Oil removal tank and produced water treatment system

Abstract

The embodiment of the utility model provides an oil removal tank and a produced water treatment system, and belongs to the field of oilfield development ground engineering. The oil removal tank comprises a tank body used for containing oilfield produced water and forming an oil-water separation interface; the water distribution device is arranged in the tank body and is lower than the oil-water separation interface; the water collecting device is arranged in the tank body and is lower than the oil-water separation interface; the oil collecting device comprises an oil collecting barrel, the oil collecting barrel is arranged in the tank body, and an oil collecting opening of the oil collecting barrel is higher than the oil-water separation interface; the heating device comprises a first heating piece, and the first heating piece is arranged in the tank body and located on the oil-water separation interface or the upper portion of the oil-water separation interface; and the blowdown device is arranged at the bottom of the tank body. The structure of the existing oil removal tank is improved, and the heating device is arranged on the oil-water separation interface or the upper part of the oil-water separation interface, so that the temperature of oil can be ensured to be above the condensation point under the cold condition, the oil collection difficulty is reduced, oil-water separation is promoted, and the quality of the treated produced water is ensured to reach the standard.

Description

TECHNICAL FIELD

[0001] The utility model relates to oilfield development ground engineering field, concretely relates to a kind of oil removal tank and produced water treatment system. BACKGROUND

[0002] Oilfield produced water treatment process refers to a series of technical measures for treating produced water generated in the oil production process of oilfield. The traditional oilfield produced water treatment process is mainly based on "large tank sedimentation", and mainly uses oil removal tank to treat produced water.

[0003] However, the existing oil removal tank has problems such as difficult oil collection, low oil-water separation efficiency, and non-standard water quality of treated sewage in winter, extremely cold areas or high condensate oilfield conditions. SUMMARY

[0004] The purpose of the embodiment of the utility model is to provide an oil removal tank and a produced water treatment system, to solve the problems of the existing oil removal tank, such as difficult oil collection, low oil-water separation efficiency, and non-standard water quality of treated sewage.

[0005] In order to achieve the above purpose, the present disclosure provides an oil removal tank, which comprises: a tank body for containing oilfield produced water and forming an oil-water separation interface; a water distribution device arranged in the tank body below the oil-water separation interface; a water collection device arranged in the tank body below the oil-water separation interface; an oil collection device comprising an oil collection barrel arranged in the tank body with the oil collection port of the oil collection barrel being higher than the oil-water separation interface; a heating device comprising a first heating element arranged in the tank body at or above the oil-water separation interface; and a sewage discharge device arranged at the bottom of the tank body.

[0006] In some embodiments, the oil collection port of the oil collection barrel comprises a plurality of oil collection holes, which are uniformly spaced and distributed around the upper part of the sidewall of the oil collection barrel, and each oil collection hole has a diameter ranging from 2 cm to 4 cm.

[0007] In some embodiments, the oil collection device comprises: an oil collection pipeline with an oil collection port connected to the oil outlet of the oil collection barrel; a liquid level meter arranged in the oil collection barrel; and a liquid level control valve arranged on the oil collection pipeline and connected to the liquid level meter.

[0008] In some embodiments, the oil collection device further comprises an oil collection tank arranged around the upper part of the inner wall of the tank body and higher than the oil-water separation interface; and the oil collection port of the oil collection pipeline is connected to the oil outlet of the oil collection tank.

[0009] In some embodiments, a first heating element surrounds the oil collection port of the oil collecting tank and is laid in one or more layers on the oil-water separation interface or above it; the first heating element is equipped with a first steam pipeline and a first condensation pipeline; wherein, the first steam pipeline is connected to the air inlet of the first heating element and a first steam control valve is provided on the first steam pipeline; the first condensation pipeline is connected to the air outlet of the first heating element and a first condensation control valve is provided on the first condensation pipeline.

[0010] In some embodiments, a thermometer is provided inside the oil collection tank; the first heating element is also equipped with a temperature sensor; and the first steam control valve is connected to the thermometer and the temperature sensor respectively.

[0011] In some embodiments, the heating device further includes a second heating element disposed within the tank and below the oil-water separation interface; the second heating element is equipped with a second steam line and a second condensate line.

[0012] In some embodiments, the sewage discharge device includes a manhole and a sewage discharge valve.

[0013] In some embodiments, the top of the oil tank is provided with a breather valve, a safety valve, and a light-transmitting hole.

[0014] This disclosure also provides a produced water treatment system, which includes the oil removal tank in any of the above embodiments, for treating oilfield produced water by removing oil and impurities.

[0015] This disclosure improves the structure of existing oil removal tanks by installing a heating device at or above the oil-water separation interface. This ensures that the oil temperature is above its freezing point in cold conditions, thereby reducing the difficulty of oil recovery, promoting oil-water separation, and ensuring that the treated produced water meets the standards.

[0016] Other features and advantages of the embodiments disclosed herein will be described in detail in the following detailed description section. Attached Figure Description

[0017] The accompanying drawings are provided to further illustrate the embodiments of this disclosure and form part of the specification. They are used together with the following detailed description to explain the embodiments of this disclosure, but do not constitute a limitation thereof. In the drawings:

[0018] Figure 1 This is a schematic flow diagram of the produced water treatment process provided according to the embodiments of this disclosure;

[0019] Figure 2 This is a schematic diagram of the structure of a conventional oil removal tank according to an embodiment of this disclosure;

[0020] Figure 3 This is a schematic diagram of the oil removal tank provided according to Embodiment 1 of this disclosure;

[0021] Figure 4 This is a schematic diagram of the oil removal tank provided according to Embodiment 2 of this disclosure;

[0022] Figure 5 This is a partial structural schematic diagram of the oil removal tank provided according to Embodiment 2 of this disclosure;

[0023] Figure 6 This is a partial structural schematic diagram of the oil removal tank provided according to Embodiment 2 of this disclosure.

[0024] Explanation of reference numerals in the attached figures

[0025] 1. Tank body; 2. Water distribution device; 3. Water collection device; 4. Oil collection device; 5. Heating device; 6. Sewage discharge device; 7. Breathing valve; 8. Safety valve; 9. Light transmission hole; 41. Oil collection tank; 42. Oil collection trough; 43. Oil collection pipeline; 44. Liquid level gauge; 45. Liquid level control valve; 46. Thermometer; 47. Oil collection hole; 51. First heating element; 52. Second heating element; 53. First steam control valve; 54. First condensate control valve; 55. Temperature sensor; 61. Manhole; 62. Sewage discharge valve; A. Air inlet; B. Air outlet. Detailed Implementation

[0026] The specific embodiments of this disclosure will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit the scope of this disclosure.

[0027] Currently, most oilfields primarily use "large tank settling" as their produced water treatment process. Produced water separated from each station is transported to a combined station for centralized treatment. After natural settling to remove oil and flocculation settling to remove impurities, it is preferentially used for reinjection into the producing formation. According to the requirements of "Oilfield Produced Water Treatment Design Specification GB 50428-2015" and "Oil Removal Tank Design Specification SY / T 0083-2008", the oil content of the water effluent from the oil removal tank should not exceed 50 mg / L; the suspended solids content should not exceed 20 mg / L; and the oilfield produced water reinjection water quality requires that both the oil content and suspended solids be below 5 mg / L.

[0028] In traditional water treatment processes primarily based on "large tank settling," the oil removal tank is a crucial component, playing a key role in the removal of oil and impurities from oily wastewater. It directly impacts the efficiency of oil recovery and whether reinjected water meets standards. Common produced water treatment process flows are shown below. Figure 1 .

[0029] refer to Figure 1As shown, a common produced water treatment process may include: 1) Oil and impurity removal: Produced water undergoes preliminary treatment in an oil removal tank to remove floating oil and impurities. 2) Settling: Produced water after oil removal enters a settling tank for further removal of suspended solids. 3) Buffering: Settled produced water flows into a buffer tank, which regulates water flow and balances the water pressure and flow rate of subsequent treatment processes, ensuring the continuity and stability of the treatment process. 4) Filtration: Produced water in the buffer tank then enters a filtration system, which may employ sand filtration, activated carbon filtration, or other filtration technologies to remove finer suspended solids and some dissolved substances. 5) Buffer tank treatment: Filtered produced water finally flows into a buffer tank, which collects the treated water and can be stored or reused as needed.

[0030] An oil separator tank is a circular, vertical or horizontal steel structure used to remove crude oil from produced water. The tank removes crude oil and suspended solids from the produced water by naturally separating them based on density differences during vertical flow, and also acts as a buffer to ensure stable operation of the treatment system. The selection of the oil separator tank type should be based on the determined process flow, operating environment, produced water quality, oil properties in the produced water, treatment scale, and post-treatment water quality requirements. A simplified structural diagram of a common oil separator tank is shown below. Figure 2 As shown.

[0031] like Figure 2 As shown, a typical oil removal tank structure includes: an inlet water pipeline, a distributor, several distribution pipelines connected to the distributor, a collector, several suction pipelines connected to the collector, an outlet water pipeline, an oil collection trough (circling the tank wall), an oil receiving pipeline, an overflow pipeline, a light-transmitting hole, and a siphon breaking pipe. Specifically, the produced water enters the tank through the inlet water pipeline and exits through the outlet water pipeline. An oil-water separation interface forms within the tank; after stratification, the oil layer flows through the oil collection trough into the oil receiving pipeline, the water layer flows through the collector into the outlet water pipeline, and the sludge layer settles at the bottom. A ring-shaped, evenly distributed sludge discharge pipeline at the bottom of the tank can be used for sludge removal.

[0032] Existing oil removal tank structures suffer from problems such as poor oil-water separation, long natural settling time, slow oil recovery, and low oil removal efficiency in practical use. For example, CN106621484A (disclosing a settling oil removal tank, produced water treatment system, and treatment method) uses a vertical flow tank with a uniform water distribution system. It consists of a primary treatment settling oil removal tank and a secondary treatment chemical adjustment cyclone reaction separation device. After two stages of treatment, the produced water has an effective reduction in oil and suspended solids. However, this device has certain defects in terms of liquid inlet distribution and sludge removal facilities, resulting in low operating efficiency. Furthermore, the device does not consider problems such as poor oil-water separation, upper liquid solidification, and difficulty in oil recovery in the collection tank due to low oil layer temperatures in winter, extremely cold regions, and high-pour-point oilfields.

[0033] In order to improve the shortcomings of existing oil removal tanks, such as difficulty in effectively insulating the oil layer at the top of the tank during operation in extremely cold conditions such as winter, resulting in difficulties in oil collection, low oil-water separation efficiency, and substandard water quality of treated wastewater, it is urgent to propose a new oil removal tank structure.

[0034] Based on this, Embodiment 1 of this disclosure provides an oil removal tank, as referenced Figure 3 As shown, Figure 3 This is a structural schematic diagram of the oil removal tank provided according to Embodiment 1 of this disclosure.

[0035] like Figure 3 As shown, the oil removal tank provided in Embodiment 1 of this disclosure includes: a tank body 1, a water distribution device 2, a water collection device 3, an oil collection device 4, a heating device 5, and a sewage discharge device 6.

[0036] Tank 1 is used to contain produced water from the oil field and form an oil-water separation interface.

[0037] The water distribution device 2 is located inside the tank 1 and below the oil-water separation interface. The basic structure of the water distribution device 2 may include a water distributor and several water distribution pipes connected to the water distributor, which are used to introduce oilfield produced water into the tank 1.

[0038] The water collection device 3 is located inside the tank 1 and below the oil-water separation interface. The basic structure of the water collection device 3 may include a water collector and several suction pipes connected to the water collector, which are used to discharge the extracted water after oil and impurity removal into the tank 1.

[0039] The oil collecting device 4 includes an oil collecting tank, which is located inside the tank body 1 and has its oil collection port higher than the oil-water separation interface. It is mainly used to collect the oil layer after oil-water separation. It should be noted that in existing oil removal tank structures, some oil collecting devices are also present, located around the inner wall of the tank. These devices mainly collect oil from the edge area of ​​the tank, resulting in a slow collection rate. Furthermore, when the oil has solidified and has poor fluidity, it is difficult to collect oil from the central area, making oil collection challenging. The oil collecting tank of this disclosure can be located in the central area of ​​the tank, thereby enabling oil collection from the center, accelerating the collection rate, and allowing for the recovery of heated oil, thus reducing the difficulty of oil collection.

[0040] The heating device 5 includes a first heating element, which is located inside the tank 1 at or above the oil-water separation interface. The first heating element is positioned at or above the oil-water separation interface to prevent the floating oil phase from solidifying at the top of the tank. It should be noted that some existing oil removal tanks have heating coils at the bottom of the tank, primarily for promoting oil-water separation, but they do not consider the possibility of oil solidification at the top in cold conditions such as winter. During operation in cold conditions such as winter, the bottom heating coils are prone to uneven heating and difficulty in effectively insulating the oil layer at the top of the tank, resulting in difficulties in oil recovery. The heating device of this disclosure is mainly located at or above the oil-water separation interface, which can meet the heating and insulation requirements of the upper oil layer, while also promoting oil-water separation downwards, thereby increasing the oil-water separation rate.

[0041] The sewage discharge device 6 is located at the bottom of the tank 1 and is mainly used to periodically clean the mud and sludge that have settled at the bottom of the tank 1.

[0042] This invention improves the existing oil removal tank structure by installing a heating device at or above the oil-water separation interface to directly transfer heat to the top oil layer, ensuring that the temperature at the top of the tank is above the oil's freezing point. This effectively solves the problem of oil layer solidification under extremely cold conditions. Furthermore, for highly emulsified produced water, compared to conventional settling methods, it significantly reduces the settling time, promotes oil-water separation, and ensures that the water quality meets standards.

[0043] Based on this, Embodiment 2 of this disclosure provides an oil removal tank, as referenced Figure 4 As shown, Figure 4 This is a schematic diagram of the oil removal tank provided according to Embodiment 2 of this disclosure.

[0044] like Figure 4 As shown, the oil removal tank provided in Embodiment 2 of this disclosure, in addition to the tank body 1, water distribution device 2, water collection device 3, oil collection device 4, heating device 5, and sewage discharge device 6 of Embodiment 1, may also include a water inlet pipeline, a breather valve 7, a safety valve 8, a light-transmitting hole 9, an overflow system, a siphon breaking pipe, and a water outlet pipeline. It should be noted that the working pressure of the oil removal tank is 0.7 MPa. To prevent overpressure of the tank, in addition to the breather valve 7 and the safety valve 8, a manual venting valve connected to the venting pipeline may be further provided. When the pressure exceeds the set pressure, it will be vented through the venting pipeline to ensure the safe and stable pressure inside the tank.

[0045] The oil collection device 4 may include an oil collection tank 41 and an oil collection trough 42. The oil collection trough is arranged around the upper part of the inner wall of the tank body 1 and is higher than the oil-water separation interface. By combining the oil collection tank 41 with the oil collection trough 42 structure, the oil layer can be collected from all directions, improving the oil collection efficiency.

[0046] The oil collection device 4 may also include an oil receiving pipeline 43, a level gauge, and a level control valve 45, mainly used to control the liquid level in the oil collection tank. The oil receiving port of the oil receiving pipeline 43 is connected to the oil outlet of the oil collection tank 41 and the oil outlet of the oil collection trough 42, respectively. The level gauge is located inside the oil collection tank 41 (see reference). Figure 6 The level control valve 45 is located on the oil receiving pipeline 43 and connected to the level gauge. It should be noted that, according to relevant standards and specifications, the oil accumulation thickness in a vertical oil removal tank should not exceed 0.8m. Therefore, a level gauge is installed inside the oil collection tank 41, and a level control valve 45 is installed on the oil receiving pipeline to ensure that the oil level in the oil collection tank is within a reasonable range.

[0047] In one specific implementation, reference is made to... Figure 5 As shown, the oil collection tank 41 may include multiple oil collection holes 47, which are evenly spaced and distributed around the upper side wall of the oil collection tank 41. The diameter of each oil collection hole ranges from 2cm to 4cm. Heated floating oil enters the oil collection tank 41 through the multiple oil collection holes 47 at the top of the tank for recycling, completing the entire floating oil recycling process. It should be noted that setting the diameter of the oil collection holes to 2cm to 4cm not only allows for the flow and recycling of heated floating oil but also allows small, solidified oil droplets to pass through, thereby reducing the risk of clogging while improving oil collection efficiency.

[0048] The heating device 5 may include a first heating element 51 and a second heating element 52. The first heating element is equipped with a first steam line and a first condenser line. The first steam line is connected to the air inlet of the first heating element and is equipped with a first steam control valve 53; the first condenser line is connected to the air outlet of the first heating element and is equipped with a first condensation control valve 54. The second heating element 52 is located inside the tank and below the oil-water separation interface, and is equipped with a second steam line and a second condenser line. In this embodiment, the first heating element can heat and maintain the temperature of the upper floating oil, while the second heating element can improve the oil-water separation efficiency of the produced water from the bottom.

[0049] In one specific implementation, reference is made to... Figure 6 As shown, the first heating element 51 surrounds the oil inlet of the oil collecting tank 41 and is laid in one or more layers on or above the oil-water separation interface. The oil collecting tank 41 is equipped with a thermometer 46 and a level gauge 44. The first heating element 51 is equipped with a temperature sensor 55, and the first steam control valve is connected to the thermometer and the temperature sensor respectively.

[0050] Specifically, the first heating element 51 can be a steam coil, where A is the air inlet and B is the air outlet. Self-regulating valves are installed at A and B respectively. By sensing the temperature of the oil layer through a temperature sensor, the first steam control valve and the first condensation control valve are automatically interlocked to ensure that the temperature of the upper part of the tank is maintained at 3-5°C above the freezing point of the oil.

[0051] The sewage discharge device 6 may include a manhole 61 and a sewage discharge valve 62.

[0052] This embodiment improves upon the existing oil removal tank structure by adding a steam coil heating system at or above the oil-water separation interface. The multi-layer steam coil, equipped with an oil collection tank, heats the oil layer to meet the recovery requirements of hardened floating oil, improving oil-water separation efficiency and further reducing settling and demulsification time. The steam coil is equipped with a self-regulating temperature control valve. A temperature sensor detects the oil layer temperature to remotely control the steam inlet and outlet valves, ensuring the temperature at the top of the tank remains above the oil's freezing point by 3-5°C. The heated floating oil is recovered through the oil collection port at the top of the collection tank or through the oil collection trough into the oil collection pipeline.

[0053] The following combines the above embodiments and Figures 3 to 6 The corresponding processes are described in detail below. The description is only for the purpose of facilitating the understanding of the embodiments of this disclosure and is not intended to further limit the embodiments of this disclosure.

[0054] Hardened floating oil heating and insulation process: To address the problem of uneven heating at the bottom of the oilfield deoiling tank under extreme conditions such as winter, which prevents the recovery of floating oil, a first heating element 51 (specifically a spiral steam heating coil) can be added to the upper part of the tank. Temperature sensors 55 are used to regulate the first steam control valve 53 and the first condensation control valve 54, thereby achieving heating and insulation of the upper floating oil. A thermometer 46 ensures that the oil temperature inside the tank is maintained 3-5°C above its freezing point.

[0055] Oil collection tank floating oil recovery process: Heated and hardened floating oil overflows into the tank through multiple oil collection holes 47 at the top of the oil collection tank 41, realizing the floating oil recovery process. The oil collection tank 41 is connected to the oil collection trough 42 to realize the entire oil collection work. The high and low liquid level limits of the oil collection tank 41 are set to 0.8m and 0.1m respectively. When the liquid level in the tank reaches a certain height, the liquid level control valve 45 will be opened.

[0056] The overall workflow of the oil removal tank is as follows: Oily wastewater enters the central cylinder of the tank through the inlet pipeline and is then distributed to the settling zone by the water distribution device 2. During this process, small oil particles that do not have the ability to float due to the relative density difference between oil and water enter the water collection device 3 with the water and flow out of the oil removal tank through the outlet pipeline. The oil layer that floats and accumulates is collected through the oil collection tank 41 and the oil collection trough 42, and then flows out of the tank through the oil collection pipeline 43.

[0057] Safety venting and wastewater discharge procedures: To prevent overpressure within the recovery tank, an automatic venting procedure and a manual venting procedure are installed on the tank top. The automatic venting procedure involves keeping the normally open valve always open. If the pressure exceeds the tank's maximum allowable pressure, venting will occur through the venting pipeline to ensure the safety and stability of the pressure system. The manual venting procedure involves opening the manual venting valve and regulating the pressure within the tank through the venting pipeline. Furthermore, for the wastewater discharge procedure, the oil removal tank can be drained periodically by manually opening and closing the wastewater discharge valve 62.

[0058] The above process is simple to operate, meets the requirements for oil recovery under extreme temperature conditions such as winter, improves oil removal efficiency, promotes oil-water separation, and ensures that water quality meets standards.

[0059] This disclosure also provides a produced water treatment system, which includes the oil removal tank in any of the above embodiments, for treating oilfield produced water by removing oil and impurities.

[0060] The beneficial effects of the produced water treatment system provided in this disclosure are the same as those of the oil removal tank provided in the above embodiments, and will not be repeated here.

[0061] These embodiments are provided to make the disclosure thorough and complete, and to fully express the scope of the disclosure to those skilled in the art. It should be noted that, unless otherwise specifically stated, the relative arrangement of components and steps, material composition, numerical expressions, and values ​​set forth in these embodiments should be interpreted as exemplary only and not as limiting.

[0062] It should be noted that, in the description of this disclosure, unless otherwise stated, "a plurality of" means two or more; the terms "upper," "lower," "left," "right," "inner," and "outer," etc., indicating orientation or positional relationship, are only for the convenience of describing this disclosure and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this disclosure. When the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0063] Furthermore, the terms "first," "second," and similar terms used in this disclosure do not indicate any order, quantity, or importance, but are merely used to distinguish different parts. "Vertical" is not strictly vertical, but within the permissible margin of error. "Parallel" is not strictly parallel, but within the permissible margin of error. Terms such as "including" or "contains" mean that the element preceding the word encompasses the element listed after the word, and do not exclude the possibility of encompassing other elements as well.

[0064] It should also be noted that, in the description of this disclosure, unless otherwise expressly specified and limited, the terms "installed," "connected," and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in this disclosure depending on the specific circumstances. When a particular device is described as being located between a first device and a second device, an intermediary device may or may not be present between the particular device and the first or second device.

[0065] All terms used in this disclosure have the same meaning as understood by one of ordinary skill in the art to which this disclosure pertains, unless otherwise specifically defined. It should also be understood that terms defined in general dictionaries should be interpreted as having meanings consistent with their meanings in the context of the relevant art, and not as idealized or highly formalized, unless expressly defined herein.

[0066] Techniques, methods, and equipment known to those skilled in the art may not be discussed in detail, but where appropriate, they should be considered part of the specification.

[0067] The above are merely embodiments of this disclosure and are not intended to limit the scope of this disclosure. Various modifications and variations can be made to this disclosure by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this disclosure should be included within the scope of the claims of this disclosure.

Claims

1. An oil removal tank, characterized in that, The oil removal tank includes: Tank body, the tank body being used to contain produced water from the oilfield and to form an oil-water separation interface; A water distribution device is located inside the tank and below the oil-water separation interface; A water collection device is located inside the tank and below the oil-water separation interface; An oil collection device includes an oil collection tank, which is located inside the tank and the oil collection port of the oil collection tank is higher than the oil-water separation interface. The heating device includes a first heating element disposed within the tank and above the oil-water separation interface; and, A sewage discharge device is located at the bottom of the tank.

2. The oil removal tank according to claim 1, characterized in that, The oil collection tank has multiple oil collection holes at equal intervals, which are distributed around the upper side wall of the oil collection tank, and the diameter of each oil collection hole ranges from 2cm to 4cm.

3. The oil removal tank according to claim 1 or 2, characterized in that, The oil collection device includes: An oil collection line, wherein the oil collection port of the oil collection line is connected to the oil outlet of the oil collection tank; A level gauge is installed inside the oil collection tank; and, A level control valve is located on the oil receiving pipeline and connected to the level gauge.

4. The oil removal tank according to claim 3, characterized in that, The oil collection device further includes an oil collection trough, which is arranged around the upper part of the inner wall of the tank and is higher than the oil-water separation interface; the oil collection port of the oil collection pipeline is connected to the oil outlet of the oil collection trough.

5. The oil removal tank according to claim 1, characterized in that, The first heating element surrounds the oil collection tank's oil inlet and is laid in one or more layers on the oil-water separation interface or its upper part; The first heating element is equipped with a first steam pipeline and a first condensate pipeline; wherein, The first steam pipeline is connected to the air inlet of the first heating element, and a first steam control valve is provided on the first steam pipeline; The first condenser line is connected to the gas outlet of the first heating element, and a first condensation control valve is provided on the first condenser line.

6. The oil removal tank according to claim 5, characterized in that, The oil collection tank is equipped with a thermometer; the first heating element is also equipped with a temperature sensor; the first steam control valve is connected to the thermometer and the temperature sensor respectively.

7. The oil removal tank according to claim 1, characterized in that, The heating device further includes a second heating element, which is disposed in the tank and below the oil-water separation interface; the second heating element is equipped with a second steam pipeline and a second condensate pipeline.

8. The oil removal tank according to claim 1, characterized in that, The sewage discharge device includes a manhole and a sewage discharge valve.

9. The oil removal tank according to claim 1, characterized in that, The top of the oil removal tank is equipped with a breather valve, a safety valve, and a light-transmitting hole.

10. A produced water treatment system, characterized in that, The produced water treatment system includes an oil removal tank as described in any one of claims 1 to 9, for treating produced water from oilfields to remove oil and impurities.

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