A closed-loop multi-stage air flotation oil removal device for produced water in oilfields

Abstract

This invention discloses a closed-loop multi-stage air flotation oil removal device for oilfield produced water, comprising a horizontal cylindrical body; the inner cavity of the horizontal cylindrical body is divided into a cyclone separation zone, an inclined plate oil separator, a baffle flocculation zone, and a three-phase separation zone; the cyclone separation zone is connected to the oilfield produced water delivery pipe; the three-phase separation zone is equipped with a water outlet and a dissolved air water outlet, and the gas phase zone is equipped with a gas outlet; the oilfield produced water delivery pipe, the inclined plate oil separator, and the baffle flocculation zone are all connected to the outlet of the dissolved air water tank, the inlet of the dissolved air water tank is connected to the outlet of the dissolved air pump, and the inlet of the dissolved air pump is connected to the gas outlet and the dissolved air water outlet; a first oil collection trough is provided at the top of the cyclone separation zone, the inclined plate oil separator, and the baffle flocculation zone; a second oil collection trough is provided in the three-phase separation zone. This invention integrates multiple stages of separation, including the cyclone separation zone, the inclined plate oil separator, the baffle flocculation zone, and the three-phase separation zone, forming a multi-stage separation system with good oil-water separation effect and high separation efficiency; it integrates treatment and buffering functions; and the dissolved air source is recycled.

Description

Technical Field

[0001] This invention belongs to the field of oilfield produced water treatment technology, specifically relating to a closed multi-stage air flotation oil removal device for oilfield produced water. Background Technology

[0002] Produced water treatment is a crucial part of oilfield development and production. After treatment, the produced water meets the reservoir water injection standards for water-driven oil recovery. At the same time, it helps to recover as much crude oil as possible from the produced water. Air flotation technology is currently a highly efficient oil-water separation technology in the field of produced water treatment.

[0003] Existing air flotation devices typically use nitrogen, air, or associated natural gas as their gas source. After the gas is released, it is often directly discharged into the atmosphere, making it impossible to recycle and posing environmental risks. Secondly, existing air flotation devices usually cannot achieve multi-stage air-water contact flotation separation, resulting in low oil-water separation efficiency. Thirdly, existing air flotation devices are usually only for treatment purposes, requiring the installation of buffer tanks (pools) and other structures after treatment, resulting in numerous supporting facilities and a large land area. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a closed multi-stage air flotation oil removal device for oilfield produced water.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A closed-loop multi-stage air flotation oil removal device for produced water in oilfields, comprising a horizontal cylindrical body;

[0007] The inner cavity of the horizontal cylinder is sequentially divided into a swirl separation zone, an inclined plate oil separator, a baffle flocculation zone, and a three-phase separation zone along the axial direction.

[0008] The bottom ends of the cyclone separation zone, the inclined plate oil separator, the baffle flocculation zone, and the three-phase separation zone are connected, and the top ends of the cyclone separation zone, the inclined plate oil separator, the baffle flocculation zone, and the three-phase separation zone are connected through the gas phase zone at the top of the horizontal cylinder's inner cavity.

[0009] The cyclone separation zone is connected to the oilfield produced water delivery pipeline;

[0010] The three-phase separation zone is equipped with a water outlet pipe and a dissolved air water outlet, and the gas phase zone is equipped with a gas outlet.

[0011] The oilfield produced water delivery pipe, inclined plate oil separator, and baffle flocculation zone are all connected to the outlet of the dissolved gas water tank. The inlet of the dissolved gas water tank is connected to the outlet of the dissolved gas pump. The inlet of the dissolved gas pump is connected to the gas outlet and the dissolved gas water outlet.

[0012] The top of the cyclone separation zone, the inclined plate oil separator, and the baffle flocculation zone is provided with a first oil collection tank.

[0013] A second oil collection tank is provided in the three-phase separation zone.

[0014] Preferably, the inner cavity of the horizontal cylinder is sequentially divided into a swirl separation zone, an inclined plate oil separator, a baffle flocculation zone, and a three-phase separation zone along the axial direction by several parallel baffles.

[0015] The partition is perpendicular to the central axis of the horizontal cylinder;

[0016] The front and rear ends of the partition are fixedly connected to the inner sidewall of the horizontal cylinder, respectively.

[0017] Preferably, a vertical cyclone separator is provided in the cyclone separation zone;

[0018] The bottom end of the vertical cyclone tube is sealed to the inner wall of the horizontal cylinder, and the top end of the vertical cyclone tube is open.

[0019] The lower end of the vertical cyclone tube is provided with a tangential inlet, and the interior of the vertical cyclone tube is provided with helical blades, the radial outer end of which is fixedly connected to the inner wall of the vertical cyclone tube.

[0020] The tangential inlet is connected to the oilfield produced water delivery pipe.

[0021] Preferably, an oil separator baffle is provided on the side of the inclined plate oil separator near the cyclone separation zone. The oil separator baffle divides the inclined plate oil separator into a first dissolved air water injection zone and an inclined plate zone that are connected at the top. The oil separator baffle is perpendicular to the central axis of the horizontal cylinder.

[0022] The inclined plate area is provided with several inclined plates parallel to the axial direction of the horizontal cylinder. The front and rear ends of the inclined plates are fixedly connected to the inner sidewall of the horizontal cylinder, and the bottom end of the inclined plate is inclined towards the direction of the baffle flocculation zone compared to the top end.

[0023] The outlet of the dissolved air water tank is connected to the dissolved air water release pipe located in the first dissolved air water injection zone.

[0024] Preferably, the included angle between the inclined plate and the oil separator baffle is 45° to 60°.

[0025] Preferably, the spacing between adjacent inclined plates along the axial direction of the horizontal cylinder is 800-100mm.

[0026] Preferably, a baffle plate is provided on the side of the baffle flocculation zone near the inclined plate oil separator, and the baffle plate divides the baffle flocculation zone into a contact zone and a separation zone that are connected at the top.

[0027] The lower part of the baffle plate is a straight plate structure perpendicular to the central axis of the horizontal cylinder, and the upper part of the baffle plate is bent towards the separation zone.

[0028] A dissolved air release pipe for connecting to the outlet of the dissolved air tank is provided between the lower straight plate structure of the baffle and the corresponding baffle.

[0029] Preferably, a three-phase separation zone partition is provided on the side of the three-phase separation zone near the baffle flocculation zone, and the three-phase separation zone partition divides the three-phase separation zone into a flow guiding zone and a three-phase separation zone that are connected at the top.

[0030] The three-phase separation partition is perpendicular to the central axis of the horizontal cylinder;

[0031] A three-phase separator is provided in the three-phase separation zone. A separator inlet is provided between the partition of the three-phase separation zone and the three-phase separator. A gas phase outlet is provided at the top of the three-phase separator. A liquid phase outlet extending to the purified water buffer zone is provided at the bottom of the three-phase separator.

[0032] Preferably, the first oil collection trough includes a first main oil collection trough symmetrically arranged in the front-back direction, and the first main oil collection trough extends along the axial direction of the horizontal cylinder.

[0033] Between the two rows of primary oil collection channels, corresponding to the positions above the cyclone separation zone, the inclined plate oil separator, and the baffle flocculation zone, a primary oil collection channel is vertically arranged, and the primary oil collection channel is connected to the primary oil collection channel.

[0034] A liftable throttle gate is provided on one side of the first throttle recovery trough;

[0035] An oil collection pipe is provided at the bottom of the first oil collection sub-tank, and the end of the oil collection pipe extends through the wall of the horizontal cylinder.

[0036] Preferably, the second oil collection groove is symmetrically arranged along the front and rear direction of the horizontal cylinder, and the second oil collection groove extends along the axial direction of the horizontal cylinder;

[0037] A second oil collection pipe is provided at the bottom of the second oil collection tank, and the end of the second oil collection pipe extends out of the wall of the horizontal cylinder.

[0038] The beneficial effects of this invention are:

[0039] The oil removal device of this invention integrates multiple stages, including a cyclone separation zone, an inclined plate oil separator, a baffle flocculation zone, and a three-phase separation zone, forming a multi-stage separation process with good oil-water separation effect and high separation efficiency. It integrates processing and buffering functions, and the equipment is small in size and occupies a small area. The dissolved gas source in this invention is recycled, resulting in low operating costs. After the device is in operation, there are no VOCs or other gas emissions, making it safe and environmentally friendly. Attached Figure Description

[0040] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments of this application and their descriptions are used to explain this application and do not constitute an undue limitation of this application.

[0041] Figure 1 This is a schematic front view of the structure of the closed-loop multi-stage air flotation oil removal device for oilfield produced water according to the present invention;

[0042] Figure 2 This is a schematic top view of the structure of the closed-loop multi-stage air flotation oil removal device for oilfield produced water according to the present invention;

[0043] in:

[0044] 1-Horizontal cylinder, 101-Baffle, 102-Water outlet pipe, 103-Dissolved gas water outlet, 104-Air outlet, 105-Manhole, 106-Sewage pipe, 107-Pressure relief port, 108-Pressure detection port, 109-Air inlet, 110-Liquid level detection port 110;

[0045] 2-Swirl separation zone, 201-Vertical swirling tube, 202-Tangential inlet, 203-Helical blade;

[0046] 3-Inclined plate oil separator, 301-Oil separator baffle, 302-First dissolved air water injection zone, 303-Inclined plate zone, 304-Inclined plate;

[0047] 4-Baffled flocculation zone, 401-Baffled zone baffle, 402-Contact zone, 403-Separation zone;

[0048] 5-Three-phase separation zone, 501-Three-phase separation zone baffle, 502-Flow guide zone, 503-Three-phase separation zone, 504-Three-phase separator, 505-Separator inlet, 506-Gas phase outlet, 507-Liquid phase outlet, 508-Pure water buffer zone;

[0049] 6-Gas phase region;

[0050] 7-Dissolved air tank, 8-Dissolved air pump;

[0051] 9-First oil collection trough, 901-First main oil collection trough, 902-First secondary oil collection trough, 903-Energy collection valve, 904-Lifting screw, 905-Oil collection pipe;

[0052] 10-Second oil collection tank,

[0053] 11-Oilfield produced water delivery pipe, 12-Dissolved gas water release pipe, 1201-Release port. Detailed Implementation

[0054] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0055] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments according to this application. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0056] In this invention, terms such as "upper," "lower," "bottom," and "top" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are merely relational terms determined for the convenience of describing the structural relationship of the various components or elements of this invention, and do not specifically refer to any component or element in this invention, and should not be construed as limiting this invention.

[0057] In this invention, terms such as "connected" and "linked" should be interpreted broadly, indicating a fixed connection, an integral connection, or a detachable connection; a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can determine the specific meaning of these terms in this invention based on the specific circumstances, and they should not be construed as limitations on the invention.

[0058] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0059] like Figure 1-2 As shown, a closed multi-stage air flotation oil removal device for produced water in oilfields includes a horizontal cylindrical body 1.

[0060] The inner cavity of the horizontal cylindrical body 1 is sequentially divided into a cyclone separation zone 2, an inclined plate oil separator 3, a baffle flocculation zone 4, and a three-phase separation zone 5 along the axial direction.

[0061] The bottom ends of the cyclone separation zone 2, the inclined plate oil separator 3, the baffle flocculation zone 4, and the three-phase separation zone 5 are connected, and the top ends of the cyclone separation zone 2, the inclined plate oil separator 3, the baffle flocculation zone 4, and the three-phase separation zone 5 are connected through the gas phase zone 6 at the top of the inner cavity of the horizontal cylinder 1.

[0062] The cyclone separation zone 2 is connected to the oilfield produced water delivery pipe 11;

[0063] The three-phase separation zone 5 is provided with a water outlet pipe 102 and a dissolved air water outlet 103, and the gas phase zone 6 is provided with a gas outlet 104.

[0064] The oilfield produced water delivery pipe 11, the inclined plate oil separator 3, and the baffle flocculation zone 4 are all connected to the outlet of the dissolved gas water tank 7. The inlet of the dissolved gas water tank 7 is connected to the outlet of the dissolved gas pump 8. The inlet of the dissolved gas pump 8 is connected to the gas outlet 104 and the dissolved gas water outlet 103.

[0065] The top of the cyclone separation zone 2, the inclined plate oil separator 3, and the baffle flocculation zone 4 is provided with a first oil collection trough 9;

[0066] A second oil collection tank 10 is provided in the three-phase separation zone 5.

[0067] Preferably, the inner cavity of the horizontal cylindrical body 1 is sequentially divided into a swirl separation zone 2, an inclined plate oil separator 3, a baffle flocculation zone 4, and a three-phase separation zone 5 along the axial direction by a number of parallel baffles 101.

[0068] The partition 101 is perpendicular to the central axis of the horizontal cylinder 1;

[0069] The front and rear ends of the partition 101 are fixedly connected to the inner sidewall of the horizontal cylinder 1, respectively.

[0070] Specifically, the top of the partition 101 is higher than the top of the first oil collection trough 9.

[0071] Preferably, a vertical cyclone separator 201 is provided in the cyclone separation zone 2;

[0072] The bottom end of the vertical vortex tube 201 is sealed to the inner wall of the horizontal cylinder 1, and the top end of the vertical vortex tube 201 is open.

[0073] The lower end of the vertical vortex tube 201 is provided with a tangential inlet 202, and the interior of the vertical vortex tube 201 is provided with a helical blade 203, the radial outer end of the helical blade 203 being fixedly connected to the inner wall of the vertical vortex tube 201.

[0074] The tangential inlet 202 is connected to the oilfield produced water delivery pipe 11.

[0075] Preferably, an oil separator baffle 301 is provided on the side of the inclined plate oil separator 3 near the cyclone separation zone 2. The oil separator baffle 301 divides the inclined plate oil separator 3 into a first dissolved air water injection zone 302 and an inclined plate zone 303 that are connected at the top. The oil separator baffle 302 is perpendicular to the central axis of the horizontal cylinder 1.

[0076] The inclined plate area 303 is provided with several inclined plates 304 parallel to the axial direction of the horizontal cylinder 1. The front and rear ends of the inclined plates 304 are fixedly connected to the inner sidewall of the horizontal cylinder 1, and the bottom end of the inclined plate 304 is inclined towards the direction of the baffle flocculation area 4 compared with the top end.

[0077] The outlet of the dissolved air water tank 7 is connected to the dissolved air water release pipe 12 located in the first dissolved air water injection zone 302.

[0078] Specifically, the top of the oil separator baffle 301 is higher than the bottom of the baffle 101 and lower than the bottom of the first oil collection trough 9, and the top of the oil separator baffle 301 is higher than the top of the inclined plate 304.

[0079] Preferably, the included angle between the inclined plate 304 and the oil separator plate 301 is 45° to 60°.

[0080] Preferably, the spacing between adjacent inclined plates 304 along the axial direction of the horizontal cylinder 1 is 800-100mm.

[0081] Preferably, a baffle plate 401 is provided on the side of the baffle flocculation zone 4 near the inclined plate oil separator 3, and the baffle plate 401 divides the baffle flocculation zone 4 into a contact zone 402 and a separation zone 403 that are connected at the top.

[0082] The lower part of the baffle plate 401 is a straight plate structure perpendicular to the central axis of the horizontal cylinder 1, and the upper part of the baffle plate 401 is bent toward the separation zone 403.

[0083] A dissolved air release pipe 12 is provided between the lower straight plate structure of the baffle 401 and the corresponding baffle 101 for connecting to the outlet of the dissolved air tank 7.

[0084] Specifically, the top of the baffle plate 401 is higher than the bottom of the baffle plate 101 and lower than the bottom of the first oil collection tank 9.

[0085] The purpose of contact zone 402 is to provide opportunities for contact and adhesion between flocculent particles, oil droplets and bubbles. The water flow of the flocculent bubble aggregates (bubbles with attached flocs), free bubbles and unattached flocculent particle suspensions flows to separation zone 403, where free bubbles and flocculent bubble aggregates float to the surface.

[0086] Preferably, a three-phase separation zone partition 501 is provided on the side of the three-phase separation zone 5 near the baffle flocculation zone 4, and the three-phase separation zone partition 501 divides the three-phase separation zone 5 into a flow guiding zone 502 and a three-phase separation zone 503 that are connected at the top.

[0087] The three-phase separation partition 501 is perpendicular to the central axis of the horizontal cylinder 1;

[0088] A three-phase separator 504 is provided in the three-phase separation zone 503. A separator inlet 505 is provided between the three-phase separation zone partition 501 and the three-phase separator 504. A gas phase outlet 506 is provided at the top of the three-phase separator 504. A liquid phase outlet 507 extending to the purified water buffer zone 508 is provided at the bottom of the three-phase separator 504.

[0089] Specifically, the top of the three-phase separation partition 501 is higher than the bottom of the partition 101.

[0090] Preferably, the first oil collection trough 9 includes a first main oil collection trough 901 symmetrically arranged in the front-back direction, and the first main oil collection trough 901 extends along the axial direction of the horizontal cylinder 1.

[0091] Between the two rows of primary oil collection channels 901, at positions corresponding to the upper parts of the cyclone separation zone 2, the inclined plate oil separator 3, and the baffle flocculation zone 4, there are vertically arranged primary oil collection channels 902, and the primary oil collection channels 902 are connected to the primary oil collection channels 901.

[0092] A liftable oil collection gate 903 is provided on one side of the first oil collection sub-slot 902. The lifting and lowering control of the oil collection gate 903 can be achieved using existing technology. For example, the front and rear sides of the oil collection gate 903 are vertically slidably engaged with the side wall of the corresponding first oil collection sub-slot 902. The interior of the oil collection gate 903 is threadedly engaged with the lifting screw 904. The lifting screw 904 extends vertically and is rotatably engaged with the top of the horizontal cylinder 1. When the lifting screw 904 is rotated, the oil collection gate 903 can be lifted and lowered. When the oil collection gate 903 rises, it forms an oil collection port that allows the floating oil at the top to enter the first oil collection sub-slot 902.

[0093] An oil collection pipe 905 is provided at the bottom end of the first oil collection sub-tank 902, and the port of the oil collection pipe 905 extends out of the wall of the horizontal cylinder 1.

[0094] Preferably, the second oil collection groove 10 is symmetrically arranged along the front and rear direction of the horizontal cylinder, and the second oil collection groove 10 extends along the axial direction of the horizontal cylinder 1.

[0095] A second oil collection pipe is provided at the bottom of the second oil collection tank 10, and the end of the second oil collection pipe extends out of the wall of the horizontal cylinder 1.

[0096] Specifically, the top of the second oil collection tank 10 is lower than the gas phase outlet at the top of the three-phase separator 504.

[0097] In this application, the dissolved air water release pipe 12 extends in the front-to-back direction, and the dissolved air water release pipe 12 is provided with a plurality of upward-facing release ports 1201.

[0098] In this application, a manhole 105 is provided at the top of the horizontal cylinder 1 corresponding to the cyclone separation zone 2, the inclined plate oil separator 3, the baffle flocculation zone 4, and the three-phase separation zone 5. A drain pipe 106 is provided on the horizontal cylinder 1 at the bottom of the vertical cyclone cylinder 201 and at the bottom of the horizontal cylinder 1 corresponding to the cyclone separation zone 2, the inclined plate oil separator 3, the baffle flocculation zone 4, and the three-phase separation zone 5 outside the vertical cyclone cylinder 201.

[0099] In this application, the horizontal cylinder 1 is also provided with a pressure relief port 107, a pressure detection port 108, and an air inlet 109, and the water purification buffer zone 508 is provided with a liquid level detection port 110.

[0100] A closed-loop multi-stage air flotation oil removal device for oilfield produced water is implemented as follows:

[0101] Oilfield produced water containing dissolved gas enters through the oilfield produced water delivery pipe 11 into the tangential inlet 202, forming a vortex. Under the enhanced vortex effect of the spiral blades 203, the two light components, oil and gas, gather towards the center of the vertical vortex tube 201, while the water phase moves towards the wall of the vertical vortex tube 201. After leaving the vertical vortex tube 201, the two light components, oil and gas, continue to gather upward under the action of inertia. During this process, the less dense gas phase rises to the top gas phase zone 6, while the oil phase forms an oil film on the water surface as it moves upward. The remaining liquid phase leaves the vertical vortex tube 201 and falls to the bottom of the vortex separation zone 2 outside the vertical vortex tube 201 under the action of gravity, flowing towards the inclined plate oil separator 3.

[0102] After separation in the cyclone separation zone 2, the liquid phase enters the first dissolved air water injection zone 302, where it comes into contact with and mixes with the dissolved air water. Oil droplets in the liquid phase are collided and adsorbed by the bubbles released by the dissolved air water. Then, it enters the inclined plate zone 303. During the flow through each inclined plate 304, the bubbles that adsorb oil droplets and other suspended oil impurities float to the water surface. The oil droplets and oil impurities remain in the oil film, while the bubbles rise to the top gas phase zone 6 after bursting. The remaining liquid phase enters the baffle flocculation zone 4 from the bottom of the inclined plate zone 303.

[0103] After separation by the inclined plate oil separator 3, the liquid phase enters the contact zone 402, where it comes into contact with and mixes with dissolved air and water. The phases of flocculated particles, oil droplets, and bubbles come into contact and attach. Then, the liquid phase of the suspension of flocculent bubble aggregates (bubbles with attached flocs), free bubbles, and unattached flocculent particles flows to the separation zone 403. In the separation zone 403, free bubbles and flocculent bubble aggregates float to the surface, while the remaining liquid phase enters the three-phase separation zone 5.

[0104] After separation in the baffle flocculation zone 4, the liquid phase is guided by the flow guide zone 502 and enters the separator inlet 505. The gas in the liquid phase rises to the gas phase zone 6 through the gas phase outlet 506, and the liquid phase enters the clean water buffer zone 508 through the liquid phase outlet 507. In the clean water buffer zone 508, oil droplets float to the liquid surface.

[0105] Among them, the gas that rises into the gas phase zone 6 enters the dissolved gas pump 8 through the top gas outlet 104;

[0106] When an oil film of a certain thickness forms on the surface of the liquid in the cyclone separation zone 2, the inclined plate oil separator 3, and the baffle flocculation zone 4, the oil collection valve 903 is opened upwards, and the oil layer at the top overflows to the first oil collection auxiliary tank 902, and then flows out of the horizontal cylinder 1 through the corresponding oil collection pipe 905 for collection.

[0107] When the liquid level in the clean water buffer zone 508 exceeds the top of the second oil collection tank 10, the oil layer at the top of the liquid level in the clean water buffer zone 508 enters the second oil collection tank 10 and is collected through the second oil collection pipe.

[0108] The water treated by the device is discharged through the outlet pipe 102, while the inlet water of the dissolved air pump 8 is also supplied by the water in the clean water buffer zone 508.

[0109] The oil removal device of this invention integrates multiple stages, including a cyclone separation zone 2, an inclined plate oil separator 3, a baffle flocculation zone 4, and a three-phase separation zone 5, forming a multi-stage separation process with good oil-water separation effect and high separation efficiency. It integrates processing and buffering functions, and the equipment is small in size and occupies a small area. The dissolved gas source in this invention is recycled, resulting in low operating costs. After the device is in operation, there are no VOCs or other gas emissions, making it safe and environmentally friendly.

[0110] While the specific embodiments of the present invention have been described above in conjunction with the accompanying drawings, they are not intended to limit the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art without creative effort based on the technical solutions of the present invention are still within the protection scope of the present invention.

Claims

1. A closed-loop multi-stage air flotation oil removal device for produced water in oilfields, comprising a horizontal cylindrical body; characterized in that, The inner cavity of the horizontal cylinder is sequentially divided into a swirl separation zone, an inclined plate oil separator, a baffle flocculation zone, and a three-phase separation zone along the axial direction. The bottom ends of the cyclone separation zone, the inclined plate oil separator, the baffle flocculation zone, and the three-phase separation zone are connected, and the top ends of the cyclone separation zone, the inclined plate oil separator, the baffle flocculation zone, and the three-phase separation zone are connected through the gas phase zone at the top of the horizontal cylinder's inner cavity. The cyclone separation zone is connected to the oilfield produced water delivery pipeline; The three-phase separation zone is equipped with a water outlet pipe and a dissolved air water outlet, and the gas phase zone is equipped with a gas outlet. The oilfield produced water delivery pipe, inclined plate oil separator, and baffle flocculation zone are all connected to the outlet of the dissolved gas water tank. The inlet of the dissolved gas water tank is connected to the outlet of the dissolved gas pump. The inlet of the dissolved gas pump is connected to the gas outlet and the dissolved gas water outlet. The top of the cyclone separation zone, the inclined plate oil separator, and the baffle flocculation zone is provided with a first oil collection tank. A second oil collection tank is provided in the three-phase separation zone.

2. The closed-loop multi-stage air flotation oil removal device for produced water in oilfields as described in claim 1, characterized in that, The inner cavity of the horizontal cylinder is sequentially divided into a swirl separation zone, an inclined plate oil separator, a baffle flocculation zone, and a three-phase separation zone along the axial direction by several parallel baffles. The partition is perpendicular to the central axis of the horizontal cylinder; The front and rear ends of the partition are fixedly connected to the inner sidewall of the horizontal cylinder, respectively.

3. The closed-loop multi-stage air flotation oil removal device for produced water in oilfields as described in claim 1, characterized in that, A vertical cyclone separator is installed within the cyclone separation zone; The bottom end of the vertical cyclone tube is sealed to the inner wall of the horizontal cylinder, and the top end of the vertical cyclone tube is open. The lower end of the vertical cyclone tube is provided with a tangential inlet, and the interior of the vertical cyclone tube is provided with helical blades, the radial outer end of which is fixedly connected to the inner wall of the vertical cyclone tube. The tangential inlet is connected to the oilfield produced water delivery pipe.

4. The closed-loop multi-stage air flotation oil removal device for produced water in oilfields as described in claim 1, characterized in that, An oil separator baffle is provided on the side of the inclined plate oil separator near the cyclone separation zone. The oil separator baffle divides the inclined plate oil separator into a first dissolved air water injection zone and an inclined plate zone that are connected at the top. The oil separator baffle is perpendicular to the central axis of the horizontal cylinder. The inclined plate area is provided with several inclined plates parallel to the axial direction of the horizontal cylinder. The front and rear ends of the inclined plates are fixedly connected to the inner sidewall of the horizontal cylinder, and the bottom end of the inclined plate is inclined towards the direction of the baffle flocculation zone compared to the top end. The outlet of the dissolved air water tank is connected to the dissolved air water release pipe located in the first dissolved air water injection zone.

5. The closed-loop multi-stage air flotation oil removal device for produced water in oilfields as described in claim 4, characterized in that, The angle between the inclined plate and the oil separator baffle is 45° to 60°.

6. The closed-loop multi-stage air flotation oil removal device for produced water in oilfields as described in claim 4, characterized in that, The spacing between adjacent inclined plates along the axial direction of the horizontal cylinder is 800-100mm.

7. The closed-loop multi-stage air flotation oil removal device for produced water in oilfields as described in claim 1, characterized in that, A baffle plate is provided on the side of the baffle flocculation zone near the inclined plate oil separator. The baffle plate divides the baffle flocculation zone into a contact zone and a separation zone that are connected at the top. The lower part of the baffle plate is a straight plate structure perpendicular to the central axis of the horizontal cylinder, and the upper part of the baffle plate is bent towards the separation zone. A dissolved air release pipe for connecting to the outlet of the dissolved air tank is provided between the lower straight plate structure of the baffle and the corresponding baffle.

8. The closed-loop multi-stage air flotation oil removal device for produced water in oilfields as described in claim 1, characterized in that, A three-phase separation zone partition is provided on the side of the three-phase separation zone near the baffle flocculation zone. The three-phase separation zone partition divides the three-phase separation zone into a flow guiding zone and a three-phase separation zone that are connected at the top. The three-phase separation partition is perpendicular to the central axis of the horizontal cylinder; A three-phase separator is provided in the three-phase separation zone. A separator inlet is provided between the partition of the three-phase separation zone and the three-phase separator. A gas phase outlet is provided at the top of the three-phase separator. A liquid phase outlet extending to the purified water buffer zone is provided at the bottom of the three-phase separator.

9. The closed-loop multi-stage air flotation oil removal device for produced water in oilfields as described in claim 1, characterized in that, The first oil collection trough includes a first main oil collection trough symmetrically arranged in the front-back direction, and the first main oil collection trough extends along the axial direction of the horizontal cylinder. Between the two rows of primary oil collection channels, corresponding to the positions above the cyclone separation zone, the inclined plate oil separator, and the baffle flocculation zone, a primary oil collection channel is vertically arranged, and the primary oil collection channel is connected to the primary oil collection channel. A liftable throttle gate is provided on one side of the first throttle recovery trough; An oil collection pipe is provided at the bottom of the first oil collection sub-tank, and the end of the oil collection pipe extends through the wall of the horizontal cylinder.

10. The closed-loop multi-stage air flotation oil removal device for produced water in oilfields as described in claim 1, characterized in that, The second oil collection groove is symmetrically arranged along the front and rear direction of the horizontal cylinder, and the second oil collection groove extends along the axial direction of the horizontal cylinder; A second oil collection pipe is provided at the bottom of the second oil collection tank, and the end of the second oil collection pipe extends out of the wall of the horizontal cylinder.

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