Oilfield produced water treatment system

Abstract

The utility model relates to an oilfield produced water treatment system which comprises two stages of air floatation tanks, a coagulating sedimentation device, an oxidation tank, a high-power concentration membrane device and a forced evaporation device which are connected in sequence, a floating oil water outlet of a first-stage air floatation tank is connected with a second-stage air floatation tank, and a clear liquid water production port is connected with the coagulating sedimentation device; the coagulating sedimentation device comprises a tubular membrane system and a solid-liquid separation device, a liquid inlet of the tubular membrane system is connected with the primary air floatation tank, a mud-containing water outlet is connected with the solid-liquid separation device, and a permeated water production port is connected with the oxidation tank; the oxidation pond is provided with two stages, and an outlet of the second-stage oxidation pond is connected with the high-power concentration membrane device; the high-power concentration membrane device comprises a disc-type reverse osmosis membrane and a disc-type nanofiltration membrane, an inlet of the disc-type reverse osmosis membrane is connected with the secondary oxidation pond, a concentrated water outlet is connected with the disc-type nanofiltration membrane, and an outlet of the disc-type nanofiltration membrane is connected with the forced evaporation device; according to the oil field produced water treatment device, advanced oxidation and disc-type membrane processes are coupled, and oil field produced water can be effectively treated and can be recycled.

Description

[Technical field]

[0001] The utility model relates to the technical field of oilfield produced water treatment, in particular to an oilfield produced water treatment system. [Background Technology]

[0002] Oilfield produced water is the formation water discharged during the oil extraction process. It has a large amount of water and is characterized by high salt content, high hardness, high organic matter concentration and complex composition. It also contains surfactant compounds added during the oil extraction process. Direct discharge of this type of wastewater will seriously pollute the environment and damage the ecology. In addition, due to the influence of geography and resource endowment, the composition of produced water in different regions often varies greatly, and even for the same oil field, the amount and composition of produced water will change greatly as the exploitation progresses. The above problems further increase the difficulty of treating this type of wastewater. A single treatment method is difficult to effectively solve this problem, and the water produced by a single treatment technology is difficult to meet the requirements of discharge and reinjection. Therefore, multiple processes need to be coupled to achieve efficient desalination, efficient removal of organic matter, and large operational flexibility to adapt to produced water in different regions and at different times.

[0003] The patent with publication number CN115403181A discloses an oilfield produced water treatment system, which uses a regulating tank combined with a decolorization, gel breaking and flocculation sedimentation tank for treatment. The patent with publication number CN114920385A discloses an oilfield produced water treatment process, including decolorization, gel breaking, flocculation sedimentation and filtration. Among them, multi-media filtration or quartz sand filtration is used, and the water quality and treatment efficiency of the produced water are difficult to control. In addition, the patent with publication number CN113816457A discloses an integrated treatment process system for oilfield acidic produced water, which is treated with flotation as the core, but the process is relatively simple and may have certain operational flexibility limitations.

[0004] The "oil removal + biochemical + filtration" process and the "sedimentation oil removal + biochemical + filtration" process are commonly used return water treatment technologies, in which the filtration device adopts a spiral reverse osmosis membrane element. However, due to the complex organic matter in the produced water composition, the biochemical treatment has less operational flexibility, the difficulty of adjusting parameters is greater, and the effluent is often difficult to meet the standards. In addition, the water recovery rate of spiral reverse osmosis membrane elements is low, and due to the complex composition of produced water, the membrane elements are prone to membrane pollution and fouling, and need to be cleaned frequently, which seriously affects the treatment efficiency. Therefore, a technology for efficiently treating organic matter in produced water is needed, that is, it can adjust the treatment parameters synchronously according to the changes in the water inlet conditions at any time. The technology must also be able to filter the produced water without pollution and fouling, and achieve efficient high-fold concentration, and the produced water quality is high to meet the reuse requirements. [Contents of the utility model]

[0005] The purpose of the utility model is to solve the above-mentioned shortcomings and provide an oilfield produced water treatment system, which couples the advanced oxidation and tube membrane process and can effectively treat the oilfield produced water to meet the needs of reuse.

[0006] In order to achieve the above purpose, an oilfield produced water treatment system is designed, which includes a flotation tank, a coagulation sedimentation device, an oxidation tank, a high concentration membrane device and a forced evaporation device connected in sequence, wherein:

[0007] The flotation tank comprises a primary flotation tank and a secondary flotation tank, the floating oil water outlet of the primary flotation tank is connected to the inlet of the secondary flotation tank through a pipeline, the secondary flotation tank is provided with a reflux port, the reflux port is connected to the primary flotation tank through a pipeline, and the clear liquid of the secondary flotation tank is refluxed to the primary flotation tank, and the clear liquid water outlet of the primary flotation tank is connected to the coagulation sedimentation device through a pipeline;

[0008] The coagulation and sedimentation device comprises a tubular membrane system and a solid-liquid separation device, wherein the solid-liquid separation device is a filter press, wherein the liquid inlet of the tubular membrane system is connected to the clear liquid outlet of the primary flotation tank via a pipeline, the tubular membrane system is provided with a coagulant inlet, the muddy water outlet of the tubular membrane system is connected to the inlet of the solid-liquid separation device via a pipeline, the solid-liquid separation device is provided with a reflux port 2, and the clear liquid is refluxed to the tubular membrane system via the reflux port 2, and the permeate outlet of the tubular membrane system is connected to the oxidation tank via a pipeline;

[0009] The oxidation pool comprises a primary oxidation pool and a secondary oxidation pool, the permeate water outlet of the tubular membrane system is connected to the primary oxidation pool and the secondary oxidation pool respectively through pipelines, the primary oxidation pool and the secondary oxidation pool are arranged in parallel, an oxidant inlet is arranged on the primary oxidation pool, the outlet of the primary oxidation pool is connected to the inlet of the secondary oxidation pool through a pipeline, and the outlet of the secondary oxidation pool is connected to a high-concentration membrane device through a pipeline;

[0010] The high-concentration membrane device comprises a vault tube reverse osmosis membrane and a vault tube nanofiltration membrane, the inlet of the vault tube reverse osmosis membrane is connected to the secondary oxidation tank through a pipeline, the concentrated water outlet of the vault tube reverse osmosis membrane is connected to the inlet of the vault tube nanofiltration membrane, the produced water of the vault tube nanofiltration membrane flows back to the vault tube reverse osmosis membrane through a pipeline, the vault tube reverse osmosis membrane is provided with a fresh water outlet, and the outlet of the vault tube nanofiltration membrane is connected to a forced evaporation device through a pipeline;

[0011] The forced evaporation device is a multiple-effect evaporation or a mechanical compression evaporation MVR.

[0012] Furthermore, the forced evaporation device is provided with a fixed salt outlet and a fresh water outlet, and solid salt products are obtained through the fixed salt outlet, and fresh water is obtained through the fresh water outlet, and the fresh water is mixed with the fresh water produced by the tube-type reverse osmosis membrane as system produced water.

[0013] Furthermore, a gas collecting device is provided above the primary oxidation tank and the secondary oxidation tank, and the gas collecting device is connected to the primary flotation tank. The gas collecting device is used to transport unreacted ozone to the bubble generating device in the primary flotation tank, so as to use the unreacted ozone in the oxidation process as an added gas in the flotation process, which not only makes full use of the ozone but also can carry out oxidation treatment in the flotation part.

[0014] Furthermore, an adsorption resin is arranged between the secondary oxidation tank and the disc-tube reverse osmosis membrane. Before the produced water after the secondary oxidation tank enters the disc-tube reverse osmosis membrane, the adsorption resin is first used to remove impurity ions such as boron, calcium, and magnesium. Therefore, according to the concentration of boron, calcium, and magnesium ions in the solution, the adsorption resin can be selectively connected to remove impurity ions such as boron, calcium, and magnesium, so as to reduce the pollution of the subsequent membrane system.

[0015] Furthermore, the secondary flotation tank contains a polymer resin with oil-water separation function. The clear liquid after the secondary flotation is pumped into the polymer resin in the flotation tank through a pump, the oil produced by the polymer resin is discharged, and the clear liquid produced by the polymer resin is returned to the primary flotation tank as the secondary flotation clear liquid.

[0016] Compared with the prior art, the utility model has the following advantages:

[0017] (1) The utility model is an oilfield produced water treatment system that couples advanced oxidation and sintered tube reverse osmosis processes, combines multi-stage flotation and multi-stage split flow oxidation to treat produced water, is simple to operate, improves treatment efficiency, and introduces reflux in the membrane system to achieve efficient concentration and filtration;

[0018] (2) Based on flotation and coagulation sedimentation, the utility model uses ozone oxidation combined with oxidants for deep oxidation, which has high efficiency in removing organic matter, large operational flexibility, little influence by water quality, and negligible amplification effect;

[0019] (3) After oxidation treatment, the utility model uses a tube-type reverse osmosis membrane assembly for concentration and filtration, with a high degree of automation and a high water recovery rate, which can reach more than 80%;

[0020] (4) The utility model has a high concentration multiple, greatly reduces the amount of concentrated water, has a stable membrane process, is resistant to pollution, and has a low cleaning frequency. The water produced in this process is stable, the water volume is easy to adjust, and the water quality is high. It can be used in life and industry, and can also be injected back into the oil field;

[0021] In summary, the utility model provides an oilfield produced water treatment system, which couples the advanced oxidation and tube membrane processes, and can effectively treat the oilfield produced water to meet the needs of reuse. [Drawings]

[0022] Figure 1 It is a principle block diagram of the utility model;

[0023] Figure 2 It is a structural schematic diagram of the utility model. [Specific implementation method]

[0024] As shown in the attached drawings, the utility model provides an oilfield produced water treatment system, including a flotation tank, a coagulation sedimentation device, an oxidation tank, a high concentration membrane device and a forced evaporation device connected in sequence, wherein:

[0025] The flotation tank includes a primary flotation tank and a secondary flotation tank. The floating oil water outlet of the primary flotation tank is connected to the inlet of the secondary flotation tank through a pipeline. The secondary flotation tank is provided with a reflux port, which is connected to the primary flotation tank through a pipeline, and the clear liquid of the secondary flotation tank is refluxed to the primary flotation tank. The clear liquid water outlet of the primary flotation tank is connected to the coagulation sedimentation device through a pipeline.

[0026] The coagulation and sedimentation device includes a tubular membrane system and a solid-liquid separation device. The solid-liquid separation device is a filter press. The liquid inlet of the tubular membrane system is connected to the clear liquid outlet of the primary flotation tank through a pipeline. The tubular membrane system is provided with a coagulant inlet. The muddy water outlet of the tubular membrane system is connected to the inlet of the solid-liquid separation device through a pipeline. The solid-liquid separation device is provided with a reflux port 2, and the clear liquid is refluxed to the tubular membrane system through the reflux port 2. The permeate outlet of the tubular membrane system is connected to the oxidation tank through a pipeline.

[0027] The oxidation pool includes a primary oxidation pool and a secondary oxidation pool. The permeate water outlet of the tubular membrane system is connected to the primary oxidation pool and the secondary oxidation pool respectively through pipelines. The primary oxidation pool and the secondary oxidation pool are arranged in parallel. An oxidant inlet is arranged on the primary oxidation pool. The outlet of the primary oxidation pool is connected to the inlet of the secondary oxidation pool through a pipeline. The outlet of the secondary oxidation pool is connected to a high-concentration membrane device through a pipeline.

[0028] The high-concentration membrane device comprises a vault tube reverse osmosis membrane and a vault tube nanofiltration membrane. The inlet of the vault tube reverse osmosis membrane is connected to the secondary oxidation tank through a pipeline. The concentrated water outlet of the vault tube reverse osmosis membrane is connected to the inlet of the vault tube nanofiltration membrane. The produced water of the vault tube nanofiltration membrane flows back to the vault tube reverse osmosis membrane through a pipeline. The vault tube reverse osmosis membrane is provided with a fresh water outlet. The outlet of the vault tube nanofiltration membrane is connected to the forced evaporation device through a pipeline.

[0029] The forced evaporation device is a multi-effect evaporation or a mechanical compression evaporation MVR.

[0030] Among them, the forced evaporation device is provided with a fixed salt outlet and a fresh water outlet, and a solid salt product is obtained through the fixed salt outlet, and the solid salt product is a system product. Fresh water is obtained through the fresh water outlet, and the fresh water is mixed with the fresh water produced by the tube-type reverse osmosis membrane as the system water. The secondary flotation tank contains a polymer resin with oil-water separation function. The clear liquid after the secondary flotation is pumped into the polymer resin in the flotation tank through a pump, and the oil produced by the polymer resin is discharged. The clear liquid produced by the polymer resin is returned to the primary flotation tank as the secondary flotation clear liquid.

[0031] A gas collection device is provided above the primary oxidation tank and the secondary oxidation tank. The gas collection device is connected to the primary flotation tank. The gas collection device is used to transport unreacted ozone to the bubble generating device in the primary flotation tank. The purpose is to use the unreacted ozone in the oxidation process as an added gas in the flotation process, which not only makes full use of the ozone but also can perform oxidation treatment in the flotation part. An adsorption resin is provided between the secondary oxidation tank and the disc-tube reverse osmosis membrane. The produced water after the secondary oxidation tank is firstly removed from the impurity ions such as boron, calcium and magnesium by the adsorption resin before entering the disc-tube reverse osmosis membrane. Therefore, according to the concentration of boron, calcium and magnesium ions in the solution, the adsorption resin can be selectively connected to remove the impurity ions such as boron, calcium and magnesium, so as to reduce the pollution of the subsequent membrane system.

[0032] The treatment method of the oilfield produced water treatment system described in the utility model comprises the following steps:

[0033] 1) The produced water from the oil field is input into the primary flotation tank. The secondary flotation tank uses the water containing floating oil in the primary flotation tank as feed and is provided with a reflux component to return the clear liquid from the secondary flotation tank to the primary flotation tank, and the clear liquid from the primary flotation tank is used as produced water;

[0034] 2) After the primary flotation clear liquid is added with coagulant, it is concentrated by tubular membrane, and the concentrated muddy water enters the filter press to obtain the solid filter cake, which is the sludge. The clear liquid is returned to the tubular membrane system for secondary treatment. This part uses the permeate of the tubular membrane as the produced water and enters the next stage of treatment;

[0035] 3) The permeate produced by the tubular membrane is divided into the primary oxidation pool and the secondary oxidation pool. The two-stage oxidation pool uses micro-nano ozone bubbles for oxidation and cooperates with oxidants. The two-stage parallel connection uses oxidants to remove organic matter. At the same time, the oxidation effect is regulated by combining the diversion of the raw water treatment.

[0036] 4) The produced water of the secondary oxidation tank enters the disc-tube reverse osmosis membrane, the concentrated water of the disc-tube reverse osmosis membrane enters the disc-tube nanofiltration membrane, the produced water of the disc-tube nanofiltration membrane flows back to the disc-tube reverse osmosis membrane, and the fresh water produced by the disc-tube reverse osmosis membrane is the produced water of the system;

[0037] 5) The outlet of the disc-tube nanofiltration membrane is connected to a forced evaporation device to obtain solid salt as the system product. The obtained fresh water is mixed with the water produced by the disc-tube reverse osmosis membrane to become the system's produced water.

[0038] Among them, the influent of the primary oxidation tank and the secondary oxidation tank is diverted, wherein 5%-50% of the water output or flow of the tubular membrane system is diverted to the secondary oxidation tank, where the oxidation process is adjusted and controlled by the diversion flow, the water after the primary oxidation enters the secondary oxidation, and then is diverted to join the unoxidized tubular membrane produced water, the oxidant is effectively utilized, and the oxidation effect can be accurately adjusted by diversion adjustment.

[0039] The oxidant added to the primary oxidation tank is a mixed solution of hydrogen peroxide and iron salt, in which the mass content of hydrogen peroxide is controlled at 0.1%-5%, and the concentration range of trivalent iron ions in the iron salt is 0.01%-0.5%. The concentrated water of the tubular membrane system has a mud content of 1%-30% before entering the solid-liquid separation device. The floating oil content in the water containing floating oil entering the secondary floating tank from the primary flotation tank is controlled at 0.01%-5%.

[0040] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments:

[0041] As attached Figure 1 and attached Figure 2 As shown, the oilfield produced water system includes an air flotation tank, a coagulation sedimentation device, an oxidation tank, a high-concentration membrane device, and a forced evaporation device connected in sequence;

[0042] The flotation tank is a two-stage flotation tank. The secondary flotation tank uses the water containing floating oil from the primary flotation as feed material and is provided with a reflux component to reflux the clear liquid of the stage to the primary flotation, with the clear liquid of the primary flotation as produced water. The oil content of the water containing floating oil entering the secondary flotation tank from the primary flotation tank is controlled at 0.01%-5%. The secondary flotation tank contains a polymerized resin with an oil-water separation function. The clear liquid after the secondary flotation is pumped into the polymerized resin part of the flotation tank through a pump, and the oil produced by the polymerized resin is discharged. The clear liquid produced by the polymerized resin is used as the secondary flotation clear liquid.

[0043] The clear liquid from the secondary flotation enters the coagulation sedimentation device, which contains a tubular membrane part and a solid-liquid separation part. The solid-liquid separation device is a filter press. After the first-stage flotation clear liquid is added with coagulant, it enters the filter press after being concentrated by the tubular membrane. Before the concentrated water enters the solid-liquid separation device, the solid content is 1%-30%. The solid filter cake obtained by the filter press is the sludge, and the clear liquid is returned to the tubular membrane system for secondary treatment. This part uses the permeate water of the tubular membrane as the produced water and enters the oxidation tank.

[0044] The oxidation pool is a two-stage oxidation pool. The oxidation pool uses micro-nano ozone bubbles for oxidation and cooperates with oxidants. The two-stage parallel connection makes full use of the oxidants to remove organic matter, and at the same time combines the diversion of raw water treatment to adjust the oxidation effect. Among them, there are gas collection devices above the two-stage oxidation pools, and they are connected to the primary flotation pool to transport the unreacted ozone to the bubble generating device in the flotation pool. The purpose is to use the unreacted ozone in the oxidation process as an added gas in the flotation process, which not only makes full use of ozone but also can be oxidized in the flotation part. In addition, the influent of the multi-stage oxidation pool is diverted, and 5%-50% of the water produced by the tubular membrane system is diverted to the secondary oxidation pool. The oxidation process is adjusted and controlled by the diversion rate. The water after the primary oxidation enters the secondary oxidation, and then the water produced by the unoxidized tubular membrane is diverted and added. The oxidation effect is accurately adjusted by diversion adjustment. The oxidant added to the primary oxidation pool is a mixed solution of hydrogen peroxide and iron salt. The mass content of hydrogen peroxide is controlled at 0.1%-5%, and the concentration range of trivalent iron ions in the iron salt is 0.01%-0.5%.

[0045] The produced water after oxidation is highly concentrated by a membrane device. The high-concentration membrane device includes a disc-type reverse osmosis membrane and a disc-type nanofiltration membrane part. The concentrated water of the disc-type reverse osmosis membrane enters the disc-type nanofiltration membrane group. The produced water of the disc-type nanofiltration membrane flows back to the disc-type reverse osmosis membrane. The produced water of the disc-type reverse osmosis membrane is the produced water of this part. Before entering the high-concentration membrane device, according to the concentration of boron, calcium and magnesium ions in the solution, adsorption resin can be selectively connected to remove impurity ions such as boron, calcium and magnesium, in order to reduce the pollution of the subsequent membrane system. The concentrated liquid of the disc-type nanofiltration membrane part enters the forced evaporation device, which is a multi-effect evaporation or mechanical compression evaporation (MVR). Solid salt is obtained as the system product. Fresh water is mixed with the produced water of the disc-type reverse osmosis membrane in the membrane device to be the produced water of the system.

[0046] The treatment effect of this device system is as follows: (1)

[0048] (2)

[0050] (3)

[0052]

[0053] In summary, the utility model discloses an oilfield produced water treatment system, including a flotation tank, a coagulation sedimentation device, an oxidation tank, a high-concentration membrane device, and a forced evaporation device connected in sequence; the flotation tank is a two-stage countercurrent flotation, the coagulation sedimentation device includes a tubular membrane part and a solid-liquid separation part, the oxidation tank is a two-stage parallel flow oxidation tank, and micro-nano ozone bubbles are used in combination with an oxidant for nutrient treatment, and the high-concentration membrane device includes a vortex tube reverse osmosis membrane (DTRO) and a vortex tube nanofiltration membrane (DTNF) part. The utility model couples the oxidation and membrane concentration system operation, and each process section combines a multi-stage, reflux method to effectively treat the oilfield produced water, and the final produced water meets the requirements of reuse or reinjection.

[0054] The contents not described in detail in this specification belong to the prior art known to professional and technical personnel in the field. The standard parts used can be purchased from the market, and special-shaped parts can be customized according to the records in the specification and drawings. The specific connection methods of each part adopt mature conventional means such as bolts, rivets, welding, etc. in the prior art. The machinery, parts and equipment adopt conventional models in the prior art, and the circuit connection adopts the conventional connection method in the prior art, which will not be described in detail here.

[0055] The present invention is not limited to the above-mentioned implementation modes, and any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principle of the present invention shall be considered as equivalent replacement modes and shall be included in the protection scope of the present invention.

Claims

1. An oilfield produced water treatment system, characterized in that: It includes a flotation tank, a coagulation sedimentation device, an oxidation tank, a high concentration membrane device and a forced evaporation device connected in sequence, wherein: The flotation tank comprises a primary flotation tank and a secondary flotation tank, the floating oil water outlet of the primary flotation tank is connected to the inlet of the secondary flotation tank through a pipeline, the secondary flotation tank is provided with a reflux port, the reflux port is connected to the primary flotation tank through a pipeline, and the clear liquid of the secondary flotation tank is refluxed to the primary flotation tank, and the clear liquid water outlet of the primary flotation tank is connected to the coagulation sedimentation device through a pipeline; The coagulation and sedimentation device comprises a tubular membrane system and a solid-liquid separation device, wherein the solid-liquid separation device is a filter press, wherein the liquid inlet of the tubular membrane system is connected to the clear liquid outlet of the primary flotation tank via a pipeline, the tubular membrane system is provided with a coagulant inlet, the muddy water outlet of the tubular membrane system is connected to the inlet of the solid-liquid separation device via a pipeline, the solid-liquid separation device is provided with a reflux port 2, and the clear liquid is refluxed to the tubular membrane system via the reflux port 2, and the permeate outlet of the tubular membrane system is connected to the oxidation tank via a pipeline; The oxidation pool comprises a primary oxidation pool and a secondary oxidation pool, the permeate water outlet of the tubular membrane system is connected to the primary oxidation pool and the secondary oxidation pool respectively through pipelines, the primary oxidation pool and the secondary oxidation pool are arranged in parallel, an oxidant inlet is arranged on the primary oxidation pool, the outlet of the primary oxidation pool is connected to the inlet of the secondary oxidation pool through a pipeline, and the outlet of the secondary oxidation pool is connected to a high-concentration membrane device through a pipeline; The high-concentration membrane device comprises a vault tube reverse osmosis membrane and a vault tube nanofiltration membrane, the inlet of the vault tube reverse osmosis membrane is connected to the secondary oxidation tank through a pipeline, the concentrated water outlet of the vault tube reverse osmosis membrane is connected to the inlet of the vault tube nanofiltration membrane, the produced water of the vault tube nanofiltration membrane flows back to the vault tube reverse osmosis membrane through a pipeline, the vault tube reverse osmosis membrane is provided with a fresh water outlet, and the outlet of the vault tube nanofiltration membrane is connected to a forced evaporation device through a pipeline; The forced evaporation device is a multiple-effect evaporation or a mechanical compression evaporation MVR.

2. The oilfield produced water treatment system according to claim 1, characterized in that: The forced evaporation device is provided with a fixed salt outlet and a fresh water outlet, and solid salt products are obtained through the fixed salt outlet, and fresh water is obtained through the fresh water outlet. The fresh water is mixed with the fresh water produced by the tube-type reverse osmosis membrane as system produced water.

3. The oilfield produced water treatment system according to claim 1, characterized in that: A gas collecting device is provided above the primary oxidation pool and the secondary oxidation pool. The gas collecting device is connected to the primary flotation pool and is used to transport unreacted ozone to the bubble generating device in the primary flotation pool.

4. The oilfield produced water treatment system according to claim 1, characterized in that: An adsorption resin is arranged between the secondary oxidation tank and the disc-tube reverse osmosis membrane. The produced water after the secondary oxidation tank is firstly removed from the boron, calcium and magnesium impurity ions by the adsorption resin before entering the disc-tube reverse osmosis membrane.

5. The oilfield produced water treatment system according to claim 1, characterized in that: The secondary flotation tank contains a polymerized resin with an oil-water separation function. The clear liquid after the secondary flotation is pumped into the polymerized resin in the flotation tank through a pump, the oil produced by the polymerized resin is discharged, and the clear liquid produced by the polymerized resin is returned to the primary flotation tank as the secondary flotation clear liquid.

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