An oily wastewater treatment system based on ultrasonic cavitation effect and synergistic negative pressure membrane separation

Abstract

An oily wastewater treatment system based on ultrasonic cavitation effect and negative pressure membrane separation, relating to the field of oilfield oily wastewater treatment technology, includes a negative pressure membrane filtration unit, an ultrasonic generation unit, and a backwashing unit. Through an ultrasonic transducer array, a strong cavitation effect is generated during the negative pressure membrane filtration process, disrupting the binding force between adhesive contaminants in the oily wastewater and the membrane surface. Simultaneously, combined with an intelligent backwashing device, efficient membrane fouling control is achieved. By optimizing the layout of the ultrasonic transducer array and the structural design of the negative pressure membrane assembly, highly efficient purification is achieved for suspended solids particles ≤1μm in diameter and oil content ≤5mg / L, meeting the high standards for reinjection water in ultra-low permeability reservoirs (level 5.1.1 water quality indicators in SY / T 5329-2022). Compared with existing technologies, this invention significantly improves membrane flux recovery rate, extends membrane lifespan, reduces cleaning energy consumption and cleaning cycles, and simultaneously reduces the use of chemical agents, avoiding the risk of chemical residues and secondary pollution.

Description

Technical Field

[0001] This utility model belongs to the field of oilfield oily wastewater treatment technology, and particularly relates to an oily wastewater treatment system based on ultrasonic cavitation effect synergistic negative pressure membrane separation. Background Technology

[0002] During oilfield extraction, oily wastewater has a complex composition, including crude oil, colloids, suspended solids, and dissolved organic matter. Direct reinjection can lead to formation pore blockage, which is particularly harmful to ultra-low permeability reservoirs (such as shale oil and tight sandstone reservoirs). Currently, membrane separation technology is widely used in the industry for deep treatment, but the following technical bottlenecks exist:

[0003] Membrane fouling is severe and difficult to clean: Oil and grease in oily wastewater easily adhere to the membrane surface and the inside of the membrane pores. Under the traditional negative pressure suction mode, pollutants quickly form a dense filter cake layer, which is difficult to remove by conventional hydraulic backwashing (flux recovery rate after backwashing is <60%), resulting in a sharp increase in transmembrane pressure difference (TMP) and a shortened membrane life (average replacement cycle <6 months).

[0004] Low backwashing efficiency: Existing technologies rely on high-pressure water backwashing (such as 0.3-0.5MPa pulsed water flow), but it is ineffective at removing high-viscosity pollutants (such as asphalt and wax), requiring frequent addition of chemical cleaning agents (such as NaOH and surfactants), leading to the risk of chemical residues (residual amount >50mg / L) and secondary pollution.

[0005] The reinjection water standards are stringent: ultra-low permeability reservoirs require the median suspended solids particle size of reinjection water to be ≤1μm and the oil content to be ≤5mg / L ("5.1.1" standard). Traditional single membrane separation or atmospheric pressure ultrasonic-assisted technology (such as CN207385207U) is difficult to consistently meet the standards due to insufficient cavitation intensity and inefficient membrane fouling control (suspended solids exceedance rate >30%).

[0006] Among existing improvement solutions, ultrasonic cleaning technology has been attempted for membrane fouling control, but its design has significant limitations:

[0007] Cavitation effect is limited: Ultrasonic energy decays rapidly under normal pressure, and the cavitation bubble collapse intensity is low (<10MPa), which cannot effectively destroy the oil-film interface bonding force.

[0008] Inappropriate transducer layout: The transducer is fixed on one side (such as CN207385207U), which leads to uneven sound field distribution on the membrane surface and poor cleaning effect at the far end.

[0009] Lack of synergistic mechanism: Ultrasonic waves, negative pressure membrane filtration, and pulse backwashing do not form a dynamic synergy, resulting in high cleaning energy consumption (>0.5kWh / m³) and long cycle (>2h / cycle). Utility Model Content

[0010] To overcome the shortcomings of existing technologies, this invention provides an oily wastewater treatment system based on ultrasonic cavitation effect and synergistic negative pressure membrane separation, aiming to achieve efficient membrane fouling control and long-term stable compliance of reinjected water. This system is particularly suitable for reinjected water treatment in ultra-low permeability oil reservoirs (permeability <10mD), ensuring compliance with the "5.1.1" water quality index requirements in SY / T 5329-2022.

[0011] The technical solution provided by this utility model is: an oily wastewater treatment system based on ultrasonic cavitation effect and negative pressure membrane separation, comprising a main cylinder, a negative pressure membrane filtration unit, an ultrasonic generating unit, a backwashing unit, a water quality monitoring unit, and an automatic control unit; an outer cylinder is fitted outside the main cylinder, with an annular cavity between the outer cylinder and the main cylinder, and a concentrated water drain outlet at the lower part of the annular cavity; a purified water cylinder is fixedly connected to the upper part of the outer cylinder; the ultrasonic generating unit includes a transducer assembly, which is vertically installed in the center inside the main cylinder, and the transducer assembly includes a transducer flange, a transducer mounting cylinder, and ultrasonic transducers. The ultrasonic transducers are evenly distributed in a hexagonal shape inside the transducer mounting cylinder, and a three-dimensional ultrasonic field is generated by phase difference control; the transducer flange is installed at the upper end of the transducer mounting cylinder, and a purified water outlet pipe is connected to the transducer flange, and the transducer flange is fixedly connected to the purified water cylinder. The system includes a fixed connection; the negative pressure membrane filtration unit comprises a negative pressure membrane assembly, which includes a negative pressure membrane located around the transducer mounting cylinder. All negative pressure membranes are arranged in a uniform hexagonal pattern, matching the hexagonal distribution of the ultrasonic transducer array, causing the fluid to generate a spiral flow on the surface of the negative pressure membrane, reducing concentration polarization. A negative pressure membrane mounting perforated plate is provided above the negative pressure membrane, and all negative pressure membranes are connected to the negative pressure membrane mounting perforated plate. The outer edge of the negative pressure membrane mounting perforated plate is fixedly connected to the outer cylinder, and the inner edge of the negative pressure membrane mounting perforated plate is sealed to the transducer mounting cylinder; the backwashing unit includes a backwash inlet main pipe and a backwash water branch pipe. The backwash water branch pipe has a hexagonal structure, matching the hexagonal distribution of the ultrasonic transducer and the negative pressure membrane array, optimizing fluid distribution and reducing dead zones. The backwash water branch pipe is located inside the main cylinder below the negative pressure membrane; the lower part of the main cylinder has a sewage inlet.

[0012] A further technical solution is as follows: the negative pressure membrane includes an upper fixing component, a lower fixing component, and hollow fiber membrane filaments. Both the upper and lower fixing components are cylindrical structures. The upper and lower ends of the hollow fiber membrane filaments extend into the upper and lower fixing components, respectively, thereby fixing both ends of the hollow fiber membrane filaments.

[0013] A further technical solution is that the spacing between adjacent ultrasonic transducers is 1 / 6 of the diameter of the transducer mounting cylinder.

[0014] A further technical solution is: the lower part of the main cylinder has a conical cylinder, which is called a mud collecting cone, and the lower end of the mud collecting cone is a sewage outlet.

[0015] A further technical solution is that the ultrasonic transducer array operates under negative pressure, with a negative pressure range of -0.08 to -0.1 MPa.

[0016] Compared with the prior art, the beneficial effects of this utility model are as follows:

[0017] 1. Improve membrane flux recovery rate: Through the synergistic effect of ultrasonic cavitation and intelligent backwashing, the membrane flux recovery rate is significantly improved (>90%), and the membrane service life is extended (>12 months).

[0018] 2. Reduced cleaning energy consumption and cycle: Optimized ultrasonic transducer array layout and multi-mode cleaning strategy reduce cleaning energy consumption to <0.3kWh / m³ and shorten the cleaning cycle to <1h / cycle.

[0019] 3. Reduce the use of chemical agents: Reduce the frequency and amount of chemical cleaning agents used, avoiding the risk of agent residue and secondary pollution.

[0020] 4. Stable compliance: Through real-time water quality monitoring and automated control, the treated water quality is ensured to stably meet the "5.1.1" standard in "SY / T5329-2022", with suspended solids particle size ≤1μm and oil content ≤5mg / L.

[0021] Structural optimization: The rational transducer layout and membrane module design improve the overall performance and stability of the system.

[0022] 5. Uniform Sound Field Distribution: The backwash water branch pipes, negative pressure membrane, and ultrasonic transducers are all hexagonally distributed, with the six sets of transducers symmetrically arranged in a hexagonal pattern. The angle between the central axes of adjacent transducers is 60°±2°, and the spacing between adjacent transducers is 1 / 6 of the membrane module diameter. A three-dimensional ultrasonic field is generated through phase difference control, ensuring a uniform sound field distribution on the membrane surface. This significantly improves the far-end cleaning effect and solves the problem of uneven sound field caused by the unilateral arrangement of transducers in existing technologies.

[0023] 6. Enhanced Cavitation Effect: The hexagonal transducer array, through phase control, enables ultrasonic energy to form standing wave interference on the membrane surface, improving the cavitation effect by more than 30% compared to the traditional ring array. This more effectively disrupts the oil-film interface bonding, enhancing the cleaning effect. Under negative pressure, the cavitation intensity (>15MPa) is significantly higher than under positive pressure (<8MPa).

[0024] 7. Reduce concentration polarization: The hexagonal distribution of the membrane module creates a spiral flow pattern on the membrane surface, which reduces concentration polarization by 15% compared to a rectangular arrangement. This helps maintain stable membrane flux and extends the membrane's lifespan.

[0025] 8. Optimized fluid dynamics: The hexagonal distribution of the backwash water branch pipes and negative pressure membrane matches the ultrasonic transducer array, optimizing fluid distribution, reducing dead zones in water flow, making backwashing more thorough, and improving overall treatment efficiency.

[0026] 9. Enhanced system stability and reliability: Through reasonable structural design and optimized cleaning strategy, the system exhibits higher stability during long-term operation and can continuously and stably meet the high standard requirements for reinjection water in ultra-low permeability reservoirs.

[0027] 10. Negative Pressure Synergistic Effect: The ultrasonic transducer array operates only under negative pressure, with a negative pressure range of -0.08 to -0.1 MPa. Under negative pressure, the formation and collapse of cavitation bubbles are more intense, and the cavitation intensity (>15 MPa) is significantly higher than that under positive pressure (<8 MPa), which can more effectively disrupt the oil-film interface bonding force and improve the cleaning effect.

[0028] 11. Intelligent feedback control: The automated control unit dynamically adjusts the ultrasonic power (20~40kHz) and backwashing cycle (0.5~1h) based on the dual-parameter feedback of real-time transmembrane pressure difference (TMP) and water oil content to achieve intelligent control.

[0029] 12. Backwashing Synergistic Effect: The ultrasonic transducer works continuously during the backwashing stage, and the backwash water flow rate is positively correlated with the ultrasonic frequency (the frequency increases by 5kHz for every 0.2m / s increase in flow rate), thus enhancing the cleaning effect. Attached Figure Description

[0030] Figure 1 This is a cross-sectional view of the entire utility model.

[0031] Figure 2 This is a three-dimensional structural diagram of the present invention.

[0032] Figure 3 This is a three-dimensional structural diagram of the negative pressure membrane assembly in this utility model.

[0033] Figure 4 This is a schematic diagram of the negative pressure membrane in this utility model.

[0034] Figure 5 yes Figure 4 Top view of the structure.

[0035] Figure 6 This is a schematic diagram of the backwash inlet main pipe and backwash branch pipe in this utility model.

[0036] Figure 7 This is a three-dimensional structural diagram of the transducer assembly in this utility model.

[0037] In the diagram: 101, outer cylinder; 102, purified water cylinder; 103, transducer assembly; 104, main cylinder; 105, backwash water manifold; 106, sludge collection cone; 107, support leg; 108, concentrated water drain outlet; 201, purified water outlet pipe; 202, negative pressure membrane assembly; 203, wastewater inlet; 204, drain outlet; 205, backwash water inlet; 301, negative pressure membrane mounting plate; 302, negative pressure membrane; 401, upper fixing component; 402, lower fixing component; 403, hollow fiber membrane fiber; 501, backwash water branch pipe; 502, backwash water inlet main pipe; 601, transducer flange; 602, transducer mounting cylinder; 603, ultrasonic transducer. Detailed Implementation

[0038] To make the technical problems, technical solutions, and beneficial effects of this utility model clearer, the present utility model will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present utility model and are not intended to limit the present utility model.

[0039] This embodiment includes a main cylinder 104, a negative pressure membrane filtration unit, an ultrasonic generating unit, a backwashing unit, a water quality monitoring unit, and an automated control unit.

[0040] The main cylinder 104 is the core component of the entire device. An outer cylinder 101 is fitted around the main cylinder 104, forming the external protective structure of the equipment and ensuring sufficient mechanical strength and stability during system operation. An annular cavity exists between the outer cylinder 101 and the main cylinder 104, with a concentrated water drain port 108 at the lower part of the annular cavity. Support legs 107 are installed at the lower part of the main cylinder 104.

[0041] A purified water cylinder 102 is fixedly attached to the top of the outer cylinder 101.

[0042] The ultrasonic sound-generating unit includes a transducer assembly, which is vertically installed in the center of the main cylinder 104. The transducer assembly includes a transducer flange 601, a transducer mounting cylinder 602, and ultrasonic transducers 603. The ultrasonic transducers 603 are evenly distributed in a hexagonal pattern within the transducer mounting cylinder 602. The included angle between the central axes of adjacent ultrasonic transducers 603 is 60°±2°, and the distance between adjacent ultrasonic transducers 603 is 1 / 6 of the diameter of the transducer mounting cylinder 602. A three-dimensional ultrasonic field is generated by controlling the phase difference. The transducer flange 601 is installed at the upper end of the transducer mounting cylinder 602, and a purified water outlet pipe 201 is connected to the transducer flange 601. The transducer flange 601 is fixedly connected to the purified water cylinder 102.

[0043] The negative pressure membrane filtration unit includes a negative pressure membrane assembly 202, which includes a negative pressure membrane 302. The negative pressure membrane 302 is located around the transducer mounting cylinder 602. All the negative pressure membranes 302 are arranged in a hexagonal pattern, matching the hexagonal distribution of the ultrasonic transducer array 603, so that the fluid generates a spiral flow on the surface of the negative pressure membrane 302, reducing concentration polarization. A negative pressure membrane mounting perforated plate 301 is provided above the negative pressure membrane 302. All the negative pressure membranes 302 are connected to the negative pressure membrane mounting perforated plate 301. The outer edge of the negative pressure membrane mounting perforated plate 301 is fixedly connected to the outer cylinder 101, and the inner edge of the negative pressure membrane mounting perforated plate 301 is sealed to the transducer mounting cylinder 602. The negative pressure membrane 302 includes an upper fixing member 401, a lower fixing member 402, and a hollow fiber membrane filament 403. Both the upper fixing member 401 and the lower fixing member 402 are cylindrical structures. The upper and lower ends of the hollow fiber membrane filament 403 extend into the upper fixing member 401 and the lower fixing member 402, respectively, thereby fixing both ends of the hollow fiber membrane filament 403.

[0044] The backwash unit includes a backwash water manifold 105, which comprises a backwash water inlet main pipe 502 and a backwash water branch pipe 501. The backwash water branch pipe 501 is located inside the main cylinder 104 below the negative pressure membrane 302. The backwash water branch pipe 501 has a hexagonal structure, which matches the hexagonal distribution of the ultrasonic transducer 603 and the negative pressure membrane 302 array, optimizing fluid distribution and reducing dead zones in the water flow. The lower part of the main cylinder 104 has a sewage inlet 203.

[0045] The lower part of the main cylinder 104 is equipped with a conical cylinder, which is called the mud collecting cone 106. The lower end of the mud collecting cone 106 is the sewage outlet 204.

[0046] The ultrasonic transducer array 603 operates under negative pressure, with a negative pressure range of -0.08 to -0.1 MPa.

[0047] The specific working process of this embodiment is as follows:

[0048] 1. System Start-up: Oily wastewater enters the negative pressure membrane 302 for filtration through the wastewater inlet 203. The outer cylinder 101 serves as the external protective structure of the system, ensuring that the equipment is not affected by the external environment during operation. The vacuum equipment is connected to the purified water outlet pipe 201. After the vacuum equipment is started, a negative pressure environment of -0.08 to -0.1 MPa is formed and maintained in the upper part of the main cylinder 104. Under the action of negative pressure, the wastewater is filtered through the negative pressure membrane 302. The negative pressure membrane 302 is installed on the negative pressure membrane mounting plate 301, in which the hollow fiber membrane fibers 403 are kept stable by the fixation of the upper fixing member 401 and the lower fixing member 402. Water passes through the hollow fiber membrane fibers 403, while oil is blocked by the hollow fiber membrane fibers 403. The filtered purified water is discharged through the purified water outlet pipe 201 and can be directly reinjected into the oil reservoir.

[0049] During the filtration process, part of the sewage entering through the sewage inlet 203 is filtered through the negative pressure membrane 302, and the other part overflows from the upper end of the main cylinder 104 into the outer cylinder 101 and is discharged from the concentrated water outlet 108. The amount of water discharged from the concentrated water outlet 108 accounts for about 10% of the total amount of water entering through the sewage inlet 203. The purpose of setting the concentrated water outlet 108 is to reduce the concentration of impurities in the raw liquid.

[0050] 2. Ultrasonic Cleaning: When the ultrasonic transducer 603 is powered on, the array of ultrasonic transducers 603 generates a cavitation effect on the surface of the negative pressure membrane 302, which disrupts the adhesion between oil and the membrane, preventing membrane fouling. Under negative pressure, the cavitation intensity (>15MPa) is significantly higher than that under positive pressure (<8MPa), which can more effectively disrupt the oil-film interface adhesion.

[0051] 3. Backwashing: When the membrane flux drops to the set value, the automatic control unit initiates the backwashing procedure. The backwash water pump injects cleaning fluid into the main cylinder 104 through the backwash water inlet 205. The backwash water system, consisting of the backwash water branch pipe 501 and the backwash water inlet main pipe 502, ensures that the cleaning fluid is evenly and effectively distributed to all parts of the negative pressure membrane module 202. Simultaneously, the ultrasonic transducer array 603 continues to operate, utilizing the vibration of ultrasonic waves to enhance the cleaning effect. The backwash water flow rate is positively correlated with the ultrasonic frequency (for every 0.2 m / s increase in flow rate, the frequency increases by 5 kHz), ensuring a highly efficient and thorough cleaning process. The cleaned wastewater is discharged from the system through the drain outlet 204.

[0052] 4. Water Quality Monitoring and Control: The water quality monitoring unit monitors the effluent water quality in real time, detecting key indicators such as suspended solids particle size and oil content in the purified water using sensors. Monitoring data is fed back to the automated control unit, which dynamically adjusts the ultrasonic power (20~40kHz) and backwashing cycle (0.5~1h) based on this data and parameters such as transmembrane pressure difference (TMP). For example, if water quality indicators are detected to be close to the threshold or the transmembrane pressure difference increases, the system will appropriately increase the ultrasonic power or shorten the backwashing cycle to ensure that the effluent water quality consistently meets standards.

[0053] In this application, the structure of the water quality monitoring unit and the automatic control unit is flexible, as long as they can achieve the functions described in this application. The specific structure of the water quality monitoring unit and the automatic control unit is not within the scope of protection claimed in this application, and therefore will not be described in detail in this application.

Claims

1. An oily wastewater treatment system based on ultrasonic cavitation effect synergistic with negative pressure membrane separation, comprising a main cylinder (104), a negative pressure membrane filtration unit, an ultrasonic generation unit, a backwashing unit, a water quality monitoring unit, and an automated control unit; characterized in that: The main cylinder (104) is fitted with an outer cylinder (101), and an annular cavity is left between the outer cylinder (101) and the main cylinder (104). The annular cavity is connected to a concentrated water drain outlet (108). A purified water cylinder (102) is fixedly connected to the top of the outer cylinder (101). The ultrasonic generating unit includes a transducer assembly, which is vertically installed in the center of the interior of the main cylinder (104). The transducer assembly includes a transducer flange (601), a transducer mounting cylinder (602), and an ultrasonic transducer ( The ultrasonic transducers (603) are evenly distributed in a hexagonal shape inside the transducer mounting cylinder (602); the transducer flange (601) is installed at the upper end of the transducer mounting cylinder (602), and a purified water outlet pipe (201) is connected to the transducer flange (601), and the transducer flange (601) is fixedly connected to the purified water cylinder (102); the negative pressure membrane filter unit includes a negative pressure membrane assembly (202), and the negative pressure membrane assembly (202) includes a negative pressure membrane (302). The negative pressure membrane (302) is located on the periphery of the transducer mounting cylinder (602). All the negative pressure membranes (302) are arranged in a hexagonal pattern, matching the hexagonal distribution of the ultrasonic transducer (603) array. A negative pressure membrane mounting plate (301) is provided above the negative pressure membrane (302). All the negative pressure membranes (302) are connected to the negative pressure membrane mounting plate (301). The outer edge of the negative pressure membrane mounting plate (301) is fixedly connected to the outer cylinder (101). The inner edge of (301) is sealed to the transducer mounting cylinder (602); the backwash unit includes a backwash water inlet main pipe (502) and a backwash water branch pipe (501). The backwash water branch pipe (501) has a hexagonal structure, which matches the hexagonal distribution of the ultrasonic transducer (603) and the negative pressure membrane (302) array. The backwash water branch pipe (501) is located in the main cylinder (104) below the negative pressure membrane (302); the lower part of the main cylinder (104) has a sewage inlet (203).

2. The oily wastewater treatment system based on ultrasonic cavitation effect synergistic negative pressure membrane separation according to claim 1, characterized in that: The negative pressure membrane (302) includes an upper fixing member (401), a lower fixing member (402), and a hollow fiber membrane filament (403). The upper fixing member (401) and the lower fixing member (402) are both cylindrical structures. The upper end and the lower end of the hollow fiber membrane filament (403) extend into the upper fixing member (401) and the lower fixing member (402) respectively, thereby fixing the two ends of the hollow fiber membrane filament (403) with the upper fixing member (401) and the lower fixing member (402).

3. The oily wastewater treatment system based on ultrasonic cavitation effect synergistic negative pressure membrane separation according to claim 1, characterized in that: The spacing between adjacent ultrasonic transducers (603) is 1 / 6 of the diameter of the transducer mounting cylinder (602).

4. The oily wastewater treatment system based on ultrasonic cavitation effect and synergistic negative pressure membrane separation according to claim 1, characterized in that: The lower part of the main cylinder (104) is equipped with a conical cylinder, which is called the mud collecting cone (106), and the lower end of the mud collecting cone (106) is the sewage outlet (204).

5. The oily wastewater treatment system based on ultrasonic cavitation effect synergistic negative pressure membrane separation according to claim 1, characterized in that: The ultrasonic transducer (603) array operates under negative pressure, with a negative pressure range of -0.08 to -0.1 MPa.

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