Coal chemical high-salinity wastewater advanced treatment system and method

Abstract

The application relates to a coal chemical high-salt wastewater advanced treatment system and method. A medicament defluorination and desilication unit is used for receiving coal chemical high-salt raw water, removing silicon and fluorine ions in the water by adding medicaments, and precipitating and separating sludge impurities; a flotation unit is used for further removing suspended particulate matters and oil pollutants in the wastewater and generating dregs; a resin adsorption unit is connected with a water outlet end of the flotation unit, and is used for adsorbing and removing organic COD pollutants in the wastewater; a multistage membrane treatment unit is connected with a water outlet end of the resin adsorption unit, and is used for separating ultrafiltration concentrated water, nanofiltration concentrated water containing divalent salt, sodium chloride reverse osmosis concentrated water and reverse osmosis produced water; a sodium hypochlorite preparation unit is communicated with a reverse osmosis concentrated water outlet of the multistage membrane treatment unit, and is used for preparing sodium hypochlorite; a miscellaneous salt crystallization and harmless treatment unit is communicated with a nanofiltration concentrated water outlet of the multistage membrane treatment unit, and is used for evaporating and crystallizing the divalent salt concentrated water to produce miscellaneous salt, and for harmless treatment.

Description

Technical Field

[0001] This application relates to the field of coal chemical industry wastewater treatment technology, and in particular to a deep treatment system and method for high-salt coal chemical wastewater. Background Technology

[0002] Coal chemical production processes generate large quantities of high-salinity wastewater. This wastewater is complex, with total dissolved solids (TDS) generally exceeding 50,000 mg / L, and in some cases reaching over 100,000 mg / L. It also contains high concentrations of chlorides, sulfates, fluoride ions, silicon, macromolecular organic matter, suspended solids, and oil pollutants, with COD concentrations often exceeding 1000 mg / L. Current mainstream treatment processes involve membrane concentration followed by evaporation and crystallization. The resulting mixed salts are classified as hazardous waste, leading to high disposal costs. Furthermore, sodium chloride and water resources cannot be recovered, resulting in significant resource waste and contradicting energy conservation, circular economy, and green chemical development policies.

[0003] Existing publicly available technologies for the resource recovery of high-salt wastewater have significant drawbacks: Insufficient pretreatment capacity results in poor removal of silicon, fluorine, and macromolecular organic matter. The system is also poorly adaptable to water quality fluctuations. Complex influent from coal chemical plants can easily cause continuous fouling of nanofiltration and reverse osmosis membrane elements, making it impossible for the system to operate stably for a long period of time. Some processes lack multi-stage resin deep COD removal steps, resulting in the continuous retention of organic matter in the membrane system, which accelerates membrane aging, significantly increases cleaning frequency, and raises operating costs. After salt separation, only the mixed salts are crystallized, and the concentrated sodium chloride solution is not utilized for resource recovery. Only hazardous waste mixed salts are produced, resulting in poor economic benefits. There is no unified collection and filter press unit for sludge and flotation scum, and disorderly stacking of pollutant-containing sludge can easily cause secondary pollution. The evaporation crystallization condensate and reverse osmosis water were not designed with a return and reuse path, resulting in a large consumption of fresh process water. Summary of the Invention

[0004] This application provides a deep treatment system and method for high-salt wastewater from coal chemical industry, which solves the problems of easy membrane fouling, large output of mixed salt and hazardous waste, lack of resource utilization of salt, low water reuse rate, and easy secondary pollution caused by sludge and scum in the existing coal chemical high-salt wastewater treatment process.

[0005] On the one hand, this application provides a deep treatment system for high-salt wastewater from coal chemical industry, including a chemical defluorination and desiliconization unit, an air flotation unit, a resin adsorption unit, and a multi-stage membrane treatment unit connected sequentially along the wastewater flow direction, as well as a sodium hypochlorite preparation unit and a miscellaneous salt crystallization and harmless treatment unit respectively connected to the multi-stage membrane treatment unit. The chemical defluorination and desiliconization unit is used to receive high-salinity raw water from coal chemical industry, remove silicon and fluoride ions from the water by adding chemicals, and precipitate and separate sludge impurities. The inlet of the air flotation unit is connected to the outlet of the chemical defluorination and desiliconization unit, which is used to further remove suspended particulate matter and oil pollutants from the wastewater and generate scum. The inlet of the resin adsorption unit is connected to the outlet of the air flotation unit, and is used to adsorb and remove organic COD pollutants from the wastewater. The inlet of the multi-stage membrane treatment unit is connected to the outlet of the resin adsorption unit to realize wastewater desalination and concentration, and to separate ultrafiltration concentrate, nanofiltration concentrate containing divalent salt, sodium chloride reverse osmosis concentrate and reverse osmosis permeate. The inlet of the sodium hypochlorite preparation unit is connected to the outlet of the reverse osmosis concentrate of the multi-stage membrane treatment unit, and is used to prepare sodium hypochlorite by electrolysis of concentrated sodium chloride solution. The feed inlet of the mixed salt crystallization and harmless treatment unit is connected to the nanofiltration concentrate outlet of the multi-stage membrane treatment unit. It is used to evaporate and crystallize the divalent salt concentrate to produce mixed salt, and to dry and calcine the mixed salt to render it harmless.

[0006] In one possible design, the chemical defluorination and desiliconization unit includes a homogenization equalization tank, a dosing tank, and an inclined plate sedimentation tank connected in sequence. The supernatant of the inclined plate sedimentation tank is connected to the pH equalization tank, and a sludge outlet is provided at the bottom of the inclined plate sedimentation tank.

[0007] In one possible design, the flotation unit includes a dissolved air booster pump, an air compressor, a flotation tank, a dissolved air release device, and a scum scraper. The air compressor is connected to the dissolved air booster pump pipeline, the outlet of the dissolved air booster pump extends into the flotation tank and is connected to the dissolved air release device, and the scum scraper is used to scrape off the scum on the surface of the flotation tank.

[0008] In one possible design, the resin adsorption unit includes a filter and an adsorption tower arranged in sequence. The adsorption tower is filled with a composite acrylate-based macroporous COD removal resin, and the adsorption tower is also equipped with a desorption and regeneration agent tank group.

[0009] In one possible design, the multi-stage membrane treatment unit includes an ultrafiltration membrane unit, a nanofiltration membrane unit, and a reverse osmosis membrane unit connected in series. The concentrate outlet of the ultrafiltration membrane unit is connected to the plant's biochemical system. The concentrate outlet of the nanofiltration membrane unit is connected to a salt crystallization and decontamination unit. The concentrate outlet of the reverse osmosis membrane unit is connected to a sodium hypochlorite preparation unit. The permeate outlet of the reverse osmosis membrane unit is recirculated to a chemical defluorination and desiliconization unit.

[0010] In one possible design, the sodium hypochlorite preparation unit includes a sodium hypochlorite generator, a sodium hypochlorite storage tank, and a delivery pump.

[0011] In one possible design, the mixed salt crystallization and detoxification unit includes a vacuum crystallizer separator, a heater, a condenser, a centrifuge, a vibrating fluidized bed dryer, and a high-temperature calcining rotary kiln.

[0012] In one possible design, a waste residue filter press unit is also included. The waste residue filter press unit is connected to the sludge outlet of the chemical defluorination and desiliconization unit and the scum outlet of the air flotation unit, respectively, for collecting sludge and scum and dewatering them for external transport. The waste residue filter press unit includes a sludge tank, a sludge transfer pump and a plate and frame filter press.

[0013] In one possible design, an acid-base and chemical dosing unit is also included. The acid-base and chemical dosing unit is connected to the chemical defluorination and desiliconization unit and the air flotation unit respectively, and is used to add hydrochloric acid, liquid alkali, and desiliconization and defluorination composite chemicals. The acid-base and chemical dosing unit includes a chemical storage tank, a metering pump and a stirring device.

[0014] On the other hand, this application also provides a method for deep treatment of high-salinity wastewater from coal chemical industry, which employs the high-salinity wastewater deep treatment system for coal chemical industry as described above, and includes the following steps: S1. Chemical defluorination and desiliconization pretreatment: High-salt wastewater is sent to the chemical defluorination and desiliconization unit, where chemicals are added to remove silicon and fluoride ions, and sludge is produced by sedimentation; the effluent is sent to the air flotation unit after pH adjustment. S2. Air flotation for impurity removal: The air flotation unit separates suspended solids and oils from the water, producing scum; sludge and scum are sent to the waste residue filter press unit for dewatering. S3. Resin-based deep COD removal: The effluent from the air flotation enters the resin adsorption unit, where most organic pollutants are adsorbed and removed. After the resin is saturated, it is regenerated using alkaline agents. S4. Multi-stage membrane salt concentration: The resin effluent enters the multi-stage membrane treatment unit and is treated step by step by ultrafiltration, nanofiltration and reverse osmosis; the ultrafiltration concentrate is sent to the biochemical system, the nanofiltration concentrate is sent to the miscellaneous salt crystallization and harmless treatment unit, the sodium chloride reverse osmosis concentrate is sent to the sodium hypochlorite preparation unit, and the reverse osmosis permeate is returned to the front end. S5. Sodium hypochlorite preparation: Sodium chloride reverse osmosis concentrate is adjusted to the desired concentration and then sent to the sodium hypochlorite preparation unit for electrolysis to generate sodium hypochlorite solution for plant disinfection. S6. Harmless treatment of mixed salt crystals: Nanofiltration concentrate enters the mixed salt crystallization and harmless treatment unit for vacuum evaporation and crystallization. The salt crystals are dried and calcined at high temperature to be converted into general solid waste for resource utilization. The crystallization condensate is returned to the upstream process for reuse.

[0015] The beneficial effects of this application are as follows: The coal chemical high-salt wastewater deep treatment system of this application has a multi-stage pre-purification process. It sets up a three-stage pre-purification process of chemical defluorination and desiliconization, air flotation, and special resin to remove silicon, fluorine, suspended solids, oil, and macromolecular organic matter in sequence. This eliminates the pollution of ultrafiltration, nanofiltration, and reverse osmosis membrane elements by complex impurities in coal chemical high-salt wastewater. The system can operate stably for a long period of time, reducing the cost of membrane cleaning, replacement, and maintenance.

[0016] Sodium hypochlorite is produced by electrolysis of concentrated sodium chloride water for internal use, realizing the resource utilization and revenue generation of salt; divalent miscellaneous salts are rendered harmless through high-temperature calcination, transforming hazardous waste into general solid waste that can be reused, significantly reducing the amount of hazardous waste transported for disposal and substantially reducing hazardous waste disposal costs.

[0017] All reverse osmosis permeate and evaporation crystallization condensate are returned to the front-end homogenization equalization tank as process water, significantly reducing the amount of fresh water supplied to the system, which meets the requirements of the coal chemical industry's water conservation and energy saving policy.

[0018] Equipped with an independent waste residue filter press unit, it collects sludge and flotation scum from sedimentation tanks in a unified manner, and transports them off-site in a standardized manner after dewatering by plate and frame filter press, avoiding secondary pollution of soil and groundwater caused by the random dumping of sludge containing high salt and high organic matter.

[0019] Equipped with a complete acid and alkali and chemical dosing unit, it can precisely adjust the dosage of liquid alkali, hydrochloric acid, and desiliconization and defluorination agents according to the real-time water quality of the influent. It has strong adaptability to the working conditions of large fluctuations in fluoride, silicon, and TDS in high-salt wastewater from coal chemical industry, and the treated water quality is stable and controllable.

[0020] The ultrafiltration concentrate is sent to the plant's biochemical system for degradation, and all clean water and condensate are internally recycled and reused. The system does not discharge high-salt waste liquid directly, meeting the strictest domestic coal chemical wastewater discharge standards and helping enterprises create green factories.

[0021] The method for deep treatment of high-salinity wastewater from coal chemical industry provided in this application, because it adopts the high-salinity wastewater deep treatment system for coal chemical industry in this application, also includes all the above-mentioned advantages of the high-salinity wastewater deep treatment system for coal chemical industry. Attached Figure Description

[0022] Figure 1 A flowchart of a coal chemical high-salt wastewater deep treatment system provided in the embodiments of this application; Detailed Implementation The technical solutions of this application will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0023] The following is combined with Figure 1 This application describes the coal chemical high-salt wastewater deep treatment system provided in the embodiments.

[0024] The coal chemical high-salt wastewater deep treatment system provided in this application includes a chemical defluorination and desiliconization unit, an air flotation unit, a resin adsorption unit, and a multi-stage membrane treatment unit connected sequentially along the wastewater flow direction, as well as a sodium hypochlorite preparation unit and a miscellaneous salt crystallization and harmless treatment unit respectively connected to the multi-stage membrane treatment unit; and a waste residue pressure filtration unit and an acid-base and chemical dosing unit are also provided.

[0025] The chemical defluorination and desiliconization unit is the core pretreatment unit of this system. It is used to receive high-salt raw water from coal chemical industry, and remove silicon ions and fluoride ions from the water by adding compound defluorination and desiliconization agents and adjusting the pH with acid and alkali. Sludge impurities are generated by sedimentation and separation. The chemical defluorination and desiliconization unit includes a homogenization equalization tank, a dosing tank, and an inclined plate sedimentation tank connected sequentially along the water flow. The supernatant of the inclined plate sedimentation tank is connected to the pH adjustment tank, and a sludge outlet is located at the bottom of the inclined plate sedimentation tank. The homogenization equalization tank is used to homogenize and adjust the raw water and process water to balance water quality fluctuations. The dosing tank adds liquid alkali and a compound of magnesium chloride and polyaluminum chloride to create an alkaline precipitation environment for the removal of silicon and fluoride. The inclined plate sedimentation tank allows the silicon and fluoride precipitates to settle by gravity. The pH adjustment tank adds dilute hydrochloric acid to restore the wastewater to the neutral range to meet the pH requirements of the downstream air flotation and resin influent. The bottom sludge outlet is connected to the waste residue filter press unit to discharge the settled sludge.

[0026] The inlet of the air flotation unit is connected to the outlet of the chemical defluorination and desiliconization unit to further remove suspended particulate matter and emulsified oil pollutants from the wastewater, generating scum during the process. The air flotation unit contains a dissolved air booster pump, an air compressor, an air flotation tank, a dissolved air release device, and a scum scraper. The air compressor is connected to the dissolved air booster pump pipeline, and the outlet of the dissolved air booster pump extends into the air flotation tank and is connected to the dissolved air release device, generating 5-15μm microbubbles. These bubbles adsorb suspended solids and oil droplets, which float to the surface. The scum scraper continuously removes scum from the surface of the air flotation tank, and the scum is then transported to the waste residue filter press unit.

[0027] The inlet of the resin adsorption unit is connected to the outlet of the air flotation unit, which is used to deeply adsorb and remove organic COD pollutants from wastewater, greatly reducing the risk of organic pollution in the downstream membrane system.

[0028] The resin adsorption unit includes a precision filter and an adsorption tower arranged sequentially along the water flow. The adsorption tower is filled with composite acrylate-based macroporous COD removal resin. The adsorption tower is equipped with a desorption and regeneration reagent tank group. The air flotation effluent first passes through the filter to intercept fine particles, and then enters the resin tower to adsorb large molecular organic matter. After the resin is saturated, 30% liquid alkali is delivered into the tower by the regeneration reagent tank group to complete the desorption and regeneration. The resin can be recycled and reused.

[0029] The inlet of the multi-stage membrane treatment unit is connected to the outlet of the resin adsorption unit. It is the core module for salt separation and concentration in the system. It is used to separate monovalent and divalent salts in wastewater and concentrate brine. It can separate and produce four types of materials: ultrafiltration concentrate, nanofiltration concentrate containing divalent salts, sodium chloride reverse osmosis concentrate, and reverse osmosis permeate.

[0030] The multi-stage membrane treatment unit includes ultrafiltration membrane units, nanofiltration membrane units, and reverse osmosis membrane units connected in series along the water flow.

[0031] The ultrafiltration membrane unit's concentrate outlet is connected to the plant's biochemical system (ultrafiltration concentrate has low salt content, is rich in organic matter, and undergoes biochemical degradation); the nanofiltration membrane unit's concentrate outlet is connected to the salt crystallization and harmless treatment unit (nanofiltration concentrate is rich in divalent salts such as sulfate); the reverse osmosis membrane unit's concentrate outlet is connected to the sodium hypochlorite preparation unit (reverse osmosis concentrate is rich in monovalent sodium chloride); the reverse osmosis membrane unit's permeate outlet is recirculated to the chemical defluorination and desiliconization unit for use as process water for reuse.

[0032] The inlet of the sodium hypochlorite preparation unit is connected to the reverse osmosis concentrate outlet of the multi-stage membrane treatment unit. This is used to prepare sodium hypochlorite disinfectant by electrolysis of concentrated sodium chloride solution, which is then supplied to the plant for disinfection of wastewater and circulating water.

[0033] The sodium hypochlorite preparation unit includes a sodium hypochlorite generator, a sodium hypochlorite storage tank, and a transfer pump. Reverse osmosis sodium chloride concentrate is fed into the generator for electrolysis to generate sodium hypochlorite solution. The finished solution is temporarily stored in the storage tank and then transported to various disinfection points in the plant area via the transfer pump.

[0034] The feed inlet of the mixed salt crystallization and harmless treatment unit is connected to the nanofiltration concentrate outlet of the multi-stage membrane treatment unit. It is used to vacuum evaporate and crystallize the concentrate enriched with divalent salts, precipitate solid mixed salts, and perform dry and high-temperature calcination harmless treatment on the mixed salts, transforming hazardous waste mixed salts into general solid waste that can be utilized by resources.

[0035] The mixed salt crystallization and harmless treatment unit includes a vacuum crystallizer, heater, condenser, centrifuge, vibrating fluidized bed dryer, and high-temperature calcination rotary kiln. Nanofiltration concentrate enters the vacuum crystallizer, is heated by the heater to evaporate the water, and the gas phase enters the condenser to condense and recover the condensate back to the front end. After the salt slurry reaches the standard solid content, it is sent to the centrifuge for solid-liquid separation. The solid mixed salt is dried by the fluidized bed and then sent to the rotary kiln for high-temperature calcination to completely decompose the residual organic matter in the salt.

[0036] The waste residue filter press unit is connected to the sludge outlet of the chemical defluorination and desiliconization unit and the scum outlet of the air flotation unit, respectively, for the unified collection of settled sludge and air flotation scum, which are then dewatered by filter press and transported off-site for disposal. The waste residue filter press unit includes a sludge tank, a sludge transfer pump, and a plate and frame filter press; the sludge and scum first enter the sludge tank for temporary storage, and then are sent to the plate and frame filter press for dewatering by the transfer pump. The moisture content of the sludge cake is controlled to be below 80% before being transported off-site for disposal.

[0037] The acid / alkali and chemical dosing unit is connected to the chemical defluorination and desiliconization unit and the air flotation unit, respectively, and is used to add hydrochloric acid, liquid alkali, combined desiliconization and defluorination agents, and air flotation aids to the upstream processes. The acid / alkali and chemical dosing unit includes various chemical storage tanks, metering pumps, and stirring devices; various chemicals are stored in the tanks, the stirring device ensures uniform mixing of chemicals, and the metering pumps precisely control the dosage of chemicals to adapt to different water quality fluctuation conditions.

[0038] Based on the same general inventive concept, this application also provides a method for the deep treatment of high-salinity wastewater from coal chemical industry. The method employs the aforementioned deep treatment system for high-salinity wastewater from coal chemical industry to treat the wastewater, and includes the following complete treatment steps: S1, Chemical defluorination and desilication pretreatment High-salinity raw water from coal chemical plants is sent to the homogenization and equalization tank of the chemical defluorination and desiliconization unit, where it is mixed and homogenized with process water to balance fluctuations in TDS, fluoride, silicon, and COD. Then, liquid alkali is added to the dosing tank to adjust the system pH to 10-11, followed by the addition of magnesium chloride and polyaluminum chloride compound defluorination and desiliconization agents. Silicon and fluoride ions precipitate as hydroxides. The mixed wastewater flows by gravity into an inclined plate sedimentation tank for gravity settling, and the bottom sludge is transported to the waste residue filter press unit. The supernatant from the sedimentation tank enters the pH adjustment tank, where dilute hydrochloric acid is added to adjust the pH to 6-9. After meeting the standards, the effluent is sent to the air flotation unit.

[0039] S2, Air flotation impurity removal treatment After pH adjustment, the wastewater enters the air flotation unit, where an air compressor and a dissolved air booster pump work together to generate dissolved air water. This dissolved air release device generates 5-15μm microbubbles. The bubbles adsorb suspended particulate matter and emulsified oil in the water and float to the surface to form scum. The scum is continuously collected by a scum scraper and transported to the waste sludge filter press unit. The air flotation unit has a removal rate of over 90% for suspended solids and oil pollutants. The sludge and scum are collected together in a sludge tank and dewatered by a plate and frame filter press. The sludge cake with a moisture content of less than 80% is transported off-site for disposal.

[0040] S3, Resin-based COD Removal The effluent from the air flotation process first passes through a 10μm precision filter to intercept fine impurities, and then is sent to an adsorption tower filled with composite acrylate-based macroporous resin. The wastewater flow rate is controlled at 5 BV / h. The resin specifically adsorbs large molecular organic COD in the wastewater, significantly reducing the organic pollution load of the downstream membrane system. After the resin is saturated (saturation capacity 200 BV), it is desorbed and regenerated by passing 30% liquid alkali. After regeneration, the resin can be reused in the adsorption process.

[0041] S4, Multi-stage membrane salt concentration Wastewater, after organic matter has been removed by resin, sequentially enters the ultrafiltration membrane unit, nanofiltration membrane unit, and reverse osmosis membrane unit for salt separation and concentration. 1) The ultrafiltration membrane unit adopts a tubular ultrafiltration membrane, which can retain large molecular pollutants with a molecular weight >1000Da and fine suspended solids, with a COD rejection rate of 70% and a water production rate of 85%. The ultrafiltration concentrate has low salt content and high organic matter concentration, and is sent to the plant's biochemical system for degradation. The ultrafiltration permeate is sent to the nanofiltration membrane unit. 2) The nanofiltration membrane unit retains divalent ions and organic pollutants of 80-1000 Da, with a desalination rate of 97% and a water production rate of 75%; the nanofiltration concentrate is enriched with divalent sulfate and transported to the miscellaneous salt crystallization and harmless treatment unit; the nanofiltration permeate (sodium chloride monovalent salt solution) is sent to the reverse osmosis membrane unit. 3) The reverse osmosis membrane unit efficiently retains monovalent sodium chloride, with a desalination rate of 99.5% and a water production rate of 60%. The purified water produced by reverse osmosis is returned to the chemical defluorination and desiliconization unit as homogenized process water. The reverse osmosis concentrate is concentrated to a 7% sodium chloride solution and then sent to the sodium hypochlorite preparation unit.

[0042] S5, Sodium hypochlorite resource utilization preparation The 7% sodium chloride concentrate produced by reverse osmosis is diluted with process water to control the sodium chloride concentration to be stable at 2%-3% before being sent to the sodium hypochlorite generator. Through electrolysis, a sodium hypochlorite solution with a mass fraction of about 1% is generated, which is stored in a storage tank and then supplied to the plant's circulating water and wastewater treatment plant for disinfection, thus realizing the resource utilization of sodium chloride in wastewater.

[0043] S6. Harmless treatment of mixed salt crystals The concentrated divalent salt water discharged from the nanofiltration unit is sent to the vacuum crystallization separator of the mixed salt crystallization and harmless treatment unit; the system maintains a vacuum of 0.06 MPa, and the heater heats the wastewater to 80°C for circulation evaporation; the gas phase generated by evaporation enters the condenser for cooling, and the condensate is returned to the front-end chemical defluorination and desiliconization unit for reuse; when the solid content of the salt slurry in the crystallization separator exceeds 15%, the salt slurry is sent to a centrifuge for solid-liquid separation; the separated solid mixed salt enters the vibrating fluidized bed dryer to remove free water; the dried mixed salt is mixed with fly ash and then sent to a high-temperature calcination rotary kiln for calcination at 850°C-1200°C for 10-12 hours to completely decompose the residual organic matter in the salt; after calcination, the mixed salt is converted into general solid waste, which can be used as a filter guide material, granular filler aggregate, and wastewater treatment adsorption substrate for resource utilization.

[0044] The following is a detailed explanation using the treatment of high-salinity wastewater generated by a coal chemical project as an example.

[0045] The main pollutant indicators of high-salinity wastewater generated by a certain coal chemical project are as follows:

[0046] The concentration indicators of major pollutants in high-salt wastewater from a certain coal chemical plant are shown in the table above. The system described in this invention includes, in sequence, a chemical defluorination and desiliconization unit, a high-efficiency air flotation unit, a special resin adsorption unit, a multi-stage membrane treatment unit, a mixed salt crystallization unit, a mixed salt harmless treatment unit, a sodium hypochlorite preparation unit, a waste residue pressure filtration unit, and an acid / alkali and chemical dosing unit.

[0047] Based on the water quality of the high-salinity wastewater, a certain amount of process water is introduced into the homogenization and equalization tank for preparation (high-salinity water: process water = 1:4). After preparation, the wastewater is introduced into the chemical desiliconization and defluorination tank. Liquid alkali is added to adjust the pH to 10-11, and then desiliconization and defluorination agents are added to the tank. The desiliconization and defluorination agents (1400ppm) of polyaluminum chloride and magnesium chloride compound (1:8) are used to remove most of the silicon and fluoride ions in the wastewater. After sedimentation in the inclined plate sedimentation tank, the sludge is collected in the bottom sludge hopper and enters the sludge tank. The clear liquid enters the pH adjustment tank. Dilute hydrochloric acid is added to the pH adjustment tank to adjust the pH to 6-9, and then the wastewater is introduced into the high-efficiency air flotation unit.

[0048] In the high-efficiency air flotation unit, the air-to-water ratio is controlled at 1:3-1:5. The air flotation unit generates a large number of fine bubbles (5-15μm in diameter). Suspended particles rise to the water surface with the bubbles, forming foam scum, thereby separating suspended solids in the water. At the same time, air flotation can also remove oil pollutants from wastewater. The air flotation process has a removal rate of over 90% for suspended solids and oil pollutants. The scum generated by air flotation is pumped into a sludge tank.

[0049] The sludge and waste residue generated by the inclined plate sedimentation tank and the air flotation process are transported to the sludge tank for temporary storage via sludge pipelines. Then, they are pumped into the waste residue filter press unit by sludge pumps. After being dewatered by plate and frame filter press, the sludge cake is transported off-site for disposal once the moisture content is below 80%.

[0050] The effluent from the high-efficiency air flotation unit enters the special resin adsorption unit. After being filtered by a 10μm precision filter, the wastewater is pumped to the COD removal resin adsorption tower (resin filling volume is V1). The COD removal resin is a composite acrylate-based macroporous adsorption resin. The flow rate in the tower is controlled at 5V1 / h. The adsorbed effluent enters the COD removal resin product water tank and is pumped to the multi-stage membrane system unit. After the resin adsorption reaches saturation (200V1), the COD removal resin is desorbed and regenerated using 30% liquid alkali.

[0051] After most of the organic matter is removed by resin adsorption, the high-salt wastewater enters the multi-stage membrane system unit. First, it undergoes ultrafiltration, using a tubular ultrafiltration membrane structure. After passing through a precision filter (5μm) in the ultrafiltration system, the high-salt wastewater enters the ultrafiltration membrane. The ultrafiltration membrane has a pore size of approximately 0.01-0.1μm, a stable desalination rate of approximately 45%, a COD rejection rate of 70%, and a water production rate of 85%. It can remove large molecular pollutants with a molecular weight >1000Da and fine particulate suspended solids from the wastewater. The maximum operating pressure is 4.14MPa, and the maximum influent sludge density index (SDI) is 5. Ultrafiltration permeate enters the nanofiltration membrane system. The ultrafiltration concentrate has a low salt content but a high organic content and is then treated in the plant's biochemical process. The ultrafiltration permeate is further treated by the nanofiltration membrane system to obtain nanofiltration concentrate and nanofiltration permeate (sodium chloride solution). The nanofiltration membrane has a pore size of approximately 1nm-10nm and can retain pollutants with molecular weights of 80-1000Da and divalent ions, with a stable desalination rate of 97%, a permeate rate of 75%, and a maximum operating pressure of 41Bar. The nanofiltration concentrate enters the mixed salt crystallization unit, and the nanofiltration permeate enters the reverse osmosis membrane system for concentration. The reverse osmosis membrane has a pore size of approximately 0.1nm and can retain pollutants with molecular weights less than 80Da and monovalent ions, with a stable desalination rate of 99.5%, a permeate rate of 60%, and a maximum operating pressure of 41Bar. After concentration by the reverse osmosis membrane, the wastewater finally produces approximately 7% reverse osmosis concentrate (sodium chloride solution). The reverse osmosis permeate is used as process water and is reused in the equalization tank as distribution water.

[0052] After the reverse osmosis concentrate and process water are mixed, the sodium chloride concentration is kept at 2%-3% and then introduced into the sodium hypochlorite generator. The sodium hypochlorite solution (about 1%) is prepared by electrolysis and used for disinfection in the facility.

[0053] In the membrane system, nanofiltration concentrate enters the mixed salt crystallization unit, is pumped to the mixed salt crystallization separator by the mixed salt wastewater lift pump, and then to the heater by the forced circulation pump. The wastewater circulates in the crystallization separator and the heater. It is heated to 80°C by steam in the shell side of the heater. The gas-liquid mixture is separated by the gas-liquid separator. The cooling circulating water is passed into the steam condenser. The gas phase is condensed in the condenser to produce steam condensate, which is reused in the homogenization equalization tank as blending water. The liquid phase is returned to the crystallization separator to continue evaporation. A vacuum pump is started to establish an evaporation crystallization vacuum system (vacuum degree 0.06MPa). The high-salt wastewater continuously evaporates in the crystallizer. Samples are taken periodically at the sampling port to test the solid content of the crystallized salt. When the solid content of the crystallized salt in the crystallizer is greater than 15%, the mother liquor of the mixed salt is fed into a centrifuge through a discharge pump to separate the mother liquor and the mixed salt. The produced mixed salt is dried by a vibrating fluidized bed dryer. After drying, it is mixed with fly ash admixture in proportion and then calcined at a calcination temperature of 850℃-1200℃. The material is rendered harmless after calcination for 10-12 hours. The produced waste salt is general solid waste and can be used as a filter guide material, granular filler material, or wastewater treatment adsorption substrate.

[0054] The aforementioned system and method for the deep treatment and resource utilization of high-salinity wastewater from coal chemical plants separates sodium chloride and other salts. Sodium chloride is then used to prepare sodium hypochlorite for resource utilization, while the other salts are calcined and rendered harmless before being used as filtration and permeation materials, granular fillers, or wastewater treatment adsorption substrates for comprehensive utilization. Simultaneously, this system and method do not generate secondary pollution. The concentrated water produced by the ultrafiltration membrane enters the biological treatment system, and the reverse osmosis permeate can be reused at the upstream end for water distribution and reagent preparation. This system and method not only recovers salts from high-salinity wastewater from coal chemical plants, achieving resource recycling, but also significantly reduces the cost of high-salinity wastewater treatment. Furthermore, the generation of sodium hypochlorite creates significant economic benefits, contributing to cost reduction and efficiency improvement for enterprises.

[0055] In the description of this application, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc., indicating the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application.

[0056] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0057] In this application, unless otherwise expressly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection, an electrical connection, or a connection that allows communication between components; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise expressly limited. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0058] In this application, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0059] Although embodiments of this application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting this application. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of this application.

Claims

1. A deep treatment system for high-salinity wastewater from coal chemical industry, characterized in that, It includes a chemical defluorination and desiliconization unit, an air flotation unit, a resin adsorption unit, and a multi-stage membrane treatment unit connected sequentially along the wastewater flow direction, as well as a sodium hypochlorite preparation unit and a miscellaneous salt crystallization and harmless treatment unit respectively connected to the multi-stage membrane treatment unit. The chemical defluorination and desiliconization unit is used to receive high-salinity raw water from coal chemical industry, remove silicon and fluoride ions from the water by adding chemicals, and precipitate and separate sludge impurities. The inlet of the air flotation unit is connected to the outlet of the chemical defluorination and desiliconization unit, which is used to further remove suspended particulate matter and oil pollutants from the wastewater and generate scum. The inlet of the resin adsorption unit is connected to the outlet of the air flotation unit, and is used to adsorb and remove organic COD pollutants from the wastewater. The inlet of the multi-stage membrane treatment unit is connected to the outlet of the resin adsorption unit, which is used to realize wastewater desalination and concentration, and separate ultrafiltration concentrate, nanofiltration concentrate containing divalent salt, sodium chloride reverse osmosis concentrate and reverse osmosis permeate. The inlet of the sodium hypochlorite preparation unit is connected to the reverse osmosis concentrate outlet of the multi-stage membrane treatment unit, and is used to prepare sodium hypochlorite by electrolysis of concentrated sodium chloride solution. The feed inlet of the mixed salt crystallization and harmless treatment unit is connected to the nanofiltration concentrate outlet of the multi-stage membrane treatment unit, which is used to evaporate and crystallize the divalent salt concentrate to produce mixed salt, and to dry and calcine the mixed salt to render it harmless.

2. The deep treatment system for high-salinity wastewater from coal chemical industry according to claim 1, characterized in that, The chemical defluorination and desiliconization unit includes a homogenization and equalization tank, a dosing tank, and an inclined plate sedimentation tank connected in sequence. The supernatant of the inclined plate sedimentation tank is connected to the pH adjustment tank, and a sludge outlet is provided at the bottom of the inclined plate sedimentation tank.

3. The deep treatment system for high-salinity wastewater from coal chemical industry according to claim 1, characterized in that, The dissolved air flotation unit includes a dissolved air booster pump, an air compressor, a flotation tank, a dissolved air release device, and a scum scraper. The air compressor is connected to the dissolved air booster pump pipeline. The outlet end of the dissolved air booster pump extends into the flotation tank and is connected to the dissolved air release device. The scum scraper is used to scrape off the scum on the surface of the flotation tank.

4. The deep treatment system for high-salinity wastewater from coal chemical industry according to claim 1, characterized in that, The resin adsorption unit includes a filter and an adsorption tower arranged in sequence. The adsorption tower is filled with a composite acrylate-based macroporous COD removal resin, and the adsorption tower is also equipped with a desorption and regeneration agent tank group.

5. The deep treatment system for high-salinity wastewater from coal chemical industry according to claim 1, characterized in that, The multi-stage membrane treatment unit includes an ultrafiltration membrane unit, a nanofiltration membrane unit, and a reverse osmosis membrane unit connected in series. The concentrate outlet of the ultrafiltration membrane unit is connected to the plant's biochemical system. The concentrate outlet of the nanofiltration membrane unit is connected to the miscellaneous salt crystallization and harmless treatment unit. The concentrate outlet of the reverse osmosis membrane unit is connected to the sodium hypochlorite preparation unit. The permeate outlet of the reverse osmosis membrane unit is recirculated to the chemical defluorination and desiliconization unit.

6. The deep treatment system for high-salinity wastewater from coal chemical industry according to claim 1, characterized in that, The sodium hypochlorite preparation unit includes a sodium hypochlorite generator, a sodium hypochlorite storage tank, and a delivery pump.

7. The system for deep treatment and resource utilization of high-salinity wastewater from coal chemical industry according to claim 1, characterized in that, The mixed salt crystallization and detoxification unit includes a vacuum crystallization separator, a heater, a condenser, a centrifuge, a vibrating fluidized bed dryer, and a high-temperature calcining rotary kiln.

8. The deep treatment system for high-salinity wastewater from coal chemical industry according to claim 1, characterized in that, It also includes a waste residue filter press unit, which is connected to the sludge outlet of the chemical defluorination and desiliconization unit and the scum outlet of the air flotation unit, respectively, for collecting sludge and scum and dewatering them for external transport; the waste residue filter press unit includes a sludge tank, a sludge transfer pump and a plate and frame filter press.

9. The deep treatment system for high-salinity wastewater from coal chemical industry according to claim 1, characterized in that, It also includes an acid-base and chemical dosing unit, which is connected to the chemical defluorination and desiliconization unit and the air flotation unit respectively, and is used to add hydrochloric acid, liquid alkali, and desiliconization and defluorination composite agents; the acid-base and chemical dosing unit includes a chemical storage tank, a metering pump and a stirring device.

10. A method for deep treatment of high-salinity wastewater from coal chemical industry, characterized in that, The coal chemical high-salinity wastewater deep treatment system according to any one of claims 1-9 includes the following steps: S1. Chemical defluorination and desiliconization pretreatment: High-salt wastewater is sent to the chemical defluorination and desiliconization unit, where chemicals are added to remove silicon and fluoride ions, and sludge is produced by sedimentation; the effluent is sent to the air flotation unit after pH adjustment. S2. Air flotation for impurity removal: The air flotation unit separates suspended solids and oils from the water, producing scum; sludge and scum are sent to the waste residue filter press unit for dewatering. S3. Resin-based deep COD removal: The effluent from the air flotation enters the resin adsorption unit, where most organic pollutants are adsorbed and removed. After the resin is saturated, it is regenerated using alkaline agents. S4. Multi-stage membrane salt concentration: The resin effluent enters the multi-stage membrane treatment unit and is treated step by step by ultrafiltration, nanofiltration and reverse osmosis; the ultrafiltration concentrate is sent to the biochemical system, the nanofiltration concentrate is sent to the miscellaneous salt crystallization and harmless treatment unit, the sodium chloride reverse osmosis concentrate is sent to the sodium hypochlorite preparation unit, and the reverse osmosis permeate is returned to the front end. S5. Sodium hypochlorite preparation: Sodium chloride reverse osmosis concentrate is adjusted to the desired concentration and then sent to the sodium hypochlorite preparation unit for electrolysis to generate sodium hypochlorite solution for plant disinfection. S6. Harmless treatment of mixed salt crystals: Nanofiltration concentrate enters the mixed salt crystallization and harmless treatment unit for vacuum evaporation and crystallization. The salt crystals are dried and calcined at high temperature to be converted into general solid waste for resource utilization. The crystallization condensate is returned to the upstream process for reuse.

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