrane systems, so that the whole set of system has high retention rate and high concentration efficiency (recovery rate); and the process also adopts an energy recovery device to recover and reuse the residual energy of the high-pressure running membrane system, so that the energy consumption of the whole process is reduced.

Description

Technical Field

[0001] The invention belongs to the field of water treatment, and in particular relates to a method for treating membrane-making DMF wastewater by quality separation. Background Art

[0002] N,N-dimethylformamide (DMF) is an organic solvent used in the production process of reverse osmosis membranes. It is generally used as a solvent for chemical reaction monomers in membrane production and does not directly participate in the chemical synthesis process. Therefore, the wastewater generated after membrane production will contain a higher concentration of DMF.

[0003] DMF is harmful to the human body and the natural environment. It can enter the human body through the respiratory tract, digestive tract and skin contact, and has an inhibitory effect on microorganisms and even kills them. Since DMF has stable chemical properties and does not participate in the chemical synthesis process, and general distillation equipment requires the concentration of DMF in wastewater to reach more than 10%, while the concentration of DMF in membrane wastewater does not reach 10%, the method of concentrating and separating DMF in membrane wastewater and then distilling and purifying it can be adopted to efficiently recycle and use DMF, reduce the cost of production raw materials and the waste of water in the distillation process.

[0004] At present, the DMF wastewater membrane concentration process generally collects the wastewater generated in each production stage and then uses a membrane system to concentrate it. This process has a series of problems such as low concentration efficiency, long working time, and high energy consumption. Summary of the invention

[0005] In view of this, the object of the present invention is to provide a method for the separation and treatment of membrane DMF wastewater, which has a high DMF recovery rate and concentration efficiency and low energy consumption.

[0006] The present invention provides a method for treating DMF wastewater by quality separation, comprising the following steps:

[0007] The low-concentration DMF wastewater generated during the membrane production process enters the first raw water tank, passes through the first security filter and the first high-pressure pump, and enters the first membrane device for the first-stage treatment. The produced water of the first membrane device passes through the first and second high-pressure pumps and enters the first and second membrane devices for the second-stage treatment. The concentrated water of the first and second membrane devices returns to the first raw water tank for cyclic treatment. The produced water of the first and second membrane devices is the treated clean water.

[0008] The high-concentration DMF wastewater generated during the membrane production process enters the second raw water tank, passes through the second security filter and the second high-pressure pump, and enters the second membrane device for treatment. The concentrated water from the second membrane device returns to the second raw water tank for cyclic treatment. During the cyclic treatment process, the wastewater in the second raw water tank is continuously concentrated. After the DMF concentration of the wastewater is concentrated to the set value, it is sent to the distillation process for DMF recovery.

[0009] The concentrated water from the first membrane device and the produced water from the second membrane device enter the third raw water tank, and then enter the third membrane device for treatment after passing through the third safety filter and the third high-pressure pump. The produced water from the third membrane device returns to the first raw water tank for cyclic treatment; the concentrated water from the third membrane device returns to the third raw water tank for cyclic treatment. During the cyclic treatment process, the wastewater in the third raw water tank is continuously concentrated. After the DMF concentration of the wastewater is concentrated to the set value, it returns to the second raw water tank for cyclic treatment.

[0010] During the operation of the second membrane device, the energy is recovered and reused through the energy recovery device matched with the second membrane device;

[0011] During the operation of the third membrane device, the energy is recovered and reused through the energy recovery device matched with the third membrane device;

[0012] The DMF concentration of the low-concentration DMF wastewater is 0.1-1 wt %, and the DMF concentration of the high-concentration DMF wastewater is 2-6 wt %.

[0013] Preferably, during the operation of the second membrane device, the energy recovered by the energy recovery device supporting the second membrane device is supplied to the first stage high pressure pump and / or the first stage membrane device;

[0014] During the operation of the third membrane device, the energy recovered by the energy recovery device associated with the third membrane device is supplied to the second high-pressure pump and / or the second membrane device.

[0015] Preferably, the lift of the first stage high pressure pump is 200-250m.

[0016] Preferably, the first stage membrane device is of single-stage design, using low-pressure brackish water membrane elements, and the recovery rate is 45-55%.

[0017] Preferably, the lift of the first and second high-pressure pumps is 150-200m.

[0018] Preferably, the first and second membrane devices are of dual-stage design, using low-pressure brackish water membrane elements, with a recovery rate of 65-75%.

[0019] Preferably, the lift of the second high-pressure pump is 400-500 m.

[0020] Preferably, the second membrane device is of single-stage design, using low-pressure brackish water membrane elements, and has a recovery rate of 5-10%.

[0021] Preferably, the lift of the third high-pressure pump is 600-700m.

[0022] Preferably, the third membrane device is a single-stage design, using high-pressure seawater desalination membrane elements, and the recovery rate is 25-30%.

[0023] Compared with the prior art, the present invention provides a method for treating DMF wastewater produced by membrane production by quality separation, comprising the following processes: low-concentration DMF wastewater produced in the membrane production process enters the first raw water tank, passes through the first security filter and the first high-pressure pump, enters the first membrane device for first-stage treatment, the product water of the first membrane device passes through the first and second high-pressure pumps, enters the first and second membrane devices for second-stage treatment, the concentrated water of the first and second membrane devices returns to the first raw water tank for circulation treatment, and the product water of the first and second membrane devices is the treated clean water; high-concentration DMF wastewater produced in the membrane production process enters the second raw water tank, passes through the second security filter and the second high-pressure pump, enters the second membrane device for treatment, and the concentrated water of the second membrane device returns to the second raw water tank for circulation treatment; during the circulation treatment process, the wastewater in the second raw water tank is not The concentrated water of the first membrane device and the produced water of the second membrane device enter the third raw water tank, pass through the third security filter and the third high-pressure pump, and then enter the third membrane device for treatment. The produced water of the third membrane device returns to the first raw water tank for circulation treatment. The concentrated water of the third membrane device returns to the third raw water tank for circulation treatment. During the circulation treatment, the wastewater in the third raw water tank is continuously concentrated. After the DMF concentration of the wastewater is concentrated to the set value, it returns to the second raw water tank for circulation treatment. During the operation of the second membrane device and the third membrane device, the energy is recovered and reused by the corresponding energy recovery device. The DMF concentration of the low-concentration DMF wastewater is 0.1-1wt%, and the DMF concentration of the high-concentration DMF wastewater is 2-6wt%. In the reverse osmosis membrane production process, the amount of membrane wastewater and DNF concentration generated in different production stages are different, and the water quality and amount fluctuate greatly. For example, in the membrane casting stage, the amount of wastewater generated is low and the DMF concentration is high, while in the rinsing stage, the amount of wastewater increases exponentially, while the DMF concentration is greatly reduced. The present invention adopts multiple membrane systems to receive and treat membrane wastewater by quality, and at the same time, concentrated and produced water reflux is set between each membrane system, so that the whole system has a high interception rate and high concentration efficiency (recovery rate); and the process also adopts an energy recovery device to recycle the residual energy of the high-pressure membrane system, thereby reducing the energy consumption of the overall process. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0025] Figure 1It is a schematic flow chart of a method for treating membrane-making DMF wastewater by quality control provided by an embodiment of the present invention.

[0026] Explanation of the reference numerals: 1 is low-concentration DMF wastewater, 2 is the first raw water tank, 3 is the first security filter, 4 is the first level one high-pressure pump, 5 is the first level one membrane device, 6 is the first level two high-pressure pump, 7 is the first level two membrane device, 8 is purified water, 9 is high-concentration DMF wastewater, 10 is the second raw water tank, 11 is the second security filter, 12 is the second high-pressure pump, 13 is the second membrane device, 14 is the de-distillation treatment process, 15 is the third raw water tank, 16 is the third security filter, 17 is the third high-pressure pump, 18 is the third membrane device, 19 is the energy recovery device supporting the third membrane device, and 20 is the energy recovery device supporting the second membrane device. DETAILED DESCRIPTION

[0027] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0028] The present invention provides a method for treating DMF wastewater by quality separation, such as Figure 1 As shown, the following process is included:

[0029] The low-concentration DMF wastewater 1 generated during the membrane production process enters the first raw water tank 2, passes through the first security filter 3 and the first high-pressure pump 4, and enters the first membrane device 5 for first-stage treatment. The produced water of the first membrane device 5 passes through the first-second high-pressure pump 6 and enters the first-second membrane device 7 for second-stage treatment. The concentrated water of the first-second membrane device 7 returns to the first raw water tank 2 for cyclic treatment. The produced water of the first-second membrane device 7 is the treated clean water 8.

[0030] The high-concentration DMF wastewater 9 generated during the membrane production process enters the second raw water tank 10, passes through the second security filter 11 and the second high-pressure pump 12, and enters the second membrane device 13 for treatment. The concentrated water of the second membrane device 13 returns to the second raw water tank 10 for cyclic treatment. During the cyclic treatment process, the wastewater in the second raw water tank 10 is continuously concentrated. After the DMF concentration of the wastewater is concentrated to the set value, it is sent to the distillation treatment process 14 for DMF recovery.

[0031] The concentrated water from the first membrane device 5 and the produced water from the second membrane device 13 enter the third raw water tank 15, and after passing through the third security filter 16 and the third high-pressure pump 17, enter the third membrane device 18 for treatment. The produced water from the third membrane device 18 returns to the first raw water tank 2 for cyclic treatment; the concentrated water from the third membrane device 18 returns to the third raw water tank 15 for cyclic treatment. During the cyclic treatment process, the wastewater in the third raw water tank 15 is continuously concentrated. After the DMF concentration of the wastewater is concentrated to the set value, the obtained high-concentration wastewater is returned to the second raw water tank 10 for cyclic treatment.

[0032] During the operation of the second membrane device 13, the energy is recovered and reused by the energy recovery device 20 matched with the second membrane device;

[0033] During the operation of the third membrane device 18, the energy is recovered and reused through the energy recovery device 19 associated with the third membrane device.

[0034] In the treatment method provided by the present invention, the DMF concentration of the low-concentration DMF wastewater 1 is 0.1-1wt%, preferably 0.3-0.6wt%; the DMF concentration of the high-concentration DMF wastewater 9 is 2-6wt%, preferably 5-6wt%.

[0035] In the treatment method provided by the present invention, the DMF concentration of the wastewater sent to the distillation treatment step 14 for DMF recovery is preferably ≥10wt%.

[0036] In the treatment method provided by the present invention, the DMF concentration of the high-concentration wastewater returned to the second raw water tank 10 is preferably 2-6 wt %, and more preferably 5-6 wt %.

[0037] In the treatment method provided by the present invention, during the operation of the second membrane device 13, the operating pressure of the matching second high-pressure pump 12 is high, and the energy recovery device 20 matching the second membrane device is used to recover the high-pressure energy in the concentrated water on the concentrated water return pipeline of the second membrane device 13, and the recovered energy can be supplied to the first-stage high-pressure pump 4 and / or the first-stage membrane device 5.

[0038] In the treatment method provided by the present invention, during the operation of the third membrane device 18, the operating pressure of the third high-pressure pump 17 is high, and the energy recovery device 19 supporting the third membrane device is used to recover the high-pressure energy in the concentrated water in the reflux pipeline of the high-concentration wastewater discharged from the third raw water tank 15 and returned to the second raw water tank 10. The recovered energy can be supplied to the second high-pressure pump 12 and / or the second membrane device 13.

[0039] In the treatment method provided by the present invention, the head of the first stage high-pressure pump 4 is preferably 200-250m.

[0040] In the treatment method provided by the present invention, the first-stage membrane device 5 is preferably a single-stage design, preferably using a low-pressure brackish water membrane element, and the recovery rate is preferably 45-55%; the model of the low-pressure brackish water membrane element can specifically be BW-8040FR.

[0041] In the treatment method provided by the present invention, the lift of the first and second high-pressure pumps 6 is preferably 150-200 m.

[0042] In the treatment method provided by the present invention, the first and second membrane devices 7 are preferably of dual-stage design, preferably using low-pressure brackish water membrane elements, and the recovery rate is preferably 65-75%; the model of the low-pressure brackish water membrane element can specifically be BW-8040FR.

[0043] In the treatment method provided by the present invention, the head of the second high-pressure pump 12 is preferably 400-500 m.

[0044] In the treatment method provided by the present invention, the second membrane device 13 is preferably a single-stage design, preferably using a low-pressure brackish water membrane element, and the recovery rate is preferably 5-10%; the model of the low-pressure brackish water membrane element can specifically be BW-8040FR.

[0045] In the treatment method provided by the present invention, the head of the third high-pressure pump 17 is preferably 600-700 m.

[0046] In the treatment method provided by the present invention, the third membrane device 18 is preferably a single-stage design, preferably using a high-pressure seawater desalination membrane element, and the recovery rate is preferably 25-30%; the model of the high-pressure seawater desalination membrane element can specifically be SW-8040MR.

[0047] The treatment method provided by the present invention has a high DMF recovery rate and concentration efficiency, and has low energy consumption. More specifically, it has the following advantages:

[0048] 1) Due to the use of differentiated treatment, small-scale water tanks and membrane systems can be used, saving floor space and equipment costs.

[0049] 2) Since multiple membrane systems are used for quality separation treatment, wastewater with different DMF concentrations can be treated at the same time, reducing the time required for concentration.

[0050] 3) Since concentrated and produced water recirculation is set between each membrane system, the final discharged clean water contains almost no DMF, and the total DMF recovery rate is high.

[0051] 4) Since energy recovery devices are installed between each membrane system and are reasonably distributed among the membrane systems, the entire system can operate in an energy-saving manner.

[0052] For the purpose of greater clarity, the invention is described in detail through the following examples.

[0053] Example 1

[0054] according to Figure 1 The process shown is used to separate and treat DMF wastewater from membrane production. The parameters of key equipment are as follows:

[0055] The first stage high pressure pump 4: head 200 ~ 250m;

[0056] The first stage membrane device 5: recovery rate 45-55%, single-stage design, using low-pressure brackish water series membrane elements; the membrane element model used is BW-8040FR anti-pollution membrane element. Under standard test conditions (2000ppmNaCl, 225psi, 25℃, pH=7-8, 15% recovery rate), the minimum desalination rate of a single membrane element of BW-8040FR membrane element is 99.65%, and the water production is 9500GPD.

[0057] The first and second stage high pressure pump 6: head 150~200m;

[0058] The first and second stage membrane device 7: the recovery rate is 65-75%, the double stage design, the low pressure brackish water series membrane element is adopted; the membrane element model used is the BW-8040FR anti-pollution membrane element.

[0059] Second high-pressure pump 12: head 400-500m;

[0060] The second membrane device 13 has a recovery rate of 5-10%, a single-stage design, and uses a low-pressure brackish water series membrane element; the membrane element model used is a BW-8040FR anti-pollution membrane element.

[0061] The third high-pressure pump 17: head 600-700m;

[0062] The third membrane device 18: recovery rate 25-30%, single-stage design, using high-pressure seawater desalination series membrane elements. The membrane element model used is SW-8040MR membrane element. Under the SW-8040MR standard test conditions (32000ppm NaCl, 800psi, 25℃, pH=7-8, 8% recovery rate), the minimum desalination rate of a single membrane element is 99.70% and the water production is 7500GPD.

[0063] The processing process is as follows:

[0064] During the rinsing stage of the membrane production process, wastewater with a DMF concentration of 0.3-0.5wt% is continuously generated (set as A tons / hour), or when the production line is changed, a large amount of wastewater with a DMF concentration of 0.5-0.8wt% is generated at one time (about 3 times the value of A); low-concentration DMF wastewater 1 first enters the first raw water tank 2, passes through the first security filter 3 and the first high-pressure pump 4, and enters the first membrane device 5 for the first-stage treatment. The concentrated water of the first membrane device 5 (DMF concentration is about twice that of the inlet water) enters the third raw water tank 15 for storage. The produced water of the first membrane device 5 enters the first membrane device 7 for the second stage treatment through the first high-pressure pump 6. The concentrated water of the first membrane device 7 returns to the first raw water tank 2 for circulation treatment. The produced water of the first membrane device 7 is the treated clean water 8, and its DMF concentration is almost 0%, which can be reused or discharged;

[0065] During the film casting stage of the membrane production process, wastewater with a DMF concentration of 5-6% (also about A tons / hour) is continuously produced. The high-concentration DMF wastewater 9 first enters the second raw water tank 10, passes through the second security filter 11 and the second high-pressure pump 12, and enters the second membrane device 13 for treatment. The concentrated water of the second membrane device 13 returns to the second raw water tank 10 for cyclic treatment; during the cyclic treatment process, the wastewater in the second raw water tank 10 is continuously concentrated, and after the DMF concentration of the wastewater is concentrated to 10wt%, it is sent to the distillation treatment process 14 for DMF recovery; the DMF concentration of the produced water of the second membrane device 13 is 0.6-1wt%, which can be regarded as medium-concentration wastewater, and enters the third raw water tank 15 for storage;

[0066] When the amount of wastewater with medium concentration stored in the third raw water tank 15 meets the operating conditions of the third membrane device 18, the third membrane device 18 starts to perform concentration operation, and the wastewater with medium concentration passes through the third security filter 16 and the third high-pressure pump 17 and enters the third membrane device 18 for treatment, and the produced water (DMF concentration is 0.1-0.2%) of the third membrane device 18 is returned to the first raw water tank 2 for circulation treatment; the concentrated water of the third membrane device 18 is returned to the third raw water tank 15 for circulation treatment. During the circulation treatment process, the wastewater in the third raw water tank 15 is continuously concentrated. After the DMF concentration of the wastewater is concentrated to about 6wt%, it goes to the second raw water tank 10, and then continues to be further concentrated by the second membrane device 13 to a DMF concentration of 10wt%, and then goes to the distillation treatment process 14 for DMF recovery;

[0067] During the operation of the second membrane device 13, the energy recovered by the energy recovery device 20 of the second membrane device is supplied to the first stage high-pressure pump 4 and the first stage membrane device 5; during the operation of the third membrane device 18, the energy recovered by the energy recovery device 19 of the third membrane device is supplied to the second high-pressure pump 12 and the second membrane device 13.

[0068] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for treating DMF wastewater by quality separation, characterized in that: The process includes: The low-concentration DMF wastewater generated during the membrane production process enters the first raw water tank (2), passes through the first security filter (3) and the first high-pressure pump (4), and then enters the first membrane device (5) for first-stage treatment. The water produced by the first membrane device (5) passes through the first high-pressure pump (6) and enters the first membrane device (7) for second-stage treatment. The concentrated water of the first and second membrane devices (7) returns to the first raw water tank (2) for cyclic treatment. The water produced by the first and second membrane devices (7) is the treated clean water. High-concentration DMF wastewater generated during the membrane production process enters the second raw water tank (10), passes through the second security filter (11) and the second high-pressure pump (12), and enters the second membrane device (13) for treatment. The concentrated water from the second membrane device (13) returns to the second raw water tank (10) for cyclic treatment. During the cyclic treatment process, the wastewater in the second raw water tank (10) is continuously concentrated. After the DMF concentration of the wastewater is concentrated to a set value, it is sent to a distillation treatment process for DMF recovery. The concentrated water from the first primary membrane device (5) and the produced water from the second membrane device (13) enter the third raw water tank (15), pass through the third safety filter (16) and the third high-pressure pump (17), and then enter the third membrane device (18) for treatment. The produced water from the third membrane device (18) returns to the first raw water tank (2) for cyclic treatment; the concentrated water from the third membrane device (18) returns to the third raw water tank (15) for cyclic treatment. During the cyclic treatment process, the wastewater in the third raw water tank (15) is continuously concentrated. After the DMF concentration of the wastewater is concentrated to a set value, it returns to the second raw water tank (10) for cyclic treatment. During the operation of the second membrane device (13), energy is recovered and reused through an energy recovery device (20) matched with the second membrane device; During the operation of the third membrane device (18), energy is recovered and reused through an energy recovery device (19) matched with the third membrane device; The DMF concentration of the low-concentration DMF wastewater is 0.1-1 wt %, and the DMF concentration of the high-concentration DMF wastewater is 2-6 wt %.

2. The separation treatment method according to claim 1 is characterized in that during the operation of the second membrane device (13), the energy recovered by the energy recovery device (20) matched with the second membrane device is supplied to the first stage high pressure pump (4) and / or the first stage membrane device (5); During the operation of the third membrane device (18), energy recovered by the energy recovery device (19) associated with the third membrane device is supplied to the second high-pressure pump (12) and / or the second membrane device (13).

3. The separation method according to claim 1 is characterized in that the head of the first stage high pressure pump (4) is 200 to 250 m.

4. The separation treatment method according to claim 1 is characterized in that the first-stage membrane device (5) is a single-stage design, using low-pressure brackish water membrane elements, and the recovery rate is 45-55%.

5. The separation method according to claim 1 is characterized in that the lift of the first and second high-pressure pumps (6) is 150-200 m.

6. The separation treatment method according to claim 1 is characterized in that the first and second membrane devices (7) are of double-stage design, using low-pressure brackish water membrane elements, and the recovery rate is 65-75%.

7. The separation method according to claim 1, characterized in that the head of the second high-pressure pump (12) is 400-500m.

8. The separation treatment method according to claim 1 is characterized in that the second membrane device (13) is of single-stage design, using low-pressure brackish water membrane elements, and the recovery rate is 5-10%.

9. The separation method according to claim 1, characterized in that the head of the third high-pressure pump (17) is 600-700m.

10. The separation treatment method according to claim 1, characterized in that the third membrane device (18) is of single-stage design, using high-pressure seawater desalination membrane elements, and the recovery rate is 25-30%.

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