A two-stage cyclone separator series oil removal process installed inside the tank

Abstract

This invention relates to the field of oily wastewater treatment technology, and more particularly to a two-stage hydrocyclone oil separator series oil removal process installed inside a tank. The process involves connecting a primary hydrocyclone and a secondary hydrocyclone in series inside a wastewater storage tank, with oily wastewater passing through both treatment units sequentially. The primary hydrocyclone utilizes a first centrifugal force field to separate heavy oil and solid particles. The secondary hydrocyclone, with its larger aspect ratio and smaller cone angle, generates a stronger centrifugal force field, achieving deep separation of fine oil droplets. The heavy and light oil phases generated by the two stages converge into the same oil collection pipe for recovery, and the purified effluent enters the main space of the wastewater storage tank. This invention effectively solves the problem of insufficient efficiency in simultaneous separation of heavy oil and fine oil droplets by a single-stage hydrocyclone through a staged separation mechanism, improving the quality of the effluent, and has the advantages of compact structure and simple operation.

Description

Technical Field

[0001] This invention relates to the field of oily wastewater treatment technology, and in particular to an oil removal process using a two-stage cyclone separator connected in series inside a tank. Background Technology

[0002] In the application of oil removal technology for industrial oily wastewater storage tanks, the existing single-stage hydrocyclone oil removal process uses a hydrocyclone as the core equipment. Its working principle is based on centrifugal separation. By pumping in oily wastewater, a high-speed rotating flow field is formed inside the hydrocyclone, generating strong centrifugal force. Due to the density difference between oil and water, the lighter oil phase gathers and rises towards the central axis of the hydrocyclone under the action of centrifugal force, and is discharged and recovered through the top overflow port, while the heavier water phase moves downward along the wall of the tank and is output from the bottom outlet. This achieves efficient oil-water separation, reduces the oil content of the wastewater, and meets the subsequent treatment or discharge requirements of the storage tank.

[0003] Existing single-stage hydrocyclone oil removal processes suffer from the following technical challenges: When treating industrial oily wastewater, the hydrocyclone design, based on a single separation principle, struggles to simultaneously optimize the internal flow field and centrifugal force distribution for both dense, easily settling heavy oil and small, easily emulsified fine oil droplets, resulting in insufficient separation efficiency. For example, in the oil removal process of oily wastewater storage tanks in the petrochemical industry, the wastewater often contains heavy oil deposited from the equipment and fine oil droplets formed through mixing. While a single-stage hydrocyclone can partially remove heavy oil, the fine oil droplets, due to their low inertia, easily pass through the separation zone and are discharged with the effluent, causing the effluent oil content to exceed standards and thus affecting the compliance of subsequent biological treatment or direct discharge. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a two-stage cyclone oil separator series oil removal process installed inside the tank, which solves the technical problem that the existing single-stage cyclone oil removal process cannot efficiently separate heavy oil and fine oil droplets, resulting in poor oily wastewater treatment effect.

[0005] To solve the above-mentioned technical problems, the specific technical solution of the present invention is as follows: This invention provides a tank-mounted two-stage cyclone separator series oil removal process, comprising: Step 1: The oily wastewater generated by the upstream unit is introduced into a primary cyclone separator installed inside the wastewater storage tank. The oily wastewater includes heavy oil and fine oil droplets. Step 2: In the first-stage cyclone separator, the introduced oily wastewater is separated by the first centrifugal force field, so that the heavy oil accumulates at the bottom to form a heavy oil phase, while the remaining water becomes the first-stage effluent and is discharged from the top. Step 3: The discharged primary effluent is introduced into a secondary cyclone oil separator that is also installed inside the wastewater storage tank; Step 4: In the secondary cyclone oil separator, the primary effluent is separated by a second centrifugal force field with an intensity higher than that of the first centrifugal force field, causing fine oil droplets to gather at the top to form a light oil phase and be continuously discharged, while the remaining water becomes purified effluent and is discharged from the bottom. Step 5: Periodically discharge the heavy oil phase that has accumulated at the bottom of the first-stage cyclone separator, and at the same time collect the light oil phase that is continuously discharged from the top of the second-stage cyclone separator, so that the heavy oil phase and the light oil phase flow together into a single oil collection pipe. Step 6: The purified effluent discharged from the bottom of the secondary cyclone oil separator is sent into the main space of the wastewater storage tank.

[0006] Furthermore, the oil removal process of the two-stage hydrocyclone oil separator in series in the tank described in this invention, wherein the oily wastewater generated by the upstream device is introduced into the first-stage hydrocyclone oil separator installed inside the wastewater storage tank, includes: Receives oily wastewater from petrochemical production plants; The oily wastewater transported through the pipeline is guided through the inlet rectifying structure before entering the primary cyclone oil separator.

[0007] Furthermore, the present invention provides a two-stage cyclone oil separator series oil removal process within the tank. In the first-stage cyclone oil separator, the introduced oily wastewater is separated by a first centrifugal force field, including: The oily wastewater is tangentially introduced into the primary cyclone separator to generate a rotating flow field; In the rotating flow field, the dense heavy oil and solid particles move toward the container wall and downward, while the less dense water phase and fine oil droplets move upward in the central region. The upward-moving aqueous phase and fine oil droplets flow out from the top outlet, becoming the primary effluent.

[0008] Furthermore, the present invention includes a two-stage cyclone oil separator series oil removal process inside the tank, wherein the discharge of the first-stage effluent is introduced into a second-stage cyclone oil separator also installed inside the wastewater storage tank, comprising: The primary effluent discharged from the top of the primary cyclone separator flows into a closed connecting pipe. Relying on gravity or system residual pressure, the primary effluent in the connecting pipe enters from the inlet on the side of the secondary cyclone oil separator.

[0009] Furthermore, the present invention describes a two-stage cyclone oil separator series oil removal process within the tank. In the second-stage cyclone oil separator, the introduced first-stage effluent is separated by a second centrifugal force field with an intensity higher than the first centrifugal force field, including: The secondary cyclone separator has a larger aspect ratio than the primary cyclone separator and a smaller cone angle than the primary cyclone separator; The primary effluent introduced into the secondary cyclone oil separator, having the aforementioned aspect ratio and cone angle, undergoes a longer rotational path, causing fine oil droplets to collide, coalesce, and migrate toward the central axis region.

[0010] Furthermore, the present invention describes a two-stage cyclone separator series oil removal process inside the tank, wherein the process of collecting fine oil droplets at the top to form a light oil phase and continuously discharging it includes: Fine oil droplets migrating towards the central axis region converge in the central low-pressure area, forming a continuous oil core; The oil core moves upward through the overflow pipe provided at the top; The upward-moving oil core is continuously discharged from the outlet of the overflow pipe, forming the light oil phase.

[0011] Furthermore, the present invention describes a two-stage cyclone separator series oil removal process within the tank, wherein the heavy oil phase accumulated at the bottom of the first-stage cyclone separator is periodically discharged, while the light oil phase continuously discharged from the top of the second-stage cyclone separator is collected, so that the heavy oil phase and the light oil phase converge into a single oil collection pipe, comprising: The drain valve located at the underflow port of the first-stage cyclone separator is opened periodically to discharge the accumulated heavy oil phase. Meanwhile, the overflow pipe at the top of the secondary cyclone separator continuously discharges the accumulated light oil phase; The heavy oil phase discharged from the underflow port of the first-stage cyclone separator flows into one pipe, and the light oil phase discharged from the top overflow pipe of the second-stage cyclone separator flows into another pipe. The two pipes are connected to the same oil collecting pipe, so that the heavy oil phase and the light oil phase can be combined in the oil collecting pipe.

[0012] Furthermore, the present invention includes a two-stage cyclone oil separator series oil removal process inside the tank, wherein the purified effluent discharged from the bottom of the two-stage cyclone oil separator is sent into the main space of the wastewater storage tank, comprising: The purified effluent flows out from the outlet at the bottom of the secondary cyclone oil separator; The purified water flowing out from the outlet enters the main space of the wastewater storage tank; The purified effluent entering the main space is stored in the wastewater storage tank.

[0013] Furthermore, the present invention provides a two-stage hydrocyclone oil separator series oil removal process in the tank, wherein the first-stage hydrocyclone oil separator and the second-stage hydrocyclone oil separator are arranged in the wastewater storage tank in a manner of stacking vertically or horizontally side by side. Furthermore, the bottom outlet of the primary cyclone oil separator and the bottom outlet of the secondary cyclone oil separator are both located above the bottom of the wastewater storage tank in terms of spatial height.

[0014] Furthermore, the present invention employs a two-stage hydrocyclone oil separator series oil removal process within the tank. The structural parameters of the first-stage hydrocyclone oil separator are determined based on the requirements for separating heavy oil and solid particles; the structural parameters of the second-stage hydrocyclone oil separator are determined based on the requirements for separating fine oil droplets; the purified effluent after treatment by the first-stage and second-stage hydrocyclone oil separators in series has a lower oil content than the effluent treated by using only the first-stage or only the second-stage hydrocyclone oil separators.

[0015] The beneficial effects of this invention are: This invention utilizes a first centrifugal force field in the primary hydrocyclone to preferentially separate dense heavy oil and solid particles, effectively reducing the load on subsequent treatment units. Simultaneously, a second centrifugal force field with even greater intensity is used in the secondary hydrocyclone for deep separation of fine oil droplets. This two-stage tandem process overcomes the technical bottleneck of single-stage hydrocyclones, which struggle to efficiently remove both heavy oil and fine oil droplets simultaneously due to their limited flow field and centrifugal force distribution. Since both hydrocyclones are integrated within the same wastewater storage tank, the investment in additional external tanks is avoided, simplifying the piping layout. Furthermore, by optimizing the structural parameters of the primary and secondary hydrocyclones to suit the physical characteristics of heavy oil and fine oil droplets respectively, the invention achieves graded and targeted removal of different pollutants within a limited space, significantly improving overall oil removal efficiency and the stability of effluent quality. Attached Figure Description

[0016] To more clearly illustrate the technical solution of the present invention, the drawings used in the embodiments will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on the drawings without creative effort.

[0017] Figure 1 This is a schematic diagram of the process of the present invention.

[0018] The reference numerals in the attached diagram are as follows: 1-oily wastewater inlet, 2-cyclone oil separator A, 3-cyclone oil separator B, 4-oil outlet, 5-water outlet, 6-wastewater storage tank. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with specific embodiments and corresponding drawings. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention. The technical solutions provided by various embodiments of this invention will be described in detail below with reference to the accompanying drawings.

[0020] To better understand the purpose of this invention, the invention will be described in further detail below.

[0021] Please see Figure 1 The present invention provides a tank-mounted two-stage cyclone separator series oil removal process, comprising: Step 1: The oily wastewater generated by the upstream unit is introduced into a primary cyclone separator installed inside the wastewater storage tank. The oily wastewater includes heavy oil and fine oil droplets. Step 2: In the first-stage cyclone separator, the introduced oily wastewater is separated by the first centrifugal force field, so that the heavy oil accumulates at the bottom to form a heavy oil phase, while the remaining water becomes the first-stage effluent and is discharged from the top. Step 3: The discharged primary effluent is introduced into a secondary cyclone oil separator that is also installed inside the wastewater storage tank; Step 4: In the secondary cyclone oil separator, the primary effluent is separated by a second centrifugal force field with an intensity higher than that of the first centrifugal force field, causing fine oil droplets to gather at the top to form a light oil phase and be continuously discharged, while the remaining water becomes purified effluent and is discharged from the bottom. Step 5: Periodically discharge the heavy oil phase that has accumulated at the bottom of the first-stage cyclone separator, and at the same time collect the light oil phase that is continuously discharged from the top of the second-stage cyclone separator, so that the heavy oil phase and the light oil phase flow together into a single oil collection pipe. Step 6: The purified effluent discharged from the bottom of the secondary cyclone oil separator is sent into the main space of the wastewater storage tank.

[0022] Oily wastewater is transported from upstream petrochemical production units via pipeline to oily wastewater inlet 1, and then enters the primary cyclone separator 2 located inside the wastewater storage tank 6. Before entering the primary cyclone separator 2, the oily wastewater flows through an inlet rectifying structure to stabilize the flow and reduce turbulence, creating favorable conditions for subsequent centrifugal separation. The oily wastewater includes dense heavy oil and fine oil droplets with small particle sizes. The primary cyclone separator 2 generates a rotating flow field through tangential water inlet, forming the first centrifugal force field.

[0023] Under the action of the first centrifugal force field, dense heavy oil and solid particles acquire greater centrifugal force, are thrown towards the inner wall of the first-stage cyclone oil separator 2 and move downwards, accumulating at the bottom to form a heavy oil phase. The remaining water and fine oil droplets move upwards in the central region and are discharged from the top outlet as first-stage effluent. The heavy oil content of the first-stage effluent is significantly reduced, but it still contains fine oil droplets.

[0024] The effluent from the first stage is introduced into the second-stage hydrocyclone oil separator 3 via a sealed connecting pipe, relying on gravity or system residual pressure. The second-stage hydrocyclone oil separator 3 has a larger aspect ratio and a smaller cone angle than the first-stage hydrocyclone oil separator 2, thereby generating a stronger second centrifugal force field. The effluent from the first stage undergoes a longer rotation path within the second-stage hydrocyclone oil separator 3, where fine oil droplets collide, coalesce, and migrate towards the central axis region.

[0025] Fine oil droplets migrating towards the central axis region converge in the central low-pressure zone to form a continuous oil core. This oil core moves upwards through the top overflow pipe and is continuously discharged from the outlet, forming a light oil phase. The remaining water becomes purified effluent and is discharged from the bottom of the secondary cyclone oil separator 3. The oil content of the purified effluent meets the standards for subsequent treatment or discharge.

[0026] The heavy oil phase at the bottom of the primary cyclone separator 2 is discharged periodically by opening the drain valve, while the light oil phase at the top of the secondary cyclone separator 3 is continuously discharged through the overflow pipe. The heavy and light oil phases are respectively piped into the same oil collection pipe, and finally recovered from the drain port 4. The oil collection pipe transports the concentrated oil phase to the oil recovery system for resource recovery.

[0027] The purified effluent discharged from the bottom of the secondary cyclone separator 3 enters the main space of the wastewater storage tank 6 through the outlet 5 for storage. The primary cyclone separator 2 and the secondary cyclone separator 3 are arranged in the wastewater storage tank 6 in a stacked or horizontally parallel configuration, with their bottom outlets located above the bottom of the tank to avoid interference from sediment. This series design allows for the graded separation of heavy oil and fine oil droplets based on their different physical characteristics, improving overall oil removal efficiency.

[0028] Oily wastewater is transported from upstream petrochemical production units via pipeline to oily wastewater inlet 1, and then enters the primary cyclone separator 2 located inside the wastewater storage tank 6. Before entering the primary cyclone separator 2, the oily wastewater flows through an inlet rectifying structure. The inlet rectifying structure uses a perforated plate or guide vane design to stabilize the influent flow and reduce turbulence fluctuations, creating uniform flow field conditions for subsequent centrifugal separation. Oily wastewater generated by petrochemical production units typically contains heavy oil and fine oil droplets. The inlet rectifying structure, by homogenizing the flow velocity distribution, prevents impurities from depositing at pipe bends or joints.

[0029] Oily wastewater enters the cylindrical section of the primary cyclone separator 2 tangentially, forming a high-speed rotating flow field. This rotating flow field generates a first centrifugal force field. Dense heavy oil and solid particles gain high acceleration under the centrifugal force, are thrown towards the inner wall of the primary cyclone separator 2, and spiral downwards along the wall. Heavy oil and solid particles accumulate at the bottom conical section of the primary cyclone separator 2 to form a heavy oil phase, while the less dense water phase and fine oil droplets move upwards in the central low-pressure zone and are discharged from the top outlet as primary effluent. The intensity of the first centrifugal force field is controlled by the inlet flow velocity and structural dimensions of the primary cyclone separator 2 to meet the heavy oil separation requirements.

[0030] The primary effluent flows out from the top outlet of the primary hydrocyclone separator 2 and into a closed connecting pipe. This connecting pipe, made of corrosion-resistant material, relies on gravity or residual system pressure to transport the primary effluent to the inlet on the side of the secondary hydrocyclone separator 3. The sealed design prevents gas ingress or pressure loss, and the inclined arrangement of the connecting pipe utilizes the elevation difference to promote gravity flow. The residual system pressure is provided by upstream pumping equipment.

[0031] The secondary cyclone oil separator 3 has a larger aspect ratio than the primary cyclone oil separator 2, and a smaller cone angle. The increased aspect ratio extends the fluid rotation path, while the reduced cone angle enhances flow field stability, together forming a second centrifugal force field with a higher intensity than the first centrifugal force field. After the primary effluent enters the secondary cyclone oil separator 3, fine oil droplets collide and coalesce under the strong centrifugal force, increasing in size and migrating towards the central axis region. The second centrifugal force field achieves efficient separation of fine oil droplets by optimizing the cyclone separator structural parameters.

[0032] Fine oil droplets migrating towards the central axis region converge in the low-pressure zone at the center of the secondary cyclone separator 3, forming a continuous oil core. The oil core moves upward through an overflow pipe located at the top. The insertion depth of the overflow pipe is optimized through calculation. The oil core is continuously discharged from the overflow pipe outlet, forming a light oil phase. The discharge process of the light oil phase is driven by the density difference between oil and water and the central negative pressure, achieving automated continuous operation.

[0033] The bottom outlet of the primary cyclone separator 2 is equipped with a drain valve, which is opened periodically to discharge the accumulated heavy oil phase. The top overflow pipe of the secondary cyclone separator 3 continuously discharges the light oil phase. The heavy oil phase is transported through one pipeline, and the light oil phase is transported through another pipeline; both pipelines connect to the same oil collection pipeline 4. Oil collection pipeline 4 collects the heavy and light oil phases and transports them uniformly to the oil recovery system. The drain valve is electrically or pneumatically controlled and operates periodically based on the liquid level sensor signal.

[0034] The purified effluent flows out from the bottom outlet of the secondary cyclone oil separator 3 and enters the main space of the wastewater storage tank 6 through the outlet 5. The outlet 5 is located on the side wall or bottom of the wastewater storage tank 6. The purified effluent mixes with the still water in the tank within the main space, further settling residual suspended solids. The wastewater storage tank 6 provides buffer capacity to facilitate a stable inflow of water to subsequent treatment units.

[0035] The primary hydrocyclone separator 2 and the secondary hydrocyclone separator 3 are installed in the wastewater storage tank 6 either stacked vertically or horizontally side-by-side. When stacked vertically, the secondary hydrocyclone separator 3 is located above the primary hydrocyclone separator 2, utilizing gravity to reduce pumping energy consumption; when horizontally side-by-side, they are connected by pipes to save vertical space. The bottom outlets of the primary hydrocyclone separator 2 and the secondary hydrocyclone separator 3 are installed higher than the bottom of the wastewater storage tank 6 to prevent sediment from clogging the outlets.

[0036] The structural parameters of the primary hydrocyclone oil separator 2 are determined based on the requirements for separating heavy oil and solid particles, including diameter, cone angle, and inlet size, to optimize the collection efficiency of heavy components. The structural parameters of the secondary hydrocyclone oil separator 3 are determined based on the requirements for separating fine oil droplets, focusing on the length-to-diameter ratio and overflow pipe diameter to improve the coalescence effect of fine oil droplets. After the two-stage hydrocyclone oil separators are connected in series, the oil content of the purified effluent is lower than that of single-stage treatment. This is because the primary hydrocyclone oil separator 2 removes heavy oil, reducing the load on the secondary stage, while the secondary hydrocyclone oil separator 3 focuses on the deep separation of fine oil droplets.

[0037] Oily wastewater is transported from upstream petrochemical production units via pipeline to oily wastewater inlet 1, and then enters the primary cyclone separator 2 located inside the wastewater storage tank 6. Before entering the primary cyclone separator 2, the oily wastewater flows through an inlet rectifying structure. The inlet rectifying structure uses a perforated plate or guide vane design to stabilize the influent flow and reduce turbulence fluctuations, creating uniform flow field conditions for subsequent centrifugal separation. Oily wastewater generated by petrochemical production units typically contains dense heavy oil and fine oil droplets. The inlet rectifying structure homogenizes the flow velocity distribution, preventing impurities from depositing at pipe bends or joints.

[0038] Oily wastewater enters the cylindrical section of the primary cyclone separator 2 tangentially, forming a high-speed rotating flow field. This rotating flow field generates a first centrifugal force field. Dense heavy oil and solid particles gain high acceleration under the centrifugal force, are thrown towards the inner wall of the primary cyclone separator 2, and spiral downwards along the wall. Heavy oil and solid particles accumulate at the bottom conical section of the primary cyclone separator 2, forming a heavy oil phase, while the less dense water phase and fine oil droplets move upwards in the central low-pressure zone and are discharged from the top outlet as primary effluent. The intensity of the first centrifugal force field is controlled by the inlet velocity and structural dimensions of the primary cyclone separator 2. The structural parameters of the primary cyclone separator 2 are determined according to the requirements for separating heavy oil and solid particles, including diameter, cone angle, and inlet size, to optimize the collection efficiency of heavy components.

[0039] The primary effluent flows out from the top outlet of the primary hydrocyclone separator 2 and into a closed connecting pipe. This connecting pipe, made of corrosion-resistant material, relies on gravity or residual system pressure to transport the primary effluent to the inlet on the side of the secondary hydrocyclone separator 3. The sealed design prevents gas ingress or pressure loss, and the inclined arrangement of the connecting pipe utilizes the elevation difference to promote gravity flow. The residual system pressure is provided by upstream pumping equipment.

[0040] The secondary cyclone oil separator 3 has a larger aspect ratio than the primary cyclone oil separator 2, and a smaller cone angle. The increased aspect ratio extends the fluid rotation path, while the reduced cone angle enhances flow field stability, together forming a second centrifugal force field with a higher intensity than the first centrifugal force field. After the primary effluent enters the secondary cyclone oil separator 3, fine oil droplets collide and coalesce under strong centrifugal force, increasing in size and migrating towards the central axis region. The structural parameters of the secondary cyclone oil separator 3 are determined according to the requirements for separating fine oil droplets, emphasizing the aspect ratio and overflow pipe diameter to improve the fine oil droplet coalescence effect. The fine oil droplets migrating towards the central axis region converge in the low-pressure zone at the center of the secondary cyclone oil separator 3, forming a continuous oil core. The oil core moves upward through the overflow pipe at the top; the overflow pipe insertion depth is optimized through calculation, and the oil core is continuously discharged from the overflow pipe outlet, forming a light oil phase. The light oil phase discharge process is driven by the oil-water density difference and the central negative pressure, achieving automated continuous operation.

[0041] The bottom outlet of the primary cyclone separator 2 is equipped with a drain valve, which is opened periodically to discharge the accumulated heavy oil phase. The top overflow pipe of the secondary cyclone separator 3 continuously discharges the light oil phase. The heavy oil phase is transported through one pipeline, and the light oil phase is transported through another pipeline; both pipelines connect to the same oil collection pipeline 4. Oil collection pipeline 4 collects the heavy and light oil phases and transports them uniformly to the oil recovery system. The drain valve is electrically or pneumatically controlled and operates periodically based on the liquid level sensor signal.

[0042] The purified effluent flows out from the bottom outlet of the secondary cyclone oil separator 3 and enters the main space of the wastewater storage tank 6 through the outlet 5. The outlet 5 is located on the side wall or bottom of the wastewater storage tank 6. The purified effluent mixes with the still water inside the tank within the main space, further settling residual suspended solids. The wastewater storage tank 6 provides buffer capacity to facilitate stable water intake for subsequent treatment units. The primary cyclone oil separator 2 and the secondary cyclone oil separator 3 are installed in the wastewater storage tank 6 in a stacked or horizontally parallel configuration. When stacked, the secondary cyclone oil separator 3 is located above the primary cyclone oil separator 2, utilizing gravity to reduce pumping energy consumption; when horizontally parallel, they are connected by pipes to save vertical space. The bottom outlets of the primary cyclone oil separator 2 and the secondary cyclone oil separator 3 are installed higher than the bottom of the wastewater storage tank 6 to prevent sediment from clogging the outlets.

[0043] After being treated by a series connection of a primary hydrocyclone oil separator 2 and a secondary hydrocyclone oil separator 3, the oil content of the purified effluent is lower than that of effluent treated using only the primary hydrocyclone oil separator 2 or only the secondary hydrocyclone oil separator 3. The primary hydrocyclone oil separator 2 removes heavy oil, reducing the load on the secondary hydrocyclone oil separator 3, while the secondary hydrocyclone oil separator 3 focuses on the deep separation of fine oil droplets. This achieves graded and targeted removal of pollutants with different physical properties within a single wastewater storage tank 6, improving overall oil removal efficiency and effluent quality.

[0044] In the petrochemical production process, oily wastewater is transported from upstream units through pipelines to oily wastewater inlet 1, and then enters a hydrocyclone oil separator A2 housed inside wastewater storage tank 6. The oily wastewater includes dense heavy oil and fine oil droplets. Before entering hydrocyclone A2, it flows through an inlet rectifying structure, such as a perforated plate or guide vanes, to stabilize the flow and reduce turbulence. Hydrocyclone A2 generates a rotating flow field through tangential water inlet, forming a first centrifugal force field. The dense heavy oil and solid particles move towards the wall and downwards under centrifugal force, accumulating at the bottom to form the heavy oil phase, while the water phase and fine oil droplets move upwards in the central region, exiting as primary effluent from the top. The primary effluent is then introduced into hydrocyclone B3 through a sealed connecting pipe by gravity or system residual pressure. Hydrocyclone B3 has a larger length-to-diameter ratio and a smaller cone angle than hydrocyclone A2, generating a stronger second centrifugal force field. The primary effluent undergoes a longer rotational path within the hydrocyclone oil separator B3, where fine oil droplets collide, coalesce, and migrate towards the central axis region. In the central low-pressure zone, they converge to form a continuous oil core. This oil core moves upward through the top overflow pipe, continuously discharging the light oil phase. The remaining water becomes the purified effluent and is discharged from the bottom. The heavy oil phase at the bottom of the hydrocyclone oil separator A2 is discharged periodically by opening the oil drain valve, while the light oil phase at the top of the hydrocyclone oil separator B3 is continuously discharged through the overflow pipe. Both oil phases converge through pipes into the oil collection pipe at the oil drain port 4 for unified recycling. The purified effluent enters the main space of the wastewater storage tank 6 from the outlet 5 for storage, and the oil content of the effluent meets the requirements for subsequent treatment.

[0045] The structural parameters of the hydrocyclone oil separator A2 are optimized according to the requirements for separating heavy oil and solid particles. For example, the diameter is selected in the range of 100 mm to 200 mm, and the cone angle is set to 10 degrees to 20 degrees to enhance the collection efficiency of heavy components. The inlet rectifying structure adopts a stainless steel perforated plate with a pore size of 5 mm to 10 mm to uniformly distribute the water flow. The inlet flow velocity of oily wastewater in the hydrocyclone oil separator A2 is controlled at 2 m / s to 3 m / s to ensure that the first centrifugal force field is sufficient to separate heavy oil. The primary effluent flows out from the top outlet of the hydrocyclone oil separator A2 and enters the hydrocyclone oil separator B3 by gravity through a 50 mm diameter PVC connecting pipe arranged at an angle, utilizing the elevation difference. The length-to-diameter ratio of the hydrocyclone oil separator B3 is designed to be 5:1 to 8:1, and the cone angle is reduced to 5 degrees to 10 degrees. The strength of the second centrifugal force field is achieved by increasing the inlet flow velocity to 3 m / s to 4 m / s. Under the action of strong centrifugal force, fine oil droplets agglomerate, and the particle size increases to more than 50 micrometers, which is convenient for separation. The oil drain valve is electrically controlled and opens once every 4 hours based on the liquid level sensor signal to drain the heavy oil phase; the light oil phase is continuously discharged through the overflow pipe. The insertion depth of the overflow pipe is optimized to 0.3 to 0.5 times the diameter of the hydrocyclone to ensure stable rise of the oil core.

[0046] Inside wastewater storage tank 6, hydrocyclone oil separators A2 and B3 are installed in a stacked configuration, with B3 positioned above A2 to save space and reduce energy consumption by utilizing gravity. The bottom outlets of both A2 and B3 are 500 mm above the bottom of wastewater storage tank 6 to prevent interference from bottom sediments. Typical components of oily wastewater from refineries include 100 mg / L to 200 mg / L of heavy oil and 50 mg / L to 100 mg / L of fine oil droplets. After two-stage series treatment, the oil content of the purified effluent is reduced to below 10 mg / L, meeting the influent standards for biological treatment. Oil collection pipes transport the heavy and light oil phases to the oil recovery system. Due to the higher viscosity of the heavy oil phase, the pipes are heat-insulated to maintain fluidity; the light oil phase flows directly into the storage tank. The main space of wastewater storage tank 6 provides buffer capacity. The purified water mixes with the water in the tank to further settle residual suspended solids. The tank volume is designed to be between 100 cubic meters and 500 cubic meters depending on the treatment capacity.

[0047] For oily wastewater with high suspended solids content, such as produced water from oil fields, a large-diameter discharge valve is installed at the underflow port of hydrocyclone A2 to periodically discharge solid particles and prevent clogging. The overflow pipe diameter of hydrocyclone B3 is adjusted according to the fine oil droplet load, for example, selecting 20 mm to 30 mm to ensure smooth discharge of the light oil phase. The connecting pipes are made of corrosion-resistant materials such as FRP to extend their service life. The system operating pressure is maintained at 0.1 MPa to 0.3 MPa, relying on the residual pressure of the pump to drive the process, requiring no additional power. Monitoring points are set at the oily wastewater inlet 1 and outlet 5. An online oil analyzer tracks the treatment effect in real time, and the data is fed back to the control system to automatically adjust the oil discharge frequency. This configuration has shown in actual operation in the petrochemical park that the oil removal efficiency has increased to over 95%, significantly improving the effluent quality compared to a single-stage hydrocyclone.

Claims

1. A process for removing oil from a tank using a two-stage cyclone separator in series, characterized in that, include: Step 1: The oily wastewater generated by the upstream unit is introduced into a primary cyclone separator installed inside the wastewater storage tank. The oily wastewater includes heavy oil and fine oil droplets. Step 2: In the first-stage cyclone separator, the introduced oily wastewater is separated by the first centrifugal force field, so that the heavy oil accumulates at the bottom to form a heavy oil phase, while the remaining water becomes the first-stage effluent and is discharged from the top. Step 3: The discharged primary effluent is introduced into a secondary cyclone oil separator that is also installed inside the wastewater storage tank; Step 4: In the secondary cyclone oil separator, the primary effluent is separated by a second centrifugal force field with an intensity higher than that of the first centrifugal force field, causing fine oil droplets to gather at the top to form a light oil phase and be continuously discharged, while the remaining water becomes purified effluent and is discharged from the bottom. Step 5: Periodically discharge the heavy oil phase that has accumulated at the bottom of the first-stage cyclone separator, and at the same time collect the light oil phase that is continuously discharged from the top of the second-stage cyclone separator, so that the heavy oil phase and the light oil phase flow together into a single oil collection pipe. Step 6: The purified effluent discharged from the bottom of the secondary cyclone oil separator is sent into the main space of the wastewater storage tank.

2. The oil removal process using a two-stage cyclone separator in series inside the tank as described in claim 1, characterized in that, The process of introducing oily wastewater generated by the upstream unit into a primary hydrocyclone oil separator installed inside a wastewater storage tank includes: Receives oily wastewater from petrochemical production plants; The oily wastewater transported through the pipeline is guided through the inlet rectifying structure before entering the primary cyclone oil separator.

3. The oil removal process using a two-stage cyclone separator in series inside the tank as described in claim 2, characterized in that, The process of separating the introduced oily wastewater within the primary cyclone separator using a first centrifugal force field includes: The oily wastewater is tangentially introduced into the primary cyclone separator to generate a rotating flow field; In the rotating flow field, the dense heavy oil and solid particles move toward the container wall and downward, while the less dense water phase and fine oil droplets move upward in the central region. The upward-moving aqueous phase and fine oil droplets flow out from the top outlet, becoming the primary effluent.

4. The oil removal process using a two-stage cyclone separator in series inside the tank as described in claim 3, characterized in that, The process of introducing the discharged primary effluent into a secondary cyclone oil separator, also installed inside the wastewater storage tank, includes: The primary effluent discharged from the top of the primary cyclone separator flows into a closed connecting pipe. Relying on gravity or system residual pressure, the primary effluent in the connecting pipe enters from the inlet on the side of the secondary cyclone oil separator.

5. The oil removal process using a two-stage cyclone separator in series inside the tank according to claim 4, characterized in that, The process of separating the introduced primary effluent within the secondary cyclone separator by a second centrifugal force field with an intensity higher than the first centrifugal force field includes: The secondary cyclone separator has a larger aspect ratio than the primary cyclone separator and a smaller cone angle than the primary cyclone separator; The primary effluent introduced into the secondary cyclone oil separator, having the aforementioned aspect ratio and cone angle, undergoes a longer rotational path, causing fine oil droplets to collide, coalesce, and migrate toward the central axis region.

6. The oil removal process using a two-stage cyclone separator in series inside the tank according to claim 5, characterized in that, The process of causing fine oil droplets to gather at the top to form a light oil phase and continuously discharge it includes: Fine oil droplets migrating towards the central axis region converge in the central low-pressure area, forming a continuous oil core; The oil core moves upward through the overflow pipe provided at the top; The upward-moving oil core is continuously discharged from the outlet of the overflow pipe, forming the light oil phase.

7. The oil removal process using a two-stage cyclone separator in series inside the tank as described in claim 6, characterized in that, The process of periodically discharging the heavy oil phase accumulated at the bottom of the primary cyclone separator and simultaneously collecting the light oil phase continuously discharged from the top of the secondary cyclone separator, so that the heavy oil phase and the light oil phase converge into a single oil collection pipe, includes: The drain valve located at the underflow port of the first-stage cyclone separator is opened periodically to discharge the accumulated heavy oil phase. Meanwhile, the overflow pipe at the top of the secondary cyclone separator continuously discharges the accumulated light oil phase; The heavy oil phase discharged from the underflow port of the first-stage cyclone separator flows into one pipe, and the light oil phase discharged from the top overflow pipe of the second-stage cyclone separator flows into another pipe. The two pipelines are connected to the same oil collecting pipeline, so that the heavy oil phase and the light oil phase can be combined in the oil collecting pipeline.

8. The oil removal process using a two-stage cyclone separator in series inside the tank according to claim 7, characterized in that, The main space from which the purified effluent discharged from the bottom of the secondary cyclone oil separator is sent into the wastewater storage tank includes: The purified effluent flows out from the outlet at the bottom of the secondary cyclone oil separator; The purified water flowing out from the outlet enters the main space of the wastewater storage tank; The purified effluent entering the main space is stored in the wastewater storage tank.

9. The oil removal process using a two-stage cyclone separator in series inside the tank as described in claim 8, characterized in that, The primary hydrocyclone oil separator and the secondary hydrocyclone oil separator are arranged in the wastewater storage tank in a manner that is either stacked vertically or horizontally side by side. Furthermore, the bottom outlet of the primary cyclone oil separator and the bottom outlet of the secondary cyclone oil separator are both located above the bottom of the wastewater storage tank in terms of spatial height.

10. The oil removal process using a two-stage cyclone separator in series inside the tank according to claim 9, characterized in that, The structural parameters of the primary hydrocyclone oil separator are determined according to the requirements for separating heavy oil and solid particles; the structural parameters of the secondary hydrocyclone oil separator are determined according to the requirements for separating fine oil droplets; the purified effluent after being treated by the primary hydrocyclone oil separator and the secondary hydrocyclone oil separator in series has a lower oil content than the effluent treated by using only the primary hydrocyclone oil separator or only the secondary hydrocyclone oil separator.

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