Coalescence-selective filtration-deep bed filtration efficient oil-water separation system and oil-water separation method

Abstract

The invention provides a coalescence-selective filtration-deep bed filtration efficient oil-water separation system which comprises a coalescence system, a selective filtration system and a deep bed filtration system, oily wastewater enters a coalescer, and tiny oil droplets are coalesced into larger oil droplets through wetting coalescence and collision coalescence; the coalesced wastewater enters a selective filter, oil droplets and water respectively flow out through an oil channel and a water channel, and primary separation is realized; according to the present invention, the water after the primary separation enters the deep bed filter to achieve the deep separation, the efficient oil-water separation and the water quality standard discharge or reuse are achieved through the combination process of coalescence, selective filtration and deep bed filtration, and the system has advantages of high treatment efficiency, low energy consumption, less carbon emission, oil and water recycling, or water standard discharge.

Description

Technical Field

[0001] The invention relates to the technical field of special wettability oil-water separation devices, and in particular to a coalescence-selective filtration-deep bed filtration high-efficiency oil-water separation system and an oil-water separation method. Background Art

[0002] Oily wastewater comes from a wide range of sources, mainly concentrated in industries such as petrochemicals and machinery manufacturing. Discharging untreated oily wastewater not only causes serious harm to the environment, but also causes waste of oil and water resources. Traditional oily wastewater treatment processes mainly include gravity sedimentation, flotation, membrane separation, adsorption, biochemical, chemical coagulation, etc. These separation methods all have certain disadvantages, such as high difficulty in resource recycling, large footprint, low separation efficiency, high energy consumption, high dosage of reagents, and easy membrane pollution. Emulsified oily wastewater is difficult to effectively separate using conventional physical or chemical methods due to its small oil droplet size and high stability. The traditional separation method is gravity multiplication sedimentation, which requires waiting for the oil droplets to float on the water surface, the oil to be pumped away from the top of the gravity separation zone, and the water to be discharged from the bottom of the gravity separation zone. It is often inefficient and cannot achieve efficient and continuous oil-water separation, and the treatment effect on the mixed liquid with larger oil droplet size is limited. For example, patent CN202410941573.8 discloses an oily wastewater treatment system, including a pre-filtration module for removing solid particles; a coalescence separation module for achieving water-oil separation; a conveying module for supplying materials; a base for supporting and installing the pre-filtration module and the coalescence separation module; the discharge end of the conveying module is connected to the feed end of the pre-filtration module; and the discharge end of the pre-filtration module is connected to the feed end of the coalescence separation module. After the oily wastewater of the invention is treated by the coalescence separation module, it is separated only by gravity sedimentation, which requires waiting for the oil droplets to float on the water surface, the oil to be pumped away from the top of the gravity separation zone, and the water to be discharged from the bottom of the gravity separation zone, and it is impossible to achieve efficient and continuous oil-water separation.

[0003] For another example, patent CN202322230909.3 discloses an oily wastewater treatment device, including a pre-filtering pool, a slag collecting box is arranged on the left side of the pre-filtering pool, a water pump is fixed in the pre-filtering pool, an oil-water separation pool is fixed on the right side of the pre-filtering pool, a water tank and an oil tank are arranged below the oil-water separation pool, and a recoil device is connected to the water tank and the pre-filtering pool; and further comprising: the pre-filtering pool is composed of a coarse grid, a fine grid, an ultrasonic transducer and a sand and gravel filter layer. The oily wastewater treatment device adopts a double filtering mechanism, which can filter and separate impurities in the oily wastewater to avoid impurities clogging the pipeline, and then cooperates with a circulating recoil mechanism, and can use the separated water to flush the filter mechanism to avoid clogging the filter mechanism, ensure the normal operation of the device, and then through the double oil-water separation mechanism, the oil-water separation effect can be guaranteed. However, the water separated by the invention also contains oil with a low concentration, and the oil concentration of the outlet water cannot meet the "Petroleum Refining Industry Pollutant Emission Standard" (GB31570-2015), and cannot be applied to actual projects.

[0004] Therefore, developing a treatment device for emulsified oily wastewater with small oil droplet size, high stability, and difficult to effectively treat by direct gravity separation is a technical problem that needs to be solved urgently. Summary of the invention

[0005] In view of the deficiencies in the prior art, the present invention provides a coalescence-selective filtration-deep bed filtration efficient oil-water separation system, which can efficiently and continuously separate oil and water, realize the recycling of oil resources and the standard discharge or reuse of water resources. The oily wastewater treatment system of the present invention increases the particle size of oil droplets through a coalescence process, realizes the physical separation of oil and water by dual-channel selective filtration, and further purifies the water quality through deep bed filtration, while realizing the recycling of backwash water, and finally obtains the water quality that meets the standard discharge or reuse, while reducing energy consumption and carbon emissions. The coalescer is used to coalesce the tiny oil droplets in the oily wastewater into larger oil droplets, thereby improving the subsequent filtration efficiency. The dual-channel selective filter includes a water channel of a super-hydrophilic underwater super-oleophobic medium and an oil channel of a super-hydrophobic super-oleophilic medium, which is used to realize the physical separation of oil and water, and the oil resources can be recycled. The deep bed filter is used to further remove low-concentration oil in the water, ensure that the water quality meets the standard, and the outlet oil concentration meets the requirement of less than 5mg / L in the "Petroleum Refining Industry Pollutant Emission Standard" (GB31570-2015). The circulation system returns the backwash water of the deep bed filter to the coalescer to achieve circulation treatment.

[0006] Specifically, the coalescence-selective filtration-deep bed filtration high-efficiency oil-water separation system provided by the present invention includes a coalescence system, a selective filtration system and a deep bed filtration system.

[0007] Furthermore, the coalescing system comprises a coalescer, wherein the coalescer is filled with a mixture of a super-hydrophobic and super-oleophilic medium and a super-hydrophilic underwater and super-oleophobic medium.

[0008] Furthermore, the mass ratio of the superhydrophobic-superoleophilic medium and the superhydrophilic underwater superoleophobic medium is 0.9-1.1:0.9-1.1, which constructs a wettability gradient from superoleophilicity to superoleophobicity, forming wetting aggregation and collision aggregation.

[0009] The wettability gradient forms an unbalanced force on the oil droplets, which can not only enhance the demulsification ability of the coalescer, but also reduce the head loss to promote the gradual coalescence and separation of the oil droplets, thereby effectively increasing the particle size of the emulsified oil droplets in the wastewater. The superoleophilic medium attracts and coalesces the tiny oil droplets through the hydrophobic force to achieve demulsification; the superoleophobic medium uses its surface properties to prevent the coalesced oil droplets from dispersing again, reducing oil loss during the treatment process.

[0010] Wetting coalescence is the process of oil droplets in the liquid phase continuously attaching, coalescing, and spreading on the surface of a super-hydrophobic and super-oleophilic medium, forming an oil film on the surface of the medium, and finally separating from the medium under the action of fluid drag and buoyancy. Collision coalescence is the process of mixing super-hydrophobic and super-oleophilic medium with super-hydrophilic underwater super-oleophobic medium to form a wettability gradient from super-oleophilic to super-oleophobic, forming an unbalanced force and tortuous channels on the oil droplets, improving the flow field, increasing the probability of collision between oil droplets, and promoting the gradual coalescence and separation of oil droplets.

[0011] Furthermore, the preparation steps of the super-hydrophilic underwater super-oleophobic medium are as follows:

[0012] S1: 190-210 g of quartz sand (QS) and 450-550 ml of NaOH solution were stirred and mixed at 20-30° C. and 600-700 r / min for 22-26 h to obtain a sand sample; to remove impurities and etch the sand surface to produce more micro- and nano-structures.

[0013] S2: The treated sand sample was washed three times with 160-220 ml of anhydrous ethanol to remove the residual NaOH and dried at 65-70 °C for 11-13 h.

[0014] Furthermore, the super hydrophobic and super oleophilic medium preparation steps are as follows:

[0015] (1) 190-210 g of superhydrophilic underwater superoleophobic quartz sand, 180-220 ml of N,N-dimethylformamide (DMF), 3-6 ml of dodecyltrimethoxysilane (DTMS), 3-6 ml of hexadecyltrimethoxysilane (HDTMS) and 3-6 ml of octadecyltrichlorosilane (OTS) were mixed in a beaker and stirred at 550-750 r / min for 22-26 h at room temperature.

[0016] (2) The sample was washed three times with 190-210 ml of anhydrous ethanol until the pH value was neutral, and then dried in an oven at 50-70 °C for 10-14 h to prepare superhydrophobic and superoleophilic quartz sand DTMS-HDTMS-OTS@QS.

[0017] The super-hydrophobic and super-oleophilic quartz sand was prepared by grafting the silane coupling agent onto the surface of the previously prepared super-hydrophilic underwater super-oleophobic quartz sand through a silanization reaction.

[0018] The hydrophobic medium is combined with three different silane coupling agents to be modified into super-hydrophobic and super-oleophilic properties. Not only does it have stronger hydrophobicity, but also because the chain lengths of the three silane coupling agents are different, they will form a long-chain-broken chain surface structure. In this way, the oil film formed on the surface of the super-hydrophobic and super-oleophilic medium is more stable and not easy to fall off under the action of water force, thus forming a more stable super-hydrophobic and super-oleophilic property in oil-water separation.

[0019] After the surface of the quartz sand is grafted with octadecyltrichlorosilane (OTS) silane coupling agent, many long alkyl chains are grafted on the surface of the quartz sand, which can adsorb and quickly pass through oil droplets, while effectively intercepting water molecules, achieving oil penetration and water interception.

[0020] Furthermore, the selective filtration system is a dual-channel filter, including a water channel and an oil channel, which are independent and arranged in parallel. The water channel is filled with a super-hydrophilic underwater super-oleophobic medium, which has a high affinity for water and a high repulsion for oil; the oil channel is filled with a super-hydrophobic super-oleophilic medium, which has a high affinity for oil and a high repulsion for water. The super-hydrophilic underwater super-oleophobic medium in the water channel preferentially adsorbs water molecules to form a continuous water flow channel, while repelling oil droplets to prevent them from passing through.

[0021] The superhydrophobic and superoleophilic media in the oil channel preferentially adsorb oil droplets to form a continuous oil flow channel, while repelling water molecules to prevent them from passing through.

[0022] The super-hydrophilic underwater super-oleophobic medium filled inside the water channel (the same as the super-hydrophilic underwater super-oleophobic medium in the coalescer): After the quartz sand is etched with NaOH, a micro-nano-level rough structure appears on the surface, and more hydrophilic groups hydroxyl (-OH) are produced on the surface, which can adsorb and quickly pass water molecules, while effectively intercepting oil droplets, achieving water penetration and oil interception.

[0023] The super-hydrophobic and super-oleophilic medium filled inside the oil channel (the same as the super-hydrophobic and super-oleophilic medium in the coalescer): after its surface is grafted with octadecyltrichlorosilane (OTS) silane coupling agent, many long alkyl chains are grafted onto the surface of quartz sand, which can adsorb and quickly pass through oil droplets, while effectively intercepting water molecules, achieving oil penetration and water interception.

[0024] Furthermore, the filter body in the deep bed filtration system is a deep bed structure, which is filled with a stimulus-responsive wettability medium, and the filter medium has the ability to switch between super oleophilicity and super oleophobicity.

[0025] Furthermore, the stimulus-responsive wettability medium is a pH-responsive switchable wettability medium, and the preparation steps thereof are as follows:

[0026] Step 1: 180-220 g of quartz sand is ultrasonically cleaned 3 times with 180-220 ml of ethanol and 180-220 ml of deionized water, each time for 13-16 min, and placed in a 70-90° C. oven to dry for 11-13 h to obtain pretreated quartz sand;

[0027] Step 2: dissolving 5-7 mL 3-(aminopropyl)triethoxysilane (APTES) and 1-3 mL 1H, 1H, 2H, 2H-perfluorooctyltrichlorosilane (FOTS) in 180-220 mL n-heptane, and stirring at 50-70° C. for 2.5-3.5 h to obtain a mixed solution;

[0028] Step 3: Add 180-220 g of pretreated quartz sand to the mixed solution prepared in step 2, and stir and mix at 550-750 r / min for 25-35 min to obtain modified quartz sand;

[0029] Step 4: Dry the modified quartz sand at 70-90°C for 11-13h to obtain the pH-responsive switchable wettability medium APTES-FOTS@QS.

[0030] APTES provides the hydrophilicity of the material, and FOTS provides the hydrophobicity of the material.

[0031] Wettability conversion mechanism: In the filtration stage, when filtering oil in low-concentration oily wastewater, an alkaline solution with a pH of ≈ 10 can be used in advance to transform the medium surface into super-hydrophobic and super-oleophilic properties. When pH ≈ 10, the medium surface is super-hydrophobic and super-oleophilic, and a small amount of oil is adsorbed on the medium surface. The water passes through the deep bed filter and meets the discharge standards, achieving the purpose of meeting the discharge standards for oily wastewater. In the backwashing stage, an acid solution with a pH of ≈ 2 can be used to transform the medium surface into super-hydrophilic underwater super-oleophobic properties. When pH ≈ 2, the medium surface is super-hydrophilic underwater super-oleophilic properties. The oil adsorbed on the medium surface is resolved by backwashing, and the backwashing water of the deep bed filter is returned to the coalescer through the circulation system to achieve circulation treatment and reduce water resource waste.

[0032] The present invention also provides a method for separating oil and water by using the above-mentioned coalescence-selective filtration-deep bed filtration high-efficiency oil-water separation system. First, the emulsified oily wastewater with oil droplet diameter less than 10 μm enters the coalescer, and the tiny oil droplets are coalesced into larger oil droplets with diameter greater than 100 μm through wetting coalescence and collision coalescence. The coalescing separator with a wettability gradient is constructed to improve the coalescence performance of the oil by 60%;

[0033] The agglomerated wastewater enters the dual-channel selective filter, and the oil droplets and water flow out through the oil channel and the water channel respectively, achieving preliminary separation. The selective separation efficiency reaches 99.99%, and the separated oil can be recovered.

[0034] The water after the initial separation enters the deep bed filter to further remove the low-concentration oil and achieve deep separation. Ensure that the water quality meets the discharge standard. The oil concentration of the deep bed filtered water meets the requirement of less than 5 mg / L in the "Petroleum Refining Industry Pollutant Emission Standard" (GB31570-2015). The backwash water of the deep bed filter is returned to the coalescer through the circulation system to achieve circulation treatment and reduce water resource waste.

[0035] Compared with the prior art, the advantages and positive effects of the present invention are:

[0036] 1. The present invention is for emulsified oily wastewater with colloidal stability. In view of the problem that its oil droplet particle size is small, the stability is high, and it is impossible to directly separate by gravity, two kinds of coalescing media, super oleophilic and super oleophobic, are loaded in the coalescer to form a wettability gradient, and a coalescing separator with a wettability gradient is constructed to achieve the purpose of demulsification and increasing the oil droplet particle size. For an oil-water mixture with a larger oil droplet particle size, a dual-channel filter with selective filtration of oil and water is constructed, so that the water phase flows out from the water channel and the oil flows out from the oil channel, and efficient and continuous separation of oil and water is achieved. The water channel is filled with a super hydrophilic underwater super oleophobic medium, and the oil channel is filled with a super hydrophobic super oleophilic medium. For low-concentration oily wastewater, in view of the problem that the backwashing efficiency of the deep bed filtration process is low and easy to clog, a deep bed filter with wettability conversion is constructed to achieve the purpose of dual high efficiency of filtration and backwashing. The filter medium loaded in the filter can realize mutual conversion between superoleophilicity and superoleophobicity through stimulus response. In the filtration stage, it is converted to superoleophilicity to achieve strong oil absorption performance, and in the backwashing stage, it is converted to superoleophobicity to make the oil adhered to the surface of the medium easily fall off.

[0037] 2. The coalescing separator with wettability gradient provided by the present invention can effectively solve the treatment problem of colloidal stable emulsified oily wastewater, improve the oil-water separation efficiency, reduce energy consumption and environmental pollution, and has significant social, economic and environmental benefits. The oil-water efficient continuous separation device and method based on dual-channel filtration technology realizes efficient and continuous separation of oil and water through selective filtration media and optimized filter structure characteristics. This technology has the advantages of high separation efficiency, strong processing capacity and wide adaptability, and has broad application prospects in industrial production, environmental protection and daily life. The deep bed filter with wettability conversion function and its oil-water separation method proposed by the present invention realize the conversion of the filter medium between super oleophilicity and super oleophobicity through a stimulus response mechanism, solving the problems of low backwashing efficiency and easy clogging in the traditional deep bed filtration process. This technology has the advantages of high filtration efficiency, good backwashing effect and low operating cost, and has broad application prospects in the field of low-concentration oily wastewater treatment.

[0038] 3. The coalescence-filtration-deep bed filtration treatment system proposed in the present invention realizes the efficient separation of oil and water and the discharge or reuse of water quality in compliance with standards through the combined process of coalescence, selective filtration and deep bed filtration, and realizes the systematic treatment of actual oily wastewater from "cradle" to "grave". The system has the advantages of high treatment efficiency, low energy consumption, low carbon emissions, and both oil and water can be recycled, or water can be discharged in compliance with standards, achieving the circular economy benefits of "discharge in compliance with standards and comprehensive utilization". The research results will have very positive significance in promoting the resource utilization of sewage, promoting the transformation and upgrading of industrial wastewater treatment technology, improving the efficiency of industrial wastewater treatment, and promoting the development of the industrial wastewater treatment industry. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 This is a schematic diagram of a coalescence-selective filtration-deep bed filtration high-efficiency oil-water separation system of Example 1;

[0040] Figure 2 is a front view of the coalescence system of Example 1;

[0041] Figure 3 is a left side view of the coalescing system of Example 1;

[0042] Figure 4 is a schematic diagram of a dual-channel selective filtration system of Example 1;

[0043] Figure 5 is a schematic diagram of the deep bed filtration system of Example 1;

[0044] In the figure: 1-agglomeration system; 2-selective filtration system; 3-deep bed filtration system; 4-water inlet; 5-oil outlet; 6-water outlet; 7-backwashing water inlet; 8-water inlet; 9-mixed filter media; 10-water distribution plate; 11-water outlet; 12-bracket; 13-mixed filter media; 14-water inlet; 15-bracket; 16-oil outlet; 17-super hydrophobic and super oleophilic medium; 18-water inlet; 19-super hydrophilic underwater super oleophobic medium; 20-water outlet; 21-bracket; 22-filter column; 23-filter media layer; 24-supporting layer; 25-water distribution layer; 26-piezometer; 27-filtered water inlet; 28-filtered overflow or backwashing water outlet; 29-backwashing water inlet; 30-rotor flowmeter; 31-filtered water outlet. DETAILED DESCRIPTION

[0045] The present invention can be better understood according to the following examples. However, it is easy for those skilled in the art to understand that the contents described in the examples are only used to illustrate the present invention, and should not and will not limit the present invention described in detail in the claims.

[0046] The technical solution of the present invention is further explained below in conjunction with implementation cases.

[0047] Example 1

[0048] This embodiment provides a coalescence-selective filtration-deep bed filtration high-efficiency oil-water separation system, such as Figure 1As shown, it includes a coalescence system 1, a dual-channel selective filtration system 2 and a deep bed filtration system 3. The oily wastewater enters the coalescence system 1 from the water inlet 4. The coalescer of the coalescence system 1 is filled with super oleophilic and super oleophobic coalescence media to form a wettability gradient. A coalescence separator with a wettability gradient is constructed to achieve the purpose of demulsification and increasing the particle size of oil droplets. In order to achieve the discharge or reuse of the actual oily wastewater, a coalescence-selective filtration-deep bed filtration high-efficiency oil-water separation system needs to be constructed. First, the emulsified oily wastewater with an oil droplet size of less than 10 μm enters the coalescence system 1 equipped with super hydrophobic super oleophilic and super hydrophilic underwater super oleophobic coalescence media from the water inlet 4. Under the action of the wettability gradient, the small-size oil droplets gradually form large oil droplets with a particle size greater than 100 μm through wetting coalescence and collision coalescence, which is convenient for subsequent oil-water separation. Subsequently, the oily wastewater flows out of the coalescence system 1 and enters the selective filtration system 2 to achieve efficient and continuous separation of oil and water. The oil flows out from the oil outlet 5 filled with super-hydrophobic and super-oleophilic filter media for recycling, and the wastewater containing a small amount of oil flows into the deep bed filtration system 3 from the water channel on the other side filled with super-hydrophilic underwater super-oleophobic media. Finally, the low-concentration oily wastewater flowing out of the dual-channel selective filtration system 2 flows into the deep bed filtration system 3 for deep separation. In the filtration stage, an alkaline solution with a pH of ≈ 10 can be used in advance to transform the surface of the medium into super-hydrophobic and super-oleophilic properties, adsorb a small amount of oil on the surface of the medium, and the water flows out through the water outlet 6 to meet the discharge standards, achieving the requirement of less than 5 mg / L in the "Petroleum Refining Industry Pollutant Emission Standard" (GB31570-2015). During the backwashing stage, an acid solution with a pH value of ≈ 2 can be used to transform the medium surface into a super-hydrophilic underwater super-oleophobic property. Water is introduced through the backwashing water inlet 7 to desorb the oil adsorbed on the medium surface. The backwashing water of the deep bed filter is returned to the coalescer through the circulation system to achieve recycling treatment and reduce water resource waste.

[0049] The present application coalescing system 1 is as Figure 2 and Figure 3 As shown, for emulsified oily wastewater with colloid stability, in order to solve the problems of small oil droplet size, high stability and inability to directly separate by gravity, two mixed media 9 of super hydrophobic and super oleophilic and super hydrophilic underwater super oleophobic are loaded in the coalescer to construct a coalescing separator with a wettability gradient to achieve the purpose of demulsification and increasing the oil droplet size.

[0050] First, the emulsified oily wastewater with oil droplet size less than 10 μm enters the coalescence system from the water inlet 8, and the water distribution of the coalescence system is uniformly achieved through the water distribution plate 10. Finally, under the action of the wettability gradient formed by the mixed medium 9, the small-size oil droplets gradually form large oil droplets with a size greater than 100 μm through wetting and collision coalescence, and then flow out of the coalescence system from the water outlet 11.

[0051] The dual-channel selective filtration system 2 of the present application is as follows Figure 4As shown, the oily wastewater treated by the coalescence system flows into the selective filtration system from the water inlet 18, realizing efficient and continuous separation of oil and water. The oil in the oil-water mixture flows out from the oil outlet 16 through the oil channel 17 equipped with super-hydrophobic and super-oleophilic media and is recycled, and the wastewater containing a small amount of oil flows out from the water outlet 20 through the water channel 19 equipped with super-hydrophilic underwater super-oleophobic media.

[0052] This application deep bed filtration system 3 as Figure 5 As shown in the figure, in order to solve the problems of low backwashing efficiency and easy clogging in the deep bed filtration process, a deep bed filter with wettability conversion is constructed to achieve the purpose of high efficiency in both filtration and backwashing. The filter medium loaded in the filter can realize the conversion between super oleophilicity and super oleophobicity through pH stimulation response. It is converted to super oleophilicity in the filtration stage to achieve strong oil absorption performance, and converted to super oleophobicity in the backwashing stage to make the oil adhered to the surface of the medium fall off easily.

[0053] First, the low-concentration oily wastewater treated by the dual-channel selective filtration system enters the deep bed filtration system from the water inlet 27. In the filtration stage, when filtering the oil in the low-concentration oily wastewater, the alkaline solution with pH≈10 can be used in advance to transform the surface of the filter layer 23 medium into super-hydrophobic and super-oleophilic properties, and the medium adsorbs a small amount of oil on the surface of the medium. The water is discharged through the filter outlet 31 to meet the standards, thereby achieving the purpose of meeting the standards for the discharge of oily wastewater. In the backwashing stage, an acid solution with pH≈2 can be used to transform the surface of the filter layer 23 medium into super-hydrophilic underwater super-oleophobic properties, and the oil adsorbed on the surface of the filter layer 23 medium is resolved through the backwashing water inlet 29. The backwashing water of the deep bed filter is returned to the coalescence system through the backwashing outlet 28 to achieve cyclic treatment and reduce water resource waste.

[0054] Example 2

[0055] This embodiment provides a method for separating oil and water using the coalescence-selective filtration-deep bed filtration high-efficiency oil-water separation system of Example 1.

[0056] First, the emulsified oily wastewater with an oil droplet size of less than 10 μm and a concentration of 200 g / L enters the coalescer. Under the action of the wetting gradient, the tiny oil droplets are coalesced into larger oil droplets with a particle size greater than 100 μm through wetting coalescence and collision coalescence. The coalescing separator with wettability gradient has an oil coalescing performance that is 60% higher than that of the coalescer filled with only a single special wettability medium.

[0057] Subsequently, the coalesced oily wastewater enters the dual-channel selective filter, and the oil and water flow out through the oil channel and the water channel respectively, achieving preliminary separation, with a separation efficiency of up to 99.99%, and the separated oil can be recycled. At this time, the oil concentration in the oily wastewater is 20 mg / L, which does not meet the requirement of less than 5 mg / L in the "Petroleum Refining Industry Pollutant Emission Standard" (GB31570-2015). Therefore, a deep bed filtration system is required to treat it to meet the standard for discharge or reuse.

[0058] Finally, the low-concentration oily wastewater separated by the dual-channel selective filtration system enters the deep bed filtration system to further remove a small amount of oil in the oily wastewater and achieve deep separation. The oil concentration of the deep bed filtration effluent meets the requirements of less than 5 mg / L in the "Petroleum Refining Industry Pollutant Emission Standard" (GB31570-2015), and the water can be discharged or reused in compliance with the standards. The backwash water of the deep bed filtration system can be returned to the coalescer for cyclic treatment to reduce water resource waste.

[0059] In summary, the present application is directed to oily wastewater with small oil droplet diameter, high stability, and inability to be directly separated by gravity, and a coalescing separator with a wettability gradient is constructed to achieve the purpose of demulsification and increasing the oil droplet diameter, and to construct a dual-channel filter with selective filtration for oil and water, so that the water phase flows out from the water channel, and the oil flows out from the oil channel, so as to achieve efficient and continuous separation of oil and water. In view of the low backwash efficiency and easy clogging problems of deep bed filtration process, a deep bed filter with wettability conversion is constructed to achieve the purpose of dual high efficiency of filtration and backwashing. The filter medium loaded in the filter can be realized by stimulus response to mutual conversion between super oleophilicity and super oleophobicity, and the filtration stage is converted to super oleophilicity to achieve strong oil absorption performance, and the backwash stage is converted to super oleophobicity to make the oil adhered to the surface of the medium fall off easily.

[0060] This technology has the advantages of high filtration efficiency, good backwashing effect and low operating cost, and has broad application prospects in the actual field of oily wastewater treatment.

[0061] The above-mentioned embodiments only express several implementation methods of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention.

Claims

1. Coalescence-selective filtration-deep bed filtration high-efficiency oil-water separation system, characterized by: Includes coalescing systems, selective filtration systems and deep bed filtration systems.

2. The coalescence-selective filtration-deep bed filtration high-efficiency oil-water separation system according to claim 1 is characterized in that: The coalescing system comprises a coalescer, wherein a mixture of a super-hydrophobic and super-oleophilic medium and a super-hydrophilic underwater and super-oleophobic medium is filled in the coalescer.

3. The coalescence-selective filtration-deep bed filtration high-efficiency oil-water separation system according to claim 2 is characterized in that: The mass ratio of superhydrophobic superoleophilic medium and superhydrophilic underwater superoleophobic medium is 0.9-1.1:0.9-1.1, which constructs a wettability gradient from superoleophilic to superoleophobic, forming wetting coalescence and collision coalescence.

4. The coalescence-selective filtration-deep bed filtration high-efficiency oil-water separation system according to claim 3 is characterized in that: The preparation steps of the super hydrophilic underwater super oleophobic medium are as follows: S1: 190-210 g of quartz sand and 450-550 ml of NaOH solution were stirred and mixed at 20-30° C. and 600-700 r / min for 22-26 h to obtain a sand sample; S2: The treated sand samples were washed three times with 160-220 ml of anhydrous ethanol to remove the residual NaOH and dried at 65-70 °C for 11-13 h.

5. The coalescence-selective filtration-deep bed filtration high-efficiency oil-water separation system according to claim 4 is characterized in that: The super hydrophobic and super oleophilic medium preparation steps are as follows: (1) 190-210 g of superhydrophilic underwater superoleophobic quartz sand, 180-220 ml of N,N-dimethylformamide, 3-6 ml of dodecyltrimethoxysilane, 3-6 ml of hexadecyltrimethoxysilane and 3-6 ml of octadecyltrichlorosilane were mixed in a beaker and stirred at 550-750 r / min for 22-26 h at room temperature. (2) The sample was washed three times with 190-210 ml of anhydrous ethanol until the pH value was neutral, and then dried in an oven at 50-70 °C for 10-14 h to prepare superhydrophobic and superoleophilic quartz sand DTMS-HDTMS-OTS@QS.

6. The coalescence-selective filtration-deep bed filtration high-efficiency oil-water separation system according to claim 1 is characterized in that: The selective filtering system is a dual-channel filter, including a water channel and an oil channel, which are independent of each other and arranged in parallel. The water channel is filled with a super-hydrophilic underwater super-oleophobic medium, and the oil channel is filled with a super-hydrophobic super-oleophilic medium.

7. The coalescence-selective filtration-deep bed filtration high-efficiency oil-water separation system according to claim 1 is characterized in that: The filter body in the deep bed filtration system is a deep bed structure, and a stimulus-responsive wettability medium is filled inside, and the filter medium has the ability to switch between super oleophilicity and super oleophobicity.

8. The coalescence-selective filtration-deep bed filtration high-efficiency oil-water separation system according to claim 7 is characterized in that: The stimulus-responsive wettability medium is a pH-responsive switchable wettability medium, and the preparation steps are as follows: Step 1: 180-220 g of quartz sand is ultrasonically cleaned 3 times with 180-220 ml of ethanol and 180-220 ml of deionized water, each time for 13-16 min, and placed in a 70-90° C. oven to dry for 11-13 h to obtain pretreated quartz sand; Step 2: dissolving 5-7 mL 3-(aminopropyl)triethoxysilane and 1-3 mL 1H, 1H, 2H, 2H-perfluorooctyltrichlorosilane in 180-220 mL n-heptane, and stirring at 50-70° C. for 2.5-3.5 h to obtain a mixed solution; Step 3: Add 180-220 g of pretreated quartz sand to the mixed solution prepared in step 2, and stir and mix at 550-750 r / min for 25-35 min to obtain modified quartz sand; Step 4: Dry the modified quartz sand at 70-90°C for 11-13h to obtain the pH-responsive switchable wettability medium APTES-FOTS@QS.

9. The method for separating oil and water by using a coalescence-selective filtration-deep bed filtration high-efficiency oil-water separation system according to any one of claims 1 to 8, characterized in that: The oily wastewater enters the coalescer, where tiny oil droplets are coalesced into larger ones through wetting and collision coalescence. The coalesced wastewater enters the dual-channel selective filter, and the oil droplets and water flow out through the oil channel and water channel respectively, achieving preliminary separation; The water after initial separation enters the deep bed filter to achieve deep separation.

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