Method for removing oil slick on top of oil field sewage settling tank and oil collecting device

Abstract

The invention relates to the technical field of oil field oil production engineering, in particular to a method for removing floating oil at the top of an oil field sewage settling tank and an oil collecting device. The problems that a worker needs to go to the tank top to operate an adjusting weir and repeatedly adjust inlet and outlet valves for oil collection of an existing settling tank, and multi-person cooperation is needed are mainly solved. S1, determining the thickness of an oil layer in the settling tank; s2, when the thickness of the oil layer is larger than the set thickness, the liquid level in the tank is increased till the production liquid level in the tank is increased to the oil receiving liquid level, and an oil receiving pump is opened to start oil receiving; s3, when the oil layer thickness is smaller than the set thickness, the oil collecting pump is closed; and S4, the liquid level in the tank is lowered, and the oil receiving liquid level is lowered to the production liquid level. The oil field sewage settling tank top floating oil removing method can automatically measure the thickness of the oil layer, when the thickness of the oil layer reaches a set value, the liquid level is automatically controlled to be above the height of the oil collecting tank, manual adjustment is not needed, the labor intensity and the safety risk of workers are reduced, and the treatment effect of the settling tank is improved.

Description

Technical Field

[0001] This invention relates to the field of oilfield wastewater treatment, specifically to a method and device for removing floating oil from the top of an oilfield wastewater settling tank. Background Technology

[0002] Currently, the standard process for oilfield wastewater treatment is a "sedimentation + filtration" process. Sedimentation, as a pre-process of filtration, primarily utilizes physical methods such as gravity separation and chemical methods such as coagulation to remove most of the oil and suspended solids from the wastewater. Filtration further reduces the oil content and suspended solids, ensuring the wastewater meets the quality standards for oilfield injection water before reinjection into the formation. The quality of oil recovery in the wastewater settling tank directly affects its treatment efficiency and is crucial for reducing the load on the filtration process, making it a key factor limiting the effectiveness of produced water treatment in oilfields. Insufficient timely oil recovery in the settling tank has two main consequences: first, the oil easily forms aged oil, which, if it enters the electrostatic precipitator, disrupts the electric field and causes operational difficulties; second, in winter, low temperatures cause the oil on the upper surface of the production liquid level in the settling tank to form a waxy crust, hindering oil recovery and reducing the effective settling space as the oil layer thickens, thus shortening the effective settling time and affecting oil-water separation.

[0003] Existing methods for oil recovery in settling tanks generally employ an intermittent oil recovery process. This primarily involves periodically adjusting the regulating weir on the top wall of the settling tank to control the liquid level, ensuring it reaches the oil recovery trough height above the production level. However, when the regulating weir malfunctions, the only recourse is to control the tank's outlet valve to forcibly raise the liquid level until it reaches the oil recovery height. Both of these level control methods have certain drawbacks.

[0004] If a regulating weir is used in a settling tank, manual operation of the handwheel on the weir from the top of the tank is required to move the weir up and down, thus raising or lowering the water level inside the tank to meet the required liquid level height during oil recovery. Because the operating torque of the handwheel on the regulating weir is relatively large, it is usually difficult for a single worker to complete the raising and lowering of the weir. Furthermore, the worker operates on the tank, standing on the top plate of the regulating weir box, where the area below is prone to corrosion, and the operating environment is susceptible to the accumulation of volatile flammable gases, posing a potential safety hazard.

[0005] When controlling the tank level using the tank outlet valve, oil recovery requires the cooperation of multiple people. With 2-3 people working together, assuming accurate level gauge readings, they assist with manual observation, telephone communication, and assessment of the oil layer thickness for oil recovery. Significant fluctuations in incoming liquid volume can easily lead to inaccurate level readings, failure to recover oil, overflow from the settling tank, or overflow from the recovery water pool. Summary of the Invention

[0006] To overcome the shortcomings of existing settling tanks that require workers to operate the regulating weir on top of the tank, repeatedly adjust the inlet and outlet valves, and require multiple people to cooperate, this invention provides a method and device for removing floating oil from the top of an oilfield wastewater settling tank. This method can automatically measure the oil layer thickness. When the oil layer thickness reaches the set value, it automatically controls the liquid level to be above the height of the oil collection tank without manual adjustment, reducing the labor intensity and safety risks of employees and improving the treatment effect of the settling tank.

[0007] The technical solution of this invention is: a method for removing floating oil from the top of an oilfield wastewater settling tank, comprising the following steps:

[0008] S1. Determine the thickness of the oil layer inside the settling tank;

[0009] S2. When the oil layer thickness is greater than the set thickness, raise the liquid level in the tank until the production liquid level in the tank reaches the oil collection level, and turn on the oil collection pump to start collecting oil.

[0010] S3. When the oil layer thickness is less than the set thickness, turn off the oil recovery pump;

[0011] S4. Lower the liquid level in the tank so that the oil collection level drops to the production level.

[0012] Furthermore, in step S1, the oil layer thickness h in the settling tank... 油 Calculated based on the liquid level H in the settling tank and the pressure gauge reading P at the bottom of the tank:

[0013] P = ρ 水 gh 水 +ρ 油 gh 油

[0014] H = h 水 +h 油

[0015] In the formula: ρ 水 The density of water is 1.0 × 10⁻⁶. 3 kg / m 3 ;ρ 油 The density of the oil is 0.86 × 10⁻⁶. 3 kg / m 3 g is the acceleration due to gravity, 9.81 m / s²; h 水 The height of the water layer is in meters (m); h 油 Let be the oil layer thickness, in meters (m).

[0016] The method for removing floating oil from the top of the oilfield wastewater settling tank, in step S2, the method for raising the liquid level in the tank includes: closing the opening of the outlet valve and increasing the inflow of water.

[0017] Furthermore, when adjusting the liquid level in the tank by reducing the opening of the outlet valve, the adjusted outlet valve flow rate V2′ is:

[0018]

[0019] In the formula: V2′ is the flow velocity of the liquid in the pipeline at the outlet valve after adjustment, m / s; V2 is the flow velocity of the liquid in the pipeline at the outlet valve before adjustment, m / s; h1 is the production liquid level, m; h2 is the oil collection liquid level, m.

[0020] Furthermore, in step S2, when the liquid level in the tank is adjusted by increasing the opening of the inlet valve, the adjusted inlet valve flow rate V3 is:

[0021] V3=(S△h+A4V4) / A2

[0022] △h=h2-h1

[0023] In the formula: V3 is the liquid velocity in the pipeline at the inlet valve of the settling tank for recycled water, m / s; V4 is the liquid velocity in the pipeline at the outlet of the settling tank for oil recovery, m / s; S is the cross-sectional area of ​​the tank, m². 2 A4 represents the cross-sectional area of ​​the oil recovery pipeline exiting the settling tank, in meters. 2 A2 is the area of ​​the tank outlet, in meters. 2 .

[0024] Furthermore, in step S4, the method for lowering the liquid level in the tank includes: increasing the opening of the outlet valve and reducing the inlet water volume.

[0025] Furthermore, the influent volume includes the main influent pipeline to the settling tank, the influent pipeline to the wastewater recovery process in the wastewater recovery pond, and other influent pipelines to the settling tank.

[0026] An oil collection device for the oilfield wastewater settling tank top floating oil removal method includes a settling tank, an inlet water pipeline, an outlet water pipeline and an oil collection pipeline connected to the settling tank, an oil collection trough provided inside the settling tank at the top, an oil collection pipeline inside the tank connected to the oil collection trough, an oil collection pipeline connected to the other end of the oil collection pipeline inside the tank, and an oil collection pump connected to the oil collection pipeline.

[0027] Furthermore, the oil receiving pipeline is connected to the inlet electric valve of the oil receiving pump, and the oil receiving pump outlet is connected to the oil receiving pump outlet electric valve. The water inlet pipeline is equipped with an inlet electric valve, and the water outlet pipeline is equipped with an outlet electric valve. The oil receiving pump inlet electric valve, the oil receiving pump outlet electric valve, the water inlet electric valve, and the water outlet electric valve are all connected to the control system.

[0028] Furthermore, an regulating weir is provided at the upper edge of the settling tank, and an overflow pipeline is connected to the bottom of the regulating weir. The overflow pipeline is connected to the outlet pipeline.

[0029] Furthermore, a buffer water tank is connected to the outlet water pipeline, and a booster water pump is connected to the buffer water tank. The booster water pump is connected to the control system.

[0030] This invention offers the following advantages: By adopting the above-mentioned solution, this method effectively achieves automatic control of the liquid level above the oil collection trough based on the measured oil layer thickness, and automatic start / stop of the oil collection pump without altering the existing settling tank structure. This reduces the labor intensity and safety risks for employees and improves the treatment efficiency of the settling tank. Compared to existing technologies that add electric mechanisms inside the tank and at the top where oil and gas are present, the safety risks are lower. Compared to existing in-tank floating oil collection technology, the modification costs are lower, and there are no limitations on the number and location of in-tank floating oil collection devices due to the existing space constraints of the water outlet and supporting accessories. Sludge does not need to enter the oil collection tank, and there is no need to add an oil-water interface meter. After the liquid level is adjusted above the oil collection trough height, there is no need to repeatedly adjust the water flow, and the sludge layer can be stably controlled above the oil collection trough. The addition of a flushing process for the inlet and outlet pipelines of the oil collection pump and a process to ensure the evacuation of sludge from the inlet pipeline of the oil collection pump solves the problem of sludge condensation in the oil collection pipeline preventing the oil collection pump from operating normally in intermittent oil collection. Attached Figure Description

[0031] Figure 1 This is a flowchart of the present invention;

[0032] Figure 2 This is a schematic diagram of the water inlet, water outlet, and oil recovery pipelines of the settling tank;

[0033] Figure 3 This is a front view of the settling tank in this invention;

[0034] Figure 4 It is along Figure 3 Sectional view of AA;

[0035] Figure 5 It is along Figure 3 A cross-sectional view of BB.

[0036] In the diagram, 1-inlet water pipeline, 2-inlet water pipeline electric valve, 3-oil collection pipeline, 4-oil collection pump inlet electric valve, 5-oil collection pump, 6-oil collection pump outlet electric valve, 7-outlet water pipeline, 8-outlet water pipeline electric valve, 9-overflow pipeline, 10-water collection pipeline, 11-regulating weir, 12-heat tracing pipeline, 13-in-tank oil collection pipeline, 14-recovery pool water pipeline, 15-recovery water pipeline electric valve, 16-oil collection tank. Detailed Implementation

[0037] The present invention will now be described in detail with reference to the accompanying drawings and embodiments. The technical solutions in the embodiments of the present invention will be clearly and completely described. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0038] In the description of this invention, it is necessary to understand that the orientations or positional relationships indicated by terms such as "upper," "lower," "left," "right," "inner," "outer," "top," and "bottom" are based on the orientations or positional relationships shown in the accompanying drawings. They are intended only to facilitate the description of this invention and to simplify the description, and are not intended to indicate or imply that the components referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0039] Depend on Figure 1 , Figure 2 As shown, a method for removing floating oil from the top of an oilfield wastewater settling tank includes the following steps:

[0040] S1. Determine the oil layer thickness inside the settling tank. The oil layer thickness can be calculated in the following ways: by using the liquid level in the settling tank and the pressure gauge reading at the bottom of the tank; by using the difference between the added oil-water interface meter and the existing level gauge; or by measuring the oil layer thickness using a radar level gauge or ultrasonic level gauge. The following example illustrates the method of calculation using the liquid level in the settling tank and the pressure gauge reading at the bottom of the tank:

[0041] Oil layer thickness h in settling tank 油 Calculated based on the liquid level H in the settling tank and the pressure gauge reading P at the bottom of the tank:

[0042] P = ρ 水 gh 水 +ρ 油 gh 油 (1)

[0043] H = h 水 +h 油 (2)

[0044] In the formula: ρ 水 The density of water is 1.0 × 10⁻⁶. 3 kg / m 3 ;ρ 油 The density of the oil is 0.86 × 10⁻⁶. 3 kg / m 3 g is the acceleration due to gravity, 9.81 m / s²; h 水 The height of the water layer is in meters (m); h 油 Let be the oil layer thickness, in meters (m).

[0045] The oil layer thickness h can be calculated using formulas (1) and (2). 油 .

[0046] If the pressure gauge at the bottom of the tank reads 0.12 MPa, the liquid level in the settling tank is 12.3 m, and the densities of water and oil are 1.0 × 10⁻⁶ and 1.0 × 10⁻⁶ respectively, then... 3 kg / m 3 0.86×10 3 kg / m 3 According to formula (1),

[0047] P = ρ 水 gh 水 +ρ 油 gh 油 (1)

[0048] 0.12×10 6 =9.81×10 3 (12.3-h 油 )+9.81×0.86×10 3 h 油

[0049] Calculate the oil layer thickness h 油约 It is 0.5m.

[0050] S2. When the oil layer thickness exceeds the set thickness, raise the liquid level in the tank until the production liquid level in the tank reaches the oil recovery level, then turn on the oil recovery pump to start oil recovery. According to the "Design Specification for Oilfield Produced Water Treatment" GB50428, the oil layer thickness should not exceed 0.8 meters, and is generally set at 0.3 meters to 0.7 meters. When the measured or calculated oil layer thickness exceeds the set value, oil recovery is required.

[0051] Methods to raise the liquid level in the tank include: closing the outlet valve opening, increasing the inlet valve opening, and reducing the discharge rate of the recovery water pump. These measures can be carried out separately or simultaneously until the production liquid level rises to the oil recovery liquid level.

[0052] (i) When adjusting the liquid level in the tank by closing the water outlet valve, the opening degree of the electric valve is calculated by comparing the set oil recovery level with the liquid level height measured by the liquid level gauge in the tank, and the switching quantity of the electric valve at the outlet of the settling tank is controlled by the liquid level PID control.

[0053] According to the fluid continuity equation of the settling tank, A1V1=A2V2, during normal production, the flow rate at the tank outlet pipeline is calculated according to Bernoulli's equation (wastewater is considered an incompressible liquid due to its low oil content), as shown in formula (3).

[0054]

[0055] In the formula: V2′ is the flow velocity of the liquid in the pipeline at the outlet valve after adjustment, m / s; V2 is the flow velocity of the liquid in the pipeline at the outlet valve before adjustment, m / s; h1 is the production liquid level, m; h2 is the oil collection liquid level, m; p1 is the pressure value at the outlet pipe when the liquid level is h1, Pa; p2 is the pressure value at the outlet pipe when the liquid level is h2, Pa; h0 is the height value at the outlet pipe, m; ρ is the density of water, kg / m³. 3 g; is the acceleration due to gravity, m / s². 2 .

[0056] Since the outlet pipelines are at the same height and the settling tank is an atmospheric pressure facility, in order to ensure continuous flow in the system, the above formula can be transformed into formulas (4) and (5).

[0057]

[0058] According to formula (5), V2′ can be calculated. The automatic oil collection PLC system program automatically adjusts the outlet valve based on the calculated outlet valve flow rate.

[0059] For example, a settling tank has dimensions of Φ7.6m × 13.4m, a production liquid level of 11.6m, an oil collection liquid level of 12.4m, and inlet and outlet dimensions of Φ325mm × 6mm. Its daily processing capacity is 4500 cubic meters. Figure 2 When collecting oil, the liquid level needs to be raised from the production liquid level h1 to the oil collection liquid level h2.

[0060] According to the fluid continuity equation in the settling tank, A1V1=A2V2, during normal production...

[0061] Inlet and outlet liquid flow rate Q = 4500 ÷ 24 = 187.5 cubic meters / hour

[0062] Outflow rate υ2 = Q / A = 187.5 ÷ (0.313) 2 (×π)×4=0.68 m / s,

[0063] According to formula (5), the adjusted flow rate V2′ of the outlet valve is 0-0.68 m / s, and the average value is 0.34 m / s. The average rise height of the liquid surface Δh = h2-h1 is calculated to be 0.018 m.

[0064] According to the linear relationship of the regulating valve flow, the outlet valve can be directly set to 50% opening when the oil is collected, so that the liquid level rises more smoothly. After the liquid level reaches the oil collection height, the opening of the outlet electric valve is controlled according to formula (5). This not only reduces the number of times and time required to adjust the electric valve, but also ensures the stability of the liquid level changes in other settling tanks throughout the station.

[0065] (ii) When the liquid level in the tank is adjusted by increasing the opening of the inlet valve, the continuity equation for the fluid entering and leaving the settling tank when it is collecting wastewater from the wastewater recovery tank is:

[0066] A1V1+A3V3=A2V2+S△h+A4V4 (6)

[0067] In the formula: V3 is the liquid velocity in the pipeline at the inlet valve of the settling tank for recycled water, m / s; V4 is the liquid velocity in the pipeline at the outlet of the settling tank for oil recovery, m / s; S is the cross-sectional area of ​​the tank, m². 2 A4 represents the cross-sectional area of ​​the oil recovery pipeline exiting the settling tank, in meters. 2 V2 represents the flow velocity of the liquid in the pipeline at the outlet valve before regulation, in m / s; A1 and A2 are the cross-sectional areas of the inlet and outlet pipelines of the settling tank, in m³. 2 V1 represents the liquid flow velocity in the pipeline at the inlet valve of the settling tank.

[0068] To reduce fluctuations in the treated wastewater volume, the inlet and outlet liquid volumes remain constant, and formula (6) becomes:

[0069] V3=(S△h+A4V4) / A2 (7)

[0070] Where Δh = h2 - h1(8)

[0071] According to formulas (7) and (8), the liquid velocity V3 in the pipeline at the inlet valve of the settling tank can be calculated. The automatic oil recovery PLC system program issues corresponding instructions to the electric valve of the settling tank inlet pipeline to increase the water inlet flow to the settling tank, thereby increasing the liquid level in the settling tank. The electric valve can be installed in the valve chamber of the settling tank or on the front-end process valve connected to the inlet or outlet pipeline of the settling tank, and its installation height is 0.3 meters to 2 meters. In addition to being the main water inlet pipeline of the settling tank, the water inlet pipeline of the settling tank can also be the water inlet pipeline of the wastewater recovery tank process, or other liquid inlet pipelines that can enter the settling tank.

[0072] When the liquid level in the settling tank is controlled by adjusting the opening of the inlet valve, an electric valve can be installed within 0.3-2 meters of the valve chamber height of the settling tank. Alternatively, it can be installed on the upstream process valve connected to the inlet pipeline of the settling tank, with the connected pipeline being the inlet water pipeline for the wastewater recovery process. When the settling tank is receiving wastewater from the wastewater recovery tank, the fluid continuity equation for the inlet and outlet of the settling tank is:

[0073] A1V1+A3V3=A2V2+S△h+A4V4 (6)

[0074] To reduce fluctuations in the treated wastewater volume, the inlet and outlet liquid volumes remain constant, and formula (6) becomes:

[0075] V3=(S△h+A4V4) / A2 (7)

[0076] For example, if the settling tank has dimensions of Φ7.6m × 13.4m, the production liquid level is 11.6m, the oil collection height is 12.4m, and the daily processing capacity is 4500 cubic meters, the volume increase required from the production liquid level to the oil collection level is V = S(h2 - h1) = 36.24 cubic meters. During normal production, the inlet and outlet liquid flow rates are Q = 4500 ÷ 24 = 187.5 cubic meters / hour, while the configured recovery water pump has a discharge capacity of Q... 收水 The flow rate is 50 cubic meters per hour, the volume of the recovery tank is 400 cubic meters, the inlet and outlet of the settling tank are both Φ325mm×6mm, and the displacement of the oil recovery pump is Q. 收油 With a flow rate of 6 cubic meters per hour and a recovery pump efficiency of 85%, increasing the inlet flow velocity by 0.16 m / s has a minimal impact on the influent. To reduce production fluctuations, the recovery pump can be started first, operating at a rate of S(h2-h1) / (Q). 收水 When η) = 1 hour, stop the water recovery pump and start the oil recovery pump. When the production liquid level is lower than the oil recovery level, start the water recovery pump again and run for half an hour. Then stop the pump to recover the oil. Repeat this process.

[0077] (iii) The discharge rate of the recovery water pump can also be reduced to gradually increase the production liquid level. When the production liquid level reaches the oil recovery level, the automatic oil recovery PLC system program opens the inlet valve of the oil recovery pump, the oil recovery pump, and the outlet valve of the oil recovery pump to start oil recovery.

[0078] For the settling tank in the example above, the discharge rate of the recovery water pump can also be adjusted to 18 cubic meters per hour. Variable frequency control is still used. After running at full load for 2 hours, variable frequency control is used to reduce the discharge rate to 6 cubic meters per hour, the same as the oil recovery pump, so that the increased liquid inflow is balanced with the oil discharge, facilitating stable control of the production liquid level.

[0079] S3. When the oil layer thickness is less than the set thickness, the system sequentially closes the oil recovery pump outlet valve, the oil recovery pump, and the oil recovery pump inlet valve to stop oil recovery.

[0080] S4. Lower the liquid level in the tank to bring the oil recovery level down to the production level. Methods to lower the liquid level in the tank include: increasing the opening of the outlet valve, decreasing the opening of the inlet valve, and increasing the discharge rate of the recovery water pump. These measures can be carried out separately or simultaneously until the oil recovery level drops to the production level. The opening of the outlet valve can be calculated using formula (5), and the opening of the inlet valve can be calculated using formula (7).

[0081] Before starting the automatic oil collection PLC system for the settling tank, the inlet pipeline of the oil collection pump can be flushed using a wastewater recovery pump. Before stopping the system, the oil collection pump can be allowed to continue running for a specified period. This period is calculated by dividing the sum of the volumes of the settling tank's central oil collection container and the oil collection pipeline by the outlet flow rate of the oil collection pump. This ensures that there is no residual oil in the oil collection pipeline and prevents the oil from condensing and becoming uncollectible after the system stops operating.

[0082] An oil collection device used in a method for removing floating oil from the top of an oilfield wastewater settling tank, such as... Figures 3 to 5 The system includes a settling tank, to which an inlet pipeline 1, an outlet pipeline 7, and an oil collection pipeline 3 are connected. The inlet pipeline 1 is equipped with an inlet electric valve 2 and can also be connected to a recovery tank inlet pipeline 14. The recovery tank inlet pipeline 14 is equipped with a recovery water pipeline electric valve 15, through which water is received from the wastewater recovery tank. The outlet pipeline 7 is equipped with an outlet electric valve 8 and is connected to a recovery water pump, which is connected to a control system.

[0083] The settling tank has an oil collection trough 16 located at the top inside, with several oil collection troughs 16 arranged radially inside the tank. An oil collection trough is located at the center of the tank, below the oil collection troughs 16. The oil collection troughs 16 collect sludge oil and then flow into the oil collection trough. An oil collection pipeline 13 is connected to the oil collection trough inside the tank. The outlet of the oil collection pipeline 13 is connected to an oil collection pipeline 3. An oil collection pump 5 is connected to the oil collection pipeline 3. An oil collection pump inlet electric valve 4 is installed at the inlet of the oil collection pump 5, and an oil collection pump outlet electric valve 6 is installed at the outlet.

[0084] An regulating weir 11 is provided at the upper edge of the settling tank. The bottom of the regulating weir 11 is connected to the overflow pipeline 9. When the liquid level is too high, the liquid flows out from the regulating weir 11 and enters the overflow pipeline 9. The overflow pipeline 9 is connected to the outlet pipeline 7.

[0085] The electric valve 8 at the inlet of the oil recovery pump, the electric valve 6 at the outlet of the oil recovery pump, the electric valve 2 on the water inlet pipeline, and the electric valve 8 on the water outlet pipeline are all connected to the automatic oil recovery PLC system program. The settling tank is also equipped with a heat tracing pipeline 12 for heating the liquid inside the tank to enhance the settling and separation effect.

[0086] The method for removing floating oil from the top of the oilfield wastewater settling tank compares the set liquid level with the liquid level measured by the tank's level gauge. It then uses a PID control system to regulate the opening and closing of the electric valves at the settling tank's outlet or inlet, smoothly maintaining the liquid level between the oil recovery level and the production level. To reduce the frequency and duration of electric valve adjustments and ensure the stability of production level changes in other settling tanks throughout the plant, the PID control algorithm uses Bernoulli's equation to directly adjust the opening of the electric valves.

[0087] This method, without altering the existing settling tank structure, effectively achieves automatic control of the liquid level above the oil collection trough based on the measured oil layer thickness, and automatically starts and stops the oil collection pump. This reduces the labor intensity and safety risks for employees, and improves the treatment efficiency of the settling tank. Compared to existing technologies that add electric mechanisms inside the tank and at the top where oil and gas are present, this method carries lower safety risks. Compared to existing in-tank floating oil collection technology, the modification cost is lower, and there are no limitations on the number and location of in-tank floating oil collection devices due to the existing space available for water outlets and support accessories. The sludge does not need to enter the oil collection tank, and there is no need to add an oil-water interface meter. Once the liquid level is adjusted above the oil collection trough, there is no need to repeatedly adjust the water flow, and the sludge layer can be stably controlled above the oil collection trough. The method also incorporates flushing processes for the inlet and outlet pipelines of the oil collection pump and processes to ensure the evacuation of sludge from the inlet pipeline of the oil collection pump, solving the problem of sludge condensation in the oil collection pipeline and the inability of the oil collection pump to operate normally in intermittent oil collection.

[0088] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is chosen to best explain the principles, practical application, or technical improvements to the embodiments in the market, or to enable others skilled in the art to understand the embodiments disclosed herein.

Claims

1. A method for removing floating oil from the top of an oilfield wastewater settling tank, characterized in that... Includes the following steps: S1. Determine the thickness of the oil layer inside the settling tank; S2. When the oil layer thickness is greater than the set thickness, raise the liquid level in the tank until the production liquid level in the tank reaches the oil collection level, and turn on the oil collection pump to start collecting oil. S3. When the oil layer thickness is less than the set thickness, turn off the oil recovery pump; S4. Lower the liquid level in the tank so that the oil collection level drops to the production level.

2. The method for removing floating oil from the top of an oilfield wastewater settling tank according to claim 1, characterized in that: In step S1, the oil layer thickness h in the settling tank 油 Calculated based on the liquid level H in the settling tank and the pressure gauge reading P at the bottom of the tank: P=ρ 水 gh 水 +ρ 油 gh 油 H=h 水 +h 油 In the formula: ρ 水 The density of water is 1.0 × 10⁻⁶. 3 kg / m 3 ;ρ 油 The density of the oil is 0.86 × 10⁻⁶. 3 kg / m 3 g is the acceleration due to gravity, 9.81 m / s²; h 水 The height of the water layer is in meters (m); h 油 Let be the oil layer thickness, in meters (m).

3. The method for removing floating oil from the top of an oilfield wastewater settling tank according to claim 1, characterized in that: In step S2, the method of raising the liquid level in the tank includes: closing the opening of the water outlet valve and increasing the inflow of water.

4. The method for removing floating oil from the top of an oilfield wastewater settling tank according to claim 3, characterized in that: When the liquid level in the tank is adjusted by closing the outlet valve, the adjusted outlet valve flow rate V2′ is: In the formula: V2′ is the flow velocity of the liquid in the pipeline at the outlet valve after adjustment, m / s; V2 is the flow velocity of the liquid in the pipeline at the outlet valve before adjustment, m / s; h1 is the production liquid level, m; h2 is the oil collection liquid level, m.

5. The method for removing floating oil from the top of an oilfield wastewater settling tank according to claim 3, characterized in that: In step S2, when the liquid level in the tank is adjusted by increasing the opening of the inlet valve, the adjusted inlet valve flow rate V3 is: V3=(S△h+A4V4) / A2 △h=h2-h1 In the formula: V3 is the liquid velocity in the pipeline at the inlet valve of the settling tank for recycled water, m / s; V4 is the liquid velocity in the pipeline at the outlet of the settling tank for oil recovery, m / s; S is the cross-sectional area of ​​the tank, m². 2 A4 represents the cross-sectional area of ​​the oil recovery pipeline exiting the settling tank, in meters. 2 A2 is the area of ​​the tank outlet, in meters. 2 .

6. The method for removing floating oil from the top of an oilfield wastewater settling tank according to claim 1, characterized in that: In step S4, the methods for lowering the liquid level in the tank include: increasing the opening of the outlet valve and reducing the inlet water volume.

7. The method for removing floating oil from the top of an oilfield wastewater settling tank according to claims 3 and 6, characterized in that: The influent volume includes the main influent pipeline to the settling tank, the influent pipeline to the wastewater recovery process in the wastewater recovery pond, and other influent pipelines to the settling tank.

8. An oil collection device for the method of removing floating oil from the top of an oilfield wastewater settling tank according to any one of claims 1-6, comprising a settling tank, wherein an inlet pipeline (1), an outlet pipeline (7), and an oil collection pipeline (3) are connected to the settling tank, characterized in that: An oil collection trough (16) is provided above the interior of the settling tank. An oil collection pipeline (13) is connected to the oil collection trough (16). The other end of the oil collection pipeline (13) is connected to an oil collection pipeline (3). An oil collection pump (5) is connected to the oil collection pipeline (3).

9. The oil recovery device according to claim 8, characterized in that: The oil receiving pipeline (3) is connected to the oil receiving pump inlet electric valve (4), the oil receiving pump (5) outlet is connected to the oil receiving pump outlet electric valve (6), the water inlet pipeline (1) is equipped with a water inlet electric valve (2), and the water outlet pipeline (7) is equipped with a water outlet electric valve (8); the oil receiving pump inlet electric valve (8), the oil receiving pump outlet electric valve (6), the water inlet electric valve (2), and the water outlet electric valve (8) are all connected to the control system.

10. The oil recovery device according to claim 8, characterized in that: An regulating weir (11) is provided at the upper edge of the settling tank. The bottom of the regulating weir (11) is connected to the overflow pipeline (9), which is connected to the outlet pipeline (7).

11. The oil recovery device according to claim 8, characterized in that: The outlet pipeline (7) is connected to a buffer water tank, and the buffer water tank is connected to a lifting water pump, which is connected to the control system.

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