Treatment system and treatment method for tar-containing wastewater

Abstract

The invention discloses a treatment system and a treatment method for tar-containing wastewater, and belongs to the field of water treatment. The coarse grain separation unit is composed of an inner tank and an outer tank, the inner tank is arranged in the outer tank, and the lower end of the inner tank penetrates through the outer tank; the inner tank is used for settling oil removal, and the outer tank is used for coalescing oil removal; a water inlet of the demulsification filtering unit is communicated with a water outlet of the outer tank after coalescence and oil removal, and the demulsification filtering unit is used for demulsification and oil removal while secondary coalescence and oil removal. The treatment method comprises a coarse grain separation process and a demulsification separation process. According to the oil removal device and method for the oily sewage, the oil-water separation efficiency of the tar-containing wastewater can be enhanced, the tar-containing wastewater separation effect is good under the lower ultrasonic demulsification frequency, it is ensured that the water quality of the deoiled sewage is stable, good conditions are created for subsequent treatment, and long-term stable operation of a sewage treatment system is facilitated.

Description

Technical Field

[0001] The invention belongs to water treatment technology, and more specifically, relates to a treatment system and a treatment method for tar-containing wastewater. Background Art

[0002] Coal pyrolysis wastewater contains complex components such as tar, petroleum hydrocarbons, phenol, etc. Among them, compared with petrochemical oil-containing wastewater, coal pyrolysis wastewater contains tar. Tar is sticky and contains asphalt, which is easy to solidify at low temperatures. This makes it difficult to treat tar-containing wastewater: residual tar blocks the treatment equipment, tar-coated agglomerated materials reduce the efficiency of the oil remover, and oil blocks the respiration and metabolism of microorganisms.

[0003] After searching, the patent application document with Chinese patent application number 202011163336.1 and application publication date May 13, 2022 discloses a method for removing oil from high-concentration oily wastewater. The oil removal method includes a cyclone oil remover, an ultrasonic demulsification reactor and a corrugated oil removal device arranged in sequence, and an ultrasonic transducer unit and an ultrasonic generator are arranged on the ultrasonic demulsification reactor; a particle size detector is arranged at the inlet of the ultrasonic demulsification reactor, and a separation detector and a return pipeline are separated on the outlet pipeline, and the other end of the return pipeline is connected to the inlet of the ultrasonic demulsification reactor; the oil-water separation of the oily wastewater is carried out by a combination of cyclone oil removal, ultrasonic demulsification and sedimentation oil removal. However, on the one hand, this oil removal method is only applicable to petrochemical oily wastewater, and the following problems will occur in the treatment of tar-containing wastewater: in the cyclone oil remover, the cyclone tube is small, and the tar adheres to the tube wall for a long time and is easy to clog; and the density difference of the tar-containing wastewater is small, and the centrifugal effect is not good. On the other hand, the device is complex and occupies a large space overall. Summary of the invention

[0004] 1. Problem to be solved

[0005] One of the purposes of the present invention is to provide a treatment system for tar-containing wastewater, aiming to enhance the oil-water separation efficiency of the tar-containing wastewater.

[0006] Another object of the present invention is to provide a method for treating tar-containing wastewater, which can achieve better separation effect on tar-containing wastewater at a lower ultrasonic demulsification frequency, ensure the stability of the wastewater quality after oil removal, create good conditions for subsequent treatment, and be beneficial to the long-term stable operation of the sewage treatment system to provide an oil-containing wastewater removal device and method.

[0007] 2. Technical solution

[0008] In order to solve the above problems, the technical solution adopted by the present invention is as follows:

[0009] According to the purpose of the present invention, the first aspect of the present invention provides a treatment system for tar-containing wastewater, comprising:

[0010] The coarse particle separation unit is composed of an inner tank and an outer tank, wherein the inner tank is placed inside the outer tank, and the lower end of the inner tank passes through the outer tank; the inner tank is used for sedimentation and oil removal, and the outer tank is used for coalescence and oil removal;

[0011] The demulsification and filtration unit has a water inlet connected to the water outlet of the outer tank after coalescence and oil removal, and is used for secondary coalescence and oil removal and simultaneous demulsification and oil removal.

[0012] When the above technical scheme is adopted, the tar in the tar-containing wastewater is viscous and difficult to handle, and direct demulsification treatment is prone to clogging. In this application, the oil is first coarsened and then separated. At the same time, the oil particles in the discharged wastewater are smaller and then enter the demulsification and separation treatment. The tar-containing wastewater is effectively treated by combining coagulation and demulsification oil removal.

[0013] As a possible implementation, in the coarse particle separation unit:

[0014] The inner tank includes a guide area, an inclined plate separation area, a sedimentation area, an oil sludge collection area and an oil-water separation area. The guide area extends into the inner tank from top to bottom. The inclined plate separation area is arranged between the outer wall of the guide area and the inner wall of the inner tank. The inclined plate separation area forms a channel inclined to the inner wall of the inner tank. The sedimentation area is arranged below the guide area and the inclined plate separation area. The oil sludge collection area is arranged at the lower end of the inner tank. The oil-water separation area is located at the upper part of the inner tank and the outer tank, that is, above the inclined plate separation area.

[0015] A coalescing plate separation zone is arranged in the outer tank, and the coalescing plate separation zone is located between the outer tank and the inner tank and below the oil-water separation zone.

[0016] As a possible implementation solution, the inclined plate separation zone is filled with inclined plate fillers.

[0017] As a possible implementation scheme, the demulsification filtration unit includes a horizontal shell, a coalescing filter element is installed inside the shell, an ultrasonic generator is wrapped around the shell where the coalescing filter element is located, and an oil collecting bag is connected above the shell.

[0018] When the above technical solution is adopted, the tar-containing wastewater is first coarsened and subjected to the first oil-water separation by combining sedimentation and oil removal by a coarse particle separation unit + agglomeration oil removal, and then enters the sedimentation area in the inner tank from the diversion area. The medium oil and light oil in the sedimentation area with a density smaller than that of water float to the inclined plate separation area. Although the channel inclined to the inner wall of the inner tank sacrifices part of its volume relative to the vertical channel, it can prolong its residence time in the inclined plate separation area. In the inclined plate separation area, the oil, particulate matter and water are separated faster, and the heavy oil in the sedimentation area with a density larger than that of water sinks to the sludge collection area and is discharged. The medium oil and light oil that float up after passing through the inclined plate separation area enter the oil-water separation area and float on top. The wastewater enters the outer tank from the upper opening of the inner tank. After the coarsening effect of the coalescing plate separation area, the oil in the wastewater is coarsened and floats upward. The wastewater that passes through the coalescing plate separation area flows downward to the outlet below the outer tank and enters the demulsification filtration unit. The demulsification filtration unit performs a second oil-water separation and oil removal for fine-particle oil-containing wastewater by combining coalescence oil removal with ultrasonic demulsification, thereby realizing effective oil-water separation of tar-containing wastewater.

[0019] As a possible implementation scheme, a baffle and an oil collecting trough are arranged in the oil-water separation area, and the lower end of the baffle is close to the opening of the inner tank. Waste water is discharged from the opening of the inner tank and flows out from the lower end of the baffle through the action of the baffle; the oil collecting trough is fixed around the upper end of the inner wall of the outer tank, and the heavy oil and light oil pass over the upper end of the baffle and enter the oil collecting trough.

[0020] As a possible implementation scheme, a water collecting unit is arranged below the separation zone of the coalescing plate, and the water collecting unit is connected to the water outlet below the outer tank, so as to discharge the wastewater at the bottom of the outer tank to the demulsification filtration unit; the water collecting unit includes a water collecting ring pipe and a water collecting cover, and the water collecting ring pipe is arranged around the inner wall of the outer tank, and several water collecting covers are arranged around the inner diameter of the water collecting ring pipe and are connected to the water collecting ring pipe.

[0021] As a possible implementation scheme, the water collecting hood includes at least one bell mouth, and preferably the water collecting hood includes two bell mouths connected in series to the water collecting ring pipe. The water collecting hood uses suction. On the one hand, the wastewater passes through the impact of the bell mouth, and the oil substances are further reduced in particle size and collected into the water collecting ring pipe; on the other hand, the bell mouth is conducive to uniform collection of water to avoid biased flow.

[0022] As a possible implementation solution, the water collecting ring pipe is preferably a polygonal pipe, which is conducive to stable fixation on the outer tank under the action of suction.

[0023] As a possible implementation scheme, in order to facilitate disassembly and cleaning, an oil scraping unit is also installed in the sludge collection area, and the scraping unit includes an oil sludge collecting bucket and an oil sludge draining bucket. The inner diameter of the oil sludge collecting bucket gradually decreases from top to bottom, which is conducive to the deposition of heavy oil, wherein the heavy oil includes asphaltene, inorganic particles sticky with oil, etc.; the oil sludge draining bucket is a cylindrical vertical arrangement of equal diameter, and uses gravity to discharge the heavy oil downward.

[0024] As a possible implementation scheme, the oil scraper unit also includes an oil scraper and a transmission motor, that is, the oil scraper and the transmission motor are installed in the oil collecting sludge bucket, and the transmission motor is electrically connected to the oil scraper to drive the oil scraper to rotate along its center to scrape off the accumulated oil on the inner wall of the oil collecting sludge bucket.

[0025] As a possible implementation, the oil scraping unit further includes a heating coil, which is wound around the outer wall of the oil sludge drain hopper and is used for heating to prevent the oil from hardening and blocking the outlet of the oil sludge drain hopper.

[0026] As a possible implementation scheme, a leveling pipe is connected between the inner tank and the outer tank. Before starting the system, the valve on the leveling pipe is opened to ensure that the inner tank and the outer tank are level, avoid excessive internal and external pressure difference, and avoid damaging the outer tank. After the water surface is level, the valve on the leveling pipe is closed and the oil-water separation operation is carried out.

[0027] The second aspect of the present invention provides a method for treating tar-containing wastewater, wherein the tar-containing wastewater is treated using the above-mentioned treatment system, and the steps of the treatment method are as follows:

[0028] S1. Coarse particle separation process: the tar-containing wastewater enters the coarse particle separation unit from the diversion area, and the coarse particle oil in the tar-containing wastewater is removed by combining sedimentation and coalescence oil removal, and the wastewater containing fine particle oil is discharged;

[0029] S2, demulsification and separation process: the wastewater containing fine-particle oil discharged in step S1 enters the demulsification filtration unit, and the wastewater containing fine-particle oil is further deoiled by a combination of coalescence deoiling and ultrasonic demulsification.

[0030] As a possible implementation scheme, before the coarse particle separation process of step S1, the tar-containing wastewater is subjected to ultrasonic demulsification treatment with a frequency of P0; after the coarse particle separation process of step S1, in the demulsification separation process of step S2, the frequency of ultrasonic demulsification is P, and P = (0.95-0.98) P0. In the case of adopting the above technical scheme, after the coarse particle separation process of the present application, the coarse particle oil is removed, and the oil-containing particle size in the wastewater is reduced, which can reduce the frequency of ultrasonic demulsification and the difficulty of the process, and is suitable for large-scale wastewater treatment.

[0031] 3. Beneficial effects

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] The present invention provides a treatment system for tar-containing wastewater, which can simultaneously realize the functions of sedimentation oil removal, inclined plate oil removal, and coalescence oil removal in a device the size of a sedimentation tank, greatly reducing the equipment footprint and reducing the material consumption of the manufacturing equipment. Among them: the coarse particle separation unit takes into account the characteristics of heavy oil pollution and easy blockage, and independently considers the removal functions of heavy oil and particulate matter. It adopts a simple structure and a large internal space for easy maintenance; the demulsification filter unit is connected to the coarse particle separation unit as an independent unit, and more diverse structures and materials can be used according to water quality conditions and treatment requirements. Under the action of superimposed ultrasonic waves, the collision frequency of fine-particle emulsified oil in the wastewater increases, and the coarsening process can be greatly accelerated. At the same time, the oil film can be quickly separated from the surface of the coalescence filter element to avoid oil passing through the filter element, thereby improving the treatment effect.

[0034] The whole set of treatment devices and methods of the present invention are more adaptable to wastewater containing complex oil sludge and have a wide range of operating loads, thus solving the problem of frequent fouling and clogging of equipment and reducing equipment maintenance and replacement of consumables. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 A schematic diagram of the overall structure of a processing system provided by an embodiment of the present invention;

[0036] Figure 2 A schematic diagram of the internal structure of the processing system provided in an embodiment of the present invention;

[0037] Figure 3 A schematic diagram of the structure of a sludge scraping unit in a processing system provided in an embodiment of the present invention;

[0038] Figure 4 A top view of a coarse particle separation unit in a processing system provided in an embodiment of the present invention;

[0039] Figure 5 A top view of a water collecting unit in a treatment system provided in an embodiment of the present invention;

[0040] In the figure:

[0041] 1. Coarse particle separation unit; 11. Inner tank; 111. Diversion area; 112. Inclined plate separation area; 113. Sedimentation area; 114. Sludge collection area; 1141. Sludge collecting bucket; 1142. Sludge drain bucket; 1143. Sludge scraper; 1144. Transmission motor; 1145. Heating coil; 115. Oil-water separation area; 116. Baffle; 12. Outer tank; 121. Coalescing plate separation area; 122. Water collecting unit; 1221. Water collecting ring pipe; 1222. Water collecting hood; 123. Oil collecting tank; 13. Leveling pipe; 2. Demulsification filter unit; 21. Coalescing filter element; 22. Ultrasonic generator; 23. Oil collecting bag; 3. Water inlet pipe; 4. Sludge drain pipe; 5. Connecting pipe; 6. Oil drain pipe; 7. Water outlet pipe. DETAILED DESCRIPTION

[0042] The present invention is further described below in conjunction with specific embodiments.

[0043] Example

[0044] A treatment system for tar-containing wastewater in this embodiment, such as Figure 1 As shown, it includes a coarse particle separation unit 1 and a demulsification filtration unit 2 which are arranged in sequence. The tar-containing wastewater enters the coarse particle separation unit 1 through the water inlet pipe 3 for sedimentation and oil removal combined with agglomeration and oil removal treatment, and then is transferred to the demulsification filtration unit 2 through the connecting pipe 5 for secondary agglomeration and oil removal and demulsification and oil removal.

[0045] Specifically, if Figure 2 As shown, the coarse particle separation unit 1 is composed of an inner tank 11 and an outer tank 12, wherein the inner tank 11 is placed inside the outer tank 12, and the lower end of the inner tank 11 passes through the outer tank 12; wherein the inner tank 11 is used for sedimentation and oil removal, and the outer tank 12 is used for agglomeration and oil removal.

[0046] The inner tank 11 includes a guide area 111, an inclined plate separation area 112, a sedimentation area 113, an oil sludge collection area 114 and an oil-water separation area 115:

[0047] The flow guide area 111 is a flow guide tube extending from top to bottom into the inner tank 11.

[0048] The inclined plate separation area 112 is arranged between the outer wall of the guide area 111 and the inner wall of the inner tank 11. The inclined plate separation area 112 is filled with inclined plate fillers to form a channel inclined to the inner wall of the inner tank 11 to extend the residence time of the wastewater.

[0049] The settling zone 113 is disposed below the guide zone 111 and the inclined plate separation zone 112 .

[0050] The sludge collection area 114 is arranged at the lower end of the inner tank 11; in order to facilitate collection, the sludge collection area 114 has a structure in which the inner diameter gradually decreases from top to bottom, and heavy oil is easily deposited in the inclined sludge collection area 114; in order to facilitate disassembly and cleaning, such as Figure 3As shown, an oil scraping unit is also installed in the oil sludge collection area 114, and the scraping unit includes an oil sludge collecting bucket 1141 and an oil sludge discharging bucket 1142. The inner diameter of the oil sludge collecting bucket 1141 gradually decreases from top to bottom to fit the oil sludge collecting area 114, which is conducive to the deposition of heavy oil. The oil sludge discharging bucket 1142 is a cylindrical vertical setting with equal diameter, and uses gravity to discharge the heavy oil. In order to avoid the hardening of heavy oil, the scraping unit also includes an oil sludge scraper 1143 and a transmission motor 1144, that is, the oil sludge scraper 1143 and the transmission motor 1144 are installed in the oil sludge collecting bucket 1141, and the transmission motor 1144 is electrically connected to the oil sludge scraper 1143, driving the oil sludge scraper 1143 to rotate along its center, so as to scrape off the accumulated oil on the inner wall of the oil sludge collecting bucket 1141. To prevent oil from hardening, the scraper unit also includes a heating coil 1145, which is wound around the outer wall of the oil sludge hopper 1142 and is used for heating to prevent oil from hardening and clogging the outlet of the oil sludge hopper 1142. The outlet of the oil sludge hopper 1142 is connected to the oil sludge pipe 4.

[0051] The oil-water separation area 115 is located at the upper part of the inner tank 11 and the outer tank 12, that is, above the inclined plate separation area 112; in order to improve the separation efficiency, a baffle 116 and an oil collecting tank 123 are arranged in the oil-water separation area 115, and the lower end of the baffle 116 is close to the opening of the inner tank 11, and the waste water is discharged from the opening of the inner tank 11 and flows out from the lower end of the baffle 116 through the action of the baffle 116; Figure 4 As shown, the oil collecting tank 123 is fixed around the upper end of the inner wall of the outer tank 12, and the heavy oil and light oil pass through the upper end of the baffle 116 and enter the oil collecting tank 123. The oil drain pipe 6 is connected to the oil collecting tank 123 for draining the oil in the oil collecting tank 123.

[0052] A coalescing plate separation zone 121 is provided in the outer tank 12. The coalescing plate separation zone 121 is located between the outer tank 12 and the inner tank 11 and below the oil-water separation zone 115. The coalescing plate separation zone 121 is filled with coalescing fillers, such as metal wire mesh and materials with molecular adsorption force, which coarsen the oil and float it up. Under the action of the coalescing plate separation zone 121, the coarse-grained oil droplets are accelerated to separate and gather upward, and the wastewater flows downward into the lower part of the outer tank.

[0053] like Figure 5As shown, a water collecting unit 122 is arranged below the coalescing plate separation zone 121, and the water collecting unit 122 is connected to the water outlet below the outer tank 12, and is used to discharge the wastewater at the bottom of the outer tank 12 to the demulsification filtration unit 2; the water collecting unit 122 includes a water collecting ring pipe 1221 and a water collecting cover 1222, the water collecting ring pipe 1221 is a polygonal pipe arranged around the inner wall of the outer tank 12, and a plurality of water collecting covers 1222 are arranged around the inner diameter of the water collecting ring pipe 1221, and are connected to the water collecting ring pipe 1221. The water collecting cover 1222 of each branch includes at least one bell mouth, and in this embodiment, the water collecting cover 1222 preferably includes two bell mouths connected in series to the water collecting ring pipe 1221, and the water collecting cover 1222 is acted by suction, on the one hand, the wastewater passes through the impact of the bell mouth, and the oil substances are further reduced in particle size and collected into the water collecting ring pipe 1221; on the other hand, the bell mouth is conducive to uniform water collection to avoid bias flow.

[0054] The inner tank 11 and the outer tank 12 are connected with a leveling pipe 13. Before starting the system, open the valve on the leveling pipe 13 to ensure that the inner tank 11 and the outer tank 12 are level, avoid excessive internal and external pressure difference, and avoid damaging the outer tank. After the water surface is level, close the valve on the leveling pipe 13 and then carry out the oil-water separation operation.

[0055] like Figure 2 As shown, the demulsification filtration unit 2 includes a horizontal shell, and the coalescing filter element 21 is horizontally arranged and evenly fixed inside the shell, the water inlet end of the coalescing filter element 21 is connected to the connecting pipe 5, and the water outlet end of the coalescing filter element 21 is connected to the outlet pipe 7; the ultrasonic generator 22 is evenly wound around the outside of the shell where the coalescing filter element 21 is located; the oil collecting bag 23 is connected to the shell above the coalescing filter element 21.

[0056] This embodiment uses the above-mentioned treatment system, and the steps of the treatment method of tar-containing wastewater are as follows:

[0057] S1. Coarse particle separation process: the tar-containing wastewater (total oil content 2500-3000 mg / L, tar accounting for more than 40%) enters the coarse particle separation unit 1 from the diversion area 111. The coarse particle separation unit 1 is filled with water. The coarse particle oil in the tar-containing wastewater is removed by combining sedimentation and coalescence oil removal, and the wastewater containing fine particle oil is discharged:

[0058] The tar-containing wastewater enters the diversion area 111 through the water inlet pipe 3, and then enters the sedimentation area 113 and the inclined plate separation area 112. In the inclined plate separation area 112, the oil, particulate matter and water are separated at an accelerated rate. The heavy oil and inorganic particles in the wastewater are separated in the sedimentation area 113 and move downward into the sludge collection area 114.

[0059] The medium oil and light oil in the wastewater are initially separated upward in the oil-water separation area 115, and the wastewater baffle 116 exits the inner tank 11 and enters the outer tank 12 downward through the coalescing plate separation area 121. Under the action of the coalescing plate separation area 121, the coarse-grained oil droplets are accelerated to separate and gather upward, and the wastewater containing fine-particle oil flows downward into the lower part of the outer tank 12.

[0060] S2, demulsification and separation process: the wastewater containing fine-particle oil discharged in step S1 enters the demulsification filtration unit 2, and further removes oil from the wastewater containing fine-particle oil by combining coalescence deoiling with ultrasonic demulsification:

[0061] The wastewater containing fine-particle oil at the bottom of the outer tank 12 is uniformly collected by the water collecting unit 122 and enters the demulsification filter unit 2 through the connecting pipe 5. The demulsification filter unit 2 is also filled with water, and the coalescing filter element 21 is immersed in water. Oil substances cannot pass through the coalescing filter element 21. The ultrasonic generator 22 is used for demulsification. The emulsified oil adheres to the surface of the coalescing filter element 21 and collides with it to increase. After that, it separates and enters the oil collecting bag 23 upward. The wastewater is discharged into the outlet pipe 7 through the coalescing filter element 21. The total oil content of the wastewater discharged from the outlet pipe 7 is less than 150 mg / L, and the tar accounts for 3-7%. In the prior art, when the coarse particle separation process of step S1 is not performed, the tar-containing wastewater is subjected to ultrasonic demulsification treatment with a frequency of 20; in this embodiment, after the coarse particle separation process of step S1, in the demulsification separation process of step S2, the frequency of the ultrasonic generator 22 can be further reduced. In this embodiment, the frequency of the ultrasonic generator 22 is set to 19 kHz.

[0062] It should be noted that after a certain period of accumulation of medium-quality oil and light-quality oil, the oil collecting bag 23 at the top of the coarse particle separation unit 1 or the top of the demulsification and filtration unit 2 reaches a certain oil layer thickness, and the inlet and outlet water volume is adjusted to raise the liquid level to the oil discharge height of the oil collecting tank 123, so that the oil enters the oil discharge pipe 6 and is discharged from the system;

[0063] The mixed sludge of heavy oil and particulate matter accumulates in the sludge collecting area 114, and the sludge adhering to the wall of the sludge collecting bucket 1141 is pushed into the bottom of the sludge draining bucket 1142 by the sludge scraper 1143, and then enters the sludge draining pipe 4 to be discharged from the system.

[0064] The above description is only by way of illustration of certain exemplary embodiments of the present invention. It is undoubted that those skilled in the art can modify the described embodiments in various ways without departing from the spirit and scope of the present invention. Therefore, the above drawings and descriptions are illustrative in nature and should not be construed as limiting the scope of protection of the claims of the present invention.

Claims

1. A system for treating tar-containing wastewater, characterized in that: include: The coarse particle separation unit (1) is composed of an inner tank (11) and an outer tank (12), wherein the inner tank (11) is placed inside the outer tank (12), and the lower end of the inner tank (11) penetrates the outer tank (12); the inner tank (11) is used for sedimentation and oil removal, and the outer tank (12) is used for coalescence and oil removal; The demulsification and filtration unit (2) has a water inlet connected to the water outlet of the outer tank (12) after coalescence and oil removal, and is used for secondary coalescence and oil removal and demulsification and oil removal at the same time.

2. A tar-containing wastewater treatment system according to claim 1, characterized in that: In the coarse particle separation unit (1): The inner tank (11) comprises a guide area (111), an inclined plate separation area (112), a sedimentation area (113), an oil sludge collection area (114) and an oil-water separation area (115); the guide area (111) extends into the inner tank (11) from top to bottom; the inclined plate separation area (112) is arranged between the outer wall of the guide area (111) and the inner wall of the inner tank (11); the inclined plate separation area (112) forms a channel inclined to the inner wall of the inner tank (11); the sedimentation area (113) is arranged below the guide area (111) and the inclined plate separation area (112); the oil sludge collection area (114) is arranged at the lower end of the inner tank (11); and the oil-water separation area (115) is located at the upper part of the inner tank (11) and the outer tank (12); A coalescing plate separation zone (121) is provided in the outer tank (12), and the coalescing plate separation zone (121) is located between the outer tank (12) and the inner tank (11) and below the oil-water separation zone (115).

3. A tar-containing wastewater treatment system according to claim 2, characterized in that: The inclined plate separation zone (112) is filled with inclined plate fillers; and the coalescing plate separation zone (121) is filled with coalescing fillers.

4. A tar-containing wastewater treatment system according to claim 1, characterized in that: The demulsification filtration unit (2) comprises a horizontal shell, a coalescing filter element (21) is installed inside the shell, an ultrasonic generator (22) is wound around the shell where the coalescing filter element (21) is located, and an oil collecting bag (23) is connected to the top of the shell.

5. A tar-containing wastewater treatment system according to claim 2, characterized in that: A baffle plate (116) and an oil collecting tank (123) are arranged in the oil-water separation zone (115). The lower end of the baffle plate (116) is close to the opening of the inner tank (11); and the oil collecting tank (123) is fixed around the upper end of the inner wall of the outer tank (12).

6. A tar-containing wastewater treatment system according to claim 1, characterized in that: A water collecting unit (122) is arranged below the coalescing plate separation zone (121), and the water collecting unit (122) is connected to the water outlet below the outer tank (12) and is used to discharge the wastewater at the bottom of the outer tank (12) to the demulsification filtration unit (2); the water collecting unit (122) comprises a water collecting ring pipe (1221) and a water collecting cover (1222); the water collecting ring pipe (1221) is arranged around the inner wall of the outer tank (12), and a plurality of water collecting covers (1222) are arranged around the inner diameter of the water collecting ring pipe (1221) and are connected to the water collecting ring pipe (1221); the water collecting cover (1222) comprises at least one bell mouth, and preferably the water collecting cover (1222) comprises two bell mouths connected in series to the water collecting ring pipe (1221).

7. A tar-containing wastewater treatment system according to claim 2, characterized in that: The oil sludge collection area (114) is also equipped with an oil scraping unit, which comprises an oil sludge collecting bucket (1141) and an oil sludge discharging bucket (1142). The inner diameter of the oil sludge collecting bucket (1141) gradually decreases from top to bottom; the oil sludge discharging bucket (1142) is a cylindrical bucket with equal diameter and is vertically arranged.

8. A tar-containing wastewater treatment system according to claim 7, characterized in that: The oil scraping unit further comprises an oil scraper (1143) and a transmission motor (1144); the oil scraper (1143) is installed in the oil collecting hopper (1141); the transmission motor (1144) is electrically connected to the oil scraper (1143) to drive the oil scraper (1143) to rotate along its center to scrape off the accumulated oil on the inner wall of the oil collecting hopper (1141); or, The oil scraping unit further comprises an oil sludge scraper (1143), a transmission motor (1144) and a heating coil (1145); the oil sludge scraper (1143) is installed in the oil sludge collecting bucket (1141); the transmission motor (1144) is electrically connected to the oil sludge scraper (1143) to drive the oil sludge scraper (1143) to rotate along its center so as to scrape off the accumulated oil on the inner wall of the oil sludge collecting bucket (1141); and the heating coil (1145) is wound around the outer wall of the oil sludge discharging bucket (1142).

9. A method for treating tar-containing wastewater, characterized in that: In order to treat tar-containing wastewater using any one of the treatment systems of claims 1 to 8, the treatment method steps are as follows: S1, coarse particle separation step: the tar-containing wastewater enters the coarse particle separation unit (1), and the coarse particle oil in the tar-containing wastewater is removed by combining sedimentation and coalescence oil removal, and the wastewater containing fine particle oil is discharged; S2, demulsification and separation process: the wastewater containing fine-particle oil discharged in step S1 enters the demulsification and filtration unit (2), and the wastewater containing fine-particle oil is further deoiled by a combination of coalescence and oil removal and ultrasonic demulsification.

10. The method for treating tar-containing wastewater according to claim 9, characterized in that: Without the coarse particle separation process of step S1, the tar-containing wastewater is subjected to ultrasonic demulsification treatment with a frequency of P0; after the coarse particle separation process of step S1, in the demulsification separation process of step S2, the frequency of ultrasonic demulsification is P, and P = (0.95-0.98) P0.

Images