Device and method for removing oil by air-entraining reflux recycling multi-stage baffle microbubble flotation

Abstract

The present invention provides a device and method for degreasing by air-entraining reflux recycling multi-stage baffle microbubble flotation, which relates to the technical field of degreasing of oilfield produced water. The device for degreasing by air-entraining reflux recycling multi-stage baffle microbubble flotation provided by the present invention includes an air flotation tank, a dissolved air pump and an electric control system. A vortex reactor, a T-shaped water inlet and an adjustable oil collection tank are arranged inside the air flotation tank. A nitrogen pressure automatic balance pipeline system, a nitrogen air-entraining reflux pipeline, a dissolved air water make-up pipeline, a dissolved air water return pipeline and an oil-containing produced water raw water pipeline are arranged outside the air flotation tank. By controlling the inlet and outlet pressures of the dissolved air pump, the dissolved air efficiency is improved and the microbubble particle size is reduced; the vortex reactor slows down the aggregation and floating speed of bubbles and prevents short-circuit flow; the nitrogen pressure automatic balance pipeline system can form a stable gas phase space at the inner top of the air flotation tank and keep the liquid level stable, and the precipitated nitrogen is recycled as the gas source of the dissolved air pump, greatly reducing the consumption of nitrogen.

Description

Technical Field

[0001] The present invention relates to the technical field of oil removal from produced water in oilfields, and particularly relates to a device and method for air-induced reflux recycling multi-stage baffle microbubble flotation oil removal. Background Technique

[0002] In the microbubble flotation oil removal technology for oilfield produced water containing oil, that is, air flotation oil removal, a large number of fine bubbles are generated in water through a dissolved air system, so that air adheres to suspended solid particles in the form of highly dispersed tiny bubbles, creating a state with a density less than that of water, and using the buoyancy principle to make it float on the water surface, thereby realizing the water treatment process of solid-liquid separation or liquid-liquid separation. Currently, air flotation methods are mainly divided into dissolved air flotation method, multiphase flow dissolved air pump air flotation method, jet air flotation method, electrocoagulation air flotation method, and biochemical air flotation method, etc. Among them, the multiphase flow dissolved air pump air flotation method generally uses a vortex pump or a gas-liquid multiphase pump. Its principle is that air and water enter the pump shell together at the inlet of the pump, and the high-speed rotating impeller cuts the inhaled air into small bubbles multiple times. The small bubbles quickly dissolve in water under the high-pressure environment in the pump to form dissolved air water, and then enter the air flotation device to complete the air flotation oil removal process.

[0003] When using a traditional multiphase flow dissolved air pump air flotation device for oil removal, the following problems mainly exist: (1) a large amount of nitrogen is consumed during the dissolved air process; (2) the dissolved air efficiency is relatively low, and most air-liquid ratios are <5%. Some dissolved air pumps also need to install an air-liquid separation tank at the pump outlet to discharge the gas that cannot be dissolved in water; (3) the dissolved air water pipeline is vertically inserted into the raw water pipeline, resulting in a large loss after the dissolved air water is mixed with the raw water, poor dissolution effect, and easy occurrence of short circuit during the backward push flow operation, and the flotation oil removal effect is relatively poor. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide a device and method for air-induced reflux recycling multi-stage baffle microbubble flotation oil removal. When using the device provided by the present invention for dissolved air flotation oil removal of oilfield produced water, the nitrogen consumption is low, the dissolved air efficiency is high, short circuit is not easy to occur, the flotation oil removal effect is good, and the oil content of the effluent can meet the standard.

[0005] In order to achieve the above invention purpose, the present invention provides the following technical solutions:

[0006] The present invention provides a device for air-induced reflux recycling multi-stage baffle microbubble flotation oil removal, including an air flotation tank 1 and a dissolved air pump 2;

[0007] The cavity of the air flotation tank 1 is divided into N flotation separation chambers 11 and an external output and reflux chamber 12 connected in series in sequence; in each of the flotation separation chambers 11, there is a first eddy current reactor 111 with an open top, a T-shaped water inlet 112, a gas communication port 113, and a first adjustable oil collection tank 114; in the external output and reflux chamber 12, there is a second eddy current reactor 121 with an open top, a second adjustable oil collection tank 122, a produced water and return water outlet 123, and a qualified water external output port 124; each first eddy current reactor 111 is provided with a first reactor inlet 1111; the second eddy current reactor 121 is provided with a second reactor inlet 1211; adjacent flotation separation chambers 11 and between the flotation separation chamber 11 and the external output and reflux chamber 12 are connected through the T-shaped water inlet 112 and the gas communication port 113; the T-shaped water inlet 112 is connected to the first reactor inlet 1111 or the second reactor inlet 1211 through a T-shaped water inlet pipeline 1121; N≥2;

[0008] On the top of the air flotation tank 1, there is a nitrogen pressure automatic balance pipeline system 31 and a nitrogen gas introduction and reflux pipeline 32; at the bottom of the air flotation tank 1, there is a dissolved air water makeup pipeline 33 and a dissolved air water return pipeline 34; on the side of the air flotation tank 1, there is an oil-containing produced water raw water pipeline 35;

[0009] The dissolved air pump 2 is provided with a water absorption and air supplement port 21 and a dissolved air water outlet 22;

[0010] The nitrogen gas introduction and reflux pipeline 32 and the dissolved air water return pipeline 34 are connected to the water absorption and air supplement port 21; the dissolved air water outlet 22 is connected to the dissolved air water makeup pipeline 33;

[0011] The dissolved air water makeup pipeline 33 is connected to the first reactor inlet 1111 through an inclined angle connection with the oil-containing produced water raw water pipeline 35; the dissolved air water makeup pipeline 33 is connected to the first reactor inlet 1111 through an inclined angle connection with the T-shaped water inlet pipeline 1121; the dissolved air water makeup pipeline 33 is connected to the second reactor inlet 1211 through an inclined angle connection with the T-shaped water inlet pipeline 1121.

[0012] Preferably, adjacent flotation separation chambers 11 and between the flotation separation chamber 11 and the external output and reflux chamber 12 are separated by a partition plate 116; the height of the partition plate 116 is 94-96% of the height of the air flotation tank, and the gas communication port 113 is located between the partition plate 116 and the upper tank wall of the air flotation tank 1.

[0013] Preferably, the angle of the inclined angle connection is 40-50°.

[0014] Preferably, each outer wall of the flotation separation chamber 11 is further provided with a first washable viewing window 115; the outer wall of the external output and reflux chamber 12 is further provided with a second washable viewing window 125;

[0015] A service water flushing pipeline 37 is provided at the inner tank top of the air flotation tank 1, and the service water flushing pipeline 37 is respectively communicated with the first washable viewing window 115 and the second washable viewing window 125.

[0016] Preferably, a first handwheel is provided on the first adjustable oil collection tank 114, and a second handwheel is provided on the second adjustable oil collection tank 122; the first handwheel and the second handwheel are arranged outside the tank of the air flotation tank 1.

[0017] The present invention provides a method for air intake reflux reuse multi-stage countercurrent microbubble flotation oil removal by using the device described in the above technical solution, including the following steps:

[0018] (1) The recycled water and nitrogen are pressurized and dissolved in the dissolved air pump 2 to generate dissolved air water containing microbubbles.

[0019] (2) The dissolved air water containing microbubbles is mixed with the original produced water containing oil in the pipeline after the dissolved air water makeup pipeline 33 and the original produced water pipeline 35 containing oil are obliquely connected to obtain dissolved air oil water.

[0020] (3) The dissolved air oil water enters the vortex reactor along the tangential direction of the bottom of the first vortex reactor 111 in the flotation separation chamber 11 and then rises in a spiral manner. The microbubbles in the dissolved air oil water first contact and flocculate with the oil droplets in the original produced water containing oil and are depressurized and released to the top layer of the dissolved air oil water. After the water flow reaches the outlet of the vortex reactor, it flows downward through the baffle. During the process of flowing downward through the baffle, the microbubbles and the oil droplets conduct a second contact and flocculation and are depressurized and released to the top layer of the dissolved air oil water to obtain a microbubble-oil droplet phase and a water phase; the oil droplets in the microbubble-oil droplet phase are collected by the first adjustable oil collection tank 114 and the second adjustable oil collection tank 122; the nitrogen gas precipitated from the microbubbles in the microbubble-oil droplet phase enters the gas phase space at the top of the tank of the air flotation tank 1 and is then transported to the dissolved air pump through the nitrogen gas intake reflux pipeline 32 for recycling.

[0021] (4) The water phase enters the next-stage flotation separation chamber through the T-shaped water inlet, and after being mixed with the dissolved air water containing microbubbles generated by the dissolved air pump in the pipeline after the dissolved air water makeup pipeline 33 and the T-shaped water inlet pipeline 1121 are obliquely connected, the operation of step (3) is repeated until the oil removal is qualified. After being qualified, the water phase enters the external output reflux chamber to obtain recycled water and qualified water. The recycled water is transported to the dissolved air pump through the dissolved air water return pipeline 34 by the recycled water outlet 123 for recycling, and the qualified water is output through the qualified water external output port 124.

[0022] Preferably, the inlet pressure of the dissolved air pump 2 is 0.03 - 0.04 MPa, and the outlet pressure is 0.9 - 1.0 MPa; the particle size of the microbubbles is 20 - 30 μm.

[0023] The pressure in the gas phase space at the top inside the air flotation tank is 0.03 - 0.04 MPa.

[0024] Preferably, the temperature of the extracted return water is 60 - 80 °C.

[0025] Preferably, the residence time of the dissolved air oil water in the flotation separation chamber is 80 - 120 s.

[0026] The present invention provides an air-entraining reflux recycling multi-stage baffle microbubble flotation oil removal device, which includes an air flotation tank 1 and a dissolved air pump 2; the cavity of the air flotation tank 1 is divided into N serially connected flotation separation chambers 11 and an external output reflux chamber 12; in each of the flotation separation chambers 11, there is a first eddy current reactor 111 with an open top, a T-shaped water inlet 112, a gas communication port 113, and a first adjustable oil collection tank 114; in the external output reflux chamber 12, there is a second eddy current reactor 121 with an open top, a second adjustable oil collection tank 122, a produced water return outlet 123, and a qualified water external output port 124; a first reactor inlet 1111 is arranged at the tangential direction of the conical bottom of each first eddy current reactor 111; a second reactor inlet 1211 is arranged at the tangential direction of the conical bottom of the second eddy current reactor 121; adjacent flotation separation chambers 11 and between the flotation separation chamber 11 and the external output reflux chamber 12 are connected through the T-shaped water inlet 112 and the gas communication port 113; the T-shaped water inlet 112 is connected to the first reactor inlet 1111 or the second reactor inlet 1211 through a T-shaped water inlet pipeline 1121; N≥2; a nitrogen pressure automatic balance pipeline system 31 and a nitrogen air-entraining reflux pipeline 32 are arranged on the top of the air flotation tank 1, a dissolved air water supply pipeline 33 and a dissolved air water return pipeline 34 are arranged at the bottom of the air flotation tank 1, and an oil-containing produced raw water pipeline 35 is arranged on the side of the air flotation tank 1; the nitrogen pressure automatic balance pipeline system 31 includes a nitrogen input pipeline 312 and a nitrogen output pipeline 313 connected to the air flotation tank 1; the dissolved air pump 2 is provided with a water absorption air supplement port 21 and a dissolved air water outlet 22; the nitrogen air-entraining reflux pipeline 32 and the dissolved air water return pipeline 34 are connected to the water absorption air supplement port 21; the dissolved air water outlet 22 is connected to the dissolved air water supply pipeline 33; the dissolved air water supply pipeline 33 is connected to the oil-containing produced raw water pipeline 35 or the bevel of the T-shaped water inlet pipeline 1121 and is respectively connected to the first reactor inlet 1111 or the second reactor inlet 1211. In the device of the present invention, by controlling the inlet and outlet pressures of the dissolved air pump, the dissolved air efficiency can be improved and the particle size of the microbubbles can be reduced, increasing the contact area between the microbubbles and the floating oil in the water; the eddy current reactor can enable the oil-water mixture to carry out multi-stage and multi-angle baffle flow, maximizing the contact and flocculation between the bubbles and the oil droplets, slowing down the upward floating speed of the bubbles and preventing short circuit, ensuring the oil removal effect; the nitrogen pressure automatic balance pipeline system can enable a stable gas phase space to be formed at the inner top of the air flotation tank and maintain the liquid level stable. During the flotation oil removal process of the dissolved air oil-water in the air flotation tank, the microbubbles formed by nitrogen continuously precipitate from the dissolved air oil-water, and then the precipitated nitrogen is transported to the dissolved air pump through the nitrogen air-entraining reflux pipeline on the top of the air flotation tank as the gas source of the dissolved air pump for recycling, greatly reducing the consumption of nitrogen and having excellent oil removal effect.

[0027] The present invention provides a method for removing oil by air-entraining reflux recycling and multi-stage baffle microbubble flotation using the device described in the above technical solution, which includes the following steps: (1) The recycled water and nitrogen are pressurized and dissolved in the dissolved air pump 2 to generate dissolved air water containing microbubbles; (2) The dissolved air water containing microbubbles is mixed with the raw produced water containing oil in the pipeline after the dissolved air water make-up pipeline 33 and the raw produced water containing oil pipeline 35 are obliquely connected to obtain dissolved air oil-water; (3) The dissolved air oil-water enters the eddy current reactor along the tangent direction of the bottom of the first eddy current reactor 111 in the flotation separation chamber 11 and rises in a spiral manner. The microbubbles in the dissolved air oil-water first contact and flocculate with the oil droplets in the raw produced water containing oil and are depressurized and released to the top layer of the dissolved air oil-water. After the water flow reaches the outlet of the eddy current reactor, it flows downward through a baffle. During the downward baffle process, the microbubbles and the oil droplets conduct a second contact flocculation and are depressurized and released to the top layer of the dissolved air oil-water to obtain a microbubble-oil droplet phase and an aqueous phase; the oil droplets in the microbubble-oil droplet phase are collected by the first adjustable oil collection tank 114 and the second adjustable oil collection tank 122; the nitrogen gas precipitated from the microbubbles in the microbubble-oil droplet phase enters the gas phase space at the top of the air flotation tank 1 and is transported to the dissolved air pump through the nitrogen air-entraining reflux pipeline 32 for recycling; (4) The aqueous phase enters the next-stage flotation separation chamber through the T-shaped water inlet, and after being mixed with the dissolved air water containing microbubbles generated by the dissolved air pump in the pipeline after the dissolved air water make-up pipeline 33 and the T-shaped water inlet pipeline 1121 are obliquely connected, the operation of step (3) is repeated until the oil removal is qualified. After being qualified, the aqueous phase enters the external transportation and reflux chamber to obtain recycled water and qualified water. The recycled water is transported to the dissolved air pump through the dissolved air water return pipeline 34 by the recycled water outlet 123 for recycling, and the qualified water is output through the qualified water external output port 124. During the operation of the device provided by the present invention, the dissolved air pump can generate microbubbles with a particle size of 20-30 μm. The microbubbles have a small particle size and a high dissolved air efficiency, increasing the contact area between the microbubbles and the floating oil in the water and improving the oil removal effect; the dissolved air oil-water rises in a spiral manner through the eddy current reactor, and through multi-stage and multi-angle baffles, the bubbles and oil droplets are maximally contacted and flocculated, slowing down the aggregation and floating speed of the bubbles and preventing short-circuit flow, ensuring the oil removal effect; during the flotation oil removal process of the dissolved air oil-water in the air flotation tank, the microbubbles formed by nitrogen gas continuously precipitate from the dissolved air oil-water and are transported to the dissolved air pump as the air source of the dissolved air pump for recycling, greatly reducing the consumption of nitrogen gas. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1Schematic diagram of the device for air-entraining reflux reuse and multi-stage baffle microbubble flotation for oil removal. Among them, 1 is the air flotation tank; 11 is the flotation separation chamber, 111 is the first eddy current reactor, 1111 is the first reactor inlet, 112 is the T-shaped water passing port, 113 is the gas communication port, 114 is the first adjustable oil collection tank; 115 is the first washable viewing window; 116 is the partition; 117 is the first dissolved air water inlet; 118 is the inlet of the raw water containing oil for extraction; 12 is the external transportation and reflux chamber, 121 is the second eddy current reactor, 1211 is the second reactor inlet, 122 is the second adjustable oil collection tank, 123 is the outlet of the extracted and recycled water, 124 is the outlet for the qualified water to be externally transported, 1241 is the qualified water storage tank; 125 is the second washable viewing window; 126 is the second dissolved air water inlet; 13 is the nitrogen inlet, 14 is the nitrogen outlet, 15 is the reflux nitrogen outlet; 2 is the dissolved air pump, 21 is the water absorption and air supplement port, 22 is the outlet of the dissolved air water; 31 is the nitrogen pressure automatic balance pipeline system, 311 is the first on-site nitrogen storage tank, 312 is the nitrogen input pipeline, 313 is the nitrogen output pipeline; 32 is the nitrogen air-entraining reflux pipeline; 33 is the dissolved air water make-up pipeline; 34 is the dissolved air water return pipeline; 35 is the pipeline for the raw water containing oil for extraction, 351 is the storage tank for the raw water containing oil for extraction; 36 is the external nitrogen air supplement system, 361 is the second on-site nitrogen storage tank, 362 is the external nitrogen air supplement pipeline;

[0029] Figure 2 Graph showing the relationship between the gas-liquid ratio of the dissolved air pump and the air saturation solubility;

[0030] Figure 3 Graph showing the relationship between the outlet pressure of the dissolved air pump and the bubble diameter. Detailed implementation mode

[0031] The present invention provides a device for air-entraining reflux reuse and multi-stage baffle microbubble flotation for oil removal, including an air flotation tank 1 and a dissolved air pump 2;

[0032] The cavity of the air flotation tank 1 is divided into N flotation separation chambers 11 and an external output and reflux chamber 12 connected in series in sequence; in each of the flotation separation chambers 11, there are provided a first vortex reactor 111 with an open top, a T-shaped water inlet 112, a gas communication port 113, and a first adjustable oil collection tank 114; in the external output and reflux chamber 12, there are provided a second vortex reactor 121 with an open top, a second adjustable oil collection tank 122, a produced water and return water outlet 123, and a qualified water external output port 124; a first reactor inlet 1111 is arranged in the tangential direction of the conical bottom of each first vortex reactor 111; a second reactor inlet 1211 is arranged in the tangential direction of the conical bottom of the second vortex reactor 121; adjacent flotation separation chambers 11 and between the flotation separation chamber 11 and the external output and reflux chamber 12 are connected through the T-shaped water inlet 112 and the gas communication port 113; the T-shaped water inlet 112 is connected to the first reactor inlet 1111 or the second reactor inlet 1211 through a T-shaped water inlet pipeline 1121; N≥2;

[0033] A nitrogen pressure automatic balance pipeline system 31 and a nitrogen introduction and reflux pipeline 32 are arranged on the top of the air flotation tank 1, a dissolved air water makeup pipeline 33 and a dissolved air water return pipeline 34 are arranged at the bottom of the air flotation tank 1, and an oil-containing produced raw water pipeline 35 is arranged on the side of the air flotation tank 1; the nitrogen pressure automatic balance pipeline system 31 includes a nitrogen input pipeline 312 and a nitrogen output pipeline 313 connected to the air flotation tank 1;

[0034] The dissolved air pump 2 is provided with a water absorption and air supplement port 21 and a dissolved air water outlet 22;

[0035] The nitrogen introduction and reflux pipeline 32 and the dissolved air water return pipeline 34 are connected to the water absorption and air supplement port 21; the dissolved air water outlet 22 is connected to the dissolved air water makeup pipeline 33;

[0036] The dissolved air water makeup pipeline 33 is connected to the oil-containing produced raw water pipeline 35 or the bevel of the T-shaped water inlet pipeline 1121 and is respectively connected to the first reactor inlet 1111 or the second reactor inlet 1211.

[0037] The device provided by the present invention includes an air flotation tank 1, and the air flotation tank 1 includes N flotation separation chambers 11 connected in series in sequence; in each flotation separation chamber 11, there are provided a first vortex reactor 111 with an open top, a T-shaped water inlet 112, a gas communication port 113, and a first adjustable oil collection tank 114; adjacent flotation separation chambers 11 are connected through the T-shaped water inlet 112 and the gas communication port 113.

[0038] In an embodiment of the present invention, the volume of each flotation separation chamber 11 is preferably the same, accounting for 1 / (N + 1) of the volume of the entire dissolved air flotation tank 1. In an embodiment of the present invention, the number N of the flotation separation chambers is preferably 2 to 5, more preferably 2 to 4, and most preferably 2 to 3.

[0039] In an embodiment of the present invention, each flotation separation chamber is preferably provided with a first dissolved air water inlet 117; the side wall of the outermost flotation separation chamber is preferably provided with an oil-containing raw water inlet 118.

[0040] In an embodiment of the present invention, the adjacent flotation separation chambers 11 are separated by a partition 116; the height of the partition 116 is preferably 94 to 96% of the height of the dissolved air flotation tank 1, more preferably 95%; the channel between the top end of the partition 116 and the wall of the dissolved air flotation tank 1 is the gas communication port 113. In an embodiment of the present invention, the gas communication port 113 is provided at the top of the dissolved air flotation tank 1, and the gas communication port accounts for 4 to 6% of the height of the dissolved air flotation tank 1, more preferably 5%.

[0041] In an embodiment of the present invention, the distance between the first eddy current reactor 111 and the bottom of the dissolved air flotation tank 1 is preferably 0.2 to 0.6 m, more preferably 0.3 to 0.4 m; each first eddy current reactor 111 is provided with a first reactor inlet 1111. In an embodiment of the present invention, the first eddy current reactor 111 is preferably a vertical eddy current reactor.

[0042] In an embodiment of the present invention, the T-shaped water passing port 112 is provided on the right side wall of the flotation separation chamber 11, and the distance from the bottom of the dissolved air flotation tank 1 accounts for 10 to 25% of the height of the dissolved air flotation tank 1, more preferably 15 to 20%.

[0043] In an embodiment of the present invention, the distance between the first adjustable oil collection trough 114 and the top of the dissolved air flotation tank 1 accounts for 15 to 30% of the height of the dissolved air flotation tank 1, more preferably 20 to 25%. In an embodiment of the present invention, the first adjustable oil collection trough 114 is provided with a first handwheel, the first handwheel is arranged outside the tank of the dissolved air flotation tank 1, and the first handwheel is used to adjust the angle of the first adjustable oil collection trough 114. In an embodiment of the present invention, the adjustable angle of the first adjustable oil collection trough 114 is preferably 0 to 60°, more preferably 10 to 50°, and most preferably 20 to 30°.

[0044] In an embodiment of the present invention, a first washable viewing window 115 is further provided on the outer wall of each flotation separation chamber 11, and the height of the oil-water interface in the flotation separation chamber 11 can be observed through the first washable viewing window 115.

[0045] In the present invention, an external output and reflux chamber 12 is further provided inside the air flotation tank 1; the flotation separation chamber 11 and the external output and reflux chamber 12 are communicated through a T-shaped water inlet 112 and a gas communication port 113. In the present invention, a second eddy current reactor 121, a second adjustable oil collection tank 122, a produced return water outlet 123, a qualified water external output port 124, and a second dissolved air water inlet 126 are provided inside the external output and reflux chamber 12.

[0046] In an embodiment of the present invention, the volume of the external output and reflux chamber 12 is preferably the same as the volume of a single flotation separation chamber 11, accounting for 1 / (N + 1) of the volume of the entire air flotation tank 1.

[0047] In an embodiment of the present invention, the distance between the second eddy current reactor 121 and the bottom of the air flotation tank 1 is preferably 0.2 - 0.6 m, more preferably 0.3 - 0.4 m. In the present invention, the second eddy current reactor is provided with a second reactor inlet 1211. In an embodiment of the present invention, the second eddy current reactor 121 is preferably a vertical eddy current reactor.

[0048] In an embodiment of the present invention, the distance between the second adjustable oil collection tank 122 and the top of the air flotation tank 1 accounts for 15 - 30% of the height of the air flotation tank 1, more preferably 20 - 25%. In an embodiment of the present invention, the second adjustable oil collection tank 122 is provided with a second handwheel, the second handwheel is arranged outside the tank of the air flotation tank 1, and the second handwheel is used to adjust the angle of the second adjustable oil collection tank 122. In an embodiment of the present invention, the adjustable angle of the second adjustable oil collection tank 122 is preferably 0 - 60°, more preferably 10 - 50°, and most preferably 20 - 30°.

[0049] In an embodiment of the present invention, the produced return water outlet 123 and the qualified water external output port 124 are arranged at the bottom of the external output and reflux chamber 12; the qualified water output from the qualified water external output port 124 is stored in a qualified water storage tank 1241. In an embodiment of the present invention, a second washable viewing window 125 is further arranged on the outer wall of the external output and reflux chamber 12, and the height of the oil-water interface inside the external output and reflux chamber 12 can be observed through the second washable viewing window 125.

[0050] In the present invention, a nitrogen inlet 13, a nitrogen outlet 14, and a reflux nitrogen outlet 15 are arranged at the top of the tank of the air flotation tank 1.

[0051] In the present invention, a nitrogen pressure automatic balancing pipeline system 31 is provided at the top of the air flotation tank 1. In an embodiment of the present invention, the nitrogen pressure automatic balancing pipeline system 31 includes a first on-site nitrogen storage tank 311, a nitrogen input pipeline 312, and a nitrogen output pipeline 313; the nitrogen input pipeline 312 is communicated with a nitrogen inlet 13, and a first regulating valve is provided on the nitrogen input pipeline 312; the nitrogen output pipeline 313 is communicated with a nitrogen outlet 14, and a second regulating valve is provided on the nitrogen output pipeline 313; the first regulating valve and the second regulating valve are preferably self-operated regulating valves for regulating the flow rate of the nitrogen; the first nitrogen storage tank 311 conveys nitrogen into the air flotation tank 1 through the nitrogen input pipeline 312, and the air flotation tank 1 returns the excess nitrogen to the first nitrogen storage tank 311 through the nitrogen output pipeline 313, so that a stable and balanced gas phase space can exist at the top inside the air flotation tank 1.

[0052] In the present invention, a nitrogen bleeding and reflux pipeline 32 is provided at the top of the air flotation tank 1. The nitrogen bleeding and reflux pipeline 32 is communicated with a reflux nitrogen outlet 15 and a water suction and air supplement port 21 of the dissolved air pump 2, and is used for recycling the nitrogen separated out from the flotation separation chamber 11 and the external output and reflux chamber 12 of the air flotation tank 1 as the gas source of the dissolved air pump 2, thereby improving the utilization rate of nitrogen. In an embodiment of the present invention, a regulating valve is further provided in the nitrogen bleeding and reflux pipeline 32, and the regulating valve is used for controlling the flow rate of the nitrogen conveyed in the nitrogen bleeding and reflux pipeline 32.

[0053] In the present invention, a dissolved air water supply pipeline 33 and a dissolved air water return pipeline 34 are provided at the bottom of the air flotation tank 1; the dissolved air water return pipeline 34 is communicated with the water suction and air supplement port 21 of the dissolved air pump 2. In an embodiment of the present invention, the dissolved air water supply pipeline 33 is provided with a branch. The dissolved air water outlet 22 of the dissolved air pump 2 is respectively communicated with a first reactor inlet 1111 of the first eddy current reactor 111 and a second reactor inlet 1211 of the second eddy current reactor 121 through the branch of the dissolved air water supply pipeline 33; a second regulating valve and a flow meter are respectively provided on the branch of each dissolved air water supply pipeline 33.

[0054] In the present invention, an oil-containing produced raw water storage tank 351 and an oil-containing produced raw water pipeline 35 are further provided at the bottom of the air flotation tank 1; the oil-containing produced raw water storage tank 351 is communicated with the first reactor inlet 1111 of the first eddy current reactor 111 through the oil-containing produced raw water pipeline 35.

[0055] In one embodiment of the present invention, a service water flushing pipeline 37 and a service water storage tank 371 are further provided at the inner tank top of the air flotation tank 1; the service water storage tank 371 is respectively communicated with the first washable viewing window 115 and the second washable viewing window 125 through the service water flushing pipeline 37. In one embodiment of the present invention, the service water is preferably municipal tap water or groundwater after suspension removal.

[0056] In one embodiment of the present invention, the device further includes an external nitrogen gas supplementing system 36, and the external nitrogen gas supplementing system 36 includes a second in-station nitrogen gas storage tank 361 and an external nitrogen gas supplementing pipeline 362. The second in-station nitrogen gas storage tank 361 is communicated with the water suction air supplementing port 21 of the dissolved air pump 2 through the external nitrogen gas supplementing pipeline 362, and nitrogen gas is supplemented into the dissolved air water return pipeline 34 when the amount of nitrogen gas transported by the nitrogen gas introduction and return pipeline 32 is insufficient, so as to supplement nitrogen gas to the dissolved air pump 2.

[0057] In the device provided by the present invention, a nitrogen pressure automatic balance pipeline system 31 and a nitrogen bleeding and reflux pipeline 32 form a nitrogen circulation dissolved air system. During the operation of the device, relying on the pressure automatic balance pipeline system, a stable gas phase space exists at the top inside the air flotation tank 1. During the oil removal process of dissolved air oil-water in the air flotation tank 1, microbubbles formed by nitrogen continuously precipitate from the dissolved air oil-water, and then the precipitated nitrogen is transported to the water suction and air supplement port 21 of the dissolved air pump 2 through the nitrogen bleeding and reflux pipeline 32, and then recycled as the gas source of the dissolved air pump 2, improving the nitrogen utilization rate and greatly reducing the nitrogen consumption. The dissolved air pump 2, the dissolved air water return pipeline 34 and the dissolved air water supply pipeline 33 form a microbubble generation system. During the operation of the device, by controlling the inlet and outlet pressures of the dissolved air pump 2, the produced return water is pressurized and mixed with the reflux nitrogen in the pump and then decompressed and released, improving the dissolved air efficiency, reducing the particle size of the generated microbubbles, increasing the contact area between the microbubbles and the floating oil in the water, and improving the oil removal effect. The air flotation tank 1, the first eddy current reactor 111 inside the air flotation tank 1, the T-shaped water inlet 112, the second eddy current reactor 121, the second T-shaped water inlet 112, the dissolved air water supply pipeline 33 and the oil-containing produced raw water pipeline 35 form an eddy current flotation system. The dissolved air oil-water spirally rises through the eddy current reactor, and then through multi-stage and multi-angle baffles, the microbubbles are maximally contacted and flocculated with the oil droplets, slowing down the floating speed of the microbubbles aggregating and preventing short-circuiting, ensuring the oil removal effect. The nitrogen pressure automatic balance pipeline system 31, the first adjustable oil collection tank 114, the first handwheel, the second adjustable oil collection tank 122, the second handwheel, the first washable viewing window 115, the second washable viewing window 125 and the service water flushing pipeline 37 form an adjustable oil collection system, ensuring that the oil-water interface inside the air flotation tank 1 is adjustable, and the angles of the first adjustable oil collection tank 114 and the second adjustable oil collection tank 122 are adjustable; the oil-water separation process is controllable, controlling the water content in the oil during the oil collection process, improving the oil collection efficiency and the oil collection effect; moreover, when the first washable viewing window 115 and the second washable viewing window 125 are blurred, the service water flushing pipeline 37 can be used for cleaning, making it easier to observe the thickness of the oil layer inside the air flotation tank 1, and realizing the adjustable and visible three-phase interface of oil, gas and water.

[0058] The present invention provides a method for air bleeding, reflux recycling, multi-stage baffle microbubble flotation and oil removal using the device described in the above technical solution, including the following steps:

[0059] (1) The produced return water and nitrogen are pressurized and dissolved in the dissolved air pump 2 to generate dissolved air water containing microbubbles;

[0060] (2) The dissolved air water containing microbubbles is mixed with the oil-containing produced raw water in the pipeline after the dissolved air water supply pipeline 33 and the oil-containing produced raw water pipeline 35 are obliquely connected to obtain dissolved air oil-water;

[0061] (3) The dissolved air oil water enters the vortex reactor along the tangential direction of the bottom of the first vortex reactor 111 in the flotation separation chamber 11 and rises in a spiral manner. The microbubbles in the dissolved air oil water first contact and flocculate with the oil droplets in the produced oil-containing raw water and are depressurized and released to the top layer of the dissolved air oil water. After the water flow reaches the outlet of the vortex reactor, it turns downward through a baffle. During the process of turning downward through the baffle, the microbubbles and the oil droplets conduct a second contact flocculation and are depressurized and released to the top layer of the dissolved air oil water, obtaining a microbubble-oil droplet phase and an aqueous phase; the oil droplets in the microbubble-oil droplet phase are collected by the first adjustable oil collection tank 114 and the second adjustable oil collection tank 122; the nitrogen gas precipitated from the microbubbles in the microbubble-oil droplet phase enters the gas phase space at the top of the tank of the air flotation tank 1 and is transported to the dissolved air pump through the nitrogen gas induced air return pipeline 32 for recycling;

[0062] (4) The aqueous phase enters the next-level flotation separation chamber through a T-shaped water inlet, and is mixed with the dissolved air water containing microbubbles generated by the dissolved air pump in the pipeline where the dissolved air water make-up pipeline 33 is obliquely connected to the T-shaped water inlet pipeline 1121, and then repeats the operation in step (3) until the oil removal is qualified. After being qualified, the aqueous phase enters the external transportation return chamber, obtaining produced return water and qualified water. The produced return water is transported to the dissolved air pump through the dissolved air water return pipeline 34 via the produced return water outlet 123 for recycling, and the qualified water is output through the qualified water external output port 124.

[0063] In the present invention, without special instructions, all raw material components are commercially available products well-known to those skilled in the art.

[0064] In the present invention, the produced return water and nitrogen gas are pressurized and dissolved in the dissolved air pump 2 to generate dissolved air water containing microbubbles. In the present invention, the inlet pressure of the dissolved air pump 2 is preferably 0.03 - 0.04 MPa, more preferably 0.032 - 0.038 MPa, and most preferably 0.035 - 0.036 MPa; the outlet pressure is preferably 0.9 - 1.0 MPa, more preferably 0.92 - 0.98 MPa, and most preferably 0.94 - 0.95 MPa. In the present invention, the particle size of the microbubbles is preferably 20 - 30 μm, more preferably 22 - 28 μm, and most preferably 24 - 25 μm. In the present invention, the temperature of the produced return water is preferably 60 - 80 °C, more preferably 65 - 75 °C, and most preferably 70 °C. In the present invention, the gas-liquid ratio of the dissolved air water containing microbubbles is preferably 8 - 12%, more preferably 9 - 11%, and most preferably 10%. The present invention controls the inlet pressure and outlet pressure of the dissolved air pump. After water is pressurized and mixed with nitrogen gas in the dissolved air pump and then depressurized and released, the dissolved air efficiency is improved, the particle size of the generated microbubbles is reduced, the contact area between the microbubbles and the floating oil in water is increased, and the oil removal effect is improved.

[0065] In the present invention, when the device is started, the oil-containing produced raw water first fills each chamber (flotation separation chamber and external output return chamber) of the air flotation tank. Among them, the liquid level of the oil-containing produced raw water does not exceed the adjustable oil collection tank, and then the dissolved air pump is started to extract the oil-containing produced raw water in the external output return chamber as the initial produced return water into the dissolved air pump.

[0066] After obtaining the dissolved air water containing microbubbles, in the present invention, the dissolved air water containing microbubbles is mixed with the oil-containing produced raw water in the pipeline after the inclined angle connection of the dissolved air water supply pipeline 33 and the oil-containing produced raw water pipeline 35 to obtain dissolved air oil-water.

[0067] In the present invention, the volume of the dissolved air water containing microbubbles is 15-30% of the volume of the oil-containing produced raw water, more preferably 20-25%. The present invention has no special limitation on the oil content of the oil-containing produced raw water. In the embodiments of the present invention, the oil content of the oil-containing produced raw water is preferably 30-100 mg / L, more preferably 50-80 mg / L, and most preferably 60-70 mg / L.

[0068] After obtaining the dissolved air oil-water, in the present invention, the dissolved air oil-water enters the vortex reactor along the tangent direction of the bottom of the first vortex reactor 111 in the flotation separation chamber 11 and rises in a spiral manner. The microbubbles in the dissolved air oil-water first contact and flocculate with the oil droplets in the oil-containing produced raw water and are decompressed and released to the top layer of the dissolved air oil-water. After the water flow reaches the outlet of the vortex reactor, it turns downward through the baffle. During the process of turning downward through the baffle, the microbubbles contact and flocculate with the oil droplets for the second time and are decompressed and released to the top layer of the dissolved air oil-water to obtain a microbubble-oil droplet phase and an aqueous phase; the oil droplets in the microbubble-oil droplet phase are collected by the first adjustable oil collection tank 114 and the second adjustable oil collection tank 122; the nitrogen gas precipitated from the microbubbles in the microbubble-oil droplet phase enters the gas phase space at the top of the air flotation tank 1 and is then transported to the dissolved air pump through the nitrogen gas induced air return pipeline 32 for recycling.

[0069] In the present invention, the pressure in the gas phase space at the top of the air flotation tank is preferably 0.03-0.04 MPa, more preferably 0.032-0.038 MPa, and most preferably 0.035-0.036 MPa. The present invention controls the pressure in the gas phase space at the top of the air flotation tank to be consistent with the inlet pressure of the dissolved air pump, which can enable the nitrogen gas released under reduced pressure in the air flotation tank 1 to smoothly enter the dissolved air pump 2 for pressurized dissolved air.

[0070] In the present invention, the residence time of the dissolved air oil-water in the flotation separation chamber is preferably 80-120 s, more preferably 90-110 s, and most preferably 100 s; a short residence time is not prone to short-circuit flow and improves the oil removal effect.

[0071] In the present invention, the dissolved-air oil-water enters the vortex reactor along the tangential direction of the conical bottom of the vortex reactor, forming the maximum couple force, enabling the dissolved-air oil-water to rise in a spiral manner, maximizing the contact flocculation between microbubbles and oil droplets. Through multi-stage and multi-angle baffle flow, short circuiting is not likely to occur, and the oil recovery rate is increased.

[0072] After obtaining the aqueous phase, the aqueous phase enters the next-stage flotation separation chamber through the T-shaped water inlet, and is mixed with the dissolved-air water containing microbubbles generated by the dissolved-air pump in the pipeline after the dissolved-air water supply pipeline 33 and the T-shaped water inlet pipeline 1121 are obliquely connected. Then, the operation of step (3) is repeated until the oil removal is qualified. The obtained aqueous phase enters the external output return chamber to obtain the produced return water and qualified water. The produced return water is transported to the dissolved-air pump through the dissolved-air water return pipeline 34 via the produced return water outlet 123 for recycling, and the qualified water is output through the qualified water external output port 124.

[0073] In the present invention, the number of repetitions is preferably 2 to 6 times, more preferably 3 to 5 times, and most preferably 4 times.

[0074] In the present invention, the temperature of the produced return water is preferably 60 to 80 °C, more preferably 65 to 75 °C, and most preferably 70 °C.

[0075] In the present invention, the aqueous phase entering the next-stage flotation separation chamber through the T-shaped water inlet can prevent short circuiting and enable smooth water flow.

[0076] In one embodiment of the present invention, the qualified water is preferably transported to the qualified water storage tank 1241 and then further processed using end facilities. The present invention has no special limitation on the end facilities and methods for the further processing, and any post-treatment facilities and methods well-known to those skilled in the art can be used.

[0077] The following Figure 1 describes a method for air-entraining reflux recycling multi-stage baffle microbubble flotation oil removal using the device provided by the present invention, including the following steps:

[0078] (1) The produced return water flowing out through the dissolved-air water return pipeline 34 generated by the external output return chamber 12 and the nitrogen gas precipitated in the air flotation tank 1 enter the dissolved-air pump 2 through the nitrogen gas air-entraining reflux pipeline 32 from the water absorption and air supplement port 21, and are pressurized and dissolved to generate dissolved-air water containing microbubbles;

[0079] (2) The dissolved-air water containing microbubbles enters the dissolved-air water supply pipeline 33 through the dissolved-air water outlet 22, and is mixed with the produced raw water containing oil transported through the produced raw water pipeline 35 in the pipeline after the dissolved-air water supply pipeline 33 and the produced raw water pipeline 35 are obliquely connected to obtain dissolved-air oil-water;

[0080] (3) The dissolved air oil water enters through the first reactor inlet 1111 along the tangent direction of the bottom of the first vortex reactor 111 in the flotation separation chamber 11 and rises in a spiral manner. The microbubbles in the dissolved air oil water first contact and flocculate with the oil droplets in the produced oil-containing raw water and are decompressed and released to the top layer of the dissolved air oil water. After the water flow reaches the outlet of the vortex reactor, it turns downward through a baffle. During the process of turning downward through the baffle, the microbubbles contact and flocculate with the oil droplets for the second time and are decompressed and released to the top layer of the dissolved air oil water, obtaining a microbubble-oil droplet phase and an aqueous phase; the oil droplets in the microbubble-oil droplet phase are collected by the first adjustable oil collection tank 114; the nitrogen gas released from the microbubbles in the microbubble-oil droplet phase is transported to the dissolved air pump 2 through the nitrogen gas induced gas return pipeline 32 for recycling; the pressure in the gas phase space at the top of the air flotation tank 1 is adjusted through the nitrogen gas pressure automatic balance pipeline system 31;

[0081] (4) The aqueous phase enters the next-stage flotation separation chamber 11 through the T-shaped water passing port 112 and mixes with the dissolved air water containing microbubbles generated by the dissolved air pump 2 in the pipeline after the dissolved air water make-up pipeline 33 is obliquely connected to the T-shaped water passing port pipeline 1121. Then, the operation in step (3) is repeated until the oil removal is qualified. The obtained aqueous phase enters the external output return chamber 12, obtaining produced return water and qualified water. The produced return water flows out through the produced return water outlet 123 and is transported to the dissolved air pump 2 through the dissolved air water return pipeline 34 for recycling, and the qualified water is output through the qualified water external output port 124.

[0082] Next, the technical solutions in the present invention will be clearly and completely described in conjunction with the embodiments in the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present invention without making creative efforts belong to the scope of protection of the present invention.

[0083] Example 1

[0084] (1) The 70°C produced return water generated in the external output return chamber 12 and the nitrogen gas precipitated in the air flotation tank 1 enter the dissolved air pump 2 through the nitrogen gas induced gas return pipeline 32 from the water absorption and air supplement port 21 and are pressurized and dissolved to produce dissolved air water containing microbubbles; the inlet pressure of the dissolved air pump 2 is 0.04 MPa, and the outlet pressure is 1 MPa; the particle size of the microbubbles is 20 - 30 μm; the gas-liquid ratio of the dissolved air water containing microbubbles is 10%.

[0085] (2) The dissolved air water containing microbubbles enters the dissolved air water make-up pipeline 33 through the dissolved air water outlet 22 and mixes with the produced oil-containing raw water transported through the produced oil-containing raw water pipeline 35 in the pipeline after the dissolved air water make-up pipeline 33 is obliquely connected to the produced oil-containing raw water pipeline 35, obtaining dissolved air oil water; among them, the source of the produced oil-containing raw water is Shengli Oilfield, the oil content is 60 mg / L, and the temperature is 70°C; the dissolved air water containing microbubbles accounts for 15% of the volume of the produced oil-containing raw water.

[0086] (3) The dissolved air oil water enters through the first reactor inlet 1111 along the tangent direction of the bottom of the first vortex reactor 111 in the flotation separation chamber 11 and rises in a spiral manner. The microbubbles in the dissolved air oil water first contact and flocculate with the oil droplets in the produced oil-containing raw water and are depressurized and released to the top layer of the dissolved air oil water. During the process of the water flowing through a 180° baffle and flowing downward, the microbubbles and the oil droplets conduct a second contact flocculation and are depressurized and released to the top layer of the dissolved air oil water, obtaining a microbubble-oil droplet phase and an aqueous phase; the oil droplets in the microbubble-oil droplet phase are collected by the first adjustable oil collection tank 114; the nitrogen gas precipitated from the microbubbles in the microbubble-oil droplet phase is transported to the dissolved air pump 2 through the nitrogen gas induced air return pipeline 32 for recycling; the pressure in the gas phase space at the top of the air flotation tank 1 is adjusted to 0.04 MPa through the nitrogen gas pressure automatic balancing pipeline system 31; the residence time of the dissolved air oil water in the flotation separation chamber is 110 s; the angle of the first adjustable oil collection tank is adjusted to 45° through the first handwheel.

[0087] (4) The aqueous phase obtained in step (3) enters the next-stage flotation separation chamber 11 through the T-shaped water passing port 112. After being mixed with the dissolved air water containing microbubbles generated by the dissolved air pump 2 in the pipeline where the dissolved air water supply pipeline 33 and the T-shaped water passing port pipeline 1121 are obliquely connected, it enters through the first reactor inlet 1111 along the tangent direction of the bottom of the first vortex reactor 111 and rises in a spiral manner. The microbubbles in the dissolved air oil water first contact and flocculate with the oil droplets in the produced oil-containing raw water and are depressurized and released to the top layer of the dissolved air oil water. During the process of the water flowing through a 180° baffle and flowing downward, the microbubbles and the oil droplets conduct a second contact flocculation and are depressurized and released to the top layer of the dissolved air oil water, obtaining a microbubble-oil droplet phase and an aqueous phase; the oil droplets in the microbubble-oil droplet phase are collected by the first adjustable oil collection tank 114; the nitrogen gas precipitated from the microbubbles in the microbubble-oil droplet phase is transported to the dissolved air pump 2 through the nitrogen gas induced air return pipeline 32 for recycling; the residence time of the dissolved air oil water in the flotation separation chamber is 110 s; the angle of the first adjustable oil collection tank is adjusted to 45° through the first handwheel.

[0088] (5) The aqueous phase obtained in step (4) enters the next-stage flotation separation chamber 11 through the T-shaped water inlet 112, mixes with the dissolved air water containing microbubbles generated by the dissolved air pump 2 in the pipeline where the dissolved air water supply pipeline 33 is obliquely connected to the T-shaped water inlet pipeline 1121, and then enters the first vortex reactor 111 through the first reactor inlet 1111 along the tangent direction of the bottom of the cone of the first vortex reactor 111 and rises in a spiral manner. The microbubbles in the dissolved air oil water first contact and flocculate with the oil droplets in the produced oil-containing raw water and are decompressed and released to the top layer of the dissolved air oil water. During the 180° turning and flowing downward of the water flow, the microbubbles and the oil droplets conduct a second contact flocculation and are decompressed and released to the top layer of the dissolved air oil water, obtaining a microbubble-oil droplet phase and an aqueous phase; the oil droplets in the microbubble-oil droplet phase are collected by the first adjustable oil collection tank 114; the nitrogen gas precipitated from the microbubbles in the microbubble-oil droplet phase is transported to the dissolved air pump 2 through the nitrogen gas induced air return pipeline 32 for recycling; the residence time of the dissolved air oil water in the flotation separation chamber is 110 s; the angle of the first adjustable oil collection tank is adjusted to 45° through the first handwheel.

[0089] (6) The aqueous phase obtained in step (5) enters the external output return chamber 12 through the T-shaped water inlet 112, mixes with the dissolved air water containing microbubbles generated by the dissolved air pump 2 in the pipeline where the dissolved air water supply pipeline 33 is obliquely connected to the T-shaped water inlet pipeline 1121, and then enters the second vortex reactor 121 through the second reactor inlet 1211 along the tangent direction of the bottom of the cone of the second vortex reactor 121 and rises in a spiral manner. The microbubbles in the dissolved air oil water first contact and flocculate with the oil droplets in the produced oil-containing raw water and are decompressed and released to the top layer of the dissolved air oil water. During the 180° turning and flowing downward of the water flow, the microbubbles and the oil droplets conduct a second contact flocculation and are decompressed and released to the top layer of the dissolved air oil water, obtaining a microbubble-oil droplet phase, produced return water, and qualified water; the oil droplets in the microbubble-oil droplet phase are collected by the second adjustable oil collection tank 122, the produced return water flows out through the produced return water outlet 123 and is transported to the dissolved air pump 2 through the dissolved air water return pipeline 34 for recycling, the qualified water is output to the qualified water storage tank 1241 through the qualified water external output port 124 and then discharged into the environment, the oil content of the qualified water is 5 mg / L, the floating oil removal rate is 92%, and the nitrogen consumption is reduced by 15%.

[0090] Example 2

[0091] The microbubble flotation for oil removal is carried out according to the method of Example 1. The relationship between the inlet pressure and outlet pressure of the dissolved air pump 2, the temperature of the produced return water, the gas-liquid ratio of the dissolved air pump, and the air saturation solubility in step (1) is as Figure 2 shown. It can be seen from Figure 2 that when the inlet pressure of the dissolved air pump 2 of the present invention is controlled to be 0.03 - 0.04 MPa and the outlet pressure is controlled to be 0.9 - 1.0 MPa, the gas-liquid ratio can reach 10% after the water at 70 °C is pressurized and mixed with the reflux nitrogen gas in the pump, the dissolved air efficiency is high, and a gas-liquid separation tank can no longer be provided at the outlet of the dissolved air pump, avoiding the waste of nitrogen gas at the outlet of the dissolved air pump.

[0092] Example 3

[0093] The relationship diagram between the outlet pressure of the dissolved air pump 2 and the diameter of the generated microbubbles in step (1) is as follows when performing oil removal by microbubble flotation according to the method of Example 1 Figure 3 shown. From Figure 3 it can be seen that in the present invention, the outlet pressure of the dissolved air pump is controlled to be 0.9-1.0 MPa and then decompressed and released, and the particle size of the generated microbubbles can be controlled within 20-30 μm. The microbubble diameter is small, which increases the contact area between the microbubbles and the floating oil in water and improves the oil removal effect.

[0094] The above is only the preferred embodiment of the present invention. It should be pointed out that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and modifications can be made, and these improvements and modifications should also be regarded as the protection scope of the present invention.

Claims

1. An air-entraining reflux and reuse multi-stage baffle microbubble flotation device for oil removal, comprising an air flotation tank (1) and a dissolved air pump (2); The cavity of the air flotation tank (1) is divided into N flotation separation chambers (11) and an external output reflux chamber (12) connected in series in sequence; in each flotation separation chamber (11), there is a first vortex reactor (111) with an open top, a T-shaped water inlet (112), a gas communication port (113), and a first adjustable oil collection tank (114); in the external output reflux chamber (12), there is a second vortex reactor (121) with an open top, a second adjustable oil collection tank (122), a produced water return outlet (123), and a qualified water external output port (124); each first vortex reactor (111) is provided with a first reactor inlet (1111); the second vortex reactor (121) is provided with a second reactor inlet (1211); adjacent flotation separation chambers (11) and between the flotation separation chamber (11) and the external output reflux chamber (12) are connected through the T-shaped water inlet (112) and the gas communication port (113); the T-shaped water inlet (112) is connected to the first reactor inlet (1111) or the second reactor inlet (1211) through a T-shaped water inlet pipeline (1121); N≥2; the oil-containing water entering the first vortex reactor (111) enters the vortex reactor along the tangent direction of the bottom of the first vortex reactor (111) in the flotation separation chamber (11) and then rises in a spiral manner. After the water flow reaches the outlet of the vortex reactor, it turns downward through a baffle, and through multi-stage and multi-angle baffles, the bubbles contact and flocculate with the oil droplets, slowing down the rising speed of the bubbles aggregating and preventing short circuit flow; The top of the air flotation tank (1) is provided with a nitrogen pressure automatic balance pipeline system (31) and a nitrogen air-entraining reflux pipeline (32), the bottom of the air flotation tank (1) is provided with a dissolved air water make-up pipeline (33) and a dissolved air water return pipeline (34), and the side of the air flotation tank (1) is provided with an oil-containing produced water raw water pipeline (35); the nitrogen pressure automatic balance pipeline system (31) includes a nitrogen input pipeline (312) and a nitrogen output pipeline (313) connected to the air flotation tank (1); The dissolved air pump (2) is provided with a water suction and air supplement port (21) and a dissolved air water outlet (22); The nitrogen air-entraining reflux pipeline (32) and the dissolved air water return pipeline (34) are connected to the water suction and air supplement port (21); the dissolved air water outlet (22) is connected to the dissolved air water make-up pipeline (33); The dissolved air water make-up pipeline (33) is connected to the first reactor inlet (1111) after being obliquely connected to the oil-containing produced water raw water pipeline (35); the dissolved air water make-up pipeline (33) is connected to the first reactor inlet (1111) after being obliquely connected to the T-shaped water inlet pipeline (1121); the dissolved air water make-up pipeline (33) is connected to the second reactor inlet (1211) after being obliquely connected to the T-shaped water inlet pipeline (1121).

2. The device according to claim 1, characterized in that, Between adjacent flotation separation chambers (11) and between the flotation separation chamber (11) and the external output and reflux chamber (12), they are separated by a partition plate (116); the height of the partition plate (116) is 94-96% of the height of the air flotation tank (1), and the gas communication port (113) is located between the partition plate (116) and the upper tank wall of the air flotation tank (1).

3. The device according to claim 1, characterized in that, The angle of the inclined connection is 40-50°.

4. The device according to any one of claims 1 to 3, characterized in that The device further includes an external nitrogen gas supplementing system (36); the external nitrogen gas supplementing system (36) is communicated with the water absorption and gas supplementing port (21).

5. The device according to any one of claims 1 to 3, characterized in that On the outer wall of each flotation separation chamber (11), a first washable viewing window (115) is further provided; on the outer wall of the external output and reflux chamber (12), a second washable viewing window (125) is further provided; On the top of the air flotation tank (1), a service water flushing pipeline (37) is provided, and the service water flushing pipeline (37) is respectively communicated with the first washable viewing window (115) and the second washable viewing window (125).

6. The device according to claim 1, characterized in that, The first adjustable oil collection tank (114) is provided with a first handwheel, and the second adjustable oil collection tank (122) is provided with a second handwheel; the first handwheel and the second handwheel are arranged outside the tank of the air flotation tank (1).

7. A method for removing oil by air-entraining reflux reuse and multi-stage baffle microbubble flotation using the device according to any one of claims 1 to 6, comprising the following steps: (1) The extracted return water and nitrogen gas are pressurized and dissolved in a dissolved air pump (2) to generate dissolved air water containing microbubbles; (2) The dissolved air water containing microbubbles is mixed with the original produced water containing oil in the pipeline after the dissolved air water supply pipeline (33) and the original produced water pipeline containing oil (35) are inclinedly connected to obtain dissolved air oil-water; (3) The dissolved air oil-water enters the vortex reactor along the tangent direction of the bottom of the first vortex reactor (111) in the flotation separation chamber (11), and then rises in a spiral manner. The microbubbles in the dissolved air oil-water first contact and flocculate with the oil droplets in the original produced water containing oil and are depressurized and released to the top layer of the dissolved air oil-water. After the water flow reaches the outlet of the vortex reactor, it flows downward through a baffle. During the downward baffle process, the microbubbles and the oil droplets conduct a second contact and flocculate and are depressurized and released to the top layer of the dissolved air oil-water to obtain a microbubble-oil droplet phase and a water phase; the oil droplets in the microbubble-oil droplet phase are collected by the first adjustable oil collection tank (114) and the second adjustable oil collection tank (122); the nitrogen gas precipitated from the microbubbles in the microbubble-oil droplet phase enters the gas phase space at the top inside the air flotation tank (1) and is then transported to the dissolved air pump through the nitrogen gas air-entraining reflux pipeline (32) for recycling; (4) The water phase enters the next-stage flotation separation chamber through a T-shaped water passing port, and after being mixed with the dissolved air water containing microbubbles generated by the dissolved air pump in the pipeline after the dissolved air water supply pipeline (33) and the T-shaped water passing port pipeline (1121) are inclinedly connected, the operation of step (3) is repeated until the oil removal is qualified. After being qualified, the water phase enters the external output and reflux chamber (12) to obtain extracted return water and qualified water. The extracted return water is transported to the dissolved air pump through the dissolved air water return pipeline (34) via the extracted return water outlet (123) for recycling, and the qualified water is output through the qualified water external output port (124).

8. The method according to claim 7, wherein The inlet pressure of the dissolved air pump (2) is 0.03 - 0.04 MPa, and the outlet pressure is 0.9 - 1.0 MPa; the particle size of the microbubbles is 20 - 30 μm; The pressure in the gas phase space at the top inside the air flotation tank (1) is 0.03 - 0.04 MPa.

9. The method according to claim 7, wherein The temperature of the extracted return water is 60 - 80 °C.

10. The method according to claim 7, characterized in that, The residence time of the dissolved air oil-water in the flotation separation chamber (11) is 80 - 120 s.

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