Coking wastewater pretreatment system

Abstract

The utility model discloses a coking wastewater pretreatment system which comprises a gravity oil removal tank, a pressurized dissolved air flotation tank connected with the gravity oil removal tank, a cavitation air flotation tank connected with the pressurized dissolved air flotation tank through a pipeline and an adjusting tank connected with the cavitation air flotation tank, and the pipeline is used for conveying a polyferric agent from the dosing device to the cavitation air floatation tank. According to the coking wastewater pretreatment system disclosed by the utility model, only small-particle oil drops can float from coking wastewater through the pressurized dissolved air flotation tank, part of large oil drops still enter the next working procedure, and after polyferric coagulation and cavitation air flotation are directly added at the rear end, the oil drops can be effectively and continuously enlarged and are floated out by large bubbles of cavitation air flotation; therefore, the oil removal effect and the suspended matter removal effect are improved, the oil content of the coking wastewater can be reduced, and good conditions are provided for subsequent biochemical treatment.

Description

Technical Field

[0001] The utility model belongs to the technical field of energy conservation and emission reduction, and specifically relates to a coking wastewater pretreatment system. Background Art

[0002] Coking wastewater is produced in the coking plant during the coking, gas purification and chemical product recovery processes. It has a complex composition, high concentration of harmful substances, high toxicity and is difficult to treat.

[0003] There are three main sources of coking wastewater: one is residual ammonia water, which is the wastewater generated during coal distillation and gas cooling, and its amount accounts for more than 1 / 2 of the total wastewater; the second is the wastewater generated during the gas purification process, such as gas final cooling water and crude benzene separation water; the third is the wastewater generated during the refining process of chemical products such as tar and crude benzene and other occasions (such as gas water seals, ground washing, cleaning of oil tanks, tanks, cars, etc.).

[0004] During the gas purification and chemical product refining process, various high-concentration process wastewaters separated from the process medium must be mixed with the remaining ammonia water, and then discharged in the form of ammonia evaporated wastewater after ammonia evaporation (some must first undergo solvent dephenolization), and then sent to the phenol-cyanide wastewater treatment station; the amount of other wastewater from the coking plant varies, but the concentration of pollutants in these waters is relatively low, and they are generally sent directly to the pretreatment system of the sewage treatment station.

[0005] The pollutants in coking wastewater mainly include chemical oxygen demand (COD), ammonia nitrogen, phenol, cyanide, etc. If they are not properly treated, they will cause damage to the ecological environment.

[0006] Modern wastewater treatment technology uses various methods to separate pollutants contained in sewage or convert them into harmless and stable substances, thereby purifying sewage. According to the working principle, it can be divided into three categories: physical method, chemical method and biological method, all of which are applied in different scenarios.

[0007] Traditional methods for treating oily wastewater mainly include physical methods (such as gravity separation, coalescence, membrane separation), chemical methods (such as coagulation, supercritical water oxidation technology), physical and chemical methods (flotation, electrocoagulation, adsorption) and biological methods (such as activated sludge treatment, membrane bioreactor). However, these methods all have certain disadvantages, such as: low membrane separation flux, high operating costs, high energy consumption, easy membrane pollution, chemical methods are prone to corrosion and re-pollution, biological methods have strict pretreatment requirements and difficult sludge treatment. In addition, a single treatment method has low resistance to hydraulic and water quality shocks, making it difficult to meet the growing demand for environmental protection, thereby limiting the practical application of such processes. Therefore, it is imperative to explore a combination of multiple processes to treat oily wastewater, improve oil removal efficiency and enhance the overall treatment effect.

[0008] As the most widely used method for treating oily wastewater, flotation technology has the advantages of good treatment effect, high efficiency and compact structure. Coking wastewater is one of the most difficult industrial wastewaters to treat. The oil and suspended solids contained in it must be removed through pretreatment. The flotation technology is currently widely used in the pretreatment process of coking wastewater.

[0009] For example, the patent document with the publication number CN117623527A discloses a coking wastewater treatment process, which relates to the field of wastewater treatment technology, and in particular to a coking wastewater treatment process, which includes the following steps: S1, preliminarily adjusting the collected coking wastewater, passing it through a sedimentation tank, and then through a flotation tank to obtain pretreated coking wastewater; S2, passing the pretreated coking wastewater into an electrochemical reaction cell, setting current density and voltage parameters; S3, adding a coking wastewater treatment agent to the electrochemical reaction cell, stirring evenly, turning on the light source, irradiating, and obtaining treated water; S4, passing the treated water through a secondary sedimentation tank, and then through a flocculation tank to obtain purified water. Among them, the coking wastewater treatment agent refers to a γ-Bi2MoO6 / graphene-loaded acrylic acid grafted polythiophene composite. In the present invention, electrochemical treatment is first performed in the electrochemical reaction cell, and after the coking wastewater treatment agent is added, rapid and efficient deep treatment is performed under the irradiation of a light source, and the coking wastewater treatment agent can be recycled.

[0010] The application of this method to the flotation tank is only to perform preliminary conditioning on the coking wastewater, and then pass it through the sedimentation tank and then the flotation tank to obtain the pre-treated coking wastewater, which fails to give full play to the function of the flotation tank.

[0011] For example, the patent document with the publication number CN116715304A discloses a coking wastewater high-efficiency flotation pretreatment device and a treatment method thereof, which discloses a coking wastewater high-efficiency flotation pretreatment device and a treatment method thereof, belonging to the field of coking wastewater treatment technology, the device includes a flotation tank, a bubble generating device arranged in the flotation tank, a water inlet pipe and a water outlet pipe connected to the flotation tank, one end of the cylinder is connected to the output end of the blower through a hollow tube, and the other end of the cylinder is connected to the output end of the first motor; each group of bubble dispersion components includes a plurality of first blades uniformly distributed along the circumference of the cylinder, a first longitudinal channel and a plurality of first transverse channels are opened on the inner side of the first blade, the first transverse channels are uniformly spaced along the longitudinal direction of the first blade, one end of the first transverse channel is connected to the first longitudinal channel, and the other end extends outward along the transverse direction of the first blade, and a through hole connected to the first longitudinal channel is opened on the surface of the cylinder. The device and method of the present invention can reduce the bubble diameter of coking wastewater during flotation pretreatment, and can improve the oil removal effect.

[0012] Although this method can reduce the bubble diameter during flotation, it is not effective in removing large-sized oil droplets in coking wastewater.

[0013] For example, the patent document with publication number CN115321764A discloses a system and method for treating coking wastewater, and provides a system and method for treating coking wastewater, which belongs to the technical field of wastewater treatment. The treatment system comprises a grease trap, a first flotation tank, a regulating tank, a composite hydrolysis acidification tank, a second flotation tank, an anoxic tank, an aerobic tank, a secondary sedimentation tank, a denitrification filter and a coagulation reaction system which are connected in series from front to back; the secondary sedimentation tank is connected to the composite hydrolysis acidification tank and the anoxic tank respectively through a nitrification liquid return pipe; a flow control device is provided on the nitrification liquid return pipe; the volume flow rate of the nitrification liquid returned to the composite hydrolysis acidification tank is controlled by the flow control device to be 0.5 to 1.5 times the volume flow rate of the wastewater flowing out of the regulating tank; the method is to treat coking wastewater using the above system. The present invention controls the nitrification liquid in the secondary sedimentation tank to flow back to the composite hydrolysis acidification tank at a specific flow rate, thereby reducing the inhibitory effects of toxic substances and water quality fluctuations in the coking wastewater on hydrolytic bacteria and acidifying bacteria, enhancing the hydrolysis acidification effect and improving biodegradability.

[0014] Although this method sets up a secondary flotation tank, they are not directly connected, and their respective functions are not organically combined, and they only serve the needs of different biochemical stages. Utility Model Content

[0015] The utility model aims to solve at least one of the technical problems existing in the prior art. To this end, the utility model provides a coking wastewater pretreatment system, the purpose of which is to reduce the oil content of the coking wastewater and provide good conditions for subsequent biochemical treatment.

[0016] In order to achieve the above-mentioned purpose, the technical solution adopted by the utility model is: a coking wastewater pretreatment system, including a gravity oil removal tank, a pressurized dissolved air flotation tank connected to the gravity oil removal tank, a vortex flotation tank connected to the pressurized dissolved air flotation tank through a pipeline, and a regulating tank connected to the vortex flotation tank, the pipeline is connected to a dosing device, and the pipeline transports the polyferric agent from the dosing device to the vortex flotation tank.

[0017] The amount of polyferric agent added to the pipeline is 500-1000 PPm of the mass of the coking wastewater.

[0018] The cavitation flotation tank and the pressurized dissolved air flotation tank are connected to a scum collection box.

[0019] The scum collecting box and the gravity degreasing tank are connected to the light oil tank.

[0020] The pressurized dissolved air flotation tank is connected to the dissolved air tank, and no polyferric iron and polyacrylamide are added to the pressurized dissolved air flotation tank.

[0021] The gravity oil removal tank is connected to the heavy oil tank.

[0022] The utility model provides a coking wastewater pretreatment system. After the coking wastewater passes through a pressurized dissolved air flotation tank, only smaller oil droplets can be floated up. Some larger oil droplets still enter the next process. After the rear end is directly added with poly-iron coagulation and vortex flotation, the oil droplets can be effectively enlarged and floated out by large bubbles of vortex flotation, thereby increasing the effect of removing oil and suspended solids. Therefore, the oil content of the coking wastewater can be reduced, providing good conditions for subsequent biochemical treatment. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] This specification includes the following drawings, which show the following contents:

[0024] Figure 1 It is a structural schematic diagram of the coking wastewater pretreatment system of the utility model;

[0025] The markings in the figure are: 1. Gravity oil removal tank; 2. Pressurized dissolved air flotation tank; 3. Vortex flotation tank; 4. Regulating tank; 5. Dosing device; 6. Dissolved air tank; 7. Heavy oil tank; 8. Scum collection box; 9. Light oil tank. DETAILED DESCRIPTION

[0026] The specific implementation methods of the utility model are further explained in detail below with reference to the accompanying drawings through the description of embodiments, with the aim of helping technicians in the field to have a more complete, accurate and in-depth understanding of the concept and technical solution of the utility model and facilitating its implementation.

[0027] like Figure 1 As shown, the utility model provides a coking wastewater pretreatment system, including a gravity oil removal tank 1, a pressurized dissolved air flotation tank 2 connected to the gravity oil removal tank 1, a vortex flotation tank 3 connected to the pressurized dissolved air flotation tank 2 through a pipeline, and a regulating tank 4 connected to the vortex flotation tank 3, the pipeline is connected to a dosing device 5, and the pipeline transports the polyferric agent from the dosing device 5 to the vortex flotation tank 3.

[0028] Specifically, if Figure 1 As shown, the coking wastewater that has been evaporated with ammonia is first pumped into the gravity oil removal tank 1 → the pressurized dissolved air flotation tank 2 → the vortex flotation tank 3 → the regulating tank 4.

[0029] There are many pollutants in coking wastewater. Directly adding it to the biochemical treatment system will cause a great impact on the system. Therefore, gravity oil removal is required to remove the heavy oil that can be removed by gravity and the light oil floating on the surface first, so as to avoid sinking during the subsequent flotation process and the need for frequent cleaning. The fine suspended oil droplets or emulsified oil and suspended matter contained in the wastewater need to be removed by flotation equipment. To remove suspended matter and remove oil, a combination of polyferric and anionic PAM (polyacrylamide) or a combination of polyaluminum chloride and anionic PAM is generally added to the flotation to remove oil and SS. At the same time, the added polyferric can also partially remove various toxic substances in the coking wastewater, such as sulfide, cyanide, thiocyanate, etc. However, because flocculants such as anionic PAM generally lead to the formation of larger flocs, which are easy to form precipitation, only coagulants such as polyferric or polyaluminum are added in the utility model to coagulate into larger particles, which float to the surface under the buoyancy of the gas to become scum and are removed by the scraper.

[0030] like Figure 1 As shown, the coking wastewater after ammonia evaporation enters the gravity deoiling tank 1 for gravity deoiling, and the gravity deoiling tank 1 is connected to the heavy oil tank 7 and the light oil tank 9. The coking wastewater after ammonia evaporation enters the gravity deoiling tank 1 alone or after being mixed with other production wastewater and domestic wastewater. After the heavy oil is removed, the light oil floating on the surface is skimmed off at the end with a skimmer. The heavy oil in the gravity deoiling tank 1 is pumped to the heavy oil tank 7 by a submerged pump, and the light oil in the gravity deoiling tank 1 is sent to the light oil tank 9. The heavy and light oils in the heavy oil tank 7 and the light oil tank 9 are all sent to the coal yard to be mixed with coal and returned to the coke oven for coking.

[0031] like Figure 1 As shown, the coking wastewater after gravity oil removal enters the pressurized dissolved air flotation tank 2, and the pressurized dissolved air flotation tank 2 is connected to the dissolved air tank 6. The combination of air flotation adopts the combination of first passing through the dissolved air flotation and then passing through the vortex air flotation. Because the dissolved air flotation will produce tiny bubbles with a diameter of 20 to 100 microns, the small-sized oil droplets in the wastewater will be adsorbed and merged into large-sized oil droplets. A layer of scum is formed on the surface, which is scraped into the scum collection box 8 by the scraper on the flotation tank. The scum in the scum collection box 8 is pumped into the light oil pool 9. No polyferric or PAM (polyacrylamide) is added to the pressurized dissolved air flotation tank 2 to avoid premature precipitation in the air flotation. Only the dissolved air water in the dissolved air tank 6 is introduced into the pressurized dissolved air flotation tank 2, and enters the pressurized dissolved air flotation tank 2 through the release head to adsorb the oil droplets in the wastewater and float to form scum.

[0032] like Figure 1As shown, the coking wastewater after the pressurized dissolved air flotation tank 2 enters the vortex flotation tank 3. The dosing device 5 adds polyferric reagent to the gravity pipe of the coking wastewater after the pressurized dissolved air flotation tank 2, and the addition ratio is 500-1000PPm of the mass of the coking wastewater. The coking wastewater after adding the polyferric reagent enters the vortex flotation tank 3. The vortex flotation tank 3 directly and evenly injects microbubbles into the sewage through the diffuser impeller without the need for pre-dissolving gas through complex dissolved air technology, and will produce fine bubbles with a diameter of 700-1500 microns. The bubbles will adsorb the larger particle size oil droplets and suspended matter that have been collided and converged by the pressurized dissolved air flotation tank 2 and generated by the addition of polyferric coagulation, thereby forming scum to be scraped off.

[0033] like Figure 1 As shown, the vortex flotation tank 3 and the pressurized dissolved air flotation tank 2 are connected to the scum collection box 8, and the scum collection box 8 is connected to the light oil tank 9. The scum scraped from the vortex flotation tank 3 and the scum scraped from the pressurized dissolved air flotation tank 2 enter the same scum collection box 8 for collection.

[0034] like Figure 1 As shown, the coking wastewater after the vortex air flotation tank 3 enters the regulating tank 4. The coking wastewater from the vortex air flotation tank 3 flows by gravity or is pumped into the regulating tank 4, where it is mixed with other wastewater for conditioning and then sent to the biochemical treatment section at the rear end. Part of the oil residue deposited at the bottom of the regulating tank 4 can be discharged regularly through a pipeline to reduce the deposition of oil residue in the regulating tank 4.

[0035] Embodiment 1

[0036] A pretreatment device for biochemical treatment of coking wastewater in a coking plant, treating 100m3 of coking wastewater 3 / h, after being degreased by gravity degreasing tank 1, it enters 2 70m 3 / h pressurized dissolved air flotation tank 2, then through the dosing device 5 to add 600PPm of polyferric (relative to the amount of coking wastewater) and then enter a treatment capacity of 120m 3 / h vortex flotation tank 3, the oil content before treatment was 80mg / l, and the oil content after treatment was only 20mg / l, and the oil removal efficiency was 75%.

[0037] The coking wastewater pretreatment system of the above structure has the following advantages:

[0038] 1. Coking wastewater generally only undergoes one stage of pressurized dissolved air flotation, which can only float up oil droplets with smaller particles. Some larger oil droplets still enter the next process, thus affecting the oil removal effect. However, the addition of poly-iron coagulation and vortex flotation at the back end can effectively continue to increase the oil droplets and be floated out by the large bubbles of vortex flotation, thereby increasing the effect of oil removal and suspended solids removal.

[0039] 2. It overturns the process route of the prior art of first removing large oil droplets by cavitation flotation and then removing small oil droplets by pressurized dissolved air flotation. Instead, the small oil droplets are first selected by pressurized dissolved air flotation. Some larger oil droplets that are enlarged by the collision of small bubbles are difficult to float out due to the insufficient buoyancy of small bubbles, but can be adsorbed and removed by large bubbles generated by cavitation flotation in the subsequent process.

[0040] 3. If vortex flotation is used first and polyferric reagent is added, only the original small number of large oil droplets in the wastewater can be floated. If pressurized dissolved air flotation is used, the bubbles produced by the latter are small, so only a very small amount of small-size oil droplets can be floated. If the oil droplets are coagulated by polyferric, it may be difficult for small bubbles to float them. Therefore, the effect of flotation to remove oil and suspended solids (SS) is poor, and it is difficult to meet the process requirements.

[0041] 4. This patent only uses polyferric as a coagulant instead of anionic PAM, which reduces the serious foaming problem on the surface of the flotation tank caused by anionic PAM as a high molecular surfactant, and also reduces the problem of precipitation in the flotation tank caused by particles being too large after flocculation. At the same time, it also reduces the consumption of reagents.

[0042] 5. The oil residue scraped from the vortex flotation tank and the oil residue scraped from the pressurized dissolved air flotation tank are collected in the same light oil collection box. Because no polyferric is added to the pressurized dissolved air flotation tank, the generated flotation has a certain surface activity, while polyferric is added to the vortex flotation tank, and the scraped oil residue also contains some polyferric, which is beneficial to reduce the foaming effect of the oil residue in the pressurized dissolved air flotation tank, prevent overflow, and improve the on-site environment.

[0043] 6. This patent does not add any reagents to the pressurized dissolved air flotation tank, and no sediment will be formed in the pressurized dissolved air flotation tank, which is beneficial to the long-term stable operation of the flotation tank.

[0044] 7. Adding the polyferric agent after removing some small-size oil droplets in the pressurized dissolved air flotation tank is beneficial to fully exert the effectiveness of the polyferric agent and reduce the consumption of the agent. At the same time, adding the agent before the air diffusion impeller of the vortex flotation tank 3 can fully stir it, which is beneficial for the polyferric agent to play the role of a coagulant and also for the polyferric agent to react with the sulfide, cyanide and thiocyanate ions in the wastewater to remove them.

[0045] The above is an exemplary description of the utility model in conjunction with the accompanying drawings. Obviously, the specific implementation of the utility model is not limited to the above-mentioned method. As long as various non-substantial improvements are made using the method concept and technical solution of the utility model; or the above concept and technical solution of the utility model are directly applied to other occasions without improvement, they are all within the protection scope of the utility model.

Claims

1. Coking wastewater pretreatment system, characterized by: The invention comprises a gravity oil removal tank, a pressurized dissolved air flotation tank connected to the gravity oil removal tank, a vortex flotation tank connected to the pressurized dissolved air flotation tank via a pipeline, and a regulating tank connected to the vortex flotation tank. The pipeline is connected to a dosing device, and the pipeline transports the polyferric agent from the dosing device to the vortex flotation tank.

2. The coking wastewater pretreatment system according to claim 1, characterized in that: The amount of polyferric agent added to the pipeline is 500-1000 PPm of the mass of the coking wastewater.

3. The coking wastewater pretreatment system according to claim 1, characterized in that: The cavitation flotation tank and the pressurized dissolved air flotation tank are connected to a scum collection box.

4. The coking wastewater pretreatment system according to claim 3, characterized in that: The scum collecting box and the gravity degreasing tank are connected to the light oil tank.

5. The coking wastewater pretreatment system according to any one of claims 1 to 4, characterized in that: The pressurized dissolved air flotation tank is connected to the dissolved air tank, and no polyferric iron and polyacrylamide are added to the pressurized dissolved air flotation tank.

6. The coking wastewater pretreatment system according to any one of claims 1 to 3, characterized in that: The gravity oil removal tank is connected to the heavy oil tank.

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