Industrial wastewater treatment device and treatment method

Abstract

The application relates to the field of industrial wastewater treatment, in particular to an industrial wastewater treatment device and method, which comprises a pretreatment unit, a membrane distillation unit, a fluidized crystallization unit, a heat energy recovery unit and a collection unit; the pretreatment unit comprises an adjusting tank and a grating filter; the membrane distillation unit comprises a hollow fiber hydrophobic membrane assembly packaged in a pressure container, a hot side flow channel and a cold side flow channel; the fluidized crystallization unit comprises a crystallization tower, a water distributor and a particle distribution plate arranged at the bottom of the crystallization tower and a medicament adding port for adding a precipitant; the heat energy recovery unit comprises a plate heat exchanger; the heat energy recovery unit is connected between the hot side flow channel outlet of the membrane distillation unit and the water outlet of the pretreatment unit; the product collection unit comprises a water production tank and a crystalline particle collector; and the product collection unit is connected with the cold side flow channel of the membrane distillation unit and the fluidized crystallization unit respectively. The application has the effect of effectively treating high-hardness wastewater and multi-pollutant wastewater.

Description

Technical Field

[0001] This application relates to the field of industrial wastewater treatment, and in particular to an industrial wastewater treatment apparatus and treatment method. Background Technology

[0002] Industrial wastewater is complex in composition, often containing toxic substances such as heavy metals, organic matter, and high concentrations of salts. Direct discharge can cause serious harm to the ecological environment and human health, thus requiring treatment through efficient purification technologies. Currently, common wastewater treatment methods include physical, chemical, and biological processes; however, these methods often suffer from low treatment efficiency, high energy consumption, or secondary pollution. Especially with the expansion of industrial scale and the surge in wastewater discharge, traditional technologies struggle to meet increasingly stringent environmental standards. Furthermore, existing technologies often focus on the removal of single pollutants, lacking comprehensive consideration for the synergistic treatment of multiple pollutants and resource recovery, resulting in high overall operating costs and insufficient sustainability.

[0003] Membrane distillation, as an emerging membrane separation process, has shown potential in industrial wastewater treatment due to its advantages of low-temperature operation and high desalination rate. However, existing membrane distillation equipment typically uses independent heating and cooling units, resulting in large system size, low efficiency, and direct discharge of large amounts of waste heat, exacerbating energy waste. Furthermore, when treating high-hardness wastewater (such as wastewater from the chemical and metallurgical industries), traditional softening technologies such as lime softening are prone to fluctuations in effluent quality due to improper dosage control, increasing the difficulty of operation and management. While reverse osmosis technology can effectively remove salt, the membrane surface is susceptible to scaling by calcium and magnesium ions, leading to decreased permeate yield and shortened membrane life. A deeper technical problem lies in the lack of intelligent coupling between heat recovery and the softening process in existing systems, making it impossible to achieve real-time hardness control and anti-scaling optimization while reducing energy consumption.

[0004] In recent years, new technologies such as fluidized bed induced crystallization deposition have attracted attention in inorganic wastewater treatment. These technologies remove pollutants through crystallization deposition and have advantages such as rapid reaction and no sludge generation. However, in complex wastewater systems, the crystallization process is easily affected by suspended solids and organic matter, leading to clogging of the packing surface and decreased efficiency. System design often neglects the synergy with upstream processes (such as membrane distillation), making it difficult to integrate waste heat with crystallization drive. Summary of the Invention

[0005] In order to effectively treat wastewater with high hardness and multiple pollutants, this application provides an industrial wastewater treatment device and treatment method.

[0006] This application provides an industrial wastewater treatment device and method, which adopts the following technical solution: An industrial wastewater treatment device and method, comprising: The pretreatment unit includes an equalization tank and a bar filter, which performs preliminary filtration and homogenization treatment on industrial wastewater; A membrane distillation unit is connected to the pretreatment unit. The membrane distillation unit includes a hollow fiber hydrophobic membrane assembly encapsulated in a pressure vessel, a hot-side flow channel, and a cold-side flow channel. The membrane distillation unit performs membrane distillation concentration on the pretreated wastewater. A fluidized bed crystallization unit is connected to the hot-side flow channel outlet of the membrane distillation unit. The fluidized bed crystallization unit induces crystallization and softens the membrane distillation concentrate. The fluidized bed crystallization unit includes a crystallization tower, a water distributor and a particle distribution plate disposed at the bottom of the crystallization tower, and a reagent dosing port for adding a precipitant. A heat recovery unit, including a plate heat exchanger, is connected between the hot-side flow channel outlet of the membrane distillation unit and the water outlet of the pretreatment unit. The heat recovery unit recovers the heat of the membrane distillation concentrate to preheat the wastewater entering the membrane distillation unit. The product collection unit includes a product water tank and a crystal particle collector. The product collection unit is connected to the cold side channel of the membrane distillation unit and the fluidized crystallization unit, respectively. The product collection unit collects the treated product water and crystal particles.

[0007] By adopting the above technical solutions, the bar screen filter in the pretreatment unit can accurately intercept suspended solids and large particulate impurities in industrial wastewater, while the equalization tank stabilizes the fluctuations in wastewater quality and quantity through homogenization, avoiding membrane fouling or operational instability in the subsequent membrane distillation unit due to influent impact. The membrane distillation unit uses hollow fiber hydrophobic membrane modules, utilizing the temperature difference between the hot-side wastewater and the cold-side condensate to drive water vapor to selectively permeate through the membrane pores, achieving both efficient wastewater concentration and avoiding the high energy consumption problem of heating wastewater to the boiling point required by traditional thermal distillation. The fluidized bed crystallization unit uses a water distributor and particle distribution plate at the bottom of the crystallization tower to ensure that the membrane distillation concentrate rises uniformly. The flow rate, combined with the precipitant added at the reagent dosing port, induces calcium and magnesium ions to crystallize and deposit on the particle surface, effectively reducing the hardness of wastewater and solving the scaling problem of high-hardness wastewater on pipe and equipment surfaces. The plate heat exchanger of the heat recovery unit transfers the heat of the concentrated liquid on the hot side of the membrane distillation to the effluent of the pretreatment unit, raising the temperature of the wastewater entering the membrane distillation unit by 40-50°C and reducing external heating energy consumption. The product collection unit's product water tank can store condensate that meets industrial reuse standards, while the crystallization particle collector collects and recovers the calcium carbonate, magnesium hydroxide, and other crystals generated by fluidized bed crystallization for reuse as cement admixtures or building material raw materials.

[0008] Preferably, the filtration accuracy of the grid filter is ≤100μm; The regulating tank is equipped with a water quality equalization device.

[0009] By adopting the above technical solutions, the bar screen filter, with a filtration accuracy of ≤100μm, can accurately intercept suspended solids with a particle size ≥100μm in industrial wastewater. This prevents such large particles from entering the subsequent membrane distillation unit and clogging the pores of the hollow fiber hydrophobic membrane. The membrane pores are typically 0.1-0.3μm. If pretreatment is insufficient, the accumulation of suspended solids can lead to a decrease in membrane flux and even irreversible fouling. The filtration accuracy of ≤100μm can control the suspended solids concentration before the membrane to ≤20mg / L, significantly extending the chemical cleaning cycle of the membrane module and reducing maintenance costs. At the same time, the water quality equalization device in the equalization tank continuously mixes the wastewater, balancing the fluctuations in the influent water quality at different times. This keeps the water quality parameters of the wastewater entering the membrane distillation unit stable, avoiding temperature imbalances on both sides of the membrane or disordered fluidization state of the carrier in the fluidized bed crystallization unit caused by sudden changes in water quality. Ultimately, this ensures the stable coordinated operation of the membrane distillation concentration and crystallization softening processes.

[0010] Preferably, the equalization tank further includes multiple inclined plate sedimentation tanks, wherein the surface loading rate of the inclined plate sedimentation tanks is 1.0-1.4 m³ / (m²·h); The water quality equalization device is a pH adjustment tank with a built-in online pH meter and NaOH / HCl dosing device. The water quality equalization device adjusts the pH value of the internal liquid to 7.0-9.0.

[0011] By adopting the above technical solution, the inclined plate sedimentation tank is set with a surface loading of 1.0-1.4 m³ / (m²·h). Based on the shallow pool theory, this increases the sedimentation area and reduces the upward flow velocity of wastewater, allowing fine suspended solids and colloidal particles with a particle size ≥20μm in the wastewater to settle rapidly. This reduces the suspended solids in the effluent from ≤20mg / L after grid filtration to ≤10mg / L, effectively reducing the amount of particles adhering to the membrane surface of the subsequent membrane distillation unit and slowing down the membrane fouling process. At the same time, the water quality equalization device monitors the pH in real time through an online pH meter and uses NaOH / HCl to precisely adjust the pH to 7.0-9.0. This range avoids hydrolytic corrosion of the membrane material under acidic conditions and prevents calcium carbonate scaling on the membrane surface caused by excessive alkalinity. It also meets the chemical stability requirements of the modified silica sand carrier in the fluidized bed crystallization unit. The neutral to slightly alkaline environment inhibits carrier dissolution and ensures its fluidization state. In addition, this pH range is the optimal condition for the reaction between the precipitant and calcium and magnesium ions, which can promote the formation of loose calcium carbonate and magnesium hydroxide crystals and improve the crystallization deposition efficiency.

[0012] Preferably, the membrane distillation unit uses a hollow fiber hydrophobic microporous membrane or a plate-type hydrophobic microporous membrane, and the hot-side flow channel and the cold-side flow channel are respectively equipped with a temperature sensor and a pressure monitor.

[0013] By adopting the above technical solutions, the hollow fiber hydrophobic microporous membrane achieves a compact device design due to its high packing density, while the plate-type hydrophobic microporous membrane reduces the flow velocity gradient on the membrane surface through its large-area flat plate structure. Both rely on their hydrophobic properties to accurately screen water and non-volatile solutes. Water vapor molecules can diffuse through the membrane pores, while solutes such as salts and organic matter are retained. The conductivity of the produced water can be stably controlled at ≤100μS / cm. At the same time, temperature sensors and pressure monitors installed in the hot and cold side channels can provide real-time feedback on the temperature difference and transmembrane pressure across the membrane. The control system dynamically adjusts the heating power on the hot side or the cooling water flow rate on the cold side accordingly. When the hot side temperature deviates from the set value, the steam volume or industrial waste heat supply is adjusted in time to ensure a stable steam pressure difference. When the cold side pressure rises abnormally, the wastewater feed flow rate is automatically reduced to prevent irreversible fouling or mechanical damage to the membrane surface due to pressure overload.

[0014] Preferably, the crystallization tower is provided with a water outlet weir at the top to prevent the loss of crystal seeds. The crystallization tower is loaded with silica sand or modified active magnesium oxide as crystal seeds, and the particle size of the crystal seeds ranges from 0.5 to 2.0 mm.

[0015] By adopting the above technical solution, the effluent weir at the top of the crystallization tower controls the effluent level and flow rate, allowing the fluidized seed crystals to remain in the tower due to gravity settling, preventing them from being lost with the supernatant of the concentrate, reducing the frequency of seed crystal replenishment and operating costs. Simultaneously, the loaded silica sand or modified active magnesium oxide, acting as seed crystals, provides ample heterogeneous nucleation centers for calcium and magnesium ions, significantly enhancing the mass transfer efficiency of calcium and magnesium ions from the liquid phase to the seed crystal surface, ultimately stabilizing the effluent hardness at ≤50mg / L. Furthermore, the seed crystal particle size of 0.5-2.0mm is optimized through fluid dynamics simulation. Seed crystals smaller than 0.5mm are easily carried away by the rising water flow, while seed crystals larger than 2.0mm have insufficient specific surface area, leading to a reduction in crystallization sites. This particle size range ensures that the seed crystals maintain good expansion rate and mass transfer uniformity within the fluidized bed, preventing both carrier accumulation and compaction that affects water flow distribution, and over-fluidization that could cause seed crystal collision and breakage, ultimately guaranteeing continuous and stable operation of the crystallization unit.

[0016] Preferably, the plate heat exchanger is disposed between the pretreatment unit and the membrane distillation unit, the plate heat exchanger is connected to the hot-side flow channel outlet of the membrane distillation unit, and the plate heat exchanger is connected to the outlet of the fluidized crystallization unit. The plate heat exchanger is made of corrosion-resistant materials.

[0017] By adopting the above technical solution, a plate heat exchanger is placed between the pretreatment unit and the membrane distillation unit, and linked to the outlet of the membrane distillation hot-side flow channel and the outlet of the fluidized bed crystallization unit. This allows for the synergistic capture of the waste heat from the membrane distillation concentrate and the waste heat from the fluidized bed crystallization unit's effluent, which is then used to preheat the pretreated wastewater. This raises the temperature of the wastewater entering the membrane distillation unit from ambient temperature to 40-50°C, significantly reducing the energy consumption for additional heating on the membrane side. Simultaneously, it maintains a stable temperature difference across the membrane, ensuring continuous stability of membrane flux and water production efficiency. Furthermore, the plate heat exchanger uses corrosion-resistant materials, effectively resisting the erosion of acids, alkalis, and heavy metal ions in industrial wastewater, preventing system shutdowns or water pollution caused by heat exchanger leaks. Its heat transfer coefficient can be maintained at 1000-1500 W / (m²·K) for a long period.

[0018] Preferably, the heater is disposed between the heat recovery unit and the membrane distillation unit, and the heater heats the preheated wastewater; The heater is an electric heating or steam heating device, and the heater is equipped with a temperature control module.

[0019] By adopting the above technical solution, the heater is set between the heat recovery unit and the membrane distillation unit. It can supplement the heating of wastewater preheated to 40-50℃ by the plate heat exchanger, precisely raising it to the optimal hot-side water temperature required for membrane distillation. This temperature range can ensure sufficient vapor pressure difference across the membrane to drive water vapor migration across the membrane, while avoiding excessive temperature that accelerates membrane material aging. The heater adopts a flexible configuration of electric heating or steam heating, which can be adapted according to the waste heat resources of the plant. When there is waste heat steam, steam heating is used first to reduce energy costs; when there is no waste heat, electric heating is used to cover different operating conditions. The temperature control module can monitor the hot-side water temperature in real time and dynamically adjust the heating power to cope with wastewater flow fluctuations or initial temperature changes, ensuring that the temperature difference across the membrane is stable within the optimal range of 20-30℃, thereby maintaining the continuous stability of membrane flux and product water quality.

[0020] Preferably, it also includes a cooling system connected to the cold-side flow channel of the membrane distillation unit, the cooling system maintaining a low temperature on the cold side, and the cooling system including a circulating water pump and a heat dissipation device.

[0021] By adopting the above technical solution, the cooling system is connected to the cold-side flow channel of the membrane distillation unit. A circulating water pump drives the cooling water to circulate, continuously absorbing the heat released by the condensation of water vapor on the cold side. The heat dissipation device efficiently dissipates this heat to the environment, maintaining a stable low temperature of 10-20℃ on the cold side. This creates a constant vapor pressure difference across the membrane, ensuring that water vapor can pass smoothly through the hydrophobic membrane. The membrane distillation permeate flux is stably maintained at 10-20 L / (m²·h), while the condensation process is thorough, and the permeate conductivity remains ≤100 μS / cm. Furthermore, the circulating water pump allows for the reuse of cooling water, reducing water consumption. The heat dissipation device continuously removes the heat absorbed by the cooling water, preventing the cooling water temperature from rising and causing a subsequent increase in the cold-side temperature. This prevents a decrease in membrane flux or insufficient condensation due to cold-side temperature fluctuations, providing long-term stable condensation conditions for the membrane distillation unit and extending the service life of the membrane module.

[0022] Preferably, the product water tank is connected to the cold side flow channel of the membrane distillation unit, the crystallization particle collector is connected to the bottom of the fluidized crystallization unit, and the crystallization particle collector is equipped with an automatic discharge valve.

[0023] By adopting the above technical solution, the product water tank is directly connected to the cold side flow channel of the membrane distillation unit, which can efficiently capture the product water formed by the condensation of water vapor, avoid secondary pollution caused by the leakage or retention of condensate, and provide a stable source for centralized storage and industrial reuse of product water, thereby improving the utilization rate of water resources. The crystallization particle collector is connected to the bottom of the fluidized bed crystallization unit, which can receive the crystal particles such as calcium carbonate and magnesium hydroxide generated during the crystallization process in real time, preventing the particles from accumulating at the bottom of the crystallization tower, which would cause blockage of the fluidized bed or disorder of the carrier fluidization state. The automatic discharge valve can be opened at timed or quantitatively according to the particle accumulation, so as to achieve undisturbed continuous discharge, ensure the stable operation of the crystallization unit 24 hours a day, and output product water and crystallization products simultaneously. In addition, the automatically discharged crystal particles can be directly recycled as cement admixtures or building material raw materials, avoiding pollution from solid waste accumulation.

[0024] An industrial wastewater treatment method includes the following steps: S1. Pretreatment: Industrial wastewater is homogenized and filtered through the pretreatment unit to remove large particulate suspended solids; S2. Membrane distillation concentration and heat recovery: The pretreated wastewater is preheated by the heat recovery unit and then enters the hot side channel of the membrane distillation unit for membrane distillation treatment to produce water vapor and concentrate. The water vapor is condensed into product water in the cold side channel and collected to the product collection unit. S3, Fluidized bed crystallization and reflux: The concentrated liquid discharged from the membrane distillation unit is introduced into the fluidized bed crystallization unit. A precipitant is added under fluidized bed conditions to allow calcium and magnesium ions to crystallize and deposit on the seed crystal surface, resulting in softened wastewater. Part of the softened wastewater is then refluxed to the heat recovery unit for heat exchange with the pretreated wastewater. S4. System Control and Monitoring: By monitoring and adjusting pH, temperature, flow rate and hardness parameters in real time, the system ensures stable operation of the device, and the crystallized particles are periodically discharged from the bottom of the fluidized crystallization unit and recycled.

[0025] By adopting the above technical solutions, S1 pretreatment homogenizes water quality and quantity and removes suspended solids ≥100μm through filtration, ensuring that the SS of the wastewater entering the membrane distillation unit is ≤10mg / L and the pH is stabilized at 7.0-9.0, avoiding pollution and damage to the membrane surface caused by particle adhesion or acid and alkali corrosion; S2 preheats the wastewater before membrane distillation using a heat recovery unit, raising the inlet water temperature from room temperature to 40-50℃, reducing external heating energy consumption by about 20%-30%, while the product water produced by membrane distillation is directly collected to the product water tank for reuse, with a product water rate of 70%-80%; S3 fluidized bed crystallization unit receives... The membrane distillation concentrate, through the induction of calcium and magnesium ion crystallization by silica sand / modified magnesium oxide seed crystals, reduces the hardness of the effluent from 500-1500 mg / L to ≤50 mg / L, solving the scaling problem of high-hardness wastewater. Part of the softened wastewater is also recycled to the heat recovery unit for heat exchange with the pretreated effluent. The S4 system controls the flow by dynamically adjusting variables such as heating power and cooling water flow rate in real time, monitoring pH, temperature, flow rate, and hardness parameters to ensure a stable temperature difference of 20-30℃ across the membrane and uniform fluidization in the crystallization tower. Simultaneously, the crystallized particles are periodically recovered via an automatic discharge valve for reuse as cement admixtures.

[0026] In summary, this application includes at least one of the following beneficial technical effects: 1. The bar screen filter in the pretreatment unit can accurately intercept suspended solids and large particulate impurities in industrial wastewater, while the equalization tank stabilizes the water quality and quantity fluctuations through homogenization, avoiding membrane fouling or operational instability in the subsequent membrane distillation unit due to influent impact. The membrane distillation unit uses hollow fiber hydrophobic membrane modules, utilizing the temperature difference between the hot-side wastewater and the cold-side condensate to drive water vapor to selectively permeate through the membrane pores, achieving efficient wastewater concentration while avoiding the high energy consumption problem of heating wastewater to the boiling point required by traditional thermal distillation. The fluidized bed crystallization unit uses a water distributor and particle distribution plate at the bottom of the crystallization tower to ensure that the membrane distillation concentrate flows at a uniform upward flow rate. The precipitant added at the dosing port induces calcium and magnesium ions to crystallize and deposit on the particle surface, effectively reducing the hardness of wastewater and solving the scaling problem of high-hardness wastewater on pipe and equipment surfaces. The plate heat exchanger of the heat recovery unit transfers the heat of the concentrated liquid on the hot side of the membrane distillation to the effluent of the pretreatment unit, raising the temperature of the wastewater entering the membrane distillation unit by 40-50°C and reducing external heating energy consumption. The product collection unit's product water tank can store condensate that meets industrial reuse standards, while the crystallization particle collector collects and recovers the calcium carbonate, magnesium hydroxide, and other crystals generated by fluidized bed crystallization for reuse as cement admixtures or building material raw materials.

[0027] 2. S1 pretreatment homogenizes water quality and quantity, and removes suspended solids ≥100μm through filtration, ensuring that the wastewater entering the membrane distillation unit has SS ≤10mg / L and a stable pH of 7.0-9.0, preventing fouling and damage to the membrane surface caused by particle adhesion or acid / alkali corrosion; S2 preheats the wastewater before membrane distillation using a heat recovery unit, raising the inlet water temperature from ambient temperature to 40-50℃, reducing external heating energy consumption by approximately 20%-30%. Simultaneously, the product water produced by membrane distillation is directly collected in the product water tank for reuse, achieving a product water rate of 70%-80%; S The 3 fluidized bed crystallization unit receives the membrane distillation concentrate and induces calcium and magnesium ion crystallization through silica sand / modified magnesium oxide seed crystals to solve the scaling problem of high-hardness wastewater. Part of the softened wastewater is also returned to the heat recovery unit for heat exchange with the pretreated effluent. The S4 system controls the system by monitoring pH, temperature, flow rate and hardness parameters in real time and dynamically adjusting variables such as heating power and cooling water flow rate to ensure that the temperature difference across the membrane is stable at 20-30℃ and the fluidization state of the crystallization tower is uniform. At the same time, the crystallized particles are periodically recovered by an automatic discharge valve and reused as cement admixtures. Attached Figure Description

[0028] Figure 1 This is a structural flow diagram of the industrial wastewater treatment device in the embodiments of this application; Figure 2 This is a flowchart of the industrial wastewater treatment steps in the embodiments of this application.

[0029] Explanation of reference numerals in the attached drawings: 1. Pretreatment unit; 11. Equalization tank; 111. Water homogenization device; 1111. Online pH meter; 1112. pH equalization tank; 112. Inclined plate sedimentation tank; 12. Bar filter; 2. Membrane distillation unit; 21. Hollow fiber hydrophobic membrane assembly; 22. Hot side flow channel; 221. Temperature sensor; 23. Cold side flow channel; 231. Pressure monitor; 3. Fluidized bed crystallization unit; 31. Crystallization tower; 32. Water distributor; 33. Particle distribution plate; 34. Reagent dosing port; 4. Heat recovery unit; 41. Plate heat exchanger; 5. Product collection unit; 51. Product water tank; 52. Crystallized particle collector; 521. Automatic discharge valve; 6. Cooling system; 61. Circulating water pump; 62. Heat dissipation device. Detailed Implementation

[0030] The following is in conjunction with the appendix Figure 1-2 This application will be described in further detail.

[0031] This application discloses an industrial wastewater treatment device and method. (Refer to...) Figure 1The industrial wastewater treatment device includes a pretreatment unit 1, a membrane distillation unit 2 connected to the pretreatment unit 1, a fluidized bed crystallization unit 3 connected to the membrane distillation unit 2, a heat recovery unit 4 connected between the outlet of the membrane distillation unit 2 and the pretreatment unit 1, and a product collection unit 5 connected to the membrane distillation unit 2 and the fluidized bed crystallization unit 3 respectively.

[0032] Pretreatment unit 1 includes an equalization tank 11 and a bar screen filter 12. Pretreatment unit 1 performs preliminary filtration and homogenization treatment on industrial wastewater. Membrane distillation unit 2 is connected to pretreatment unit 1. Membrane distillation unit 2 includes a hollow fiber hydrophobic membrane module 21 encapsulated in a pressure vessel, a hot-side channel 22, and a cold-side channel 23. Membrane distillation unit 2 concentrates the pretreated wastewater through membrane distillation. Fluidized bed crystallization unit 3 is connected to the outlet of the hot-side channel 22 of membrane distillation unit 2. Fluidized bed crystallization unit 3 induces crystallization and softens the membrane distillation concentrate. Fluidized bed crystallization unit 3 includes a crystallization tower 31 and a filter screen located at the bottom of crystallization tower 31. The unit includes a water distributor 32 and a particle distribution plate 33, as well as a reagent inlet 34 for adding precipitant; the heat recovery unit 4 includes a plate heat exchanger 41, which is connected between the outlet of the hot side channel 22 of the membrane distillation unit 2 and the outlet of the pretreatment unit 1. The heat recovery unit 4 recovers the heat of the membrane distillation concentrate to preheat the wastewater entering the membrane distillation unit 2; the product collection unit 5 includes a product water tank 51 and a crystallization particle collector 52, which is connected to the cold side channel 23 of the membrane distillation unit 2 and the fluidized crystallization unit 3 respectively. The product collection unit 5 collects the treated product water and crystallization particles.

[0033] The filtration accuracy of the bar filter 12 is ≤100μm; the equalization tank 11 is equipped with a water quality equalization device 111. The bar screen filter 12 is set with a filtration accuracy of ≤100μm, which can accurately intercept suspended solids with a particle size of ≥100μm (such as metal fragments, colloidal particles, fiber impurities, etc.) in industrial wastewater. This prevents such large particles from entering the subsequent membrane distillation unit 2 and clogging the membrane pores of the hollow fiber hydrophobic membrane. The membrane pores are usually 0.1-0.3μm. If the pretreatment is insufficient, the accumulation of suspended solids will lead to a decrease in membrane flux and even irreversible pollution. The filtration accuracy of ≤100μm can control the concentration of suspended solids before the membrane to ≤20mg / L, which can significantly extend the chemical cleaning cycle of the membrane module and reduce maintenance costs. At the same time, the water quality equalization device 111 in the equalization tank 11 continuously mixes the wastewater and balances the water quality fluctuations of the influent at different times, so that the water quality parameters of the wastewater entering the membrane distillation unit 2 remain stable. This avoids the imbalance of temperature difference on both sides of the membrane or the disorder of the fluidization state of the carrier in the fluidized crystallization unit 3 caused by sudden changes in water quality, and ultimately ensures the stable coordinated operation of the membrane distillation concentration and crystallization softening processes.

[0034] In an optional embodiment, the equalization tank 11 further includes multiple inclined plate sedimentation tanks 112, the surface loading of which is 1.0-1.4 m³ / (m²·h); in a preferred embodiment, the water quality equalization device 111 is a pH equalization tank 1112 with a built-in online pH meter 1111 and NaOH / HCl dosing device, the water quality equalization device 111 adjusts the pH value of the internal liquid to 7.0-9.0. The inclined plate sedimentation tank 112 is set with a surface loading of 1.0-1.4 m³ / (m²·h). Based on the shallow tank theory, this increases the sedimentation area and reduces the upward flow velocity of wastewater, allowing fine suspended solids and colloidal particles with a particle size ≥20μm in the wastewater to settle rapidly. This reduces the suspended solids in the effluent from ≤20mg / L after grid filtration to ≤10mg / L, effectively reducing the amount of particles adhering to the membrane surface of the subsequent membrane distillation unit 2 and slowing down the membrane fouling process. At the same time, the water quality equalization device 111 monitors the pH in real time through an online pH meter 1111 and uses NaOH / HCl to precisely adjust the pH to 7.0-9.0. This range avoids hydrolytic corrosion of the membrane material under acidic conditions and prevents calcium carbonate scaling on the membrane surface caused by excessive alkalinity. It also meets the chemical stability requirements of the modified silica sand carrier in the fluidized bed crystallization unit 3. The neutral to slightly alkaline environment inhibits carrier dissolution and ensures its fluidization state. In addition, this pH range is the optimal condition for the reaction between the precipitant and calcium and magnesium ions, which can promote the formation of loose calcium carbonate and magnesium hydroxide crystals and improve the crystallization deposition efficiency.

[0035] Membrane distillation unit 2 employs a hollow fiber hydrophobic microporous membrane or a plate-type hydrophobic microporous membrane. In an optional embodiment, the hot-side flow channel 22 and the cold-side flow channel 23 are respectively equipped with a temperature sensor 221 and a pressure monitor 231. The hollow fiber hydrophobic microporous membrane achieves a compact design due to its high packing density, while the plate-type hydrophobic microporous membrane reduces the flow velocity gradient on the membrane surface through its large-area flat plate structure. Both rely on their hydrophobic properties to accurately separate water and non-volatile solutes. Water vapor molecules can diffuse through the membrane pores, while solutes such as salts and organic matter are retained. The conductivity of the product water can be stably controlled at ≤100μS / cm, which meets the GB / T19923-2005 industrial water standard.

[0036] Meanwhile, the temperature sensor 221 and pressure monitor 231 installed in the hot-side flow channel 22 and the cold-side flow channel 23 can provide real-time feedback on the temperature difference and transmembrane pressure across the membrane. The temperature sensor 221 has an accuracy of ±0.5℃, and the pressure monitor 231 has an accuracy of ±0.1kPa. The optimal driving temperature difference across the membrane is maintained at 20-30℃, and the transmembrane pressure is ≤0.1MPa to avoid membrane deformation or rupture. Based on this, the control system dynamically adjusts the heating power on the hot side or the cooling water flow rate on the cold side. When the hot-side temperature deviates from the set value, the steam volume or industrial waste heat supply is adjusted in time to ensure stable steam pressure difference. When the cold-side pressure rises abnormally, the wastewater feed flow rate is automatically reduced to prevent irreversible contamination or mechanical damage to the membrane surface caused by pressure overload.

[0037] The crystallization tower 31 is equipped with an outlet weir at the top to prevent seed crystal loss. The crystallization tower 31 is loaded with silica sand or modified active magnesium oxide as seed crystals, with a particle size range of 0.5-2.0 mm. The outlet weir at the top of the crystallization tower 31 controls the outflow water level and flow rate to retain the fluidized seed crystals in the tower due to gravity settling, preventing them from being lost with the supernatant of the concentrate, reducing the frequency of seed crystal replenishment and operating costs. The outlet weir at the top of the crystallization tower 31 forms a downward reflux zone of 0.1-0.3 m / s by controlling the outflow water level and flow rate. The fluidized seed crystals are silica sand or modified active magnesium oxide.

[0038] In an optional embodiment, the loaded silica sand or modified active magnesium oxide serves as seed crystals, providing ample heterogeneous nucleation centers for calcium and magnesium ions. This significantly enhances the mass transfer efficiency of calcium and magnesium ions from the liquid phase to the seed crystal surface, ultimately stabilizing the effluent hardness at ≤50 mg / L. The silica sand has a rough structure with natural silica on its surface, while the modified active magnesium oxide has porous active sites formed through surface hydroxylation treatment. The range of effluent hardness stability is far lower than the 80-100 mg / L of traditional chemical precipitation methods. Furthermore, the seed crystal particle size of 0.5-2.0 mm is optimized through hydrodynamic simulation. Seed crystals smaller than 0.5 mm are easily carried away by the rising water flow, while seed crystals larger than 2.0 mm have insufficient specific surface area, resulting in a reduction in crystallization sites. This particle size range ensures that the seed crystals maintain good expansion rate and mass transfer uniformity in the fluidized bed. The expansion rate can be 30%-40%, which avoids the impact of carrier accumulation and compaction on water flow distribution, and also prevents excessive fluidization from causing seed crystal collision and breakage, ultimately ensuring the continuous and stable operation of the crystallization unit.

[0039] Plate heat exchanger 41 is disposed between pretreatment unit 1 and membrane distillation unit 2. Plate heat exchanger 41 is connected to the outlet of hot side flow channel 22 of membrane distillation unit 2, and plate heat exchanger 41 is connected to the outlet of fluidized crystallization unit 3. Plate heat exchanger 41 is made of corrosion resistant material. A plate heat exchanger 41 is placed between the pretreatment unit 1 and the membrane distillation unit 2, and linked to the outlet of the membrane distillation hot-side flow channel 22 and the outlet of the fluidized crystallization unit 3. This allows the waste heat (50-70℃) of the membrane distillation concentrate and the waste heat (30-40℃) of the effluent from the fluidized crystallization unit 3 to be captured together for preheating the pretreated wastewater. This raises the temperature of the wastewater entering the membrane distillation unit 2 from room temperature (20-25℃) to 40-50℃, significantly reducing the energy consumption of additional heating on the membrane side (by about 20%-30%). At the same time, it maintains a stable temperature difference (20-30℃) on both sides of the membrane, ensuring the continuous stability of membrane flux (10-20L / (m²·h)) and water production efficiency.

[0040] In addition, the plate heat exchanger 41 is made of corrosion-resistant materials (such as 316L stainless steel or fluoroplastics), which can effectively resist the corrosion of acids, alkalis and heavy metal ions in industrial wastewater, and avoid system shutdown or water pollution caused by heat exchanger leakage; its heat transfer coefficient can be maintained at 1000-1500W / (m²·K) for a long time (far higher than the 500W / (m²·K) of ordinary carbon steel heat exchangers).

[0041] A heater is positioned between the heat recovery unit 4 and the membrane distillation unit 2 to heat the preheated wastewater. In an optional embodiment, the heater is an electric heating or steam heating device, and it is equipped with a temperature control module. The heater, positioned between the heat recovery unit 4 and the membrane distillation unit 2, can supplement the heating of the wastewater preheated to 40-50°C by the plate heat exchanger 41, precisely raising it to the optimal hot-side water temperature required for membrane distillation. This temperature range ensures sufficient vapor pressure difference across the membrane to drive water vapor migration across the membrane, while avoiding excessively high temperatures that accelerate membrane material aging. In an optional embodiment, the optimal hot-side water temperature required for membrane distillation is 50-70°C.

[0042] The heater can be flexibly configured with either electric or steam heating, adapting to the factory's waste heat resources. When waste heat steam is available, steam heating is prioritized to reduce energy costs; when no waste heat is available, electric heating is used to cover different operating conditions. The temperature control module can monitor the hot-side water temperature in real time and dynamically adjust the heating power to cope with fluctuations in wastewater flow or changes in initial temperature. For example, when the influent temperature is as low as 15°C in winter, and only 35°C after preheating, the heater automatically replenishes the heat to 60°C, ensuring that the temperature difference across the membrane remains stable within the optimal range of 20-30°C, thereby maintaining the continuous stability of membrane flux and product water quality. In an optional embodiment, the membrane flux is maintained at 10-20 L / (m²·h), and the product water conductivity is ≤100 μS / cm.

[0043] It also includes a cooling system 6, which is connected to the cold-side flow channel 23 of the membrane distillation unit 2. The cooling system 6 maintains a low temperature on the cold side and includes a circulating water pump 61 and a heat dissipation device 62. The cooling system 6 is connected to the cold-side flow channel 23 of the membrane distillation unit 2. The circulating water pump 61 drives the cooling water to circulate, continuously absorbing the heat released by the condensation of water vapor on the cold side. The heat dissipation device 62 efficiently dissipates the heat to the environment, thereby maintaining a stable low temperature of 10-20°C on the cold side and creating a constant vapor pressure difference across the membrane, ensuring that water vapor can pass smoothly through the hydrophobic membrane. In an optional embodiment, the vapor pressure difference is an effective temperature difference of 30-50°C between the hot side (50-70°C) and the cold side (10-20°C).

[0044] Optionally, the permeate flux of membrane distillation is stably maintained at 10-20 L / (m²·h), while the condensation process is thorough and complete, and the permeate conductivity is always ≤100 μS / cm, which meets the GB / T 19923-2005 industrial water standard. Secondly, the circulation water pump 61 enables the reuse of cooling water, reducing water consumption. The heat dissipation device 62 continuously removes the heat absorbed by the cooling water, preventing the cooling water temperature from rising and causing the cold side temperature to rise. This prevents the membrane flux from decreasing or the condensation from being insufficient due to the fluctuation of the cold side temperature, providing long-term stable condensation conditions for the membrane distillation unit 2 and extending the service life of the membrane module.

[0045] The product water tank 51 is connected to the cold side flow channel 23 of the membrane distillation unit 2, and the crystallization particle collector 52 is connected to the bottom of the fluidized crystallization unit 3. The crystallization particle collector 52 is equipped with an automatic discharge valve 521. The product water tank 51 is directly connected to the cold side flow channel 23 of the membrane distillation unit 2, which can efficiently capture the product water formed by the condensation of water vapor. The conductivity of this product water is ≤100μS / cm, avoiding secondary pollution caused by the leakage or retention of condensate water. At the same time, it provides a stable source for the centralized storage and industrial reuse of product water, improving the utilization rate of water resources. The crystallization particle collector 52 is connected to the bottom of the fluidized crystallization unit 3, which can receive the crystal particles such as calcium carbonate and magnesium hydroxide generated during the crystallization process in real time, preventing the particles from accumulating at the bottom of the crystallization tower 31, which would cause fluidized bed blockage or disorder of the carrier fluidization state. The automatic discharge valve 521 can be opened at timed or quantitatively according to the particle accumulation. The automatic discharge valve 521 is triggered by a weighing sensor or level gauge, thereby realizing continuous discharge without disturbance, ensuring the stable operation of the crystallization unit 24 hours a day, and the synchronous output of product water and crystallization products. In addition, the automatically discharged crystal particles can be directly recycled as cement admixtures or building material raw materials, avoiding pollution from solid waste accumulation.

[0046] See Figure 2 An industrial wastewater treatment method includes the following steps: S1. Pretreatment: Industrial wastewater is homogenized and filtered through pretreatment unit 1 to remove large particulate suspended solids; S2, Membrane distillation concentration and heat recovery: The pretreated wastewater is preheated by the heat recovery unit 4 and then enters the hot side channel 22 of the membrane distillation unit 2 for membrane distillation treatment, generating water vapor and concentrate. The water vapor is condensed into product water in the cold side channel 23 and collected to the product collection unit 5. S3, Fluidized Crystallization and Reflux: The concentrated liquid discharged from the membrane distillation unit 2 is introduced into the fluidized crystallization unit 3. A precipitant is added in the fluidized state to allow calcium and magnesium ions to crystallize and deposit on the surface of the seed crystals, resulting in softened wastewater. Part of the softened wastewater is then refluxed to the heat recovery unit 4 for heat exchange with the pretreated wastewater. S4. System Control and Monitoring: By real-time monitoring and adjustment of pH value, temperature, flow rate and hardness parameters, the stable operation of the device is ensured, and the crystallized particles are periodically discharged from the bottom of the fluidized crystallization unit 3 and recycled.

[0047] S1 pretreatment homogenizes water quality and quantity, and removes suspended solids ≥100μm through filtration, ensuring that the wastewater entering membrane distillation unit 2 has SS ≤10mg / L and a stable pH of 7.0-9.0, preventing fouling and damage to the membrane surface caused by particle adhesion or acid / alkali corrosion. S2 preheats the wastewater before membrane distillation using heat recovery unit 4, raising the inlet water temperature from ambient temperature (20-25℃) to 40-50℃, reducing external heating energy consumption by approximately 20%-30%. Simultaneously, the product water (conductivity ≤100μS / cm) produced by membrane distillation is directly collected in product water tank 51 for reuse, achieving a product water rate of 70%-80%. S3 fluidized bed crystallization... Unit 3 receives the membrane distillation concentrate and induces calcium and magnesium ion crystallization through silica sand / modified magnesium oxide seed crystals, reducing the effluent hardness from 500-1500 mg / L to ≤50 mg / L, thus solving the scaling problem of high-hardness wastewater. Part of the softened wastewater is also returned to the heat recovery unit 4 for heat exchange with the pretreated effluent. The S4 system controls the real-time monitoring of pH, temperature, flow rate, and hardness parameters, dynamically adjusting variables such as heating power and cooling water flow rate to ensure that the temperature difference across the membrane is stable at 20-30℃ and that the fluidization state of the crystallization tower 31 is uniform. At the same time, the crystallized particles are periodically recovered through the automatic discharge valve 521 and reused as cement admixtures.

[0048] The implementation principle of this application embodiment is as follows: the bar screen filter 12 of the pretreatment unit 1 can accurately intercept suspended solids and large particulate impurities in industrial wastewater, while the equalization tank 11 stabilizes the fluctuations in wastewater quality and quantity through homogenization, avoiding membrane fouling or operational instability in the subsequent membrane distillation unit 2 due to influent impact; the membrane distillation unit 2 adopts a hollow fiber hydrophobic membrane module 21, which uses the temperature difference between the hot-side wastewater and the cold-side condensate to drive water vapor to selectively permeate through the membrane pores, achieving efficient concentration of wastewater while avoiding the high energy consumption problem of heating wastewater to the boiling point required by traditional thermal distillation; the fluidized bed crystallization unit 3 uses the water distributor 32 and particle distribution plate 33 at the bottom of the crystallization tower 31 to make the membrane distillation concentrate uniformly dispersed. The uniform upward flow velocity, combined with the precipitant added through the reagent dosing port 34, induces calcium and magnesium ions to crystallize and deposit on the particle surface, effectively reducing the hardness of the wastewater and solving the scaling problem of high-hardness wastewater on the surface of pipes and equipment. The plate heat exchanger 41 of the heat recovery unit 4 transfers the heat of the concentrated liquid on the hot side of the membrane distillation to the effluent of the pretreatment unit 1, raising the temperature of the wastewater entering the membrane distillation unit 2 by 40-50℃ and reducing external heating energy consumption. The product water tank 51 of the product collection unit 5 can store condensate that meets industrial reuse standards, while the crystallization particle collector 52 collects and recovers the crystals such as calcium carbonate and magnesium hydroxide generated by fluidized crystallization, which can be reused as cement admixtures or building material raw materials.

[0049] The above are all preferred embodiments of this application, and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. An industrial wastewater treatment device and method, characterized in that, include: The pretreatment unit (1) includes an equalization tank (11) and a bar screen filter (12), wherein the pretreatment unit (1) performs preliminary filtration and homogenization treatment on industrial wastewater; A membrane distillation unit (2) is connected to the pretreatment unit (1). The membrane distillation unit (2) includes a hollow fiber hydrophobic membrane assembly (21), a hot-side flow channel (22), and a cold-side flow channel (23) encapsulated in a pressure vessel. The membrane distillation unit (2) concentrates the pretreated wastewater by membrane distillation. The fluidized bed crystallization unit (3) is connected to the hot side flow channel (22) outlet of the membrane distillation unit (2). The fluidized bed crystallization unit (3) induces crystallization and softens the membrane distillation concentrate. The fluidized bed crystallization unit (3) includes a crystallization tower (31), a water distributor (32) and a particle distribution plate (33) located at the bottom of the crystallization tower (31), and a reagent inlet (34) for adding precipitant. The heat recovery unit (4) includes a plate heat exchanger (41). The heat recovery unit (4) is connected between the outlet of the hot side flow channel (22) of the membrane distillation unit (2) and the outlet of the pretreatment unit (1). The heat recovery unit (4) recovers the heat of the membrane distillation concentrate to preheat the wastewater entering the membrane distillation unit (2). The product collection unit (5) includes a product water tank (51) and a crystal particle collector (52). The product collection unit (5) is connected to the cold side channel (23) of the membrane distillation unit (2) and the fluidized crystallization unit (3), respectively. The product collection unit (5) collects the processed product water and crystal particles.

2. The industrial wastewater treatment device according to claim 1, characterized in that, The filtration accuracy of the grid filter (12) is ≤100μm; The regulating tank (11) is equipped with a water quality equalization device (111).

3. The industrial wastewater treatment device according to claim 2, characterized in that, The equalization tank (11) also includes multiple inclined plate sedimentation tanks (112), the surface loading of which is 1.0-1.4 m³ / (m²·h); The water quality equalization device (111) is a pH adjustment tank (1112) with a built-in online pH meter (1111) and NaOH / HCl dosing device. The water quality equalization device (111) adjusts the pH value of the internal liquid to 7.0-9.

0.

4. The industrial wastewater treatment device according to claim 1, characterized in that, The membrane distillation unit (2) adopts a hollow fiber hydrophobic microporous membrane or a plate-type hydrophobic microporous membrane. The hot side channel (22) and the cold side channel (23) are respectively equipped with a temperature sensor (221) and a pressure monitor (231).

5. The industrial wastewater treatment device according to claim 4, characterized in that, The crystallization tower (31) is provided with a water outlet weir at the top to prevent the loss of crystal seeds. The crystallization tower (31) is filled with silica sand or modified active magnesium oxide as crystal seeds, and the particle size range of the crystal seeds is 0.5-2.0 mm.

6. The industrial wastewater treatment device according to claim 1, characterized in that, The plate heat exchanger (41) is disposed between the pretreatment unit (1) and the membrane distillation unit (2). The plate heat exchanger (41) is connected to the outlet of the hot side flow channel (22) of the membrane distillation unit (2), and the plate heat exchanger (41) is connected to the outlet of the fluidized crystallization unit (3). The plate heat exchanger (41) is made of corrosion-resistant material.

7. The industrial wastewater treatment device according to claim 1, characterized in that, The heater is located between the heat recovery unit (4) and the membrane distillation unit (2), and the heater heats the preheated wastewater; The heater is an electric heating or steam heating device, and the heater is equipped with a temperature control module.

8. The industrial wastewater treatment device according to claim 1, characterized in that, It also includes a cooling system (6) connected to the cold side flow channel (23) of the membrane distillation unit (2), the cooling system (6) maintaining a low temperature on the cold side, and the cooling system (6) including a circulating water pump (61) and a heat dissipation device (62).

9. The industrial wastewater treatment device according to claim 1, characterized in that, The product water tank (51) is connected to the cold side flow channel (23) of the membrane distillation unit (2), the crystal particle collector (52) is connected to the bottom of the fluidized crystallization unit (3), and the crystal particle collector (52) is equipped with an automatic discharge valve (521).

10. An industrial wastewater treatment method, requiring the use of the industrial wastewater treatment apparatus according to any one of claims 1-9, characterized in that, Including the following steps: S1. Pretreatment: Industrial wastewater is homogenized and filtered through the pretreatment unit (1) to remove large particulate suspended solids; S2, Membrane distillation concentration and heat recovery: The pretreated wastewater is preheated by the heat recovery unit (4) and then enters the hot side channel (22) of the membrane distillation unit (2) for membrane distillation treatment to produce water vapor and concentrate. The water vapor is condensed into product water in the cold side channel (23) and collected to the product collection unit (5). S3, fluidized bed crystallization and reflux: The concentrated liquid discharged from the membrane distillation unit (2) is introduced into the fluidized bed crystallization unit (3), and a precipitant is added in the fluidized state to allow calcium and magnesium ions to crystallize and deposit on the surface of the seed crystals, resulting in softened wastewater. Part of the softened wastewater is then refluxed to the heat recovery unit (4) for heat exchange with the pretreated wastewater. S4. System control and monitoring: By real-time monitoring and regulation of pH value, temperature, flow rate and hardness parameters, the device is ensured to operate stably, and the crystallized particles are periodically discharged from the bottom of the fluidized crystallization unit (3) and recycled.

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