Low-temperature multi-effect distillation wastewater advanced treatment and reuse system and method thereof

Abstract

The application relates to the technical field of industrial wastewater treatment, and particularly discloses a low-temperature multi-effect distillation wastewater advanced treatment and recycling system and a method thereof. In order to solve the technical problems of easy corrosion, easy scaling and poor operation stability caused by the low-temperature multi-effect distillation technology, the system comprises a sewage treatment system, an ammonia removal facility, a circulating water pool, a filter, a low-temperature multi-effect distillation unit, a cooling tower, a heat exchanger, a hardness removal system and a poor-quality water disposal system. The sewage treatment system receives sewage and outputs the sewage to the ammonia removal facility, the circulating water pool, the filter, the low-temperature multi-effect distillation unit, the low-temperature multi-effect distillation unit is provided with a distilled water outlet and a concentrated salt water outlet, the concentrated salt water outlet is connected to the circulating water pool through a first branch pipe, a second branch pipe is connected to the hardness removal system and then to the circulating water pool, and a third branch pipe is connected to the poor-quality water disposal system. The application eliminates the factors of scaling and corrosion, effectively prolongs the equipment cleaning period and service life.

Description

Technical Field

[0001] This application relates to the field of industrial wastewater treatment technology, and in particular to a low-temperature multi-effect distillation wastewater deep treatment and reuse system and method. Background Technology

[0002] Industrial production processes generate large amounts of industrial wastewater. Traditional treatment methods (such as coagulation, sedimentation, filtration, and biological treatment) can ensure that industrial wastewater meets discharge standards. However, the treated reclaimed water still contains high levels of salt, hardness, and recalcitrant pollutants. Direct reuse can easily cause scaling and corrosion in equipment, affecting the safe and stable operation of the system. Meanwhile, water scarcity and the increasing demand for wastewater resource utilization make achieving deep desalination and reuse of industrial wastewater a key issue for water conservation and emission reduction in industrial enterprises.

[0003] Currently, the general process for zero-discharge industrial wastewater treatment adopts a route of "pretreatment + ultrafiltration + reverse osmosis + nanofiltration + evaporation crystallization". Ultrafiltration and reverse osmosis concentrate the wastewater, nanofiltration separates monovalent salts (sodium chloride) from divalent salts (calcium, magnesium, and sulfates), and evaporation crystallization typically uses multi-effect evaporation or MVR evaporation processes, ultimately producing industrial salt and other salts. However, this process route suffers from problems such as severe membrane fouling, frequent cleaning, high operating costs, and limited options for treating concentrated brine.

[0004] Low-Temperature Multi-Effect Distillation (LT-MED) is a mature thermal desalination technology, currently mainly used in seawater desalination. Its basic principle is to use steam as a heat source to heat and evaporate seawater through a multi-effect evaporator. The resulting water vapor is condensed to form distilled water, thus separating salt from water. LT-MED technology has advantages such as low operating temperature (maximum evaporation temperature not exceeding 70℃), high heat transfer efficiency, and high system operational flexibility.

[0005] However, directly applying low-temperature multi-effect distillation technology to industrial wastewater treatment still has significant shortcomings. First, industrial wastewater has a complex composition, containing various pollutants such as ammonia nitrogen, hardness ions (calcium and magnesium ions), and organic matter. Ammonia nitrogen, under high-temperature alkaline conditions, converts into ammonia gas, causing severe ammonia corrosion of copper heat exchange tubes. Hardness ions easily form scale on the surface of heat exchange tubes during evaporation and concentration, leading to decreased heat transfer efficiency. Existing seawater desalination systems only treat suspended solids in seawater and cannot effectively remove ammonia nitrogen and hardness ions from industrial wastewater; directly applying this technology will inevitably lead to heat exchange tube corrosion and scaling. Second, existing low-temperature multi-effect distillation systems primarily rely on online monitoring and control of evaporation temperature and salinity or mechanical cleaning for scale prevention. This is a passive approach to scale prevention, lacking a pre-treatment design to control scale ions at the source, resulting in limited scale prevention effectiveness and poor operational stability.

[0006] Existing low-temperature multi-effect distillation technology lacks pretreatment and system integration design tailored to the characteristics of industrial wastewater in the field of deep industrial wastewater treatment. This results in systems that are prone to corrosion and scaling, have poor operational stability, and rely on seawater and concentrated brine for final-effect cooling, making it difficult to achieve long-term stable application in inland industrial enterprises. Summary of the Invention

[0007] To address the technical problems of existing low-temperature multi-effect distillation technology, such as easy corrosion, easy scaling, and poor operational stability, this application provides a low-temperature multi-effect distillation wastewater deep treatment and reuse system and method.

[0008] In a first aspect, embodiments of this application provide a low-temperature multi-effect distillation wastewater deep treatment and reuse system and method, including: Wastewater treatment system, ammonia removal facilities, circulating water tank, filter, low temperature multi-effect distillation unit, cooling tower, heat exchanger, hardness removal system and poor water disposal system; The wastewater treatment system receives wastewater and outputs reclaimed water to the ammonia removal facility; after the ammonia removal facility removes ammonia nitrogen from the reclaimed water, the effluent is sent to the circulating water tank. The effluent from the circulating water tank is pumped to the filter, and the effluent from the filter is sent to the low-temperature multi-effect distillation unit. The low-temperature multi-effect distillation unit consists of a first evaporation effect, several intermediate evaporation effects, and a final condensation effect connected in series. External steam is connected to the first evaporation effect as a heat source; the final condensation effect is connected to the circulating cooling water provided by the cooling tower. The low-temperature multi-effect distillation unit is equipped with a distilled water outlet and a concentrated brine outlet. The distilled water outlet is used to deliver product water. The concentrated brine outlet is connected to a concentrated brine main pipe, which is connected to three branch pipes: The first branch pipe is connected to the inlet of the circulating water tank; The second branch pipe is connected to the inlet of the hardening removal system, and the outlet of the hardening removal system is connected to the inlet of the circulating water tank. The third branch pipe is connected to the substandard water disposal system; A circulating cooling water pipeline is provided between the cooling tower and the final condensing effect; the heat exchanger is located on the circulating cooling water pipeline or the concentrated brine main pipeline.

[0009] In some embodiments, the ammonia removal facility employs a breakpoint chlorination device, which is located on the outlet pipe of the recycled water pump in the wastewater treatment system. In some embodiments, the hardening system is any one of a fluidized bed induced crystallization hardening device, an ion exchange hardening device, or a chemical precipitation hardening device. In some embodiments, the low-temperature multi-effect distillation unit is a horizontal tube falling film evaporator, and its heat exchange tube is made of titanium tube or corrosion-resistant alloy tube. In some embodiments, the filter is a self-cleaning filter with a filtration accuracy of 50μm to 200μm. In some embodiments, the heat exchanger is a plate type, disposed on the concentrated brine pipeline and located between the low-temperature multi-effect distillation unit and the three branch pipes. In some embodiments, each of the three branch pipes is equipped with an electric regulating valve and a flow meter, and the electric regulating valve and flow meter are electrically connected to the PLC control system. Secondly, embodiments of this application provide a method for deep treatment and reuse of low-temperature multi-effect distillation wastewater, comprising the following steps: S1: Wastewater undergoes coagulation, flocculation, sedimentation, and filtration in a wastewater treatment system to remove suspended solids and organic matter, resulting in recycled water; S2: The reclaimed water enters the ammonia removal facility, where ammonia nitrogen is removed by inflection point chlorination and disinfection is performed. The effluent then enters the circulating water tank. S3: The effluent from the circulating water tank is filtered to remove suspended solids, colloids and impurities before being sent to the low-temperature multi-effect distillation unit. S4: External steam is introduced into the first evaporation effect of the low-temperature multi-effect distillation unit to heat the incoming water and cause it to evaporate. The generated secondary steam enters the subsequent evaporation effects in sequence to heat the incoming water, realizing the cascade utilization of heat. The final condensation effect uses the circulating cooling water provided by the cooling tower to condense the secondary steam into distilled water. The distilled water generated by each effect is collected and sent out as product water. S5: The concentrated brine discharged from the low-temperature multi-effect distillation unit is divided into three streams via the concentrated brine main pipe: The concentrated brine in the first branch pipe flows directly back to the circulating water tank; The concentrated brine in the second branch pipe is sent to the hardness removal system to remove calcium and magnesium ions before being returned to the circulating water tank. The concentrated brine in the third branch pipe is sent to the substandard water disposal system for cascade utilization. S6: The circulating cooling water circulates between the cooling tower and the final condenser. When the temperature of the concentrated brine exceeds the set value, the heat exchanger is activated to cool it down.

[0010] In some embodiments, the flow rate of concentrated brine in the third branch pipe is dynamically adjusted according to the difference between the recycled water inlet flow rate and the water production rate of the low-temperature multi-effect distillation unit, wherein the recycled water inlet flow rate is equal to the sum of the water production rate and the third branch flow rate. In some embodiments, the flow rate of concentrated brine in the second branch pipe is dynamically adjusted according to the hardness of the influent water entering the low-temperature multi-effect distillation unit. When the hardness of the influent water reaches or exceeds a set threshold as measured by calcium ions, the flow rate in the second branch pipe is increased; when the hardness of the influent water is lower than the set threshold, the flow rate in the second branch pipe is decreased. In summary, this application includes at least one of the following beneficial technical effects: 1. The ammonia removal facility, filter, and low-temperature multi-effect distillation unit are integrated in a specific process to construct a complete system architecture of "pretreatment → low-temperature multi-effect distillation → product water reuse". The ammonia removal facility uses breakpoint chlorination to remove ammonia nitrogen and disinfect, preventing ammonia from corroding the heat exchange tubes; the filter removes suspended solids and colloids, preventing nozzle clogging; the low-temperature multi-effect distillation unit utilizes the principle of thermal evaporation, achieving efficient separation of salts and water through multi-effect heat cascade utilization. The organic combination of these three components enables the system to simultaneously and efficiently remove dissolved salts, organic matter, ammonia nitrogen, and hardness ions from industrial wastewater in an integrated system, producing high-purity distilled water that can be directly used as industrial process water or boiler feedwater, realizing the resource reuse of industrial wastewater.

[0011] 2. The concentrated brine outlet of the low-temperature multi-effect distillation unit features a unique three-way diversion structure with corresponding control logic. The concentrated brine in the first branch pipe flows directly back to the circulating water tank, maintaining system water balance. The concentrated brine in the second branch pipe is sent to the hardness removal system to remove hardness before returning to the circulating water tank, controlling the concentration of scaling ions at the source. The flow rate of the concentrated brine in the second branch pipe is dynamically adjusted through water quality monitoring. The concentrated brine in the third branch pipe is sent to the substandard water disposal system for tiered utilization, with its flow rate dynamically adjusted based on the difference between the recycled water inflow and the produced water flow. This coordinated operation of the three branch pipes not only improves the water resource recycling rate but also effectively maintains the system's salt balance by discharging some concentrated brine, preventing the continuous accumulation of salt in the system and ensuring long-term stable operation.

[0012] 3. The circulating cooling water supplied by the cooling tower is connected to the final-effect condenser, replacing the traditional seawater cooling method that relies on seawater, allowing the system to operate normally without the need for coastal construction. Simultaneously, by installing heat exchangers on the circulating cooling water pipeline or the concentrated brine main pipe, cooling is activated when the temperature of the circulating concentrated water exceeds a set value in summer, ensuring a stable heat balance throughout the year. This significantly expands the applicability of this application to inland steel, chemical, and other enterprises.

[0013] 4. The system architecture of this application integrates multiple anti-scaling and anti-corrosion designs: the ammonia removal facility removes ammonia nitrogen to prevent ammonia corrosion, the filter removes suspended solids to prevent nozzle clogging, and the hardening system removes calcium and magnesium ions to prevent scale buildup on heat exchange tubes. Each pretreatment unit works synergistically with the low-temperature multi-effect distillation unit to eliminate factors leading to scale and corrosion at the source, avoiding the limitations of traditional passive scale prevention methods (such as online monitoring and control, and mechanical cleaning), and effectively extending the equipment cleaning cycle and service life. Attached Figure Description

[0014] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0015] Figure 1 A process flow diagram of a low-temperature multi-effect distillation wastewater deep treatment and reuse system provided in this application embodiment; Figure 2 This is a schematic diagram of the structure of a low-temperature multi-effect distillation unit provided in an embodiment of this application.

[0016] Explanation of reference numerals in the attached diagram: 1. Wastewater treatment system; 2. Ammonia removal facility; 3. Circulating water tank; 4. Filter; 5. Low-temperature multi-effect distillation unit; 51. First evaporation effect; 52. Intermediate evaporation effect; 53. Final condensation effect; 6. Cooling tower; 7. Heat exchanger; 8. Hardness removal system; 9. Poor water disposal system; 10. Concentrated brine main pipe; 11. First branch pipe; 12. Second branch pipe; 13. Third branch pipe. Detailed Implementation

[0017] To better understand the technical solutions provided in the embodiments of this specification, the technical solutions of the embodiments of this specification will be described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the embodiments of this specification and the specific features in the embodiments are detailed descriptions of the technical solutions of the embodiments of this specification, rather than limitations on the technical solutions of this specification. In the absence of conflict, the embodiments of this specification and the technical features in the embodiments can be combined with each other.

[0018] In this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, without necessarily requiring or implying any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element. The term "two or more" includes two or more cases.

[0019] The following is in conjunction with the appendix Figure 1-2 This application will be described in further detail.

[0020] In the first aspect, embodiments of this application provide a low-temperature multi-effect distillation wastewater deep treatment and reuse system, referring to... Figure 1The system comprises a wastewater treatment system 1, an ammonia removal facility 2, a circulating water tank 3, a filter 4, a low-temperature multi-effect distillation unit 5, a cooling tower 6, a heat exchanger 7, a hardness removal system 8, and a substandard water disposal system 9. Wastewater treatment system 1 mainly includes a pretreatment equalization tank, a coagulation tank, a flocculation tank, a sedimentation tank, and a filter. The sedimentation tank uses inclined tube or inclined plate sedimentation, and the filtration uses sand filtration. It is used to treat comprehensive industrial wastewater and does not include a biological treatment tank. After entering wastewater treatment system 1, the wastewater undergoes coagulation, flocculation, sedimentation, and sand filtration in sequence, effectively removing suspended solids and organic matter to generate reclaimed water. The reclaimed water is pumped to the ammonia removal facility 2, which uses a breakpoint chlorination device. The breakpoint chlorination point is located on the outlet pipe of the reclaimed water pump in wastewater treatment system 1. Liquid chlorine or sodium hypochlorite can be used as the chlorine source, with a theoretical breakpoint molar ratio of Cl2:NH3-N = 7.6:1 (mass ratio, available chlorine: ammonia nitrogen). Breakpoint chlorination has a dual function of sterilization and ammonia removal. The dosage is determined experimentally based on the amount of reducing substances and ammonia in the water, with an effective hydraulic retention time ≥30 min. Under these conditions, ammonia nitrogen in the recycled water is oxidized to nitrogen gas and removed, while bacteria in the water are killed, effectively preventing the growth of slime in subsequent pipelines and equipment, as well as ammonia corrosion of heat exchange tubes. The ammonia-removed effluent is sent to circulating water tank 3. The volume of circulating water tank 3 is determined based on the treatment capacity of the unit and the unevenness of the recycled water inflow. When the recycled water inflow is relatively stable, the volume of circulating water tank 3 is 0.5 to 1 times the treatment capacity of the low-temperature multi-effect distillation unit 5. Circulating water tank 3 is not equipped with a stirring device, but it is equipped with online monitoring instruments such as a level gauge, conductivity meter, pH meter, and temperature meter to monitor the water quality parameters of the circulating water in real time, providing a basis for system control and regulation. The effluent from the circulating water tank 3 is pumped to filter 4. Filter 4 is a self-cleaning filter with a filtration accuracy of 50μm to 200μm, preferably 100μm. As the circulating water passes through filter 4, suspended solids, colloids, and trace impurities are trapped and removed, preventing impurities from entering the subsequent low-temperature multi-effect distillation unit 5 and clogging the spray nozzles, thus ensuring the normal operation of the spray system. The filtered effluent is then sent to the low-temperature multi-effect distillation unit 5.

[0021] The low-temperature multi-effect distillation unit 5 employs a horizontal tube falling film evaporation method and is an integral structure. The effects are separated by partitions. Its heat exchange tubes are made of titanium, or copper tubes with a residual chlorine reduction device (in which case the residual chlorine entering the low-temperature multi-effect distillation unit 5 must be ≤0.1 mg / L). Titanium tubes have excellent resistance to chloride ion corrosion and are suitable for complex water quality conditions in industrial wastewater. If copper tubes are used, the residual chlorine is reduced to below 0.1 mg / L by the residual chlorine reduction device, avoiding corrosion of the copper tubes by residual chlorine. (Refer to...) Figure 2The low-temperature multi-effect distillation unit 5 consists of a first evaporation effect 51, several intermediate evaporation effects 52, and a final condensation effect 53 connected in series. External steam is connected to the first evaporation effect 51 as a heat source, and the final condensation effect 53 is connected to the circulating cooling water provided by the cooling tower 6. The low-temperature multi-effect distillation unit 5 is provided with a distilled water outlet and a concentrated brine outlet. The distilled water outlet is used to deliver product water, and the concentrated brine outlet is connected to the concentrated brine main pipe 10. The concentrated brine main pipe 10 is connected to three branch pipes: the first branch pipe 11 is connected to the inlet of the circulating water tank 3, the second branch pipe 12 is connected to the inlet of the hardness removal system 8 and the outlet of the hardness removal system 8 is connected to the inlet of the circulating water tank 3, and the third branch pipe 13 is connected to the poor water disposal system 9.

[0022] During the operation of the low-temperature multi-effect distillation unit 5, external steam enters the first evaporation effect 51 and evaporates the water sprayed onto the heating tube. The resulting secondary steam then enters the heat exchange tubes of subsequent evaporation effects to heat the water in the next effect, achieving cascade utilization of heat. The distilled water produced by each effect is collected step by step and sent out through the distilled water outlet. The secondary steam produced in the final effect is condensed into distilled water by circulating cooling water in the final condensation effect 53 and collected. During this process, dissolved salts and recalcitrant pollutants in the water remain in the concentrated brine because their boiling points are higher than water, and are separated from the steam, thus achieving efficient removal of salts and pollutants from the water. After being discharged from the main brine pipe 10, the concentrated brine is divided into three streams: the concentrated brine in the first branch pipe 11 flows directly back to the circulating water tank 3 to maintain the system's water balance; the concentrated brine in the second branch pipe 12 is sent to the hardening system 8, which preferentially uses fluidized bed induced crystallization, with sodium hydroxide and sodium carbonate as the main chemicals added. The pH value of the effluent is adjusted with hydrochloric acid. The fluidized bed induced crystallization method does not have a sedimentation tank; calcium and magnesium ions crystallize out as calcium carbonate and magnesium carbonate during the induced crystallization process. The hardened water is returned to the circulating water tank 3, controlling the concentration of scaling ions in the circulating water from the source and preventing scaling on the surface of the heat exchange tubes of the low-temperature multi-effect distillation unit 5; the concentrated brine in the third branch pipe 13 is sent to the inferior water disposal system 9 for cascade utilization, which is generally used in steel plants for processes such as sintering mixing, ironmaking slag flushing, and steelmaking slag smelting. After the concentrated brine is divided into three streams, excess salt in the system is discharged with the third stream, avoiding continuous accumulation of salt in the system and ensuring long-term stable operation.

[0023] A circulating cooling water pipeline is installed between cooling tower 6 and the final-effect condenser 53. Cooling tower 6 is an open-type cooling tower, and its cooling capacity is determined based on the processing capacity of the low-temperature multi-effect distillation unit 5 and local climate conditions. The circulating cooling water circulates between cooling tower 6 and the final-effect condenser 53, carrying the heat released during the condensation of secondary steam in the final-effect condenser 53 to cooling tower 6 for dissipation, thus maintaining stable condensation conditions in the final-effect condenser 53. Heat exchanger 7 is a plate heat exchanger installed on the outlet pipe of the concentrated brine pump (i.e., on the concentrated brine main pipe 10 and located between the low-temperature multi-effect distillation unit 5 and the three branch pipes). When the summer air temperature is high and the concentrated brine water temperature exceeds the operating temperature requirement of the low-temperature multi-effect distillation unit 5, heat exchanger 7 is put into use. Through heat exchange, it reduces the temperature of the concentrated brine returning to the circulating water tank 3, thereby reducing the overall water temperature of the circulating water tank 3 and ensuring the system's heat balance and stability throughout the year.

[0024] like Figure 1 As shown, the concentrated brine discharged from the low-temperature multi-effect distillation unit 5 is collected by the concentrated brine main pipe 10, and three branch pipes are connected to the main pipe. Each branch pipe is equipped with an electric regulating valve and a flow meter, which are remotely controlled by a PLC control system. The electric regulating valve on the third branch pipe 13 is adjusted according to the difference between the influent flow rate of the recycled water and the output water of the low-temperature multi-effect distillation unit 5. That is, the amount of inferior water consumed is equal to the influent flow rate of the recycled water minus the output water. The flow rate in the third branch pipe 13 is dynamically adjusted according to the water balance. When the influent flow rate increases or the output water flow rate decreases, the opening of the third branch pipe 13 increases, and vice versa. The electric regulating valve on the second branch pipe 12 is adjusted according to the hardness of the influent water entering the low-temperature multi-effect distillation unit 5. An online hardness monitor is installed in the circulating water tank 3. When the hardness detected by the calcium ion meter is close to or greater than 400 mg / L, the opening of the second electric regulating valve increases, allowing more concentrated brine to enter the hardness removal system 8 to remove hardness; when the hardness is lower than the set threshold, the opening of the electric regulating valve on the second branch pipe 12 decreases. The first branch pipe 11 serves as a bypass. After the second branch pipe 12 and the third branch pipe 13 are diverted, the remaining concentrated brine is all directly returned to the circulating water tank 3 through the first branch pipe 11. This forms a closed-loop control of "water quality monitoring → parameter judgment → flow regulation", realizing coordinated automatic control of system water volume, hardness and salinity.

[0025] Secondly, embodiments of this application provide a method for deep treatment and reuse of low-temperature multi-effect distillation wastewater, characterized by comprising the following steps: S1: Wastewater undergoes coagulation, flocculation, sedimentation, and filtration in wastewater treatment system 1 to remove suspended solids and organic matter, resulting in recycled water. In this step, the coagulation, flocculation, sedimentation, and filtration units work together to remove most of the suspended solids and some organic matter from the industrial wastewater, providing the necessary water quality conditions for subsequent ammonia removal and distillation.

[0026] S2: Reclaimed water enters ammonia removal facility 2, where ammonia nitrogen is removed and disinfected via breakpoint chlorination. The effluent then enters circulating water tank 3. The chlorination dosage for breakpoint chlorination is determined experimentally, with an effective hydraulic retention time ≥30 min. In this step, breakpoint chlorination removes ammonia nitrogen while simultaneously killing bacteria, effectively preventing the growth of sludge in subsequent pipelines and equipment, as well as ammonia corrosion of the heat exchange tubes.

[0027] S3: The effluent from the circulating water tank 3 is filtered by the filter 4 to remove suspended solids, colloids, and impurities before being sent to the low-temperature multi-effect distillation unit 5. In this step, the filter further traps trace impurities, protecting the spray system of the distillation unit and preventing nozzle clogging.

[0028] S4: External steam is introduced into the first evaporation effect 51 of the low-temperature multi-effect distillation unit 5 to heat the incoming water and cause it to evaporate. The generated secondary steam then enters subsequent evaporation effects to heat the incoming water, achieving cascaded heat utilization. The final condensation effect 53 uses circulating cooling water provided by the cooling tower 6 to condense the secondary steam into distilled water. The distilled water generated in each effect is collected and sent out as product water. The temperature of the first effect of the low-temperature multi-effect distillation unit 5 does not exceed 70°C, and the vacuum degree of the final effect is 90kPa~95kPa. In this step, the cascaded heat utilization mode of multi-effect distillation makes full use of the heat of the external steam. The secondary steam generated in the first effect is used as the heat source for the next effect and is transferred to the final effect, significantly reducing system energy consumption.

[0029] S5: The concentrated brine discharged from the low-temperature multi-effect distillation unit 5 is divided into three streams via the concentrated brine main pipe 10. The concentrated brine in the first branch pipe 11 flows directly back to the circulating water tank 3. The concentrated brine in the second branch pipe 12 is sent to the hardness removal system 8 to remove calcium and magnesium ions before returning to the circulating water tank 3. The concentrated brine in the third branch pipe 13 is sent to the substandard water disposal system 9 for cascade utilization. The flow rate of the concentrated brine in the third branch pipe 13 is dynamically adjusted according to the difference between the recycled water inlet flow rate and the water production rate of the low-temperature multi-effect distillation unit 5, i.e., the recycled water inlet flow rate equals the sum of the water production rate and the flow rate of the third branch pipe. The flow rate of the concentrated brine in the second branch pipe 12 is dynamically adjusted according to the hardness of the inlet water entering the low-temperature multi-effect distillation unit 5. When the inlet water hardness (calculated as calcium ions) reaches or exceeds the set threshold, the flow rate of the second branch pipe is increased; when the inlet water hardness is below the set threshold, the flow rate of the second branch pipe is decreased. In this step, the three-way diversion linkage control realizes the coordinated management of system water balance, hardness control, and salt balance.

[0030] S6: The circulating cooling water circulates between the cooling tower 6 and the final-effect condenser 53. When the temperature of the concentrated brine exceeds the set value, the heat exchanger 7 is activated to cool it down. In this step, the circulating cooling water circulates in a closed loop and is regulated in conjunction with the heat exchanger 7 to ensure the system's thermal balance remains stable throughout the year.

[0031] This application employs a low-temperature multi-effect distillation wastewater deep treatment and reuse system and method, and generates specific embodiments.

[0032] In this embodiment, the system is specifically configured as follows: Wastewater treatment system 1 adopts a conventional coagulation-sedimentation-filtration process.

[0033] The ammonia removal facility 2 adopts the breakpoint chlorination method. The chlorination location is set on the outlet pipe of the reclaimed water pump of the sewage treatment system 1, and sodium hypochlorite is used as the chlorine source.

[0034] The volume of the circulating water tank 3 is 0.8 times that of the water treated by the low-temperature multi-effect distillation unit 5, and it is equipped with a level gauge, conductivity meter, pH meter, and temperature meter.

[0035] Filter 4 is a self-cleaning filter with a filtration accuracy of 100μm.

[0036] The low-temperature multi-effect distillation unit 5 adopts a horizontal tube falling film evaporation method and has a 7-effect evaporation structure, consisting of the first evaporation effect 51, the second to seventh evaporation effects (i.e., intermediate evaporation effects 52) and the final condensation effect 53 connected in series. The heat exchange tube is made of titanium.

[0037] Cooling tower 6 is an open cooling tower.

[0038] Heat exchanger 7 is a plate heat exchanger, installed on the outlet pipe of the concentrated brine pump.

[0039] The hardness removal system 8 uses a fluidized bed induced crystallization method, and the dosing agents are sodium hydroxide and sodium carbonate. The pH value of the effluent is adjusted with hydrochloric acid.

[0040] The inferior water disposal system 9 is used for ironmaking slag flushing and steelmaking slag simmering.

[0041] The influent water quality is as follows: TDS=1400mg / L, COD=50mg / L, ammonia nitrogen=5mg / L, and total hardness (calculated as CaCO3)=750mg / L.

[0042] The processing procedure is as follows: S1: After the wastewater is treated by the coagulation-sedimentation-filtration process of wastewater treatment system 1, the effluent TDS is 1500mg / L (a small amount of salt is introduced during the coagulation and sedimentation process, so the TDS increases slightly), COD is 30mg / L, ammonia nitrogen is 3mg / L, and total hardness is 800mg / L.

[0043] S2: Reclaimed water enters ammonia removal facility 2, with a chlorination dosage of 3 mg / L (available chlorine), an effective hydraulic retention time of 45 min, and after treatment by breakpoint chlorination, the effluent ammonia nitrogen is approximately 0 mg / L.

[0044] S3: The water effluent from the circulating water tank 3 is filtered by the filter 4 to remove suspended solids, colloids and impurities before being sent to the low-temperature multi-effect distillation unit 5.

[0045] S4: External steam is introduced into the first evaporation effect 51, the temperature of the first evaporation effect 51 is 66℃, the temperature of the final condensation effect 53 is 42℃, the vacuum degree of the final effect is 93kPa, the inlet water flow rate is 1800m³ / h, and the evaporation temperatures of each effect are as follows: first effect 66℃, second effect 62.5℃, third effect 59℃, fourth effect 55.5℃, fifth effect 52℃, sixth effect 48.5℃, and seventh evaporation effect 45℃. The secondary steam generated in the seventh effect enters the final condensation effect 53 and is condensed into distilled water by the circulating cooling water. The condensation temperature of the final condensation effect 53 is 42℃.

[0046] S5: The concentrated brine is divided into three branches through the main pipe. The first branch 11 directly returns about 65% of the brine. The second branch 12 sends the brine to the hardness removal system 8 and returns about 30% after hardness removal. The third branch 13 sends the brine to the substandard water disposal system 9 about 5%. The influent flow rate of the reclaimed water is 600 m³ / h, the production water flow rate is 500 m³ / h, and the substandard water disposal flow rate is 100 m³ / h. The hardness (calculated as calcium ions) of the brine entering the low-temperature multi-effect distillation unit 5 is controlled at ≤400 mg / L.

[0047] S6: The circulating cooling water circulates between cooling tower 6 and the final condenser 53. The inlet water temperature of cooling tower 6 is 38℃ and the return water temperature is 30℃.

[0048] Treatment results: Product water TDS ≤ 5 mg / L, COD ≈ 0 mg / L, ammonia nitrogen ≈ 0 mg / L, hardness ≈ 0 mg / L, conductivity ≤ 10 μs / cm, desalination rate ≥ 99.6%, COD removal rate 100%, ammonia nitrogen removal rate 100%, energy consumption per ton of water treated is 1.1 kWh / m³, and the heat exchange tube cleaning cycle is once a year. This example fully verifies the excellent effect of the system and method of this application in the deep treatment of industrial wastewater.

[0049] In another embodiment, the number of effects in the low-temperature multi-effect distillation unit 5 is adjusted to three, consisting of a first evaporation effect 51, a second evaporation effect, a third evaporation effect (i.e., an intermediate evaporation effect 52), and a final condensation effect 53 connected in series. The temperature of the first evaporation effect 51 is 68°C, the temperature of the second evaporation effect is 55°C, the temperature of the third evaporation effect is 52°C, the temperature of the final condensation effect 53 is 40°C, and the vacuum degree of the final condensation effect 53 is 95 kPa. The remaining configuration and operating parameters are the same as in the aforementioned embodiment. The treatment results are: TDS of the produced water ≤ 6 mg / L, desalination rate ≥ 99.5%, and energy consumption per ton of water treated is 1.3 kWh / m³, indicating that the system can still maintain a high desalination rate even with a reduced number of effects.

[0050] In another embodiment, the hardness removal system 8 employs an ion exchange hardness removal device, a strongly acidic cation exchange resin, and hydrochloric acid regeneration. The remaining configuration and operating parameters are the same as in the aforementioned embodiment. The influent hardness (calculated as CaCO3) is 800 mg / L, and after treatment by the hardness removal system 8, the effluent hardness is ≤100 mg / L, with a hardness removal rate ≥87.5%. The hardness (calculated as calcium ions) entering the low-temperature multi-effect distillation unit 5 is controlled to ≤400 mg / L.

[0051] In another embodiment, the hardness removal system 8 employs a chemical precipitation hardness removal device, using sodium hydroxide and sodium carbonate as the added chemicals. A sedimentation tank is set up for solid-liquid separation, and the remaining configuration and operating parameters are the same as in the aforementioned embodiment. The influent hardness (calculated as CaCO3) is 800 mg / L, and the effluent hardness after treatment by the hardness removal system 8 is ≤150 mg / L, with a hardness removal rate ≥81.25%.

[0052] In another embodiment, the heat exchange tubes of the low-temperature multi-effect distillation unit 5 are made of copper and equipped with a residual chlorine reduction device to control the residual chlorine entering the low-temperature multi-effect distillation unit 5 to be ≤0.1mg / L. The remaining configuration and operating parameters are the same as in the aforementioned embodiment. The TDS of the product water is ≤5mg / L, and the desalination rate is ≥99.6%, indicating that the copper tubes combined with the residual chlorine reduction device can also meet the system's corrosion prevention and operation requirements.

[0053] In another embodiment, the filter 4 has a filtration accuracy of 50 μm, producing water TDS ≤ 5 mg / L and a desalination rate ≥ 99.6%; when the filtration accuracy is adjusted to 200 μm, the producing water TDS ≤ 6 mg / L and the desalination rate ≥ 99.5%, indicating that the system can operate stably within the accuracy range of 50 μm to 200 μm.

[0054] In another embodiment, the volume of the circulating water tank 3 is 0.5 times the water volume processed by the low-temperature multi-effect distillation unit 5, the system operates stably, and the quality of the produced water is comparable to that of the aforementioned embodiment; when the volume of the circulating water tank 3 is adjusted to 1 times the water volume processed, the system also operates stably, and the quality of the produced water is comparable to that of the aforementioned embodiment.

[0055] In another embodiment, the breakpoint chlorination uses liquid chlorine as the chlorine source, and the effluent ammonia nitrogen is ≈0 mg / L, indicating that both liquid chlorine and sodium hypochlorite can be used as effective chlorine sources to achieve ammonia nitrogen removal.

[0056] This application integrates the ammonia removal facility 2, filter 4, hardness removal system 8, and low-temperature multi-effect distillation unit 5 into a specific process, constructing a complete "pretreatment → low-temperature multi-effect distillation → product water reuse" system architecture. Each component is functionally interconnected and works synergistically: ammonia removal and filtration provide qualified influent water for the low-temperature multi-effect distillation, ensuring efficient and stable operation of the distillation unit; low-temperature multi-effect distillation completely removes dissolved salts that cannot be removed by the preceding pretreatment; and the three-way diversion of concentrated brine achieves coordinated management of system water balance, hardness control, and salt balance. The organic combination of these three elements enables the system to produce high-purity distilled water, which can be directly used as industrial process water or boiler feedwater. Simultaneously, the multiple anti-scaling and anti-corrosion designs eliminate factors leading to scaling and corrosion at the source, effectively extending the equipment cleaning cycle and service life; and the final-effect circulating water cooling design eliminates dependence on seawater cooling, allowing the system to be extended to inland areas. This application effectively solves the technical problems of existing technologies, such as "the system is prone to corrosion and scaling, has poor operational stability, and relies on seawater for final cooling and has a single method for treating concentrated brine", and realizes efficient deep desalination and resource reuse of industrial wastewater, which has significant technological progress.

[0057] The above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application.

[0058] Although preferred embodiments have been described in this specification, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of this specification.

[0059] Obviously, those skilled in the art can make various modifications and variations to this specification without departing from its spirit and scope. Therefore, if such modifications and variations fall within the scope of the claims and their equivalents, this specification is also intended to include such modifications and variations.

Claims

1. A low-temperature multi-effect distillation wastewater deep treatment and reuse system, characterized in that, include: Wastewater treatment system (1), ammonia removal facility (2), circulating water tank (3), filter (4), low temperature multi-effect distillation unit (5), cooling tower (6), heat exchanger (7), hardness removal system (8) and poor water disposal system (9); The wastewater treatment system (1) receives wastewater and outputs reclaimed water to the ammonia removal facility (2); after the ammonia removal facility (2) removes ammonia nitrogen from the reclaimed water, the effluent is sent to the circulating water tank (3). The effluent from the circulating water tank (3) is pumped to the filter (4), and the effluent from the filter (4) is sent to the low-temperature multi-effect distillation unit (5). The low-temperature multi-effect distillation unit (5) consists of a first evaporation effect (51), several intermediate evaporation effects (52) and a final condensation effect (53) connected in series. External steam is connected to the first evaporation effect (51) as a heat source; the final condensation effect (53) is connected to the circulating cooling water provided by the cooling tower (6). The low-temperature multi-effect distillation unit (5) is provided with a distilled water outlet and a concentrated brine outlet. The distilled water outlet is used to deliver product water. The concentrated brine outlet is connected to the concentrated brine main pipe (10), which is connected to three branch pipes: The first branch pipe (11) is connected to the inlet of the circulating water tank (3); The second branch pipe (12) is connected to the inlet of the hardening system (8), and the outlet of the hardening system (8) is connected to the inlet of the circulating water tank (3). The third branch pipe (13) is connected to the inferior water disposal system (9). A circulating cooling water pipeline is provided between the cooling tower (6) and the final condensing effect (53); the heat exchanger (7) is located on the circulating cooling water pipeline or the concentrated brine main pipe (10).

2. The low-temperature multi-effect distillation wastewater deep treatment and reuse system according to claim 1, characterized in that, The ammonia removal facility (2) adopts a breakpoint chlorination device, which is located on the outlet pipe of the recycled water pump of the wastewater treatment system (1).

3. The low-temperature multi-effect distillation wastewater deep treatment and reuse system according to claim 1, characterized in that, The hardening system (8) is any one of a fluidized bed induced crystallization hardening device, an ion exchange hardening device, or a chemical precipitation hardening device.

4. The low-temperature multi-effect distillation wastewater deep treatment and reuse system according to claim 1, characterized in that, The low-temperature multi-effect distillation unit (5) is a horizontal tube falling film evaporator, and its heat exchange tube is made of titanium tube or corrosion-resistant alloy tube.

5. The low-temperature multi-effect distillation wastewater deep treatment and reuse system according to claim 1, characterized in that, The filter (4) is a self-cleaning filter with a filtration accuracy of 50μm to 200μm.

6. The low-temperature multi-effect distillation wastewater deep treatment and reuse system according to claim 1, characterized in that, The heat exchanger (7) is a plate heat exchanger, which is installed on the concentrated brine main pipe (10) and located between the low temperature multi-effect distillation unit (5) and the three branch pipes.

7. The low-temperature multi-effect distillation wastewater deep treatment and reuse system according to claim 1, characterized in that, Each of the three branch pipes is equipped with an electric regulating valve and a flow meter, which are electrically connected to the PLC control system.

8. A method for deep treatment and reuse of low-temperature multi-effect distillation wastewater, employing the low-temperature multi-effect distillation wastewater deep treatment and reuse system as described in any one of claims 1 to 7, characterized in that, Includes the following steps: S1: Wastewater is treated by coagulation, flocculation, sedimentation and filtration in the wastewater treatment system (1) to remove suspended solids and organic matter and obtain recycled water; S2: The reclaimed water enters the ammonia removal facility (2), where ammonia nitrogen is removed by the breakpoint chlorination method and disinfected, and the effluent enters the circulating water pool (3). S3: The effluent from the circulating water tank (3) is filtered (4) to remove suspended solids, colloids and impurities, and then sent to the low-temperature multi-effect distillation unit (5). S4: External steam is introduced into the first evaporation effect (51) of the low-temperature multi-effect distillation unit (5) to heat the water and make it evaporate. The generated secondary steam enters the subsequent evaporation effects to heat the water and realize the cascade utilization of heat. The final condensation effect (53) uses the circulating cooling water provided by the cooling tower (6) to condense the secondary steam into distilled water and collects the distilled water generated by each effect as product water and sends it out. S5: The concentrated brine discharged from the low-temperature multi-effect distillation unit (5) is divided into three streams through the concentrated brine main pipe (10): The concentrated brine in the first branch pipe (11) flows directly back to the circulating water tank (3). The concentrated brine in the second branch pipe (12) is sent to the hardness removal system (8) to remove calcium and magnesium ions and then returned to the circulating water tank (3). The concentrated brine in the third branch pipe (13) is sent to the substandard water disposal system (9) for cascade utilization; S6: The circulating cooling water circulates between the cooling tower (6) and the final condenser (53). When the temperature of the concentrated brine exceeds the set value, the heat exchanger (7) is started to cool down.

9. A method for deep treatment and reuse of low-temperature multi-effect distillation wastewater according to claim 8, characterized in that, The flow rate of concentrated brine in the third branch pipe (13) is dynamically adjusted according to the difference between the influent of recycled water and the water produced by the low-temperature multi-effect distillation unit (5). The influent of recycled water is equal to the sum of the water produced and the flow rate of the third branch pipe.

10. A method for deep treatment and reuse of low-temperature multi-effect distillation wastewater according to claim 8, characterized in that, The flow rate of concentrated brine in the second branch pipe (12) is dynamically adjusted according to the hardness of the inlet water entering the low-temperature multi-effect distillation unit (5). When the hardness of the inlet water reaches or exceeds the set threshold by measuring calcium ions, the flow rate in the second branch pipe (12) is increased; when the hardness of the inlet water is lower than the set threshold, the flow rate in the second branch pipe (12) is decreased.

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