High-efficiency oilfield produced water oil removal and sedimentation integrated system and method without using reagent

Abstract

The application discloses a high-efficiency oilfield produced water deoiling and sedimentation integrated system and method, and relates to the oilfield produced water treatment technical field.The system comprises a four-stage filtration system formed by a hydrocyclone oil-water separator, a flotation settler, a pulse biological filter and an electrostatic demulsification and deoiling filter which are connected in sequence; a screw pump is used for pumping sewage in a sewage pool into the hydrocyclone oil-water separator for primary oil-water separation; the flotation settler comprises a dissolved air system which is used for generating dissolved air water and feeding the dissolved air water into the flotation settler for secondary oil-water separation; a water outlet end of the flotation settler is connected to an intermediate pool, a booster pump is used for pumping deoiled sewage in the intermediate pool into the pulse biological filter and the electrostatic demulsification and deoiling filter for fine filtration.

Description

Technical Field

[0001] This invention belongs to the field of industrial wastewater treatment technology, and in particular relates to a high-efficiency integrated system and method for chemical-free oil removal and sedimentation of produced water from oil fields. Background Technology

[0002] Produced water is an industrial wastewater generated during crude oil extraction, characterized by high oil content, high suspended solids content, and complex composition. As oilfield development enters its mid-to-late stages, the water content of produced fluids continues to rise. Coupled with increasingly stringent environmental regulations on the quality standards of reinjection water and external drainage water, efficient, stable, and low-cost oilfield produced water treatment technologies have become a key link in ensuring the sustainable development of oilfields.

[0003] Currently, oilfield produced water treatment processes both domestically and internationally are mainly classified into three categories: physical methods, chemical methods, and biological methods. Physical methods include gravity oil separation, cyclone separation, flotation, and filtration; chemical methods include chemical demulsification, flocculation sedimentation, and oxidative degradation; and biological methods include activated sludge processes and aerated biological filters. In practical engineering applications, a three-stage combined process of "oil separation-flotation-filtration" is typically used.

[0004] However, existing oilfield produced water treatment processes generally have the following shortcomings in actual operation: (1) Strong dependence on chemical agents: Existing air flotation and coagulation sedimentation units usually require continuous addition of chemical agents such as demulsifiers and flocculants, which not only has high operating costs, but also causes secondary pollution due to agent residues, which is not conducive to subsequent reinjection or discharge.

[0005] (2) The process is lengthy and the area occupied is large: Traditional multi-stage treatment processes require separate oil separators, coagulation reaction tanks, flotation tanks, sedimentation tanks, multi-stage filter tanks and other facilities. Each unit is scattered and the pipelines are complex. The infrastructure investment and land area are both large, which is not suitable for well sites or offshore platforms with limited space.

[0006] (3) Low efficiency of dissolved air flotation system: Traditional dissolved air flotation devices mostly adopt conventional pressurized dissolved air flotation method, which releases bubbles by depressurizing through a release device. The bubble particle size distribution generated by this method is relatively wide, with large bubbles rising and dissipating quickly, resulting in limited capture efficiency of fine oil droplets. The dissolved air tank is mostly a static packing structure, and gas-liquid mixing depends on the packing surface. The shear force is insufficient, making it difficult to generate a large number of submicron-sized high-concentration bubbles, which limits the further improvement of oil removal efficiency. Some dissolved air flotation devices also have problems such as gas-liquid short-flow and uneven air intake.

[0007] (4) Filter units are prone to clogging and require frequent backwashing: Filter units often use filter media such as quartz sand and walnut shells. When the oil removal efficiency at the front end of the system is unstable, a large amount of oil and suspended solids enter the filter, causing the filter media surface to clump and the pressure difference to rise rapidly. Existing backwash triggers are mostly based on time or a single pressure difference threshold, and do not have the ability to respond in advance and adapt to water quality fluctuations, which easily leads to a decrease in filtration efficiency or frequent ineffective backwashing.

[0008] (5) Insufficient resistance to shock loads: When the oil content or suspended solids concentration in the upstream water suddenly increases, the units of the traditional process cannot respond in a coordinated manner and can only passively withstand the impact, which can easily lead to the effluent water quality failing to meet the standards.

[0009] The aforementioned problems mean that traditional oilfield produced water treatment processes have room for improvement in terms of operational economy, ease of operation and maintenance, land area, and stability of water quality compliance. Therefore, there is an urgent need to develop an integrated oilfield produced water treatment system and control method that is compact, requires no additives, has high dissolved air efficiency, strong shock resistance, and possesses intelligent linkage and control capabilities. Summary of the Invention This invention provides a high-efficiency integrated system and method for oilfield produced water oil removal and sedimentation without the need for chemical additives, which has the advantages of compact process, no chemical additives, high dissolved air efficiency and strong impact resistance.

[0010] Other objects and advantages of the present invention can be further understood from the technical features disclosed herein.

[0011] To achieve one, some, or all of the above objectives or other objectives, the present invention provides a high-efficiency integrated system for chemical-free oil removal and sedimentation of produced water in oilfields. This system comprises a four-stage filtration system consisting of a cyclone oil-water separator, a flotation sedimentation machine, a pulse biological filter, and an electrostatic demulsification oil removal filter connected in sequence. A screw pump draws wastewater from a wastewater tank and pumps it into the cyclone oil-water separator for primary oil-water separation. The flotation sedimentation machine includes a dissolved air system for generating dissolved air water, which is then fed into the flotation sedimentation machine for secondary oil-water separation. The outlet of the flotation sedimentation machine is connected to an intermediate water tank, and a lift pump draws oil-removed wastewater from the intermediate water tank and pumps it into the pulse biological filter and the electrostatic demulsification oil removal filter for fine filtration.

[0012] The dissolved gas system includes a nitrogen generating device consisting of an air compressor and a nitrogen generator, and the generated nitrogen is sent into a storage tank for storage. The dissolved gas reflux pump draws oil-removed wastewater from the intermediate water tank and sends it together with the gas stored in the storage tank into the dissolved gas tank for mixing to generate dissolved gas water. The generated dissolved gas water is sent into the flotation sedimentation machine.

[0013] A water-air mixing device is also provided between the dissolved gas reflux pump and the dissolved gas tank. The water-air mixing device includes a venturi tube, which includes a constriction, a throat, and an expansion section. The throat is provided with a water inlet pipe, a check valve, and an air jet, wherein the air jet is opened at an angle. The oil-removed wastewater pumped in by the dissolved gas reflux pump enters the venturi tube through the opening of the constriction.

[0014] The constriction is provided with a baffle, which is a frustum-shaped baffle with a diameter that gradually increases toward the inside of the constriction. The oil-removed wastewater pumped in by the dissolved gas reflux pump flows toward the inner wall of the constriction through the gap between the constriction and the baffle.

[0015] The constricted neck opening is provided with a slope, which is parallel to the side of the frustum block.

[0016] The dissolved air tank includes a settling zone at the bottom, a water-air shear zone at the top, and an inlet pipe. The water-air mixture output by the water-air mixing device enters the water-air shear zone through the inlet pipe. The water-air shear zone includes a guide column and a guide cylinder arranged coaxially. The guide column is disposed inside the guide cylinder, and continuous spiral blades are disposed in the gap between the guide column and the guide cylinder. The spiral blades extend from the bottom to the top of the guide column and the guide cylinder. A nozzle is obliquely disposed at the end of the inlet pipe, and the nozzle is disposed in the direction of extension of the spiral blades. The spiral blades are fixedly connected to the inner wall of the guide cylinder. The outer wall of the guide cylinder is in contact with the inner wall of the dissolved air tank. A sloping guide surface is disposed at the top of the guide cylinder, and the bottom of the sloping guide surface is close to the outlet of the dissolved air tank.

[0017] The top of the dissolved gas tank is equipped with a conical baffle.

[0018] The pulse biofilter and the electrostatic demulsification and oil removal filter are also equipped with a backwashing system, which includes a backwashing pipeline and a backwashing fan. One end of the backwashing pipeline is connected to the booster pump, and the other end is connected to the backwashing fan. When the backwashing step is initiated by controlling the valve body, the valves of the inlet pipelines of the pulse biofilter and the electrostatic demulsification and oil removal filter are closed, and the valves of the backwashing pipeline are opened to perform the backwashing operation.

[0019] Another technical solution of the present invention provides a control method for a high-efficiency integrated system for chemical-free oil removal and sedimentation of produced water in oilfields. Based on the high-efficiency integrated system for chemical-free oil removal and sedimentation of produced water in oilfields described above, the control method includes the following steps: Step S1, Feed control: Start the screw pump to stably transport the produced water in the wastewater tank to the hydrocyclone oil-water separator, and control the feed flow rate and pressure value; Step S2, Primary hydrocyclone separation: In the hydrocyclone oil-water separator, the produced water is separated from the floating oil and large particulate suspended matter by centrifugal force. The floating oil rises and is collected, while the settled large particulate impurities are discharged from the bottom; Step S3, Secondary dissolved air flotation: The dissolved air return pump draws the oil-removed wastewater from the intermediate water tank, mixes it with nitrogen transported from the gas storage tank in a water-air mixing device, and then sends it into the dissolved air tank. The process involves high-speed shear mixing to generate dissolved air water containing micro- and nano-sized bubbles. Inside the dissolved air tank, the water-air mixture rises at high speed along the spiral channel formed by the spiral blades between the guide column and the guide cylinder. Centrifugal shear force refines the bubbles, forming high-concentration dissolved air water. The generated dissolved air water is then sent to a flotation sedimentation machine, where the bubbles attach to fine oil droplets and suspended solids in the water and float to the surface, completing the secondary oil removal process. Step S4, fine filtration: The lift pump sequentially pumps the secondary-treated oil-removed wastewater from the intermediate water tank into a pulse biological filter and an electrostatic demulsification oil removal filter to remove residual fine suspended solids and trace amounts of oil in the water. Step S5, intelligent backwash control: The operating status parameters of the pulse biological filter and the electrostatic demulsification oil removal filter are monitored. When the preset backwash trigger conditions are met, the backwash program is automatically started.

[0020] The backwash triggering conditions in step S5 include: monitoring the inlet and outlet pressure difference of the pulse biofilter and / or the electrostatic demulsification and oil removal filter; automatically triggering the backwashing procedure when the pressure difference exceeds a preset first threshold; or, triggering the backwashing procedure periodically according to a preset time cycle; the control method further includes shortening the backwash triggering cycle, setting a reference backwashing cycle T0, and acquiring the oil content value C1 detected by the online monitoring sensor in real time; comparing the reference oil content C0 with C1, and calculating the adjusted backwashing cycle T according to the following formula. new : K is the pollution intensity coefficient, with a value ranging from 0.5 to 0.8. When the calculated T new If the remaining time is less than the currently set backwash cycle, a backwash procedure will be triggered immediately.

[0021] Compared with existing technologies, the beneficial effects of this invention mainly include: 1. This invention adopts a four-stage all-physical treatment process of "cyclone oil-water separation - dissolved air flotation - pulse biological filtration - electrostatic demulsification filtration", without adding any chemical agents such as demulsifiers and flocculants throughout the entire process. On the one hand, this avoids secondary pollution caused by chemical residues from the root, making the effluent quality more conducive to subsequent reinjection or compliant discharge; on the other hand, it completely eliminates the supporting links such as reagent procurement, storage, transportation, addition and metering, significantly reducing the complexity of operation and management and long-term reagent costs. 2. The dissolved air system of this invention adds a water-air mixing device before the dissolved air tank and introduces nitrogen tangentially at the throat, realizing preliminary high-speed shear mixing of gas and liquid. At the same time, a guide tube with continuous spiral blades is set inside the dissolved air tank. The water-air mixture rises at high speed along the spiral channel, and the powerful and stable centrifugal shear force repeatedly tears and cuts the bubbles, which can generate micro-nano-scale dissolved air water with smaller particle size and higher concentration. The dissolved air water is sent into the flotation settling machine and suddenly depressurized. The dense microbubbles that are released greatly increase the probability of capturing small emulsified oil droplets and suspended particles in the water, which fundamentally improves the efficiency of secondary oil removal.

[0022] To make the above and other objects, features and advantages of the present invention more apparent and understandable, preferred embodiments are described below in detail with reference to the accompanying drawings. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the specific embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 This is a schematic diagram of a high-efficiency integrated system for oilfield produced water removal and sedimentation without the use of chemicals, according to the present invention.

[0025] Figure 2 This is a schematic diagram of the water-air mixing device of the present invention.

[0026] Figure 3 This is a schematic diagram of the dissolved gas tank of the present invention.

[0027] Figure 4 This is a schematic diagram of the backwashing system of the present invention.

[0028] In the diagram: 1. Wastewater tank; 2. Screw pump; 3. Air compressor; 4. Nitrogen generator; 5. Gas storage tank; 6. Backwash fan; 7. Cyclone oil-water separator; 8. Automatic drain valve for the fan; 9. Flotation settling machine; 9-1. Sludge scraping mechanism; 9-2. Sludge discharge port; 10. Intermediate water tank; 11. Dissolved air reflux pump; 12. Water-air mixing device; 12-1. Opening; 12-2. Slope; 12-3. Baffle; 12-4. Outlet; 12-5. Check valve; 12-6. Air jet port; 12-7. Inlet pipe; 13. Dissolved air tank; 13- 1. Settling zone; 13-2. Guide column; 13-3. Guide tube; 13-4. Spiral blade; 13-5. Guide surface; 13-6. Conical baffle; 13-7. Inlet pipe; 13-8. Nozzle; 13-9. Outlet; 14. Pulse biological filter; 15. Electrostatic demulsification and oil removal filter; 16. Booster pump; 17. Vent line; 18. Slag discharge line; 19. Inlet water line; 19-1. Inlet water valve; 20. Backwash line; 20-1. Backwash valve; 21. Fan line; 21-1. Fan valve. Detailed Implementation

[0029] The foregoing and other technical contents, features, and effects of the present invention will be clearly presented in the following detailed description of a preferred embodiment with reference to the accompanying drawings. The directional terms mentioned in the following embodiments, such as up, down, left, right, front, or back, are merely for reference to the accompanying drawings. Therefore, the directional terms used are for illustrative purposes and not for limiting the present invention.

[0030] Example 1 Example 1 provides a high-efficiency integrated system for chemical-free oil removal and sedimentation of produced water in oilfields. It includes a four-stage filtration system consisting of a cyclone oil-water separator 7, a flotation sedimentation machine 9, a pulse biological filter 14, and an electrostatic demulsification oil removal filter 15 connected in sequence. A screw pump 2 draws wastewater from a wastewater tank 1 and pumps it into the cyclone oil-water separator 7 for primary oil-water separation. The flotation sedimentation machine 9 includes a dissolved air system for generating dissolved air water, which is then fed into the flotation sedimentation machine 9 for secondary oil-water separation. The outlet of the flotation sedimentation machine 9 is connected to an intermediate water tank 10. A lift pump 16 draws oil-removed wastewater from the intermediate water tank 10 and pumps it into the pulse biological filter 14 and the electrostatic demulsification oil removal filter 15 for fine filtration.

[0031] This invention employs a four-stage, all-physical treatment process: cyclone oil-water separation, dissolved air flotation, pulsed biological filtration, and electrostatic demulsification filtration. The entire process requires no addition of demulsifiers, flocculants, or any other chemical agents. This eliminates secondary pollution caused by chemical residues, making the effluent quality more suitable for subsequent reinjection or compliant discharge. Furthermore, it completely eliminates the need for reagent procurement, storage, transportation, dosing, and metering, significantly reducing the complexity of operation and management and long-term reagent costs.

[0032] The following text, in conjunction with the appendix Figure 1-4 A detailed explanation is provided for the high-efficiency integrated system for oilfield produced water removal and sedimentation without chemical additives, as described in Example 1.

[0033] like Figure 1 As shown in Example 1, a high-efficiency integrated system for oilfield produced water removal and sedimentation without chemical agents includes a four-stage treatment device consisting of "cyclone oil-water separation, dissolved air flotation, pulse biological filtration, and electrostatic demulsification filtration".

[0034] Screw pump 2 draws produced water from the wastewater tank 1 and pumps it into a cyclone oil-water separator 7. The cyclone oil-water separator 7 typically includes a cyclone section, a conical separation section, an underflow section, an overflow assembly, and a top oil collection chamber. The cyclone oil-water separator 7 is a conventional solution in the prior art and is not the inventive point of this application; therefore, it will not be described in detail here.

[0035] The cyclone oil-water separator 7 is used for primary oil removal treatment of produced water from oil fields. After primary oil removal, the wastewater enters the flotation sedimentation unit 9. Figure 1 As shown, the flotation settling machine 9 contains a scraping mechanism 9-1, which scrapes the floating oil and particulate contaminants to the slag discharge port 9-2 and discharges them through the slag discharge pipeline 18. The flotation settling machine 9 performs secondary oil removal treatment, and the discharged oil-removed wastewater enters the intermediate water tank 10. After primary and secondary oil removal treatment, the oilfield produced water has been cleaned of most of the particulate contaminants and oil.

[0036] The core component of the flotation sedimentation unit 9 is the dissolved gas system. In Example 1, the dissolved gas system includes a nitrogen generator 4, a dissolved gas reflux pump 11, and a dissolved gas tank 13. The nitrogen generator 4 includes an air compressor 3, a nitrogen generator 4, and a gas storage tank 5. The high-pressure gas generated by the air compressor 3 is processed by the nitrogen generator 4 to generate nitrogen gas, which enters the gas storage tank 5 for pressurization to form high-pressure nitrogen gas. The dissolved gas reflux pump 11 extracts oil-removed wastewater from the intermediate water tank 10 (when the system starts working, clean water is pumped into the intermediate water tank 10). The oil-removed wastewater and high-pressure nitrogen gas enter the dissolved gas tank 13 to generate dissolved gas water.

[0037] As an optional implementation, the dissolved air water formed by mixing the oil-removed wastewater pumped directly by the dissolved air reflux pump 11 with high-pressure nitrogen contains many large bubbles. These large bubbles may defoam before entering the flotation settling machine 9, reducing the working efficiency of the flotation settling machine 9. To generate more small bubbles, Embodiment 1 provides a mechanism including a water-air mixing device 12 that mixes the oil-removed wastewater pumped by the dissolved air reflux pump 11 with high-pressure nitrogen. The water-air mixture mixed by the water-air mixing device 12 enters the dissolved air tank 13. The dissolved air tank 13 is equipped with spiral blades 13-4. The water-air mixture rises at high speed along the spiral channel, and the bubbles are repeatedly torn and cut by the strong and stable centrifugal shear force, which can generate micro-nano-scale dissolved air water with smaller particle size and higher concentration. This dissolved air water is sent into the flotation settling machine 9 for sudden depressurization. The dense microbubbles that precipitate have a significantly increased probability of capturing small emulsified oil droplets and suspended particles in the water, fundamentally improving the secondary oil removal efficiency.

[0038] like Figure 2 As shown, the water-air mixing device 12 includes a venturi tube, which comprises a constricted neck, a throat, and an expanding section. The throat is equipped with a water inlet pipe 12-7, a check valve 12-5, and a jet nozzle 12-6, wherein the jet nozzle 12-6 is angled. The degreased wastewater pumped in by the dissolved air reflux pump 11 enters the venturi tube through the opening 12-1 of the constricted neck. Due to the structure of the venturi tube, a high-pressure negative airflow is formed between the throat and the expanding section, which pressurizes the degreased wastewater flowing along the inner wall and the tangentially entering high-pressure nitrogen gas to form a high-speed water-air fluid, which flows out of the venturi tube from the outlet 12-4 and then enters the dissolved air tank 13.

[0039] To improve the high-speed mixing effect of water and air, the pumped oil-removing wastewater should flow along the inner wall of the venturi tube as much as possible. For this purpose, in Embodiment 1, a baffle 12-3 is provided at the opening 12-1 of the venturi tube. The baffle 12-3 is a frustum baffle 12-3, and its diameter gradually increases as it extends toward the inside of the constriction. The oil-removing wastewater pumped in by the dissolved air reflux pump 11 flows toward the inner wall of the constriction through the gap between the constriction and the baffle 12-3. A slope 12-2 is provided at the opening 12-1 of the constriction. The slope 12-2 is parallel to the side of the frustum baffle 12-3, which restricts the flow of the oil-removing wastewater along the gap between the slope 12-2 and the frustum baffle 12-3.

[0040] like Figure 3As shown, the dissolved air tank 13 includes a bottom settling zone 13-1, an upper water-air shear zone, and an inlet pipe 13-7; the water-air mixture output from the water-air mixing device 12 enters the water-air shear zone through the inlet pipe 13-7; wherein the inlet pipe 13-7 is arranged in the bottom settling zone 13-1, and the nozzle connected to the inlet pipe 13-7 is arranged in the water-air shear zone. The water-air shearing zone includes a coaxially arranged guide column 13-2 and a guide cylinder 13-3. The guide column 13-2 is located inside the guide cylinder 13-3, and the top of the guide cylinder 13-3 is an open structure to facilitate the discharge of the treated water-air mixture. A continuous spiral blade 13-4 is arranged in the gap between the guide column 13-2 and the guide cylinder 13-3. The spiral blade 13-4 is fixedly connected to the inner wall of the guide cylinder 13-3, and the outer wall of the guide cylinder 13-3 is in contact with the inner wall of the dissolved air tank 13. The spiral blade 13-4 extends from the bottom to the top of the guide column 13-2 and the guide cylinder 13-3. The nozzle 13-8 is positioned facing the extension direction of the spiral blade 13-4 to ensure that the ejected high-pressure water-air mixture flows in the direction of the spiral blade 13-4. As the high-pressure water-air mixture rises along the spiral blade 13-4, the powerful and stable centrifugal shear force repeatedly tears and cuts the bubbles, generating micro-nano-scale dissolved air water with smaller particle size and higher concentration. The dissolved air water is sent into the flotation settling machine 9 and suddenly depressurized. The dense microbubbles that are released greatly increase the probability of capturing small emulsified oil droplets and suspended particles in the water, which fundamentally improves the secondary oil removal efficiency.

[0041] Furthermore, a sloping guide surface 13-5 is provided at the top of the guide tube 13-3, and the bottom of the sloping guide surface 13-5 is close to the outlet 13-9 of the dissolved air tank 13. The guide slope surface 12-2 is used to assist in the discharge of the water-air mixture after shearing treatment.

[0042] As an optional implementation, the guide tube 13-3 can be set to have a diameter larger than that at the bottom, which can reduce the flow velocity of the high-speed water-air mixture. On the one hand, this facilitates the discharge of the water-air mixture through the outlet 13-9, and on the other hand, reducing the flow velocity can reduce the pressure, which is convenient for subsequent release in the flotation sedimentation machine 9.

[0043] As an optional implementation, a conical baffle 13-6 is provided on the top of the dissolved air tank 13. The conical baffle 13-6 is provided to restrict the flow direction of the water-air mixture and facilitate the discharge of the water-air mixture. On the other hand, the water-air mixture with large bubbles can be eliminated after contacting the conical baffle 13-6, thereby improving the quality of the water-air mixture.

[0044] Pulse biological filtration and electrostatic demulsification filtration are carried out in the pulse biological filter 14 and the electrostatic demulsification oil removal filter 15, respectively. These processes serve as fine filtration to remove minute particles and residual small-molecule oil from the oil-removed wastewater after secondary oil removal treatment. In this application's system, a booster pump 16 extracts oil-removed wastewater from the intermediate water tank 10 and sequentially pumps it into the pulse biological filter 14 and the electrostatic demulsification oil removal filter 15 for fine filtration.

[0045] As an optional implementation, the pulse biofilter 14 and the electrostatic demulsification and oil removal filter 15 are also equipped with a backwashing system, such as... Figure 4 As shown, the backwashing system includes a backwashing pipeline 20 and a backwashing fan 6. One end of the backwashing pipeline 20 is connected to the booster pump 16, and the other end is connected to the backwashing fan 6. When the backwashing step is initiated by controlling the valve body, the inlet valve 19-1 of the inlet pipeline 19 of the pulse biological filter 14 and the electrostatic demulsification and oil removal filter 15 is closed, and the backwashing valve 20-1 of the backwashing pipeline 20 is opened to perform the backwashing operation. The high-pressure gas generated by the backwashing fan 6 enters the backwashing pipeline 20 through the fan pipeline 21. A fan valve 21-1 is provided at the connection between the backwashing pipeline 20 and the fan pipeline 21. The fan valve 21-1 is opened during the backwashing operation.

[0046] The entire system is also equipped with an venting pipeline 17, which is connected to the flotation sedimentation machine 9, the intermediate water tank 10, the pulse biological filter 14, and the electrostatic demulsification and oil removal filter 15, for venting the wastewater to be treated in the above devices (the venting operation is performed according to the liquid conditions in each device, such as water level or pressure).

[0047] Example 2 Example 2 provides a control method for a high-efficiency integrated system for chemical-free oil removal and sedimentation of produced water in oilfields. This control method is based on the high-efficiency integrated system for chemical-free oil removal and sedimentation of produced water in oilfields described in Example 1, and includes the following steps: Step S1, Feed Control: Start the screw pump to stably transport the oilfield produced water in the sewage tank to the cyclone oil-water separator, and control the feed flow rate and pressure value; Step S2, First-stage cyclone separation: In the hydrocyclone oil-water separator, the floating oil and large particulate matter are separated from the produced water by centrifugal force. The floating oil rises and is collected, while the settled large particulate impurities are discharged from the bottom. Step S3, Secondary Dissolved Air Flotation: The dissolved gas reflux pump draws oil-removed wastewater from the intermediate water tank, mixes it with nitrogen gas delivered from the gas storage tank in the water-gas mixing device, and then sends it into the dissolved gas tank for high-speed shear mixing to generate dissolved gas water containing micro-nano-scale bubbles. Inside the dissolved air tank, the water-air mixture rises at high speed along the spiral channel formed by the spiral blades between the guide column and the guide cylinder, and the bubbles are refined by centrifugal shearing force to form high-concentration dissolved air water. The generated dissolved air water is sent into a flotation sedimentation machine. The air bubbles attach to the fine oil droplets and suspended solids in the water and float to the surface, completing the secondary oil removal process. Step S4, fine filtration: The booster pump sequentially pumps the oil-removed wastewater from the intermediate water tank, after secondary treatment, into the pulse biological filter and the electrostatic demulsification oil removal filter to remove residual fine suspended solids and trace amounts of oil in the water. Step S5, Intelligent Backwash Control: Monitor the operating status parameters of the pulse biofilter and the electrostatic demulsification and oil removal filter, and automatically start the backwash program when the preset backwash trigger conditions are met.

[0048] As an optional implementation, the backwash triggering condition in step S5 includes: Monitor the inlet and outlet pressure difference of the pulse biofilter and / or electrostatic demulsification and oil removal filter, and automatically trigger the backwashing program when the pressure difference exceeds a preset first threshold; or, trigger the backwashing program periodically according to a preset time cycle. The control method also includes shortening the backwash trigger cycle, setting a reference backwash cycle T0, and acquiring the oil content value C1 detected by the online monitoring sensor in real time; comparing the reference oil content C0 with C1, and calculating the adjusted backwash cycle T according to the following formula. new : K is the pollution intensity coefficient, with a value ranging from 0.5 to 0.8. When the calculated T new When the remaining time of the backwash cycle is less than the currently set time, a backwash procedure is immediately triggered. This shortens the backwash cycle, which can improve the efficiency of sewage treatment and avoid inefficient treatment when the system is clogged.

[0049] The above provides a detailed description of a high-efficiency integrated system and method for chemical-free oil removal and sedimentation of produced water in oilfields, as provided by this invention. Specific examples have been used to illustrate the structure and working principle of this invention. The descriptions of the embodiments above are merely for the purpose of helping to understand the method and core ideas of this invention. It should be noted that those skilled in the art can make various improvements and modifications to this invention without departing from its principles, and these improvements and modifications also fall within the scope of protection of the claims of this invention.

Claims

1. A high-efficiency integrated system for chemical-free oil removal and sedimentation of produced water from oilfields, characterized in that, It includes a four-stage filtration system consisting of a cyclone oil-water separator, a flotation sedimentation machine, a pulse biological filter, and an electrostatic demulsification and oil removal filter connected in sequence; A screw pump draws sewage from the sewage tank and pumps it into the cyclone oil-water separator for primary oil-water separation. The flotation settling machine includes a dissolved air system, which generates dissolved air water and sends it into the flotation settling machine for secondary oil-water separation. The outlet of the flotation sedimentation machine is connected to the intermediate water tank. The lift pump extracts the oil-removed wastewater from the intermediate water tank and pumps it into the pulse biological filter and the electrostatic demulsification oil removal filter for fine filtration.

2. The high-efficiency integrated system for chemical-free oil removal and sedimentation of produced water in oilfields according to claim 1, characterized in that, The dissolved gas system includes a nitrogen generating device consisting of an air compressor and a nitrogen generator, and the generated nitrogen is sent into a storage tank for storage. The dissolved gas reflux pump draws oil-removed wastewater from the intermediate water tank and sends it together with the gas stored in the gas storage tank into the dissolved gas tank for mixing to generate dissolved gas water. The generated dissolved air water is fed into the flotation sedimentation machine.

3. The high-efficiency integrated system for chemical-free oil removal and sedimentation of produced water in oilfields according to claim 2, characterized in that, A water-gas mixing device is also provided between the dissolved gas reflux pump and the dissolved gas tank. The water-gas mixing device includes a Venturi tube, which includes a constricted neck, a throat, and an expanded portion. The throat is provided with a water inlet pipe, a check valve, and a jet nozzle, wherein the jet nozzle is opened at an angle; The oil-removed wastewater pumped in by the dissolved gas reflux pump enters the Venturi tube through the opening in the constricted neck.

4. The high-efficiency integrated system for chemical-free oil removal and sedimentation of produced water in oilfields according to claim 3, characterized in that, The constriction is provided with a baffle, which is a frustum-shaped baffle with a diameter that gradually increases toward the inside of the constriction. The oil-removed wastewater pumped in by the dissolved gas reflux pump flows toward the inner wall of the constriction through the gap between the constriction and the baffle.

5. The high-efficiency integrated system for chemical-free oil removal and sedimentation of produced water in oilfields according to claim 4, characterized in that, The constricted neck opening is provided with a slope, which is parallel to the side of the frustum block.

6. The high-efficiency integrated system for chemical-free oil removal and sedimentation of produced water in oilfields according to claim 3, characterized in that, The dissolved gas tank includes a settling zone at the bottom, a water-gas shear zone at the top, and a liquid inlet pipe; The water-gas mixture output from the water-gas mixing device enters the water-gas shear zone through the liquid inlet pipe; The water-air shear zone includes a guide column and a guide cylinder arranged coaxially. The guide column is disposed inside the guide cylinder, and a continuous spiral blade is disposed in the gap between the guide column and the guide cylinder. The spiral blade extends from the bottom to the top of the guide column and the guide cylinder. The end of the liquid inlet pipe is provided with a nozzle at an angle, and the nozzle is positioned toward the extension direction of the spiral blade; The spiral blades are fixedly connected to the inner wall of the guide tube; The outer wall of the guide tube is in contact with the inner wall of the dissolved gas tank; The top of the guide tube is provided with a sloping guide surface, and the bottom of the sloping guide surface is close to the outlet of the dissolved air tank.

7. The high-efficiency integrated system for chemical-free oil removal and sedimentation of produced water in oilfields according to claim 6, characterized in that, The top of the dissolved gas tank is equipped with a conical baffle.

8. The high-efficiency integrated system for chemical-free oil removal and sedimentation of produced water in oilfields according to claim 1, characterized in that, The pulse biological filter and the electrostatic demulsification and oil removal filter are also equipped with a backwashing system, which includes a backwashing pipeline and a backwashing fan. One end of the backwash pipeline is connected to the lift pump, and the other end is connected to the backwash fan; When the valve body is controlled to start the backwashing step, the valves of the inlet water pipes of the pulse biological filter and the electrostatic demulsification and oil removal filter are closed, and the valves of the backwashing pipe are opened to perform the backwashing operation.

9. A control method for a high-efficiency integrated system for chemical-free oil removal and sedimentation in produced water from oilfields, characterized in that... Based on the high-efficiency integrated oilfield produced water chemical-free oil removal and sedimentation system according to any one of claims 1-8, the control method includes the following steps: Step S1, Feed Control: Start the screw pump to stably transport the oilfield produced water in the sewage tank to the cyclone oil-water separator, and control the feed flow rate and pressure value; Step S2, First-stage cyclone separation: In the hydrocyclone oil-water separator, the floating oil and large particulate matter are separated from the produced water by centrifugal force. The floating oil rises and is collected, while the settled large particulate impurities are discharged from the bottom. Step S3, Secondary Dissolved Air Flotation: The dissolved gas reflux pump draws oil-removed wastewater from the intermediate water tank, mixes it with nitrogen gas delivered from the gas storage tank in the water-gas mixing device, and then sends it into the dissolved gas tank for high-speed shear mixing to generate dissolved gas water containing micro-nano-scale bubbles. Inside the dissolved air tank, the water-air mixture rises at high speed along the spiral channel formed by the spiral blades between the guide column and the guide cylinder, and the bubbles are refined by centrifugal shearing force to form high-concentration dissolved air water. The generated dissolved air water is sent into a flotation sedimentation machine. The air bubbles attach to the fine oil droplets and suspended solids in the water and float to the surface, completing the secondary oil removal process. Step S4, fine filtration: The booster pump sequentially pumps the oil-removed wastewater from the intermediate water tank, after secondary treatment, into the pulse biological filter and the electrostatic demulsification oil removal filter to remove residual fine suspended solids and trace amounts of oil in the water. Step S5, Intelligent Backwash Control: Monitor the operating status parameters of the pulse biofilter and the electrostatic demulsification and oil removal filter, and automatically start the backwash program when the preset backwash trigger conditions are met.

10. The control method for a high-efficiency integrated system for chemical-free oil removal and sedimentation of produced water in oilfields according to claim 9, characterized in that, The backwash triggering conditions mentioned in step S5 include: Monitor the inlet and outlet pressure difference of the pulse biofilter and / or electrostatic demulsification and oil removal filter, and automatically trigger the backwashing program when the pressure difference exceeds a preset first threshold; or, trigger the backwashing program periodically according to a preset time cycle. The control method further includes shortening the backwash trigger cycle, setting a reference backwash cycle T0, and acquiring the oil content value C1 detected by the online monitoring sensor in real time; comparing the reference oil content C0 with C1, and calculating the adjusted backwash cycle T according to the following formula. new : K is the pollution intensity coefficient, with a value ranging from 0.5 to 0.

8. When the calculated T new If the remaining time is less than the currently set backwash cycle, a backwash procedure will be triggered immediately.

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