A filtration apparatus and filtration method for treating a petroleum production fluid

Abstract

The application discloses a kind of filtering equipment for treating oil production fluid, including pretreatment device, pretreatment device is connected with dosing mixing device, dosing mixing device is connected with surface filter;Surface filter includes upper cavity and lower cavity, after mixed sewage in dosing mixing device enters lower cavity, the pressure of lower cavity will be greater than the pressure of upper cavity, at this time, flexible filter module can be concave inward and realize filtration;When the impurities on the outer surface of flexible filter module are too much, add cleaning water into upper cavity, so that the pressure of upper cavity is greater than the pressure of lower cavity, flexible filter module can be deformed and expand to the outer surface direction, so that the impurities on the outer surface of flexible filter module are broken and peeled off.The application also discloses a kind of filtering method for treating oil production fluid.The application realizes surface filtration treatment oilfield production fluid by using flexible filter module, which can adapt to various components complex oilfield production fluid and cope with the change fluctuation of water quality.

Description

Technical Field

[0001] This invention relates to the field of oil produced fluid treatment, and more particularly to a filtration device and method for treating oil produced fluid. Background Technology

[0002] Existing oil produced fluids have a complex composition, containing various natural organic matter and hydrocarbon compounds, as well as minerals leached from formation water, such as light crude oil, paraffin wax, high-viscosity crude oil, asphaltene, organic colloids, silt, alkaline substances, anionic substances, and salts from the formation. The composition of oil produced fluids changes with the production cycle of the oil wells, typically affecting the dosage and treatment process of water treatment agents. Conventional chemical flocculation processes, in particular, are directly affected by water quality fluctuations. The same process can yield significantly different results when treating different types of water, potentially impacting or causing irreversible damage to subsequent production stages.

[0003] Furthermore, in actual treatment, considering cost factors and cost-effectiveness, the process flow is generally simplified based on water sample test results, focusing on removing pollutants with high concentrations. However, when pollutants not considered in the design enter the process flow, the treated water quality will be affected by fluctuations in the produced water quality, often exceeding the designed operating parameters, posing a significant challenge to system stability.

[0004] Furthermore, existing chemical flocculant separation methods generate large amounts of oily sludge and sediment. Current settling tanks lack adequate sludge removal and flushing capabilities, requiring periodic dredging operations and reducing production efficiency. Poor ventilation also poses a risk of poisoning from toxic gases. Moreover, the reaction in existing chemical flocculant separation methods is highly susceptible to the complexity of operating conditions, making it difficult to control and often requiring excessive chemical dosing. This results in high chemical consumption and costs.

[0005] Therefore, it is essential to design a filtration device for oil produced fluids that is adaptable to various complex water types and can cope with changes and fluctuations in the quality of the oil produced fluids. Summary of the Invention

[0006] This invention provides a filtration device and method for treating oilfield produced fluids, which is adaptable to oilfield produced fluids with various complex compositions and can cope with fluctuations in the quality of the oilfield produced fluids. The specific technical solution is as follows: A filtration device for treating produced oil fluid includes a pretreatment unit connected to a chemical mixing unit, which is also connected to a surface filter. The pretreatment unit performs air flotation separation and coarse oil removal on the produced oil fluid. The wastewater after coarse oil removal enters the chemical mixing unit and is mixed with chemicals. The mixed wastewater then enters the surface filter for filtration. The surface filter includes a filter housing comprising an upper chamber and a lower chamber, connected by a flexible filter module. The lower chamber is connected to the chemical mixing unit. The outer surface of the flexible filter module is connected to the lower chamber, and its inner surface is connected to the upper chamber. The flexible filter module includes a flexible filter membrane and an inner... The skeleton, with the flexible filter membrane sleeved on the outside of the inner skeleton, has multiple support feet that support the flexible filter membrane. In the dosing and mixing device, after the mixed wastewater enters the lower chamber, the pressure in the lower chamber is greater than that in the upper chamber. At this point, the flexible filter module can indent inwards, and water can flow through the flexible filter module into the upper chamber to achieve filtration. Impurities adhere to the outer surface of the flexible filter module. When too many impurities adhere to the outer surface of the flexible filter module, cleaning water is added to the upper chamber, and when the pressure in the upper chamber exceeds that in the lower chamber and reaches a preset value, the flexible filter module deforms and expands outwards, causing the impurities on the outer surface of the flexible filter module to break and peel off.

[0007] Furthermore, the inner frame includes a supporting cylinder, on which multiple deformation support units are provided, and on which multiple support feet are provided, forming a water flow channel between two adjacent support feet so that water can flow into the upper cavity; the support feet of the deformation support unit include T-shaped fixed support feet and S-shaped flexible support feet, with three T-shaped fixed support feet and three S-shaped flexible support feet arranged alternately on the deformation support unit.

[0008] Furthermore, the interior of the filter box is divided into upper and lower chambers by a separator. The flexible filter module is cylindrical, and there are multiple flexible filter modules, which are evenly distributed below the separator. One end of the supporting cylinder is connected to the bottom cover, and the other end of the supporting cylinder is connected to the top cover. The top cover is connected to the separator, and a water outlet is provided at the center of the top cover. The water filtered by the flexible filter membrane can enter the upper chamber through the water outlet.

[0009] Furthermore, the lower cavity is equipped with a sewage inlet and a slag discharge outlet. The sewage inlet is connected to a sewage lift pump, which can pump the mixed sewage from the dosing and mixing device into the lower cavity and continuously provide pressure. The slag discharge outlet is equipped with a valve and is connected to a slurry pump, which can discharge the impurities and fragments backwashed from the lower cavity.

[0010] Furthermore, the upper cavity is provided with a connecting port, which is connected to the clean water lift pump and the backwash pump respectively through a tee. The clean water in the upper cavity can be drawn out by the clean water lift pump; during backwashing, the backwash pump can pump the cleaning water into the upper cavity and continuously provide pressure.

[0011] Furthermore, pressure sensors are installed in both the upper and lower cavities. The pressure sensors, sewage lift pump, slag discharge valve, backwash pump, clean water lift pump, slurry pump, etc. are all connected to the PLC controller. The PLC controller switches between filtration and backwashing states based on the pressure difference.

[0012] Furthermore, the pretreatment device includes a pretreatment tank with a treatment liquid outlet on one side, which is connected to a dosing and mixing device. A trapezoidal air flotation separator is located in the middle of the pretreatment tank. A produced fluid inlet is located on one side below the trapezoidal air flotation separator. An aeration pipe is located at the bottom of the trapezoidal air flotation separator and is connected to a Roots blower. A U-shaped oil-gathering tank is located above the trapezoidal air flotation separator, with the inner wall height lower than the outer wall height. A crude oil discharge pipe is located at the middle of the vertical direction of the outer wall of the U-shaped oil-gathering tank and is connected to a ton container. A drain outlet is also located at the bottom of the trapezoidal air flotation separator, allowing water in the trapezoidal air flotation separator to sink and flow out through the drain outlet into the pretreatment tank.

[0013] Furthermore, a return channel is provided at the bottom of the U-shaped oil collection tank, and the return channel is located at the four corners of the bottom of the U-shaped oil collection tank.

[0014] A filtration method for treating produced oil fluids, using the aforementioned filtration equipment for treating produced oil fluids, includes the following steps: S1: Pre-treat the produced oil fluid to remove some of the oil, resulting in coarse oil-removed wastewater; S2: Mix the coarse oil-removing wastewater with coal-based micro powder adsorbent and hardness-removing agent to obtain mixed wastewater; S3: During the filtration of mixed wastewater, a first pressure difference is formed between the outer and inner surfaces of the flexible filter module. The first pressure difference makes the pressure on the outer surface greater than the pressure on the inner surface. The mixed wastewater passes through the outer surface of the flexible filter module, enters the inner surface, and then flows out. The filtered oil and coal-based micro powder adsorbent agglomerate on the outer surface to form an impurity filter cake. S4: A second pressure difference is formed between the inner and outer surfaces of the flexible filter module by backwashing. The pressure difference makes the pressure on the inner surface greater than that on the outer surface, driving the flexible filter module to expand and deform outward. The surface tension generated by the deformation causes the impurity filter cake to break and peel off.

[0015] Furthermore, the coal-based micro powder in step S2 has a particle size of 20-80 μm and is activated by ultrasonic cavitation during mixing.

[0016] This invention uses coal-based micro-powder as an adsorbent to treat crude oil-containing wastewater. By controlling the pressure difference between the upper and lower chambers, a flexible filter module is used to achieve surface filtration of oilfield produced fluids. This purely physical filtration oil removal technology is being applied for the first time in oilfield produced fluid treatment. It is adaptable to oilfield produced fluids with various complex compositions and can cope with fluctuations in water quality. Simultaneously, controlling the pressure difference between the upper and lower chambers causes the flexible filter membrane to deform, generating surface tension and achieving a backwashing function. The flexible filter membrane is not easily clogged and can be reused repeatedly for extended periods. Furthermore, this invention uses PLC control to coordinate the operation of various actuators, achieving a high degree of automation. This effectively reduces the physical labor intensity of workers, provides a safer and more comfortable working environment, and improves worker productivity and quality of life. This invention also eliminates the need for adding flocculants, precipitants, or other auxiliary agents, effectively reducing operating costs.

[0017] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, and in order to make the above and other objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention are described below. Attached Figure Description

[0018] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings: Figure 1 This is a perspective view of a filtration device for processing oil produced fluid according to the present invention. Figure 2 This is a schematic diagram of the internal structure of a surface filter for processing oil produced fluid according to the present invention; Figure 3 This is a schematic diagram of the structure of a flexible filter module in a filtration device for processing oil produced fluid according to the present invention. Figure 4 This is a schematic diagram of the internal skeleton of a filtration device for processing oil produced fluid according to the present invention. Figure 5 This is a perspective view of a pretreatment device for processing oil produced fluid according to the present invention. Detailed Implementation

[0019] To better understand the purpose, function, and specific design of this invention, a filtration device for processing oil produced fluids according to this invention will be described in further detail below with reference to the accompanying drawings.

[0020] like Figure 1-5As shown, a filtration device for treating oil produced fluid according to the present invention includes a pretreatment device 1, which is connected to a dosing and mixing device 2, which is connected to a surface filter 3. The pretreatment device 1 can perform air flotation separation and coarse oil removal on the oil produced fluid. The wastewater after coarse oil removal enters the dosing and mixing device 2 and is mixed with a coal-based micro-powder adsorbent and a hardness-reducing agent. The mixed wastewater then enters the surface filter 3 for filtration. The surface filter 3 includes a filter housing 31, which includes an upper cavity 32 and a lower cavity 33. The upper cavity 32 and the lower cavity 33 are connected by a flexible filter module 4. The lower cavity 33 is connected to the dosing and mixing device 2. The outer surface of the flexible filter module 4 is connected to the lower cavity 33, and the inner surface of the flexible filter module 4 is connected to the upper cavity 32. After the mixed wastewater in the mixing device 2 enters the lower chamber 33, the pressure in the lower chamber 33 will be greater than the pressure in the upper chamber 32. At this time, the flexible filter module 4 can be recessed inward, and small water molecules can flow through the flexible filter module 4 into the upper chamber 32 to achieve filtration. Impurities such as large oil molecules and mixtures of adsorbent and reagents adhere to the outer surface of the flexible filter module 4. This is the filtration state. When too many impurities adhere to the outer surface of the flexible filter module 4, cleaning water is added to the upper chamber 32 and the pressure in the upper chamber 32 is greater than the pressure in the lower chamber 33 and reaches the preset value of 0.6 MPa. The flexible filter module 4 can deform and expand towards the outer surface, so that the impurities on the outer surface of the flexible filter module 4 are broken and peeled off. The peeled impurity fragments fall below the lower chamber 33 under the action of gravity. This is the backwashing state.

[0021] Specifically, the coal-based micropowder used in this invention is made from coal as raw material and processed into extremely fine nano-carbon powder with a particle size of 20-80 μm. This particle size range is determined based on the balance between adsorption efficiency and solid-liquid separation performance. When the particle size of the coal-based micropowder is controlled within the 20-80 μm range, it can maintain sufficient specific surface area to sustain efficient adsorption kinetics, while ensuring effective retention by the flexible filter module in the filtration state to form a filter cake layer with good air permeability. The coal-based micropowder exhibits a porous structure and high specific surface area. When mixed with wastewater after coarse oil removal, it can be activated by ultrasonic cavitation. This is because the dispersibility of nano-carbon powder in water suspension mixtures is usually poor, and ultrasonic waves can increase the dispersibility of nano-carbon powder. Cavitation is the generation of a large number of nano-vacuum bubbles in the liquid by the ultrasonic transducer. These bubbles burst instantaneously, generating a fundamental wave that activates the activity of the nano-carbon powder, increasing its kinetic energy and momentum, thereby improving its dispersibility in the liquid and enhancing its adsorption of suspended solids, colloids, and oil droplets. The hardness-reducing agent can be any commonly used hardness-reducing agent. In this embodiment, the double alkali method is used, that is, sodium hydroxide and sodium carbonate are used, and the pH value is ensured to be greater than or equal to 10.

[0022] In this embodiment, the filter housing 31 is divided into upper and lower cavities by a separator 5. Multiple flexible filter modules 4 are cylindrical and evenly distributed below the separator 5. Each flexible filter module 4 includes a flexible filter membrane 41 and an inner frame 42. The flexible filter membrane 41 is fitted over the inner frame 42, which supports the flexible filter membrane 41. This ensures that when the pressure in the lower cavity 33 is greater than the pressure in the upper cavity 32, the flexible filter membrane 41 maintains its shape to guarantee its filtration function and prevents excessive deformation and rupture, thus extending its service life. When the pressure in the upper cavity 32 is greater than the pressure in the lower cavity 33 and reaches a preset value of 0.6 MPa, the flexible filter membrane 41 deforms and expands outwards away from the inner frame 42. This deformation and tearing alters the adhesion of impurities to the outer surface of the flexible filter membrane 41, causing the impurities to break and peel off.

[0023] The flexible filter membrane 41 includes an outer filter layer and an inner filter layer. The outer filter layer and the inner filter layer are bonded together and sleeved on the outer side of the inner frame 42, with the outer filter layer positioned on the outermost side and the inner filter layer positioned between the inner frame 42 and the outer filter layer. The outer and inner filter layers can be ultrasonically welded after stacking to ensure a tight bond between them. The outer filter layer prevents crude oil components from passing through while ensuring efficient permeation of water molecules. The inner filter layer has micron-level filtration capability and hydrophilic and oleophobic properties to enhance the antifouling performance of the flexible filter membrane 41.

[0024] In this embodiment, the outer filter layer is an ultra-thin tubular membrane woven from highly cross-linked aromatic polyamide (PA) fibers to ensure its mechanical strength and flexibility. This layer possesses excellent properties such as oleophobicity, hydrophilicity, flexibility, abrasion resistance, high strength, and acid and alkali resistance, effectively preventing crude oil components from passing through while ensuring efficient permeation of water molecules. Furthermore, its ultra-thin design significantly reduces fluid resistance, thereby improving overall filtration efficiency.

[0025] In this embodiment, the inner filtration layer is a polyvinylidene fluoride (PVDF) membrane. PVDF, a pore-forming agent (such as dibutyl phthalate), and a filler (such as SiO2) are dissolved in a solvent (such as a mixture of NMP and acetone, with a volume ratio of 3:7) at a mass ratio of 1:1:3. The mixture is stirred until completely dissolved, and air bubbles are removed to prepare a casting solution. Subsequently, a membrane layer with a thickness of 100-120 μm is coated onto a substrate using a coating machine and then immersed in deionized water to allow it to detach and solidify. Alternatively, a dry-wet spinning process can be used followed by curing to achieve higher porosity and uniformity. This layer has micron-level filtration capability and exhibits hydrophilic and oleophobic properties, further enhancing the antifouling performance of the flexible filter membrane 41. Simultaneously, the PVDF membrane possesses a certain degree of strength and elasticity, maintaining structural stability during long-term use.

[0026] The parameters of the flexible filter membrane in this embodiment are as follows: Pore ​​size and rejection rate: The average pore size is typically in the range of 4.55 nm to 8.48 nm; Water flux: Typically, MBR membrane modules consist of 10 or more membrane layers, and experimental data shows that their average permeate flow rate is 50-100 L / (m³). 2 •h), which also uses PVDF membranes with similar thickness and porosity, but compared to the present invention, the average permeate flow rate of the flexible filter membrane of the present invention is 50-100 L / (m³) compared to that of the MBR membrane. 2 •h) rises to hundreds or even as high as 1550 L / (m 2 •h).

[0027] Mechanical strength: Reinforced by the outer layer of highly cross-linked aromatic polyamide (PA) fiber braided tube, the tensile strength of the PVDF+PA composite flexible filter membrane in this embodiment exceeds 200 N / mm² due to the reinforcement of the surface braided PA material. 2 The tensile strength of conventional PVDF filter membranes is approximately 4.5-6.0 N / mm². 2 .

[0028] It is understood that the outer and inner filter layers can also be made of other materials with similar functions and properties. The specific materials and manufacturing methods can be selected by those skilled in the art according to the actual situation, as long as they can filter and separate water by pressure.

[0029] The inner frame 42 includes a supporting cylinder 421, on which multiple deformation support units 422 are provided. Each deformation support unit 422 has multiple support feet. The support feet support the flexible filter membrane 41, ensuring it maintains its shape and thus its filtration function, and preventing excessive deformation and rupture. A water flow channel is formed between adjacent support feet, allowing water to flow into the upper cavity 32. In this embodiment, the supporting cylinder 421 and the deformation support units 422 can be made of ABS plastic.

[0030] Furthermore, the support legs of the deformation support unit 422 in this embodiment include T-shaped fixed support legs 423 and S-shaped flexible support legs 424. There are three T-shaped fixed support legs 423 and three S-shaped flexible support legs 424, which are arranged alternately on the deformation support unit 422. When the pressure on the outer surface of the flexible filter module 4 is greater than the internal pressure, the S-shaped flexible support legs 424 gradually deform, and the cross-section of the flexible filter module 4 can change from a hexagonal shape to a triangular shape, reducing the cross-sectional area by 50%. When the pressure decreases or even becomes negative, the cross-sectional area recovers. This structure effectively ensures that the flexible filter membrane 41 maintains a certain shape under positive pressure, thereby ensuring the filtration function and preventing the flexible filter membrane 41 from excessively deforming and breaking. It also ensures that the water supply channel inside the flexible filter module 4 is unobstructed, so that water can flow into the upper cavity 32. In addition, during backwashing, the shrunken flexible filter membrane 41 can also ensure that the flexible filter membrane 41 has a certain deformation, leaving room for expansion. Furthermore, the S-shaped flexible support foot 424 can also provide restoring force for the flexible filter membrane 41, thereby effectively ensuring that the impurities on the outer surface of the flexible filter membrane 41 are reduced or even lose their adhesion due to the deformation tension of the flexible filter membrane 41 itself, thus breaking and peeling off from the outer surface of the flexible filter membrane 41.

[0031] Specifically, in the positive pressure filtration stage, the external mixed wastewater pressure is higher than the internal product water pressure. At this time, the T-shaped fixed support foot 423, with its high radial stiffness, provides a stable basic support profile for the flexible filter membrane 41, preventing the membrane from collapsing excessively inward under the positive transmembrane pressure difference and blocking the water flow channel, thus ensuring the stability of the filtration flux. At the same time, the S-shaped flexible support foot 424 is in a pre-tightened energy storage state under positive pressure. Its special geometric configuration allows it to store elastic potential energy without plastic yielding, preparing the mechanical conditions for the reverse deformation in the subsequent step S4. This coordinated control mechanism of rigidity and flexibility ensures the smooth flow of the filtration channel and the safety of the membrane during the filtration stage, avoiding the problem of decreased filtration efficiency due to simply pursuing flexibility.

[0032] When the backwashing process begins, as the internal pressure exceeds the external pressure and reaches a preset threshold, the S-shaped flexible support leg 424 deforms under the influence of the reverse pressure difference and its own elastic restoring force. Since the T-shaped fixed support leg 423 remains relatively stationary, the restoring motion of the S-shaped flexible support leg 424 guides the flexible filter membrane 41 to expand outward along a preset path, causing the cross-sectional shape of the entire flexible filter module 4 to gradually and smoothly transition from an approximate triangle to an approximate hexagon, resulting in a significant increase in the corresponding cross-sectional area. This reversible change in geometry plays a dual crucial role: firstly, the buckling stroke of the S-shaped flexible support leg 424 limits the range of membrane changes, ensuring that the flexible filter membrane 41 remains centered during contraction, limiting the maximum contraction position of the flexible filter membrane 41. Furthermore, in conjunction with the T-shaped fixed support leg 423, it provides a uniform force distribution, preventing misalignment and irregular convergence of the flexible filter membrane 41 after contraction. On the other hand, the elastic recovery force accumulated by the S-shaped structure during deformation provides an active driving force for the membrane to quickly retract to its initial hexagonal cross-section after backwashing, ensuring the cyclicality of the deformation-based peeling mechanism. If this rigid-flexible synergistic control method is not adopted, such as using only flexible supports or completely rigid supports, the membrane will either experience localized bulging during backwashing leading to stress concentration and rupture, or it will be unable to generate sufficient surface tension to effectively peel off the filter cake, making it difficult to achieve long-term stable operation.

[0033] One end of the supporting cylinder 421 is connected to the bottom cover 43, and the other end is connected to the top cover 44. The top cover 44 is connected to the separator 5. In this embodiment, the top cover 44 and the separator 5 are threaded together and sealed with a sealing ring. A water outlet 441 is provided at the center of the top cover 44, allowing water filtered by the flexible filter membrane 41 to enter the upper cavity 32 through the water outlet 441. It is worth noting that the bottom cover 43 and the top cover 44 are sealed and fixedly connected to the flexible filter membrane 41; in this embodiment, this is achieved by potting adhesive.

[0034] like Figure 2As shown, the lower cavity 33 of this embodiment is provided with a sewage inlet 331 and a sludge discharge port 332. The sewage inlet 331 is connected to a sewage lift pump. The sewage lift pump can pump the sewage mixed in the dosing and mixing device 2 into the lower cavity 33 and continuously provide pressure so that the pressure in the lower cavity 33 is greater than the pressure in the upper cavity 32, thereby realizing the function of positive pressure filtration. The sludge discharge port 332 is provided with a valve and is connected to a slurry pump. The slurry pump can discharge the impurities and fragments backwashed from the lower cavity 33. The upper cavity 32 is provided with a connecting port, which is connected to a clean water lift pump and a backwash pump respectively through a tee. The clean water in the upper cavity 32 can be drawn out by the clean water lift pump. During backwashing, the backwash pump can pump the cleaning water into the upper cavity 32 and continuously provide pressure, so that the pressure of the upper cavity 32 is greater than the pressure of the lower cavity 33 up to 0.6 MPa, so that the flexible filter module 4 can deform, thereby realizing the breaking and peeling of impurities on the outer surface of the flexible filter module 4.

[0035] Preferably, pressure sensors are installed in both the upper cavity 32 and the lower cavity 33. The pressure sensors, sewage lift pump, valve of sludge discharge port 332, backwash pump, clean water lift pump, slurry pump, etc. are all connected to the PLC controller. Backwash control is based on pressure difference. When the pressure difference between the lower cavity 33 and the upper cavity 32 increases to a critical value, which is 5.5 MPa in this embodiment (indicating that the filter cake has accumulated to the point where it needs to be cleaned), the PLC controls the backwash process. After backwashing is completed, the permeability recovers and the pressure difference returns to the normal filtration pressure difference range, which is 1.222 MPa to 5.5 MPa in this embodiment. The cycle repeats without manual operation. The switching and operation of the filtration state and backwash state are completed through automated PLC control.

[0036] The reason for using the value of 5.5 MPa is that when the pressure difference between the upper and lower chambers is between 4.722 MPa and 6.222 MPa, the mud cake thickness in this embodiment will reach about 8 mm, and the permeability of the mud cake will be between 5 and 7 mD. Taking a compromise value, with a pressure difference of 5.5 MPa between the upper and lower chambers and a mud cake permeability of 6 mD, flushing begins.

[0037] The filtration principle of this embodiment is as follows: Under normal filtration conditions, the valve of the slag discharge port 332 below the lower chamber 33 is closed, and the sewage lift pump is turned on to pump the sewage mixed with the reagent into the lower chamber 33. After a period of time, the pressure in the lower chamber 33 is greater than the pressure in the upper chamber 32. The flexible filter membrane 41 maintains a certain shape under the support of the internal skeleton. The filtration effect on the surface of the flexible filter membrane 41 forms positive pressure filtration. A seepage pressure gradient is established from the sewage inlet 331 of the lower chamber 33 to the surface of the flexible filter membrane 41, causing the complex mixture (adsorbent and crude oil water) in the chamber to spontaneously flow to the surface of the flexible filter membrane 41 where the pressure is lowest. Small water molecules permeate through the membrane and flow into the upper chamber 32, while the mixture of large oil molecules and adsorbent adheres to the outer surface of the flexible filter membrane 41. Compared with traditional gravity sedimentation, this invention has a smaller footprint.

[0038] It is worth noting that, macroscopically, the flexible filter module 4 combines positive pressure filtration and seepage mechanics, causing suspended matter in the fluid space to actively flow towards the outer surface of the flexible filter membrane 41. The filtration loss of this flexible filter membrane 41 generates a pressure difference, actively drawing adsorbent, oil-agglomerated particles, and a large amount of amorphous suspended matter to the surface of the flexible filter membrane 41, where they deposit as scale. Macroscopic adsorption and aggregation occur within the lower cavity 33, filtering on the flexible filter membrane 41 and forming scale, which is then blocked outside the flexible filter membrane 41. Only this structure can achieve the efficient application of powdered adsorbents.

[0039] The backwashing principle of this embodiment is as follows: During backwashing, the sewage lift pump of the lower chamber 33 is closed, the valve of the sludge discharge port 332 at the bottom of the lower chamber 33 is closed, the backwash pump is opened, and the clean water lift pump is closed. After a period of time, when the pressure of the upper chamber 32 is greater than that of the lower chamber 33 and reaches 0.6 MPa, the flexible filter membrane 41 is induced to deform. The flexible filter membrane 41 expands outward, thereby generating tension on the surface of the flexible filter membrane 41. The filter cake formed by impurity deposition is in contact with the surface of the flexible filter membrane 41, and is affected by the expansion and deformation of the flexible filter membrane 41, reducing or even eliminating the adhesion of the filter cake, thereby causing the hard scale filter cake to break and peel off. The fallen scale fragments are subjected to gravity and fall to the bottom of the lower chamber 33, accumulating near the sludge discharge port 332. Then, the valve of the sludge discharge port 332 at the bottom of the lower chamber 33 is opened and the slurry pump is turned on. The scale fragments are discharged from the lower chamber 33 by the slurry pump and then transported to the solid waste tank. After this step is completed, the filtration state is restored.

[0040] The pretreatment device 1 includes a pretreatment tank 11, with a treatment liquid outlet 18 on one side, which is connected to a chemical mixing device 2. A trapezoidal air flotation separator 12 is located in the middle of the pretreatment tank 11. A produced fluid inlet 13 is located on one side below the trapezoidal air flotation separator 12. An aeration pipe is located at the bottom of the air flotation separator 12 and is connected to a Roots blower. A U-shaped oil-gathering tank 14 is located above the trapezoidal air flotation separator 12. The height of the inner wall of the U-shaped oil-gathering tank 14 is lower than the height of the outer wall. A reflux channel 15 is located at the bottom of the U-shaped oil-gathering tank 14. In this embodiment, the reflux channel 15 is located at the four corners of the bottom of the U-shaped oil-gathering tank 14. A crude oil discharge pipe 16 is located at the middle of the vertical direction of the outer wall of the U-shaped oil-gathering tank 14 and is connected to a ton container 19.

[0041] Produced oil fluid is pumped into the trapezoidal air flotation separator 12 inside the pretreatment tank 11 via the produced fluid lift pump and the produced fluid inlet 13. A Roots blower pumps compressed air into the air flotation separator from the aeration pipe at the bottom of the separator. Air bubbles rise, and suspended oil droplets, under tension, adhere to the bubbles and rise together. Oil and some water flow along the inner edge of the U-shaped oil-gathering tank 14 into the U-shaped oil-gathering tank 14, maintaining the oil level in the U-shaped oil-gathering tank 14 below the height of the outer wall of the tank. After oil-water separation, the water flows back into the trapezoidal tank below through the return channel 15, while the oil enters the ton container 19 for storage via the crude oil discharge pipe 16 of the U-shaped oil-gathering tank 14. A drain outlet 17 is also provided at the bottom of the trapezoidal air flotation separator 12, allowing water in the separator to sink and flow out through the drain outlet 17 into the pretreatment tank 11. The wastewater containing oil obtained in the pretreatment tank 11 is used as treated permeable water and then pumped into the dosing and mixing device 2.

[0042] The method for filtering oil produced fluid of the present invention, using the above-mentioned filtration equipment, includes the following steps: S1: Pre-treat the produced oil fluid to remove some of the oil, resulting in coarse oil-removed wastewater; S2: Mix the coarse oil-removing wastewater with coal-based micro powder adsorbent and hardness-removing agent to obtain mixed wastewater; S3: During the filtration of mixed wastewater, a first pressure difference is formed between the outer surface and the inner surface of the flexible filter module 4. The first pressure difference makes the pressure on the outer surface greater than the pressure on the inner surface. The mixed wastewater flows out after passing through the outer surface of the flexible filter module 4 and entering the inner surface. The filtered oil and coal-based micro powder adsorbent agglomerate on the outer surface to form an impurity filter cake. S4: A second pressure difference is formed between the inner and outer surfaces of the flexible filter module 4 by backwashing. The pressure difference makes the pressure on the inner surface greater than that on the outer surface, driving the flexible filter module 4 to expand and deform outward. The surface tension generated by the deformation causes the impurity filter cake to break and peel off.

[0043] In step S3, the mixed wastewater is pumped into the lower chamber 33 of the surface filter 3. At this time, the pressure in the lower chamber 33 is higher than that in the upper chamber 32, forming a positive transmembrane pressure difference from the outside to the inside. Driven by this pressure difference, water molecules pass through the flexible filter module 4 and enter the upper chamber 32 through the outlet hole 441, while oil, micro-powder adsorbent and other impurities are trapped on the outer surface of the flexible filter module 4 and gradually accumulate to form an impurity filter cake. Since the flexible filter module 4 of the present invention is used, there is no need to worry about clogging of the flexible filter module 4 or a decrease in flux. When the flux decreases, the pressure difference between the upper and lower chambers increases. At this time, a backwashing process can be used immediately to remove scale and instantly restore the filtration flow of the flexible filter module 4. This cycle repeats continuously, and maintaining a high flow of the membrane at all times is the key to the high-speed wastewater treatment of the present invention.

[0044] In step S4, when the filtration reaches the set conditions, the supply of mixed wastewater to the lower chamber 33 is stopped, and instead, cleaning water is pumped into the upper chamber 32. The cleaning water can be the previously filtered clean water, causing the pressure in the upper chamber 32 to rise rapidly and exceed that in the lower chamber 33, forming a reverse transmembrane pressure difference from the inside out. Under this pressure difference, the flexible filter module 4 expands radially outward, increasing the membrane surface area and generating significant mechanical tension. Since the impurity filter cake is a rigid or semi-rigid aggregate, its extensibility is much lower than that of the flexible membrane material, and it cannot elongate synchronously with the membrane. Therefore, it is subjected to strong tensile stress at the interface, causing the internal bonding force of the filter cake to break down, crack, and peel off in pieces from the membrane surface. The peeled fragments settle to the bottom of the lower chamber 33 under gravity and are discharged from the system through the slag discharge port 332. This cleaning mechanism is completely different from the traditional method of relying on reverse water flow shear force to flush. It is an active physical peeling achieved from the level of material mechanical response, which can more thoroughly remove sticky oily filter cake and avoid damage to the membrane caused by high-intensity water flushing.

[0045] This invention uses coal-based micro-powder as an adsorbent to treat crude oil-containing wastewater. By controlling the pressure difference between the upper and lower chambers, a flexible filter module is used to achieve surface filtration of oilfield produced fluids. This purely physical filtration oil removal technology is being applied for the first time in oilfield produced fluid treatment. It is adaptable to oilfield produced fluids with various complex compositions and can cope with fluctuations in water quality. Simultaneously, controlling the pressure difference between the upper and lower chambers causes the flexible filter membrane to deform, generating surface tension and achieving a backwashing function. The flexible filter membrane is not easily clogged and can be reused repeatedly for extended periods. Furthermore, this invention uses PLC control to coordinate the operation of various actuators, achieving a high degree of automation. This effectively reduces the physical labor intensity of workers, provides a safer and more comfortable working environment, and improves worker productivity and quality of life. This invention also eliminates the need for adding flocculants, precipitants, or other auxiliary agents, effectively reducing operating costs.

[0046] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A filtration device for treating produced oil fluid, characterized in that, The system includes a pretreatment device connected to a dosing and mixing device, which in turn is connected to a surface filter. The pretreatment device performs air flotation separation and coarse oil removal on the produced oil. The wastewater after coarse oil removal enters the dosing and mixing device and is mixed with chemicals. The mixed wastewater then enters the surface filter for filtration. The surface filter includes a filter housing, which consists of an upper chamber and a lower chamber. The upper and lower chambers are connected by a flexible filter module. The lower chamber is connected to the dosing and mixing device. The outer surface of the flexible filter module is connected to the lower chamber, and the inner surface of the flexible filter module is connected to the upper chamber. The flexible filtration module includes a flexible filtration membrane and an inner skeleton. The flexible filtration membrane is fitted over the inner skeleton and includes an outer filtration layer and an inner filtration layer. The outer filtration layer is an ultra-thin tubular membrane woven from highly cross-linked aromatic polyamide fibers, and the inner filtration layer is a polyvinylidene fluoride membrane layer. The inner skeleton includes a supporting cylinder with multiple deformable support units on it. Each deformable support unit has multiple support feet, and a water flow channel is formed between adjacent support feet to allow water to flow into the upper cavity. The support feet of the deformable support units include T-shaped fixed support feet and S-shaped flexible support feet, with three of each type, arranged alternately on the deformable support units. The support feet support the flexible filtration membrane. After the mixed wastewater enters the lower cavity in the dosing and mixing device, the pressure in the lower cavity is greater than that in the upper cavity. At this time, the flexible filtration module can be recessed inward, and water can flow through the flexible filtration module into the upper cavity to achieve filtration. Impurities adhere to the outer surface of the flexible filtration module. When too many impurities adhere to the outer surface of the flexible filter module, when cleaning water is added to the upper cavity and the pressure in the upper cavity is greater than that in the lower cavity and reaches a preset value, the flexible filter module can deform and expand towards the outer surface, so that the impurities on the outer surface of the flexible filter module can be broken and peeled off.

2. The filtration device for treating produced oil fluid as described in claim 1, characterized in that, The filter housing is divided into upper and lower chambers by a separator. The flexible filter module is cylindrical and there are multiple flexible filter modules, which are evenly distributed below the separator. One end of the supporting cylinder is connected to the bottom cover, and the other end of the supporting cylinder is connected to the top cover. The top cover is connected to the separator, and a water outlet is provided at the center of the top cover. The water filtered by the flexible filter membrane can enter the upper chamber through the water outlet.

3. The filtration device for treating produced oil fluid as described in claim 1, characterized in that, The lower chamber is equipped with a sewage inlet and a slag discharge outlet. The sewage inlet is connected to a sewage lift pump, which can pump the mixed sewage from the dosing and mixing device into the lower chamber and continuously provide pressure. The slag discharge outlet is equipped with a valve and is connected to a slurry pump, which can discharge the impurities and fragments backwashed from the lower chamber.

4. The filtration device for treating produced oil fluid as described in claim 3, characterized in that, The upper cavity is equipped with a connecting port, which is connected to the clean water lift pump and the backwash pump respectively via a tee. The clean water in the upper cavity can be drawn out by the clean water lift pump; during backwashing, the backwash pump can pump the cleaning water into the upper cavity and continuously provide pressure.

5. The filtration device for treating produced oil fluid as described in claim 4, characterized in that, Pressure sensors are installed in both the upper and lower cavities. The pressure sensors, sewage lift pump, slag discharge valve, backwash pump, clean water lift pump, and slurry pump are all connected to the PLC controller. The PLC controller switches between filtration and backwashing states based on the pressure difference.

6. The filtration device for treating produced oil fluid as described in claim 1, characterized in that, The pretreatment unit includes a pretreatment tank with a treatment liquid outlet on one side, which is connected to a chemical mixing device. Inside the pretreatment tank, a trapezoidal air flotation separator is located in the middle. A produced fluid inlet is located on one side of the lower part of the trapezoidal air flotation separator. An aeration pipe is located at the bottom of the trapezoidal air flotation separator and is connected to a Roots blower. A U-shaped oil-gathering tank is located above the trapezoidal air flotation separator, with the inner wall height lower than the outer wall height. A crude oil discharge pipe is located at the middle of the vertical direction of the outer wall of the U-shaped oil-gathering tank and is connected to a ton container. A drain outlet is also located at the bottom of the trapezoidal air flotation separator, allowing water in the tank to sink and flow out through the drain outlet into the pretreatment tank.

7. The filtration device for treating produced oil fluid as described in claim 6, characterized in that, The bottom of the U-shaped oil collection tank is equipped with a return channel, which is located at the four corners of the bottom of the U-shaped oil collection tank.

8. A filtration method for treating produced oil fluid, employing the filtration equipment for treating produced oil fluid as described in any one of claims 1-7, characterized in that, Includes the following steps: S1: Pre-treat the produced oil fluid to remove some of the oil, resulting in coarse oil-removed wastewater; S2: Mix the coarse oil-removing wastewater with coal-based micro powder adsorbent and hardness-removing agent to obtain mixed wastewater; S3: During the filtration of mixed wastewater, a first pressure difference is formed between the outer and inner surfaces of the flexible filter module. The first pressure difference makes the pressure on the outer surface greater than the pressure on the inner surface. The mixed wastewater passes through the outer surface of the flexible filter module, enters the inner surface, and then flows out. The filtered oil and coal-based micro powder adsorbent agglomerate on the outer surface to form an impurity filter cake. S4: A second pressure difference is formed between the inner and outer surfaces of the flexible filter module by backwashing. The pressure difference makes the pressure on the inner surface greater than that on the outer surface, driving the flexible filter module to expand and deform outward. The surface tension generated by the deformation causes the impurity filter cake to break and peel off.

9. The filtration method for treating produced oil fluid as described in claim 8, characterized in that, The coal-based micro powder in step S2 has a particle size of 20-80 μm and is activated by ultrasonic cavitation during mixing.

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