Closed multi-stage air flotation oil removal method and device for oilfield produced water

Abstract

The invention relates to a closed multi-stage air flotation oil removal device and method for oilfield produced water, which are characterized in that a primary cyclone air flotation separation zone, a secondary cyclone air flotation separation zone, a bubble enrichment flotation separation zone, a micro-spin flocculation flotation separation zone and a purified water buffer zone are sequentially arranged in a closed tank body, and crude oil in the oilfield produced water is subjected to separation extraction and cascade separation; the separation efficiency is high and the effect is good; the functions of multi-stage treatment, buffering, oil collection, pollution discharge and the like of produced water are integrated, the equipment integration degree is high, the size is small, the number of supporting facilities is small, and the occupied area is small; and the operation cost is low.

Description

Technical Field

[0001] The invention relates to an oilfield produced water treatment technology, in particular to an oilfield produced water closed multi-stage flotation oil removal method and device. Background Art

[0002] Oilfield produced water treatment is an important part of oilfield development and production. After treatment, produced water reaches the reservoir water injection index and is used for water injection and oil recovery. At the same time, the crude oil carried in the produced water is recovered as much as possible. Flotation technology is a highly efficient oil-water separation technology in the field of oilfield produced water treatment. The gas source of existing flotation devices generally uses nitrogen, air or associated natural gas, etc. After the gas is released, it is often directly discharged into the atmosphere, which cannot be recycled and also poses environmental risks; secondly, existing flotation devices usually cannot achieve multi-stage gas-water contact flotation separation, and the oil-water separation efficiency is low. Thirdly, existing flotation devices usually only have treatment functions, and after treatment, they need to be equipped with buffer tanks and other structures, resulting in many supporting facilities and a large area. Summary of the invention

[0003] In view of this, the main purpose of the present invention is to provide a closed multi-stage flotation oil removal method and device for oilfield produced water. Through the technical scheme, a primary cyclone flotation separation zone, a secondary cyclone flotation separation zone, a bubble enrichment flotation separation zone, a micro-spin flocculation flotation separation zone and a water purification buffer zone are sequentially arranged in a closed tank body to separate and extract crude oil from oilfield produced water, with step-by-step separation, high separation efficiency and good effect; the equipment has high integration, small size, few supporting facilities, and small footprint; low operating cost, safety and environmental protection.

[0004] In order to achieve the above object, the technical solution of the present invention is implemented in the following ways:

[0005] A closed multi-stage flotation oil removal method for oilfield produced water, wherein a primary cyclone flotation separation zone, a secondary cyclone flotation separation zone, a bubble enrichment flotation separation zone, a micro-spin flocculation flotation separation zone and a water purification buffer zone are sequentially arranged in a closed tank body, and the method is carried out according to the following steps:

[0006] A. The produced water from the oil field enters the primary cyclone flotation separation zone and is added with dissolved air water for cyclone flotation separation. The bubbles in the dissolved air water and the oil droplets in the produced water from the oil field collide with each other, contact and adhere to each other under the action of the cyclone, and then float to the oil collection tank on the water surface of the cyclone flotation separation zone in a rotating flow state, and are collected through the oil collection pipe. The sediment in the produced water from the oil field sinks to the bottom of the primary cyclone flotation separation zone;

[0007] B. After the primary cyclone flotation separation treatment, the produced water from the oil field enters the secondary cyclone flotation separation zone from the bottom, and the dissolved air water is added to generate bubbles. The produced water from the oil field is spun through the cyclone tube, and the oil flocs go upward into the oil collection tank at the top of the circulation tube, and then are collected through the oil collection pipe. The sand in the produced water from the oil field sinks to the bottom of the secondary cyclone flotation separation zone;

[0008] C. The produced water from the oil field after the secondary cyclone flotation separation zone is added with dissolved air water and enters the bubble enrichment flotation separation zone. After the bubble enrichment and separation, the gas in the dissolved air water is released to generate large bubbles and small bubbles, and the bubbles are mixed so that the large bubbles hide in the small bubble group. The large bubbles can increase the turbulent kinetic energy of the gas-liquid two-phase flow, and the small bubbles can change the state of the microscopic gas-liquid contact interface, strengthen the adhesion and wrapping process of the bubbles on the oil droplets, and form a stable bubble-oil drop adhesion body. The oil droplets are gathered into the oil collection tank on the water surface of the bubble enrichment flotation separation zone through the guide baffle, and then collected through the oil collection pipe. The sand in the produced water of the oil field sinks to the bottom of the bubble enrichment flotation separation zone;

[0009] D. The produced water from the oil field after the bubble enrichment flotation separation zone enters the micro-spin flocculation flotation separation zone, where dissolved air water and flocculants are added for micro-spin flocculation flotation separation. The produced water from the oil field is mixed and contacted with the dissolved air water carrying the reagents again, and the migration and collision coagulation of fine particles in the water are improved through micro-vortices, which promote the mutual adhesion of the reagents and impurities in the water to form floccules that float to the oil collection tank on the water surface of the micro-spin flocculation flotation separation zone, and are collected through the oil collection pipe. The sand in the produced water from the oil field sinks to the bottom of the micro-spin flocculation flotation separation zone;

[0010] E. The produced water from the oil field that has passed through the micro-spin flocculation flotation separation zone flows into the clean water buffer zone through the high-level water outlet pipe to form clean water. The clean water at the bottom is produced into dissolved air water through the dissolved air pump and dissolved air tank outside the closed tank body to supply the dissolved air water required in step A, step B, step C and step D. The remaining clean water is discharged from the closed tank body in a quantitative and regular manner.

[0011] As a further technical solution, in step C, the diameter of large bubbles ranges from 1 mm to 5 mm, and the diameter of small bubbles ranges from less than 1 mm.

[0012] A closed multi-stage flotation oil removal device for oilfield produced water, comprising a closed tank body, an oilfield produced water delivery pipeline and a clean water output pipeline, wherein the oilfield produced water delivery pipeline and the clean water output pipeline are respectively arranged on the front and rear of the closed tank body, and characterized in that it also comprises an oil receiving tank, an oil receiving pipe, a primary cyclone flotation separation zone, a secondary cyclone flotation separation zone, a bubble enrichment flotation separation zone, a micro-spin flocculation flotation separation zone and a clean water buffer zone, wherein the primary cyclone flotation separation zone, the secondary cyclone flotation separation zone, the air bubble enrichment flotation separation zone, the micro-spin flocculation flotation separation zone and the clean water buffer zone are The bubble enrichment flotation separation zone, the micro-spin flocculation flotation separation zone and the water purification buffer zone are arranged in sequence in the closed tank body, and the oil collection tanks are horizontally arranged on the upper ends of the corresponding primary cyclone flotation separation zone, the secondary cyclone flotation separation zone, the bubble enrichment flotation separation zone and the micro-spin flocculation flotation separation zone, and the suction ports of several oil collection pipes are respectively arranged in the oil collection tanks located on the upper ends of the primary cyclone flotation separation zone, the secondary cyclone flotation separation zone, the bubble enrichment flotation separation zone and the micro-spin flocculation flotation separation zone.

[0013] As a further technical solution, it also includes a separation zone partition, which is respectively vertically fixed on the rear end of the oil collecting tank at the corresponding position of the primary cyclone flotation separation zone, the secondary cyclone flotation separation zone, the bubble enrichment flotation separation zone and the micro-spin flocculation flotation separation zone, and the upper end of the separation zone partition to the upper wall of the closed tank body is respectively arranged to be air-permeable, forming air vents that are interconnected between the primary cyclone flotation separation zone, the secondary cyclone flotation separation zone, the bubble enrichment flotation separation zone, the micro-spin flocculation flotation separation zone and the clean water buffer zone, and the lower end of the separation zone partition to the lower wall of the closed tank body is respectively arranged to be air-permeable, forming oilfield produced water zone inlets of the primary cyclone flotation separation zone, the secondary cyclone flotation separation zone, the bubble enrichment flotation separation zone, the micro-spin flocculation flotation separation zone and the clean water buffer zone.

[0014] As a further technical solution, the primary cyclone flotation separation zone also includes a dissolved air water inlet pipe, a cyclone, a primary grid slot and a secondary grid slot. The cyclone is fixed at the bottom of the closed tank body, and the top of the cyclone is open. The oilfield produced water delivery pipeline is connected in parallel with the dissolved air water inlet pipe and then enters the cyclone through the tangential inlet pipe of the cyclone, rotates in the cyclone, and flows upward from the top of the cyclone.

[0015] As a further technical solution, the secondary cyclone flotation separation zone also includes a dissolved air water outlet pipe, a secondary water inlet pipe, a cyclone tube and a circulation tube. The secondary water inlet pipe is arranged at the water inlet position of the corresponding oil field produced water partition, the cyclone tube is arranged in the circulation tube, and the outlet of the dissolved air water outlet pipe is arranged in the bottom of the circulation tube. The oil field produced water enters the bottom of the circulation tube through the secondary water inlet pipe and merges with the dissolved air water. It enters the cyclone tube and mixes with the bubbles released by the dissolved air water and then enters the circulation tube upward. The cyclone tube generates a vortex to separate oil and water. At the same time, the upward oil, gas and water in the cyclone tube will pull the water outside the cyclone tube to flow downward, forming a circulation field. After the oil and gas are separated by the cyclone, they are mainly distributed in the upper part of the circulation tube, and the water outside the cyclone tube moves downward and is discharged from the outlet.

[0016] As a further technical solution, the bubble enrichment flotation separation zone also includes a dissolved air water inlet pipe, a guide baffle and a bubble enrichment sorter, the lower part of the guide baffle is vertically arranged at a position close to the rear of the separation zone baffle located on the front side of the bubble enrichment flotation separation zone, the lower part of the guide baffle is arranged at the lower part of the bubble enrichment flotation separation zone, the lower end of the guide baffle is fixed on the lower wall of the closed tank body at the corresponding position, the upper part of the guide baffle is arranged in the middle of the bubble enrichment flotation separation zone, the upper part of the guide baffle is inclined backward, the lower end of the upper part of the guide baffle is fixedly connected to the upper end of the lower part of the guide baffle as a whole, the dissolved air water inlet pipe passes through the closed tank body, the dissolved air water outlet is arranged between the lower part of the guide baffle and the adjacent separation zone baffle, and the bubble enrichment sorter is horizontally arranged between the upper part of the guide baffle and the adjacent separation zone baffle.

[0017] As a further technical solution, the micro-spin flocculation flotation separation zone also includes a dissolved air water inlet pipe, a micro-spin water inlet pipe, a doser, a micro-spin flocculation reactor and a high-level water outlet pipe. The micro-spin flocculation reactor is composed of a mesh flow disturbance component and an annular cylinder. Several mesh flow disturbance components are arranged in two layers in the annular cylinder. The micro-spin water inlet pipe is arranged at the water inlet position of the corresponding oilfield produced water partition. The dissolved air water inlet pipe passes through the closed tank body and is divided into several arrays of dissolved air water outlets. The dissolved air water outlets are respectively arranged below the mesh flow disturbance component of the corresponding micro-spin flocculation reactor. The doser is arranged outside the closed tank body, and the drug outlet of the doser extends into the sealed tank body and is connected to the micro-spin water inlet. The high-level water outlet pipe is arranged at the water inlet position of the corresponding oilfield produced water partition.

[0018] As a further technical solution, it also includes an air inlet, an air outlet, a pressure relief port, a pressure detection port and a liquid level detection port, and the air inlet, air outlet, pressure relief port and pressure detection port are respectively arranged on the upper wall of the closed tank body at the position corresponding to the purification buffer zone.

[0019] As a further technical solution, it also includes a dissolved water pump, a dissolved water tank, a water outlet pipe, a manhole and a slag discharge hole. The water inlet of the water outlet pipe is connected to the clean water buffer zone. The water outlet pipe passes through the closed tank body and is connected to the dissolved water pump located outside the closed tank body. The dissolved water pump is connected to the dissolved air water inlet pipes of the corresponding primary cyclone flotation separation zone, secondary cyclone flotation separation zone, bubble enrichment flotation separation zone and micro-spin flocculation flotation separation zone through a connecting pipe via the dissolved water tank. Several manholes are respectively arranged on the upper wall of the closed tank body at the corresponding positions of the primary cyclone flotation separation zone, secondary cyclone flotation separation zone, bubble enrichment flotation separation zone, micro-spin flocculation flotation separation zone and clean water buffer zone. The slag discharge holes are respectively arranged on the lower wall of the closed tank body at the corresponding positions of the primary cyclone flotation separation zone, secondary cyclone flotation separation zone, bubble enrichment flotation separation zone, micro-spin flocculation flotation separation zone and clean water buffer zone.

[0020] The beneficial effects of adopting the above technical scheme are: a closed multi-stage flotation oil removal method and device for oil field produced water. Through this technical scheme, 1. Cyclone flotation and multi-stage flotation are integrated, and the oil-water separation effect is good; 2. The processing and buffering functions are integrated, the equipment is small in size and occupies a small area; 3. Step separation and high separation efficiency; 4. The dissolved air source is recycled and the operating cost is low; 5. The device is closed, there is no VOCs and other gas emissions, and it is safe and environmentally friendly. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a structural schematic diagram of the present invention;

[0022] Figure 2 It is a schematic diagram of the top view of the structure of the cyclone in the primary cyclone flotation separation zone of the present invention.

[0023] Figure 3 It is a schematic diagram of the assembly structure of the cyclone cylinder and the circulation cylinder in the secondary cyclone flotation separation zone of the present invention.

[0024] Figure 4 It is a schematic structural diagram of a micro-spin flocculation reactor in the micro-spin flocculation flotation separation zone of the present invention.

[0025] In the figure, 1 is a closed tank, 2 is a primary cyclone flotation separation zone, 3 is a secondary cyclone flotation separation zone, 4 is a bubble enrichment flotation separation zone, 5 is a micro-spin flocculation flotation separation zone, 6 is a clean water buffer zone, 7 is an oil collection tank, 8 is an oil collection pipe, 9 is a cyclone tube, 10 is a circulation tube, 11 is a guide baffle, 12 is a gas phase space zone, 13 is an oilfield produced water transmission pipeline, 14 is a clean water output pipeline, 15 is a separation zone baffle, 16 is an oilfield produced water partition water inlet, 17 is a dissolved air water inlet pipe, 18 is a Cyclone, 19 primary grid slot, 20 secondary grid slot, 21 bubble enrichment separator, 22 doser, 23 micro-spin flocculation reactor, 24 mesh spoiler component, 25 annular cylinder, 26 air inlet, 27 air outlet, 28 pressure relief port, 29 pressure detection port, 30 liquid level detection port, 31 dissolved water pump, 32 dissolved water tank, 33 water outlet pipe, 34 manhole, 35 slag discharge hole, 36 secondary water inlet pipe, 37 micro-spin water inlet pipe, 38 high-level water outlet pipe. DETAILED DESCRIPTION

[0026] The technical solution of the invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0027] The invention relates to a closed multi-stage flotation oil removal method for oilfield produced water. A primary cyclone flotation separation zone 2, a secondary cyclone flotation separation zone 3, a bubble enrichment flotation separation zone 4, a micro-spin flocculation flotation separation zone 5 and a water purification buffer zone 6 are sequentially arranged in a closed tank body 1, and the method is carried out according to the following steps:

[0028] A. The produced water from the oil field enters the primary cyclone flotation separation zone 2 and is added with dissolved air water for cyclone flotation separation. The bubbles in the dissolved air water and the oil droplets in the produced water from the oil field collide with each other, contact and adhere to each other under the action of the cyclone, and then float to the oil collection tank 7 on the water surface of the primary cyclone flotation separation zone 2 in a swirling flow state, and are collected through the oil collection pipe 8. The sediment in the produced water from the oil field sinks to the bottom of the primary cyclone flotation separation zone 2;

[0029] B. The produced water from the oil field after being treated in the primary cyclone flotation separation zone 2 enters the secondary cyclone flotation separation zone 3 from below, and the dissolved air water is added to generate bubbles. The produced water from the oil field is spun through the cyclone tube 9, and the oil flocs go upward into the oil collecting tank 7 at the top of the circulation tube 10, and then are collected through the oil collecting pipe 8. The sand in the produced water from the oil field sinks to the bottom of the secondary cyclone flotation separation zone 3;

[0030] C. The produced water from the oil field after the secondary cyclone flotation separation zone 3 is added with dissolved air water and enters the bubble enrichment flotation separation zone 4. After the bubble enrichment and sorting, the gas in the dissolved air water is released to generate large bubbles and small bubbles, and the large bubbles are mixed so that the large bubbles hide in the small bubble group. The large bubbles can increase the turbulent kinetic energy of the gas-liquid two-phase flow, and the small bubbles can change the state of the microscopic gas-liquid contact interface, strengthen the adhesion and wrapping process of the bubbles on the oil droplets, and form a stable bubble-oil drop adhesion body. The oil droplets are collected into the oil collection tank 7 on the water surface of the bubble enrichment flotation separation zone 4 through the guide baffle 11, and then collected through the oil collection pipe 8. The sand in the produced water from the oil field sinks to the bottom of the bubble enrichment flotation separation zone 4;

[0031] D. The produced water from the oil field after passing through the bubble enrichment flotation separation zone 4 enters the micro-spin flocculation flotation separation zone 5, where dissolved air water and flocculants are added for micro-spin flocculation flotation separation. The produced water from the oil field is mixed with the reagents, and the migration and collision coagulation of fine particles in the water are improved through micro-vortices, which promote the mutual adhesion of the reagents and impurities in the water to form floccules that float to the oil collection tank 7 on the water surface of the micro-spin flocculation flotation separation zone 5, and are collected through the oil collection pipe 8. The sand in the produced water from the oil field sinks to the bottom of the micro-spin flocculation flotation separation zone 5;

[0032] E. The produced water from the oil field after passing through the micro-spin flocculation flotation separation zone 5 flows into the clean water buffer zone 6 through the high-level water outlet pipe 38 to form clean water. The clean water at the bottom is produced into dissolved air water through the dissolved air pump 31 and the dissolved air tank 32 outside the closed tank body 1 to supply the dissolved air water required in step A, step B, step C and step D. The remaining clean water is quantitatively and regularly discharged from the closed tank body 1.

[0033] As a further embodiment, in step C, the diameter of the large bubbles ranges from 1 mm to 5 mm, and the diameter of the small bubbles ranges from less than 1 mm.

[0034] like Figure 1-Figure 4As shown, the oilfield produced water closed multi-stage flotation oil removal device of the present invention comprises a closed tank body 1, an oilfield produced water delivery pipeline 13 and a clean water output pipeline 14, wherein the oilfield produced water delivery pipeline 13 and the clean water output pipeline 14 are respectively arranged on the front and rear of the closed tank body 1, and further comprises an oil collecting tank 7, an oil collecting pipe 8, a primary cyclone flotation separation zone 2, a secondary cyclone flotation separation zone 3, a bubble enrichment flotation separation zone 4, a micro-spin flocculation flotation separation zone 5 and a clean water buffer zone 6, wherein the primary cyclone flotation separation zone 2, the secondary cyclone flotation separation zone 3 , bubble enrichment flotation separation zone 4, micro-spin flocculation flotation separation zone 5 and water purification buffer zone 6 are respectively arranged in sequence in the closed tank body 1, and the oil collection tank 7 is horizontally arranged on the upper ends of the corresponding primary cyclone flotation separation zone 2, secondary cyclone flotation separation zone 3, bubble enrichment flotation separation zone 4 and micro-spin flocculation flotation separation zone 5, and the suction ports of several oil collection pipes 8 are respectively arranged in the oil collection tank 7 located at the upper ends of the primary cyclone flotation separation zone 2, secondary cyclone flotation separation zone 3, bubble enrichment flotation separation zone 4 and micro-spin flocculation flotation separation zone 5.

[0035] As a further embodiment, it also includes a separation zone partition 15, which is respectively vertically fixed on the rear end of the oil collecting tank 7 at the corresponding positions of the primary cyclone flotation separation zone 2, the secondary cyclone flotation separation zone 3, the bubble enrichment flotation separation zone 4 and the micro-spin flocculation flotation separation zone 5, and the space between the upper end of the separation zone partition 15 and the upper wall of the closed tank body 1 is respectively arranged to be air-permeable, forming air vents that are interconnected between the primary cyclone flotation separation zone 2, the secondary cyclone flotation separation zone 3, the bubble enrichment flotation separation zone 4, the micro-spin flocculation flotation separation zone 5 and the clean water buffer zone 6, and the space between the lower end of the separation zone partition 15 and the lower wall of the closed tank body 1 is respectively arranged to be air-permeable, forming oilfield produced water partition water inlet 16 of the primary cyclone flotation separation zone 2, the secondary cyclone flotation separation zone 3, the bubble enrichment flotation separation zone 4, the micro-spin flocculation flotation separation zone 5 and the clean water buffer zone 6.

[0036] As a further embodiment, the primary cyclone flotation separation zone 2 also includes a dissolved air water inlet pipe 17, a cyclone 18, a primary grid slot 19 and a secondary grid slot 20. The cyclone 18 is fixed at the bottom of the closed tank body 1, and the top of the cyclone 18 is open. The oilfield produced water delivery pipeline 13 is connected in parallel with the dissolved air water inlet pipe 17 and enters the cyclone 18 through the tangential inlet pipe of the cyclone 18, rotates in the cyclone 18, and flows out from the top of the cyclone 18 upward.

[0037] As a further embodiment, the secondary cyclone flotation separation zone 3 also includes a dissolved air water inlet pipe 17, a secondary water inlet pipe 36, a cyclone tube 9 and a circulation tube 10. The secondary water inlet pipe 36 is arranged at the position of the corresponding oilfield produced water partition inlet 16, the cyclone tube 9 is arranged in the circulation tube 10, and the outlet of the dissolved air water inlet pipe 17 is arranged in the bottom of the circulation tube 10. The oilfield produced water enters the bottom of the circulation tube 10 through the secondary water inlet pipe 36 and merges with the dissolved air water. It enters the cyclone tube 9 and mixes with the bubbles released by the dissolved air water and then enters the circulation tube 10 upward. After the cyclone tube 9 cyclones, oil and water are separated. At the same time, the upward oil, gas and water in the cyclone tube 9 will pull the water outside the cyclone tube 9 to flow downward, forming a circulation field. After the oil and gas are separated by cyclone, they are mainly distributed in the upper part of the circulation tube 10, and the water outside the cyclone tube 9 moves downward and is discharged from the outlet.

[0038] As a further embodiment, the bubble enrichment flotation separation zone 4 also includes a dissolved air water inlet pipe 17, a guide baffle 11 and a bubble enrichment separator 21, the lower portion of the guide baffle 11 is vertically arranged at a position close to the rear of the separation zone baffle 15 located on the front side of the bubble enrichment flotation separation zone 4, the lower portion of the guide baffle 11 is arranged at the lower portion of the bubble enrichment flotation separation zone 4, the lower end of the guide baffle 11 is fixed on the lower wall of the closed tank body 1 at the corresponding position, the upper portion of the guide baffle 11 is arranged in the middle of the bubble enrichment flotation separation zone 4, the upper portion of the guide baffle 11 is inclined backward, the lower end of the upper portion of the guide baffle 11 is fixedly connected to the upper end of the lower portion of the guide baffle 11 as a whole, the dissolved air water inlet pipe 17 passes through the closed tank body 1, the dissolved air water outlet is arranged between the lower portion of the guide baffle 11 and the adjacent separation zone baffle 15, and the bubble enrichment separator 21 is horizontally arranged between the upper portion of the guide baffle 11 and the adjacent separation zone baffle 15.

[0039] As a further embodiment, the micro-spin flocculation flotation separation zone 5 also includes a dissolved air water inlet pipe 17, a micro-spin water inlet pipe 37, a doser 22, a micro-spin flocculation reactor 23 and a high-level water outlet pipe 38. The micro-spin flocculation reactor 23 is composed of a mesh flow disturbance component 24 and an annular tube 25. Several mesh flow disturbance components 24 are arranged in two layers in the annular tube 25. The micro-spin water inlet pipe 37 is arranged at the position of the corresponding oilfield produced water partition water inlet 16. The dissolved air water inlet pipe 17 passes through the closed tank body 1 and is divided into a plurality of dissolved air water outlets. The dissolved air water outlets are respectively arranged below the mesh flow disturbance component 24 of the corresponding micro-spin flocculation reactor 23. The doser 22 is arranged outside the closed tank body 1. The drug outlet of the doser 22 extends into the sealed tank body 1 and is connected to the micro-spin water inlet pipe 37. The high-level water outlet pipe 38 is arranged at the position of the corresponding oilfield produced water partition water inlet 16.

[0040] As a further embodiment, it also includes an air inlet 26, an air outlet 27, a pressure relief port 28, a pressure detection port 29 and a liquid level detection port 30, and the air inlet 26, the air outlet 27, the pressure relief port 28 and the pressure detection port 29 are respectively arranged on the upper wall of the closed tank body 1 at the position corresponding to the purification buffer zone 6.

[0041] As a further embodiment, it also includes a dissolved water pump 31, a dissolved water tank 32, a water outlet pipe 33, a manhole 34 and a slag discharge hole 35, the water inlet of the water outlet pipe 33 is connected to the clean water buffer 6, the water outlet pipe 33 passes through the closed tank body 1 and is connected to the dissolved water pump 31 located outside the closed tank body 1, and the dissolved water pump 31 is connected to the dissolved air in the corresponding primary cyclone flotation separation zone 2, the secondary cyclone flotation separation zone 3, the bubble enrichment flotation separation zone 4 and the micro-spin flocculation flotation separation zone 5 through the connecting pipe through the dissolved water tank 32. The water inlet pipe 17 is connected, and several holes 34 are respectively arranged on the upper wall of the closed tank body 1 at the corresponding positions of the primary cyclone flotation separation zone 2, the secondary cyclone flotation separation zone 3, the bubble enrichment flotation separation zone 4, the micro-spin flocculation flotation separation zone 5 and the clean water buffer zone 6, and the slag discharge holes 35 are respectively arranged on the lower wall of the closed tank body 1 at the corresponding positions of the primary cyclone flotation separation zone 2, the secondary cyclone flotation separation zone 3, the bubble enrichment flotation separation zone 4, the micro-spin flocculation flotation separation zone 5 and the clean water buffer zone 6.

[0042] The invention was tested in a field pilot test at a produced water treatment station in an oil field, with a treatment scale of 100m 3 / d, inlet pressure 0.5MPa, inlet water oil content 400mg / L, inlet water temperature 55℃.

[0043] During the experimental operation of the present invention, A. through the oilfield produced water delivery pipeline 13, the oilfield produced water and dissolved air water enter the cyclone 18 of the primary cyclone flotation separation zone 2, the oilfield produced water and dissolved air water are mixed and then enter the cyclone 18 tangentially, the oily wastewater sedimentation, bubbles and oil droplets collide, contact and adhere to each other under the action of the cyclone 18, the water flow rate is 4m 3 / h, tangential inlet flow rate 3.2m / s, dissolved in the cyclone 18, the natural gas in the oil field produced water is released in the form of micro bubbles, the oil droplets contained in the oil field produced water first pass through the first-level grid slot 19 for preliminary sedimentation treatment, and then pass through the second-level grid slot 20 for further sedimentation treatment. After completing the mechanical screening pretreatment, it is convenient for the oil droplets in the oil field produced water to contact and adhere with the micro bubbles released from the dissolved gas water, and rise in a rotating flow state. The oil droplets are concentrated in the middle area under the action of the cyclonic centrifugal force, and continuously coalesce and become in the process of rising. The produced water from the oil field collides and adheres to the bubbles, and finally floats to the oil collection tank 7, and is collected through the oil collection pipe 8. The produced water from the oil field enters the secondary cyclone flotation separation zone 3 through the water inlet 16 of the produced water partition of the oil field; B. The produced water from the oil field enters the circulation tube 10 of the secondary cyclone flotation separation zone 3, mixes with the bubbles released by the dissolved water, and then enters the circulation tube 10 upward, and forms a fusion effect through the cyclone tube 9. At the same time, the produced water from the oil field in the circulation tube 10 upward will pull the produced water outside the circulation tube 10 to flow downward to form a circulation field. The oil droplets are condensed and transformed through swirl and circulation. The oil produced water from the oil field that has risen to the outside of the circulation tube 10 moves downward and enters the bubble enrichment flotation separation zone 4 through the oil field produced water partition inlet 16; C. The oil field produced water enters the bubble enrichment flotation separation zone 4, and the oil field produced water is mixed with the dissolved gas water. Under the action of the bubble enrichment separator 4, the enrichment and separation effect of the microbubbles is achieved, and the gas in the dissolved gas water is released to generate large bubbles and small bubbles, and the large bubbles are mixed and redistributed to change the movement of the large bubbles. The bubbles of different sizes produced by the gas-liquid two-phase have different effects. The large bubbles can increase the turbulent kinetic energy of the gas-liquid two-phase flow, and the small bubbles can change the state of the microscopic gas-liquid contact interface, realize the fine adsorption of oil droplets, strengthen the adhesion and wrapping process of bubbles to oil droplets, form a stable bubble-oil droplet adhesion body, rise to the top oil collection tank 7, and then collect through the oil collection pipe 8 to complete the fine oil removal process. The oil field produced water enters the micro-spin flocculation flotation separation zone 5 through the oil field produced water partition inlet 16; D.The produced water from the oil field enters the lower part of the micro-spin flocculation reactor 23 of the micro-spin flocculation flotation separation zone 5. The dissolved air water inlet 17 is divided into three groups of dissolved air water inlets, namely the side wall and the center. The dissolved air water is connected in parallel with the doser 22. The doser 22 can automatically adjust the amount of the medicine according to the sewage treatment volume. The produced water from the oil field is mixed with the medicine and enters the micro-spin flocculation reactor 23 of the micro-spin flocculation flotation separation zone 5. The micro-spin flocculation reactor 23 can control the flow direction of the fluid inside and outside the annular cylinder 25 by adjusting the water flow rate of the three groups of dissolved air water inlets. When the flow rate of dissolved air water inlet in the core area is larger than that of the side wall, the produced water of the oilfield will flow toward the side wall through the pores of the vertical or inclined mesh spoiler component 24. On the contrary, the produced water of the oilfield will gather and flow toward the center while flowing axially. When the produced water of the oilfield flows through a large number of holes on the wall of the micro-spin flocculation reactor 23, countless tiny vortices are formed. According to modern coagulation theory, micro-vortices are beneficial to the migration and collision coagulation of fine particles in the water, increase the probability of contact collision, and promote the mutual adhesion of agents and impurities in the produced water of the oilfield to form flocs. Since the micro-spin flocculation reactor 23 is a hollow shell with a low internal flow rate, a large number of flocs with larger particle sizes accumulate and suspend in the water in the micro-spin flocculation reactor 23, which adsorbs fine flocs and oil droplets. The micro-spin flocculation reactor 23 has the functions of preventing short-flow of water, making the water flow evenly distributed, and improving the flow gradient. The micro-spin flocculation flotation separation zone 5 enhances the adsorption of fine impurities and oil droplets in the oil field produced water by adding reagents to enhance the bubbles, and floats them to the top oil collection tank 7, and then collects them through the oil collection pipe 8. The oil field produced water becomes clean water after passing through the micro-spin flocculation flotation separation zone 5. The top of the high-level water outlet pipe 38 overflows and flows into the clean water buffer 6; E. The separated clean water enters the clean water buffer 6. After the clean water reaches a certain water level after standing, it is discharged from the closed tank 1 through the clean water output pipeline 14. The lower wall of the closed tank 1 located in the clean water buffer 6 is provided with a water outlet pipe 33 connected to the closed tank 1. The water outlet pipe 33 is connected to the dissolved water pump 31 outside the closed tank 1. The dissolved water pump 31 is connected to the dissolved air water inlet pipe 17 of the corresponding primary cyclone flotation separation zone 2, secondary cyclone flotation separation zone 3, bubble enrichment flotation separation zone 4 and micro-spin flocculation flotation separation zone 5 through a connecting pipe through the dissolved water tank 32. .

[0044] The natural gas released from the primary cyclone flotation separation zone 2, the secondary cyclone flotation separation zone 3, the bubble enrichment flotation separation zone 4, the micro-spin flocculation flotation separation zone 5 and the water purification buffer zone 6 rises to the gas phase space zone 12 and is discharged and collected from the gas outlet 27 located on the upper wall of the closed tank body 1.

[0045] A safety valve is installed at the pressure relief port 28 at the top of the water purification buffer 6, a vacuum pressure gauge is installed at the pressure detection port 29, and an electric switch valve is installed at the gas outlet 27, which is connected to the natural gas supply pipeline in the station. When the gas phase pressure is detected to be lower than 10kPa, the valve is opened, and when it is higher than 100kPa, the valve is closed. When the ultra-high pressure is 180kPa, the safety valve is opened to release the pressure. A liquid level transmitter is installed at the liquid level detection port 30 at the bottom of the water purification buffer 6 to realize real-time monitoring of the liquid level in the closed tank 1.

[0046] During the test, the oil content of produced water reached 12 mg / L after treatment, the device operated in a completely closed manner, natural gas was basically recycled, and there was no waste gas emission.

[0047] In the embodiment of the present invention, the bubble enrichment separator 21 of the bubble enrichment flotation separation zone 4 is prior art and will not be described in detail again.

[0048] The outlet level of the high-level outlet pipe 38 of the micro-spin flocculation flotation separation zone 5 of the present invention is 1-2 cm higher than the level of the oil collecting tank 7 in each zone, thereby effectively ensuring that the oil droplets on the water surface of each zone always float in the oil collecting tank 7 or on the plane of the oil collecting tank 7.

[0049] The above description is only a preferred embodiment of the present invention and is not intended to limit the protection scope of the present invention.

Claims

1. A closed multi-stage flotation method for oil field produced water, characterized in that: The primary cyclone flotation separation zone, the secondary cyclone flotation separation zone, the bubble enrichment flotation separation zone, the micro-spin flocculation flotation separation zone and the water purification buffer zone are sequentially arranged in the closed tank body, and the following steps are followed: A. The produced water from the oil field enters the primary cyclone flotation separation zone and is added with dissolved air water for cyclone flotation separation. The bubbles in the dissolved air water and the oil droplets in the produced water from the oil field collide with each other, contact and adhere to each other under the action of the cyclone, and then float to the oil collection tank on the water surface of the cyclone flotation separation zone in a rotating flow state, and are collected through the oil collection pipe. The sand in the produced water from the oil field sinks to the bottom of the primary cyclone flotation separation zone; B. After the primary cyclone flotation separation treatment, the produced water from the oil field enters the secondary cyclone flotation separation zone from the bottom, and the dissolved air water is added to generate bubbles. The produced water from the oil field is spun through the cyclone tube, and the oil flocs go upward into the oil collection tank at the top of the circulation tube, and then are collected through the oil collection pipe. The sand in the produced water from the oil field sinks to the bottom of the secondary cyclone flotation separation zone; C. The produced water from the oil field after the secondary cyclone flotation separation zone is added with dissolved air water and enters the bubble enrichment flotation separation zone. After the bubble enrichment and separation, the gas in the dissolved air water is released to generate large bubbles and small bubbles, which are mixed so that the large bubbles hide in the small bubble group. The large bubbles can increase the turbulent kinetic energy of the gas-liquid two-phase flow, and the small bubbles can change the state of the microscopic gas-liquid contact interface, strengthen the adhesion and wrapping process of the bubbles on the oil droplets, and form a stable bubble-oil droplet adhesion body. The oil droplets are gathered into the oil collection tank on the water surface of the bubble enrichment flotation separation zone through the guide baffle, and then collected through the oil collection pipe. The sand in the produced water of the oil field sinks to the bottom of the bubble enrichment flotation separation zone; D. The produced water from the oil field after the bubble enrichment flotation separation zone enters the micro-spin flocculation flotation separation zone, where dissolved air water and flocculants are added for micro-spin flocculation flotation separation. The produced water from the oil field is mixed and contacted with the dissolved air water carrying the reagents again, and the migration and collision coagulation of fine particles in the water are improved through micro-vortices, which promote the mutual adhesion of the reagents and impurities in the water to form floccules that float to the oil collection tank on the water surface of the micro-spin flocculation flotation separation zone, and are collected through the oil collection pipe. The sand in the produced water from the oil field sinks to the bottom of the micro-spin flocculation flotation separation zone; E. The produced water from the oil field after the micro-spin flocculation flotation separation zone flows into the clean water buffer through the high-level water outlet pipe to form clean water. During the static process, the clean water remaining in the clean water buffer is located at the bottom and is supplied to step A, step B, step C and step D through the air dissolving pump and air dissolving tank outside the closed tank body to produce dissolved air water. The remaining clean water is discharged from the closed tank body quantitatively and regularly.

2. The closed multi-stage flotation oil removal method for oil field produced water according to claim 1, characterized in that: In step C, the diameter of large bubbles ranges from 1 mm to 5 mm, and the diameter of small bubbles ranges from less than 1 mm.

3. A closed multi-stage flotation oil removal device for oilfield produced water, comprising a closed tank body, an oilfield produced water delivery pipeline and a clean water output pipeline, wherein the oilfield produced water delivery pipeline and the clean water output pipeline are respectively arranged on the front and rear of the closed tank body, characterized in that: It also includes an oil collecting tank, an oil collecting pipe, a primary cyclone flotation separation zone, a secondary cyclone flotation separation zone, a bubble enrichment flotation separation zone, a micro-spin flocculation flotation separation zone and a water purification buffer zone. The primary cyclone flotation separation zone, the secondary cyclone flotation separation zone, the bubble enrichment flotation separation zone, the micro-spin flocculation flotation separation zone and the water purification buffer zone are respectively arranged in sequence in a closed tank body. The oil collecting tanks are respectively arranged horizontally on the upper ends of the corresponding primary cyclone flotation separation zone, the secondary cyclone flotation separation zone, the bubble enrichment flotation separation zone and the micro-spin flocculation flotation separation zone. The suction ports of several oil collecting pipes are respectively arranged in the oil collecting tanks located at the upper ends of the primary cyclone flotation separation zone, the secondary cyclone flotation separation zone, the bubble enrichment flotation separation zone and the micro-spin flocculation flotation separation zone.

4. The closed multi-stage flotation oil removal device for oil field produced water according to claim 3, characterized in that: It also includes a separation zone partition, which is respectively vertically fixed on the rear end of the oil collecting tank at the corresponding position of the primary cyclone flotation separation zone, the secondary cyclone flotation separation zone, the bubble enrichment flotation separation zone and the micro-spin flocculation flotation separation zone, and the upper end of the separation zone partition to the upper wall of the closed tank body is respectively arranged to be air-permeable, forming an air vent that is interconnected between the primary cyclone flotation separation zone, the secondary cyclone flotation separation zone, the bubble enrichment flotation separation zone, the micro-spin flocculation flotation separation zone and the clean water buffer zone, and the lower end of the separation zone partition to the lower wall of the closed tank body is respectively arranged to be air-permeable, forming the oilfield produced water zone inlet of the primary cyclone flotation separation zone, the secondary cyclone flotation separation zone, the bubble enrichment flotation separation zone, the micro-spin flocculation flotation separation zone and the clean water buffer zone.

5. The closed multi-stage flotation oil removal device for oilfield produced water according to claim 3, characterized in that: The primary cyclone flotation separation zone also includes a dissolved air water inlet pipe, a cyclone, a primary grid slot and a secondary grid slot. The cyclone is fixed at the bottom of the closed tank body, and the top of the cyclone is open. The oilfield produced water delivery pipeline is connected in parallel with the dissolved air water inlet pipe and then enters the cyclone through the tangential inlet pipe of the cyclone, rotates in the cyclone, and flows upward from the top of the cyclone.

6. The closed multi-stage flotation oil removal device for oil field produced water according to claim 3, characterized in that: The secondary cyclone flotation separation zone also includes a dissolved air water outlet pipe, a secondary water inlet pipe, a cyclone tube and a circulation tube. The secondary water inlet pipe is arranged at the water inlet position of the corresponding oilfield produced water partition, the cyclone tube is arranged in the circulation tube, and the outlet of the dissolved air water outlet pipe is arranged in the bottom of the circulation tube. The oilfield produced water enters the bottom of the circulation tube through the secondary water inlet pipe and merges with the dissolved air water. It enters the cyclone tube and mixes with the bubbles released by the dissolved air water. It then enters the circulation tube upward and is swirled by the cyclone tube to separate oil and water. At the same time, the upward oil, gas and water in the cyclone tube will pull the water outside the cyclone tube to flow downward, forming a circulation field. After the oil and gas are separated by the cyclone, they are mainly distributed in the upper part of the circulation tube, and the water outside the cyclone tube moves downward and is discharged from the outlet.

7. The closed multi-stage flotation oil removal device for oil field produced water according to claim 3, characterized in that: The bubble enrichment flotation separation zone also includes a dissolved air water inlet pipe, a guide baffle and a bubble enrichment separator. The lower part of the guide baffle is vertically arranged at a position close to the rear of the separation zone baffle located on the front side of the bubble enrichment flotation separation zone, the lower part of the guide baffle is arranged at the lower part of the bubble enrichment flotation separation zone, the lower end of the guide baffle is fixed on the lower wall of the closed tank body at the corresponding position, the upper part of the guide baffle is arranged in the middle of the bubble enrichment flotation separation zone, the upper part of the guide baffle is inclined backward, the lower end of the upper part of the guide baffle is fixedly connected to the upper end of the lower part of the guide baffle as a whole, the dissolved air water inlet pipe passes through the closed tank body, the dissolved air water outlet is arranged between the lower part of the guide baffle and the adjacent separation zone baffle, and the bubble enrichment separator is horizontally arranged between the upper part of the guide baffle and the adjacent separation zone baffle.

8. The closed multi-stage flotation oil removal device for oilfield produced water according to claim 3, characterized in that: The micro-spin flocculation flotation separation zone also includes a dissolved air water inlet pipe, a micro-spin water inlet pipe, a doser, a micro-spin flocculation reactor and a high-position water outlet pipe. The micro-spin flocculation reactor is composed of a mesh flow disturbance component and an annular tube. Several mesh flow disturbance components are arranged in two layers in the annular tube. The micro-spin water inlet pipe is arranged at the water inlet position of the corresponding oilfield produced water partition. The dissolved air water inlet pipe is divided into several arrays of dissolved air water outlets after passing through the closed tank body. The dissolved air water outlets are respectively arranged below the mesh flow disturbance component of the corresponding micro-spin flocculation reactor. The doser is arranged outside the closed tank body. The drug outlet of the doser extends into the sealed tank body and is connected to the micro-spin water inlet. The high-position water outlet pipe is arranged at the water inlet position of the corresponding oilfield produced water partition.

9. The closed multi-stage flotation oil removal device for oilfield produced water according to claim 3, characterized in that: It also includes an air inlet, an air outlet, a pressure relief port, a pressure detection port and a liquid level detection port, and the air inlet, air outlet, pressure relief port and pressure detection port are respectively arranged on the upper wall of the closed tank body at the position corresponding to the purification buffer zone.

10. The closed multi-stage flotation oil removal device for oilfield produced water according to claim 3, characterized in that: It also includes a dissolved water pump, a dissolved water tank, a water outlet pipe, a manhole and a slag discharge hole. The water inlet of the water outlet pipe is connected to the clean water buffer zone. The water outlet pipe passes through the closed tank body and is connected to the dissolved water pump located outside the closed tank body. The dissolved water pump is connected to the dissolved air water inlet pipes of the corresponding primary cyclone flotation separation zone, secondary cyclone flotation separation zone, bubble enrichment flotation separation zone and micro-spin flocculation flotation separation zone through a connecting pipe via the dissolved water tank. Several manholes are respectively arranged on the upper wall of the closed tank body at the corresponding positions of the primary cyclone flotation separation zone, the secondary cyclone flotation separation zone, the bubble enrichment flotation separation zone, the micro-spin flocculation flotation separation zone and the clean water buffer zone. The slag discharge holes are respectively arranged on the lower wall of the closed tank body at the corresponding positions of the primary cyclone flotation separation zone, the secondary cyclone flotation separation zone, the bubble enrichment flotation separation zone, the micro-spin flocculation flotation separation zone and the clean water buffer zone.

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