Phosphorus-containing wastewater treatment system

Abstract

The invention relates to the technical field of wastewater purification, in particular to a phosphorus-containing wastewater treatment system. Comprising a pre-purification unit, a deep purification unit, a membrane concentration unit and a multi-effect evaporation unit which are sequentially connected, the pre-purification unit is used for diluting phosphorus-containing wastewater and filtering impurities; the deep purification unit is used for receiving the wastewater treated by the pre-purification unit and filtering multivalent metal cations, macromolecular substances and divalent salts in the wastewater; the membrane concentration unit is used for receiving the wastewater treated by the deep purification unit and evaporating water at low temperature under vacuum negative pressure and steam heating so as to concentrate phosphoric acid; and the multi-effect evaporation unit is used for receiving the phosphoric acid concentrated by the membrane concentration unit and further evaporating water under steam heating so as to further concentrate the phosphoric acid, so that a phosphoric acid product with the concentration reaching the selling standard is obtained. The method is simple in process and low in operation energy consumption, phosphorus-containing wastewater can be efficiently recycled, pollution to the environment is reduced, and economic benefits are improved through recycling of phosphorus resources.

Description

Technical Field

[0001] The present application relates to the technical field of wastewater purification, and in particular to a phosphorus-containing wastewater treatment system. Background Art

[0002] Wastewater from cleaning components in the electronics industry primarily consists of phosphorus-containing wastewater and waste hydrochloric acid. Phosphorus-containing wastewater is a challenging industrial wastewater to treat. Traditionally, it is discharged directly or simply treated before being released into the environment. This leads to organic matter and heavy metal ion contamination of soil and water, harming the ecological environment. This treatment approach lacks effective waste treatment and recycling measures, contributing to the environmental pollution of phosphorus-containing wastewater.

[0003] Phosphorus-containing wastewater primarily originates from waste acid generated by component cleaning in electronics companies. Although its concentration meets the requirements of the Industrial Phosphoric Acid Standard (GB / T2091-2008), it still contains minute impurities such as inorganic particles, suspended solids, inorganic silicon, and colloids, as well as metal ions such as iron, aluminum, and zinc. Purification and refining are necessary. Furthermore, because phosphoric acid is a medium-strong acid with certain corrosive and oxidizing properties and high viscosity, high-concentration phosphorus-containing wastewater cannot be directly purified using nanofiltration membranes. Instead, it must be diluted before purification and refining, and finally concentrated to a phosphoric acid product that meets the standards.

[0004] Currently, the most common phosphoric acid treatment process is acid concentration and purification. For example, Chinese patent application No. CN212246635U discloses a clean and efficient phosphorus-containing wastewater resource recovery technology. While this technology reduces equipment investment and personnel expenses, the recovery efficiency is low, and most recovery processes use chemical neutralization, which can affect the surrounding environment. Chinese patent application No. CN115636398A discloses a phosphorus-containing wastewater treatment process. While this technology improves the recovery rate and efficiency of phosphorus-containing wastewater, it requires a high equipment investment and does not provide information on the acceptable content or intended use of the recovered phosphoric acid.

[0005] Therefore, a method for treating phosphorus-containing wastewater that can more effectively recycle phosphorus-containing wastewater and cause less pollution to the environment is needed. Summary of the Invention

[0006] In view of this, the embodiments of the present application provide a phosphorus-containing wastewater treatment system that can more effectively recycle phosphorus-containing wastewater, remove organic matter and heavy metal ions in phosphorus-containing wastewater, reduce pollution to the environment, and achieve improved economic benefits through the recycling and utilization of phosphorus resources.

[0007] The embodiment of the present application provides a phosphorus-containing wastewater treatment system, comprising a pre-purification unit, a deep purification unit, a membrane concentration unit, and a multi-effect evaporation unit connected in sequence; The pre-purification unit is used to dilute the phosphorus-containing wastewater and filter impurities; The deep purification unit is used to receive the wastewater treated by the pre-purification unit and filter out multivalent metal cations, macromolecular substances and divalent salts in the wastewater; The membrane concentration unit is used to receive the wastewater treated by the deep purification unit and evaporate water at low temperature under vacuum negative pressure and steam heating to concentrate phosphoric acid; The multi-effect evaporation unit is used to receive the phosphoric acid concentrated by the membrane concentration unit, and further evaporate water under steam heating to further concentrate the phosphoric acid to obtain a phosphoric acid product with a concentration that meets the sales standard.

[0008] In one embodiment, the pre-purification unit includes a phosphoric acid dilution tank and a ceramic tube membrane device; The input end of the phosphoric acid dilution tank is connected to pure water and phosphorus-containing wastewater, the output end is connected to the input end of the ceramic tube membrane device, and the output end of the ceramic tube membrane device is connected to the input end of the deep purification unit; The phosphoric acid dilution tank is used to dilute the phosphorus-containing wastewater using the pure water; The ceramic tube membrane device is used to filter impurities from the phosphorus-containing wastewater diluted in the phosphoric acid dilution tank, wherein the impurities include at least one of insoluble particles, colloids and inorganic silicon.

[0009] In one embodiment, the ceramic membrane used in the ceramic tubular membrane device is an acid-resistant special inorganic tubular membrane. The ceramic tubular membrane device separates substances through the screening effect of its own porous inorganic medium and the attached membrane layer.

[0010] In one embodiment, the deep purification unit includes a nanofiltration membrane device, and the nanofiltration membrane device includes a nanofiltration membrane device stage 1, a nanofiltration membrane device stage 2, and a nanofiltration membrane device permeate tank; The input end of the first section of the nanofiltration membrane device is connected to the output end of the pre-purification unit, the concentrated liquid output end of the first section of the nanofiltration membrane device is connected to the input end of the second section of the nanofiltration membrane device, the permeate output ends of the first section of the nanofiltration membrane device and the second section of the nanofiltration membrane device are connected to the input end of the permeate tank of the nanofiltration membrane device, and the output end of the permeate tank of the nanofiltration membrane device is connected to the input end of the membrane concentration unit.

[0011] In one embodiment, the membrane concentration unit includes an MD membrane evaporation device and a first concentration phosphoric acid recovery tank; The input end of the MD membrane evaporation device is connected to the output end of the deep purification unit, the output end of the MD membrane evaporation device is connected to the input end of the first concentration phosphoric acid recovery tank, and the output end of the first concentration phosphoric acid recovery tank is connected to the input end of the multi-effect evaporation unit; The MD membrane evaporation device is used to evaporate water in the phosphoric acid from the deep purification unit under vacuum negative pressure and steam heating to concentrate the phosphoric acid to a first concentration; The first-concentration phosphoric acid recovery tank is used to collect a phosphoric acid solution of the first concentration.

[0012] In one embodiment, the multiple-effect evaporation unit includes a multiple-effect evaporation device, which includes a recovery acid evaporation chamber, a recovery acid cooler, a recovery acid condensate preheater, a recovery acid heater, a vacuum device, a concentrated phosphoric acid pump, and a phosphoric acid product tank; The output end of the multi-effect evaporation device is connected to a second-concentration phosphoric acid recovery tank, and the second-concentration phosphoric acid recovery tank outputs a phosphoric acid product that meets the sales standard.

[0013] In one embodiment, the cold side inlet of the recovery acid cooler is connected to the first concentration phosphoric acid output by the membrane concentration unit, the cold side outlet is connected to the feed end of the multi-effect evaporation unit, the hot side inlet is connected to the second concentration phosphoric acid output by the multi-effect evaporation unit, and the hot side outlet is connected to the second concentration phosphoric acid recovery tank; The recovered acid cooler is used to use the first-concentration phosphoric acid output from the membrane concentration unit as a cooling medium to heat-exchange and cool the second-concentration phosphoric acid output from the multi-effect evaporation unit.

[0014] In one embodiment, it further comprises a concentrate tank and a neutralization reactor; The concentrated liquid produced by the deep purification unit and the membrane concentration unit is output to the concentrated liquid tank, the sewage output end of the concentrated liquid tank is connected to the neutralization reaction tank, and the purification output end of the concentrated liquid tank is connected to the circulating wastewater input end of the pre-purification unit; The concentrate tank is used to separate the high-concentration suspended solids and high-cations in the concentrate and output them to the neutralization reaction tank, and output the concentrate after the separation of the high-concentration suspended solids and high-cations to the pre-purification unit; The neutralization reaction tank is used to neutralize waste liquid containing high concentration of suspended solids and high cations through lime milk and generate calcium phosphate precipitate. The calcium phosphate precipitate and supernatant generated by the neutralization reaction tank are output to the incineration device for incineration.

[0015] In one embodiment, it also includes a steam condensate water tank, an evaporation condensate water tank and an RO dephosphorization device; The steam condensate output ends of the membrane concentration unit and the multi-effect evaporation unit are connected to the input end of the steam condensate tank, and the output end of the steam condensate tank is connected to the pure water input pipe of the pre-purification unit; The membrane concentration unit and the evaporation condensation water output end are connected to the input end of the evaporation condensation water tank, the output end of the evaporation condensation water tank is connected to the pure water input pipeline of the pre-purification unit, and / or to the water inlet end of the RO dephosphorization device, and the concentrated water output end of the RO dephosphorization device is connected to the filtrate tank of the ceramic tube membrane device of the deep purification unit.

[0016] In one embodiment, a waste gas absorption tower is further included. The acidic waste gas generated by the pre-purification unit, deep purification unit, membrane concentration unit and multi-effect evaporation unit is input into the waste gas absorption tower, and the output end of the waste gas absorption tower is used to connect to the waste gas incineration device.

[0017] The phosphorus-containing wastewater treatment system provided in the embodiment of the present application includes a pre-purification unit, a deep purification unit, a membrane concentration unit and a multi-effect evaporation unit connected in sequence; the pre-purification unit is used to dilute the phosphorus-containing wastewater and filter impurities; the deep purification unit is used to receive the wastewater treated by the pre-purification unit and filter out multivalent metal cations, macromolecules and divalent salts in the wastewater; the membrane concentration unit is used to receive the wastewater treated by the deep purification unit and evaporate water at low temperature under vacuum negative pressure and steam heating to concentrate phosphoric acid; the multi-effect evaporation unit is used to receive the phosphoric acid concentrated by the membrane concentration unit and further evaporate water under steam heating to further concentrate the phosphoric acid to obtain a phosphoric acid product with a concentration that meets the sales standard. Among them, the pre-purification unit is responsible for initial concentration adjustment and coarse impurity removal, creating conditions for subsequent precision processing; the deep purification unit specifically removes key impurities such as metal ions, macromolecules and salts to improve the purity of phosphoric acid; the membrane concentration unit uses the characteristics of vacuum and low-temperature evaporation to achieve initial concentration of phosphoric acid at low energy consumption; the multi-effect evaporation unit provides strong evaporation capacity to ensure that the final product reaches the required high concentration standard. This structured treatment pathway is the technical foundation for efficient, stable, and controllable phosphoric acid recovery and concentration. It maximizes heat recovery and offers lower operating energy consumption than conventional evaporation technologies. It offers advantages in environmental protection, resource recovery, and economic benefits. It efficiently recycles phosphorus-containing wastewater, reduces environmental pollution, and improves economic benefits through the recycling of phosphorus resources. The phosphorus wastewater recovery process does not involve chemical reactions, making it safer and more efficient. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings required for use in the embodiments or descriptions of the prior art. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0019] Figure 1 This is a connection diagram of a phosphorus-containing wastewater treatment system provided in one embodiment of the present application. DETAILED DESCRIPTION

[0020] In the following description, specific details such as specific system structures and techniques are provided for purposes of illustration rather than limitation to facilitate a thorough understanding of the embodiments of the present application. However, it will be apparent to those skilled in the art that the present application may be implemented in other embodiments without these specific details. In other cases, detailed descriptions of well-known systems, devices, circuits, and methods are omitted to avoid obscuring the description of the present application with unnecessary detail.

[0021] It should be understood that when used in the present specification and the appended claims, the term "comprising" indicates the presence of described features, integers, steps, operations, elements and / or components, but does not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or collections thereof.

[0022] It will also be understood that the term "and / or" used in this specification and the appended claims refers to and includes any and all possible combinations of one or more of the associated listed items.

[0023] In addition, in the description of the present application specification and the appended claims, the terms "first", "second", "third", etc. are only used to distinguish the descriptions and cannot be understood as indicating or implying relative importance.

[0024] References to "one embodiment" or "some embodiments" in this specification mean that a particular feature, structure, or characteristic described in conjunction with that embodiment is included in one or more embodiments of the present application. Thus, phrases such as "in one embodiment," "in some embodiments," "in other embodiments," and "in other embodiments" appearing in various places in this specification do not necessarily refer to the same embodiment, but rather mean "one or more but not all embodiments," unless otherwise specifically emphasized. The terms "including," "comprising," "having," and variations thereof all mean "including but not limited to," unless otherwise specifically emphasized.

[0025] like Figure 1 As shown, a phosphorus-containing wastewater treatment system provided in an embodiment of the present application includes a pre-purification unit 1, a deep purification unit 2, a membrane concentration unit 3 and a multi-effect evaporation unit 4 connected in sequence; The pre-purification unit 1 is used to dilute the phosphorus-containing wastewater and filter impurities; The deep purification unit 2 is used to receive the wastewater treated by the pre-purification unit 1 and filter out the multivalent metal cations, macromolecular substances and divalent salts in the wastewater; The membrane concentration unit 3 is used to receive the wastewater treated by the deep purification unit 2, and evaporate the water at low temperature under vacuum negative pressure and steam heating to concentrate the phosphoric acid; The multi-effect evaporation unit 4 is used to receive the phosphoric acid concentrated by the membrane concentration unit 3 and further evaporate water under steam heating to further concentrate the phosphoric acid to obtain a phosphoric acid product with a concentration that meets the sales standard.

[0026] The embodiment of the present application decomposes the complex phosphorus-containing wastewater treatment process into four logical stages: pretreatment, deep impurity removal, initial concentration, and final refining. The pre-purification unit is responsible for initial concentration adjustment and coarse impurity removal, creating conditions for subsequent precision processing; the deep purification unit specifically removes key impurities such as metal ions, macromolecules, and salts to improve the purity of phosphoric acid; the membrane concentration unit utilizes the characteristics of vacuum and low-temperature evaporation to achieve initial concentration of phosphoric acid at low energy consumption; the multi-effect evaporation unit provides powerful evaporation capacity to ensure that the final product meets the required high concentration standards. This structured treatment path is the technical basis for achieving efficient, stable, and controllable phosphoric acid recovery and concentration. It can maximize heat recovery and has the characteristics of low operating energy consumption compared to conventional evaporation technology. It has advantages in environmental protection, resource recovery, and economic benefits. It can achieve efficient recycling and utilization of phosphorus-containing wastewater, reduce pollution to the environment, and achieve improved economic benefits through the recycling and utilization of phosphorus resources. In the recovery process of phosphorus-containing wastewater, no chemical reaction is involved, which is safer and more efficient.

[0027] In one embodiment, the pre-purification unit 1 includes a phosphoric acid dilution tank 101 and a ceramic tube membrane device 102; The input end of the phosphoric acid dilution tank 101 is connected to pure water and phosphorus-containing wastewater, and the output end is connected to the input end of the ceramic tube membrane device 102, and the output end of the ceramic tube membrane device 102 is connected to the input end of the deep purification unit 2; The phosphoric acid dilution tank 101 is used to dilute phosphorus-containing wastewater using pure water; The ceramic tube membrane device 102 is used to filter impurities from the phosphorus-containing wastewater diluted in the phosphoric acid dilution tank 101 , where the impurities include at least one of insoluble particles, colloids and inorganic silicon.

[0028] In application, phosphorus-containing wastewater enters the phosphoric acid dilution tank through a transfer pump. Pure water or evaporated condensate (preferred) is added to the tank to dilute the phosphoric acid concentration to about 15%. The dilute phosphoric acid enters the ceramic membrane device of the phosphoric acid pre-purification unit through a feed pump to intercept insoluble particles, colloids, inorganic silicon and other impurities in the waste acid, and the filtrate enters the filtrate tank of the ceramic tube membrane equipment.

[0029] The phosphoric acid dilution tank in this embodiment precisely controls the phosphoric acid concentration to a level suitable for subsequent membrane treatment by adding pure water. This prevents clogging or membrane damage that could result from high-concentration phosphoric acid directly entering the membrane system. The ceramic tubular membrane device utilizes its physical filtration mechanism to effectively intercept solid impurities such as insoluble particles, colloids, and inorganic silicon in the wastewater. This combination ensures that the feed liquid entering the deep purification unit meets the required concentration and cleanliness, reducing the burden on subsequent precision membrane treatment and extending its service life.

[0030] In one embodiment, the ceramic membrane used in the ceramic tube membrane device 102 is an acid-resistant special inorganic tubular membrane. The ceramic tube membrane device 102 separates substances through the screening effect of its own porous inorganic medium and the attached membrane layer.

[0031] In application, the ceramic membrane device of the phosphoric acid pre-purification unit uses an acid-resistant special inorganic tubular membrane. This type of membrane is an inorganic membrane with special selective separation function. It adopts a dynamic "cross-flow filtration" method that is completely different from traditional filtration methods such as "full filtration" and "cake filtration". It achieves substance separation through the screening effect of its own porous inorganic medium and the attached membrane layer.

[0032] The embodiments of the present application use acid-resistant special inorganic tubular membrane materials, which enable it to operate stably for a long time in a highly acidic and potentially corrosive environment such as phosphorus-containing wastewater. The membrane's own porous inorganic medium and its surface membrane layer are used to separate substances through a screening effect. This is a purely physical process that does not require additional chemicals, avoids secondary pollution, and has a clear and reliable separation mechanism, and is relatively simple to maintain. Compared with dead-end filtration (full filtration / cake filtration), the cross-flow filtration mode (dynamic filtration) can effectively slow down membrane fouling and maintain a higher membrane flux.

[0033] In one embodiment, the deep purification unit 2 includes a nanofiltration membrane device, which includes a nanofiltration membrane device stage 1 201, a nanofiltration membrane device stage 202, and a nanofiltration membrane device permeate tank 203; The input end of the first stage 201 of the nanofiltration membrane device is connected to the output end of the pre-purification unit 1, the concentrated liquid output end of the first stage 201 of the nanofiltration membrane device is connected to the input end of the second stage 202 of the nanofiltration membrane device, the permeate output ends of the first stage 201 of the nanofiltration membrane device and the second stage 202 of the nanofiltration membrane device are connected to the input end of the permeate tank 203 of the nanofiltration membrane device, and the output end of the permeate tank of the membrane device is connected to the input end of the membrane concentration unit 3.

[0034] In application, the phosphoric acid treated in the pre-purification unit is pressurized by the nanofiltration feed pump and enters the first stage of the nanofiltration membrane equipment of the phosphoric acid deep purification unit. Driven by pressure, the nanofiltration membrane will intercept impurities such as metal ions, phosphates, and silicone in the dilute phosphoric acid. The permeate of the first stage of the nanofiltration membrane equipment enters the permeate tank of the nanofiltration membrane equipment, and the concentrated liquid enters the second stage of the nanofiltration membrane equipment for further concentration and separation of impurities. The permeate enters the permeate tank of the nanofiltration membrane equipment together.

[0035] The embodiment of the present application uses the first stage of the nanofiltration membrane equipment as the main processing unit, which selectively intercepts small molecular impurities such as multivalent metal ions, phosphates and silicones under pressure, and most of the purified permeate enters the next unit. The concentrated liquid (rich in intercepted impurities) produced in the first stage is not discharged directly, but enters the second stage of nanofiltration for further concentration and separation. This two-stage series design maximizes the recovery rate of phosphoric acid (because the permeate produced in the second stage is also collected and reused), while concentrating the impurities to a smaller volume for subsequent disposal, significantly improving the resource utilization efficiency and impurity removal efficiency of the system. In one embodiment, the membrane concentration unit 3 includes an MD membrane evaporation device 301 and a first concentration phosphoric acid recovery tank 302; The input end of the MD membrane evaporation device 301 is connected to the output end of the deep purification unit 2, the output end of the MD membrane evaporation device 301 is connected to the input end of the first concentration phosphoric acid recovery tank 302, and the output end of the first concentration phosphoric acid recovery tank 302 is connected to the input end of the multi-effect evaporation unit 4; The MD membrane evaporation device 301 is used to evaporate water in the phosphoric acid from the deep purification unit 2 under vacuum negative pressure and steam heating to concentrate the phosphoric acid to a first concentration; The first concentration phosphoric acid recovery tank 302 is used to collect phosphoric acid solution of the first concentration.

[0036] In application, the deeply purified phosphoric acid is pumped to the feed solution tank of the MD membrane evaporation equipment in the membrane concentration unit. The MD membrane evaporation equipment, under the action of a vacuum pump, creates negative pressure, drawing phosphoric acid from the feed solution tank into the MD membrane evaporation equipment. Steam heating causes the water in the phosphoric acid to evaporate into water vapor at low temperatures. Driven by the steam pressure difference across the evaporation membrane, the water vapor continuously permeates the evaporation membrane, concentrating the phosphoric acid to a concentration above 50% and entering the first concentration phosphoric acid recovery tank 302, i.e., the 50% phosphoric acid recovery tank. The evaporation condensate and steam condensate generated during the evaporation of phosphoric acid in the MD membrane evaporation equipment are collected in the evaporation condensate tank and steam condensate tank, respectively. The evaporation condensate is preferentially returned to the phosphoric acid dilution tank for use as dilution water, while the steam condensate is returned to the phosphoric acid dilution tank as dilution water, diluting the phosphoric acid. When the evaporation condensate and steam condensate are used as phosphoric acid dilution water, the remaining evaporation condensate enters the evaporation condensate RO phosphorus removal equipment for treatment, the RO produced water is used as circulating water supplementary water, and the RO concentrated water is returned to the filtrate tank of the ceramic tube membrane equipment; the remaining steam condensate returns to the pure water jelly pipe in the plant area.

[0037] The embodiments of this application utilize membrane distillation technology, which is particularly suitable for processing heat-sensitive, highly corrosive liquids that require concentration, such as phosphoric acid. Under vacuum, the boiling point of water is lowered. Combined with the lower heating steam temperature, this enables low-temperature evaporation and concentration of phosphoric acid, significantly reducing energy consumption and the risk of thermal decomposition. The MD membrane evaporation equipment concentrates phosphoric acid to above 50% (the first concentration), creating favorable conditions for subsequent multi-effect evaporation units to process higher concentrations. The first-concentration phosphoric acid recovery tank provides stable buffering and storage.

[0038] In one embodiment, the multiple-effect evaporation unit 4 includes a multiple-effect evaporation device 401, which includes a recovery acid evaporation chamber, a recovery acid cooler, a recovery acid condensate preheater, a recovery acid heater, a vacuum device, a concentrated phosphoric acid pump, and a phosphoric acid product tank; The output end of the multi-effect evaporation device 401 is connected to the second concentration phosphoric acid recovery tank 5, and the second concentration phosphoric acid recovery tank 5 outputs phosphoric acid products that meet the sales standards.

[0039] In the application, 50% phosphoric acid enters the multi-effect evaporation equipment of the multi-effect evaporation unit through a pump. Under the heating effect of steam, the water in the phosphoric acid is continuously evaporated, and the phosphoric acid is further concentrated to obtain a phosphoric acid product with a concentration of more than 75%, which enters the second concentration phosphoric acid recovery tank, namely the 75% phosphoric acid recovery tank.

[0040] The acid recovery evaporation chamber in the embodiment of this application is the primary location for water evaporation; the acid recovery heater provides the heat required for evaporation (primary steam serves as the heat source); the acid recovery condensate preheater utilizes the latent heat of secondary steam to preheat the feed, recovering heat energy; and the acid recovery cooler is responsible for cooling the final product. A vacuum system maintains the low-pressure environment required for evaporation. This integrated equipment combination is key to the efficient operation of multi-effect evaporation. By utilizing steam heat energy in a graded manner (such as preheating secondary steam generated from primary steam), it effectively improves overall thermal efficiency. Concentrated phosphoric acid pumps and phosphoric acid product tanks ensure smooth transportation and storage of the concentrated product.

[0041] In one embodiment, the cold side inlet of the recovery acid cooler is connected to the first concentration phosphoric acid output by the membrane concentration unit 3, the cold side outlet is connected to the feed end of the multi-effect evaporation unit 4, the hot side inlet is connected to the second concentration phosphoric acid output by the multi-effect evaporation unit 4, and the hot side outlet is connected to the second concentration phosphoric acid recovery tank 5; The recovered acid cooler is used to use the first-concentration phosphoric acid output from the membrane concentration unit 3 as a cooling medium to heat-exchange and cool the second-concentration phosphoric acid output from the multi-effect evaporation unit 4 .

[0042] In the multi-effect evaporation unit, the recovery acid cooler utilizes the room-temperature 50% phosphoric acid fed to the multi-effect evaporation unit as a cooling medium for heat exchange and cooling the 75% phosphoric acid discharged from the multi-effect evaporation unit. Simultaneously, the 50% phosphoric acid fed to the unit is preheated. The recovery acid condensate preheater and recovery acid heater utilize primary steam from the steam main through the recovery acid heater to circulate and heat the phosphoric acid in the recovery acid evaporation chamber. Secondary steam from the recovery acid heater outlet is then fed through the recovery acid condensate preheater to preheat the 50% phosphoric acid fed to the recovery acid evaporation chamber. The secondary steam condenses into the steam condensate tank. In addition to the primary steam, the system's internal heat is fully recycled, maximizing heat recovery.

[0043] The acid recovery cooler in this embodiment is designed as a heat exchanger, cleverly utilizing the relatively low-temperature first-concentration phosphoric acid (e.g., 50% phosphoric acid) fresh from the membrane concentration unit as a cooling medium to cool the high-temperature second-concentration phosphoric acid (e.g., 75% phosphoric acid) produced by the multi-effect evaporation unit. This process achieves dual technical benefits: on the one hand, it efficiently cools the final product to a temperature suitable for storage or transportation; on the other hand, during the cooling process, the heat released by the product phosphoric acid is used to preheat the feed phosphoric acid entering the evaporation process, significantly reducing the fresh steam consumption required to heat the feed and achieving significant energy savings and consumption reductions.

[0044] In one embodiment, it further comprises a concentrate tank 9 and a neutralization reactor 10; The concentrate produced by the deep purification unit 2 and the membrane concentration unit 3 is output to the concentrate tank 9. The sewage output end of the concentrate tank 9 is connected to the neutralization reaction tank. The purification output end of the concentrate tank 9 is connected to the circulating wastewater input end of the pre-purification unit 1. The concentrate tank 9 is used to separate the high-concentration suspended solids and high-cations in the concentrate and output them to the neutralization reaction tank, and output the concentrate after separation of the high-concentration suspended solids and high-cations to the pre-purification unit 1; The neutralization reaction tank is used to neutralize waste liquid containing high concentration of suspended solids and high cations through lime milk and generate calcium phosphate precipitate. The calcium phosphate precipitate and supernatant generated by the neutralization reaction tank are output to the incineration device for incineration.

[0045] In the embodiments of the present application, concentrate tanks are used to separate and divert the concentrate from the deep purification and membrane concentration units. Most of the concentrate, with relatively low impurity concentrations, can be returned to the front end of the pre-purification unit for recycling and concentration, which improves the overall recovery rate of valuable phosphoric acid components. For small amounts of waste concentrate that cannot be recycled and contain high concentrations of suspended solids and metal cations, lime milk is used for chemical neutralization in a neutralization reaction tank. The neutralization reaction generates a stable calcium phosphate precipitate, solidifying the harmful substances. The precipitate and supernatant are then incinerated together for complete harmless disposal. This hierarchical treatment strategy maximizes resources and minimizes waste, reducing the environmental impact of system operation.

[0046] In one embodiment, it further comprises a steam condensate water tank 6, an evaporation condensate water tank 7 and an RO dephosphorization device tower 8; The steam condensate output ends of the membrane concentration unit 3 and the multi-effect evaporation unit 4 are connected to the input end of the steam condensate tank 6, and the output end of the steam condensate tank 6 is connected to the pure water input pipe of the pre-purification unit 1; The membrane concentration unit 3 and the evaporation condensation water output end are connected to the input end of the evaporation condensation water tank 7, the output end of the evaporation condensation water tank 7 is connected to the pure water input pipeline of the pre-purification unit 1, and / or is connected to the water inlet end of the RO phosphorus removal device tower 8, and the concentrated water output end of the RO phosphorus removal device tower 8 is connected to the filtrate tank of the ceramic tube membrane device 102 of the deep purification unit 2.

[0047] The embodiments of the present application construct a closed-loop system for water resource recycling within the system. During operation, the membrane concentration unit (MD) and the multi-effect evaporation unit produce two types of condensate: steam condensate (obtained by condensation of heated steam, which is relatively pure) and evaporation condensate (obtained by evaporation of the feed liquid). After these two types of condensate are collected separately, they are preferentially reused as dilution water in the phosphoric acid dilution tank of the pre-purification unit, which directly saves on the consumption of fresh water. When there is excess evaporation condensate or the water quality requirements are more stringent, it is deeply treated by a reverse osmosis phosphorus removal device (RO): RO produced water can be used as high-quality circulating cooling water system water replenishment; because the RO concentrated water still contains a certain amount of phosphorus, it is returned to the ceramic tube membrane filtrate tank at the front end of the system for reprocessing. This design maximizes the recycling of water generated within the system, reducing the amount of clean water supply and wastewater discharge of the entire system.

[0048] In one embodiment, a waste gas absorption tower 11 is further included. The acidic waste gas generated by the pre-purification unit 1, the deep purification unit 2, the membrane concentration unit 3 and the multi-effect evaporation unit 4 is input into the waste gas absorption tower 11. The output end of the waste gas absorption tower 11 is used to connect to the waste gas incineration device.

[0049] The pre-purification, deep purification, membrane concentration and multi-effect evaporation units in the embodiments of the present application may release waste gas containing acidic components (such as phosphoric acid mist) when treating acidic wastewater. By setting up a waste gas absorption tower, these dispersed acidic waste gases are collected and introduced into the tower. In the tower, the waste gas is fully contacted and reacted with the alkaline absorption liquid (such as alkali solution) to neutralize and remove the acidic substances therein. The waste gas after pretreatment and purification is then sent to the waste gas incineration device for high-temperature incineration to achieve final harmless emission or use as combustion-supporting air. This measure effectively prevents the pollution of the atmospheric environment caused by direct emission of acidic gases and ensures the environmental friendliness of the treatment process.

[0050] The above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present application, and should all be included in the scope of protection of the present application.

Claims

1. A phosphorus-containing wastewater treatment system, characterized in that: It comprises a pre-purification unit (1), a deep purification unit (2), a membrane concentration unit (3) and a multi-effect evaporation unit (4) connected in sequence; The pre-purification unit (1) is used to dilute the phosphorus-containing wastewater and filter impurities; The deep purification unit (2) is used to receive the wastewater treated by the pre-purification unit (1) and filter out multivalent metal cations, macromolecular substances and divalent salts in the wastewater; The membrane concentration unit (3) is used to receive the wastewater treated by the deep purification unit (2), and evaporate water at low temperature under vacuum negative pressure and steam heating to concentrate phosphoric acid; The multi-effect evaporation unit (4) is used to receive the phosphoric acid concentrated by the membrane concentration unit (3), and further evaporate water under steam heating to further concentrate the phosphoric acid to obtain a phosphoric acid product with a concentration that meets the sales standard.

2. The phosphorus-containing wastewater treatment system according to claim 1, characterized in that: The pre-purification unit (1) comprises a phosphoric acid dilution tank (101) and a ceramic tube membrane device (102); The input end of the phosphoric acid dilution tank (101) is connected to pure water and phosphorus-containing wastewater, and the output end is connected to the input end of the ceramic tube membrane device (102), and the output end of the ceramic tube membrane device (102) is connected to the input end of the deep purification unit (2); The phosphoric acid dilution tank (101) is used to dilute the phosphorus-containing wastewater using the pure water; The ceramic tube membrane device (102) is used to filter impurities from the phosphorus-containing wastewater diluted in the phosphoric acid dilution tank (101), wherein the impurities include at least one of insoluble particles, colloids and inorganic silicon.

3. The phosphorus-containing wastewater treatment system according to claim 2, characterized in that: The ceramic membrane used in the ceramic tubular membrane device (102) is an acid-resistant special inorganic tubular membrane. The ceramic tubular membrane device (102) separates substances through the screening effect of its own porous inorganic medium and the attached membrane layer.

4. The phosphorus-containing wastewater treatment system according to claim 1, wherein: The deep purification unit (2) includes a nanofiltration membrane device, and the nanofiltration membrane device includes a nanofiltration membrane device stage 1 (201), a nanofiltration membrane device stage 2 (202), and a nanofiltration membrane device permeate tank (203); The input end of the first stage (201) of the nanofiltration membrane device is connected to the output end of the pre-purification unit (1), the concentrated liquid output end of the first stage (201) of the nanofiltration membrane device is connected to the input end of the second stage (202) of the nanofiltration membrane device, the permeate output ends of the first stage (201) of the nanofiltration membrane device and the second stage (202) of the nanofiltration membrane device are connected to the input end of the permeate tank (203) of the nanofiltration membrane device, and the output end of the permeate tank (203) of the nanofiltration membrane device is connected to the input end of the membrane concentration unit (3).

5. The phosphorus-containing wastewater treatment system according to claim 1, wherein: The membrane concentration unit (3) includes an MD membrane evaporation device (301) and a first concentration phosphoric acid recovery tank (302); The input end of the MD membrane evaporation device (301) is connected to the output end of the deep purification unit (2), the output end of the MD membrane evaporation device (301) is connected to the input end of the first concentration phosphoric acid recovery tank (302), and the output end of the first concentration phosphoric acid recovery tank (302) is connected to the input end of the multi-effect evaporation unit (4); The MD membrane evaporation device (301) is used to evaporate water in the phosphoric acid from the deep purification unit (2) under vacuum negative pressure and steam heating, so as to concentrate the phosphoric acid to a first concentration; The first concentration phosphoric acid recovery tank (302) is used to collect a phosphoric acid solution of the first concentration.

6. The phosphorus-containing wastewater treatment system according to claim 1, wherein: The multiple-effect evaporation unit (4) comprises a multiple-effect evaporation device (401), wherein the multiple-effect evaporation device (401) comprises a recovery acid evaporation chamber, a recovery acid cooler, a recovery acid condensate water preheater, a recovery acid heater, a vacuum device, a concentrated phosphoric acid pump, and a phosphoric acid product tank; The output end of the multi-effect evaporation device (401) is connected to a second-concentration phosphoric acid recovery tank (5), and the second-concentration phosphoric acid recovery tank (5) outputs a phosphoric acid product that meets the sales standard.

7. The phosphorus-containing wastewater treatment system according to claim 6, characterized in that: The cold side inlet of the recovery acid cooler is connected to the first concentration phosphoric acid output from the membrane concentration unit (3), the cold side outlet is connected to the feed end of the multi-effect evaporation unit (4), the hot side inlet is connected to the second concentration phosphoric acid output from the multi-effect evaporation unit (4), and the hot side outlet is connected to the second concentration phosphoric acid recovery tank (5); The recovered acid cooler is used to utilize the first-concentration phosphoric acid output from the membrane concentration unit (3) as a cooling medium to heat-exchange and cool the second-concentration phosphoric acid output from the multi-effect evaporation unit (4).

8. The phosphorus-containing wastewater treatment system according to claim 1, wherein: It also includes a concentrate tank (9) and a neutralization reactor (10); The concentrated liquid generated by the deep purification unit (2) and the membrane concentration unit (3) is output to the concentrated liquid tank (9), the sewage output end of the concentrated liquid tank (9) is connected to the neutralization reaction tank, and the purification output end of the concentrated liquid tank (9) is connected to the circulating wastewater input end of the pre-purification unit (1); The concentrate tank (9) is used to separate high-concentration suspended solids and high-cations in the concentrate and output them to the neutralization reaction tank, and output the concentrate after separation of high-concentration suspended solids and high-cations to the pre-purification unit (1); The neutralization reaction tank is used to neutralize waste liquid containing high concentration of suspended solids and high cations through lime milk and generate calcium phosphate precipitate. The calcium phosphate precipitate and supernatant generated by the neutralization reaction tank are output to the incineration device for incineration.

9. The phosphorus-containing wastewater treatment system according to claim 1, wherein: It also includes a steam condensate water tank (6), an evaporation condensate water tank (7) and an RO dephosphorization device tower (8); The steam condensate output ends of the membrane concentration unit (3) and the multi-effect evaporation unit (4) are connected to the input end of the steam condensate tank (6), and the output end of the steam condensate tank (6) is connected to the pure water input pipe of the pre-purification unit (1); The membrane concentration unit (3) and the evaporation condensation water output end are connected to the input end of the evaporation condensation water tank (7), the output end of the evaporation condensation water tank (7) is connected to the pure water input pipeline of the pre-purification unit (1), and / or is connected to the water inlet end of the RO dephosphorization device tower (8), and the concentrated water output end of the RO dephosphorization device tower (8) is connected to the filtrate tank of the ceramic tube membrane device (102) of the deep purification unit (2).

10. The phosphorus-containing wastewater treatment system according to claim 1, wherein: It also includes a waste gas absorption tower (11), wherein the acid waste gas generated by the pre-purification unit (1), the deep purification unit (2), the membrane concentration unit (3) and the multi-effect evaporation unit (4) is input into the waste gas absorption tower (11), and the output end of the waste gas absorption tower (11) is used to connect to the waste gas incineration device.

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