A chemical crystallization prilling coupling membrane interface induced crystallization calcium removal system and a calcium removal method

Abstract

The application discloses a chemical crystallization granulation coupling membrane interface induced crystallization calcium removal system and a calcium removal method, and belongs to the technical field of water treatment. The system comprises a chemical crystallization granulation unit, a membrane interface induced crystallization unit and a microcrystal separation and recycling unit. After preliminary softening of wastewater to be treated by the chemical crystallization granulation unit, the wastewater enters the membrane interface induced crystallization unit, residual calcium ions in the preliminary softening wastewater are enriched in a hydrophilic microzone of the membrane interface, combined with carbonate ions in an induced crystallization reagent, and calcium carbonate microcrystals are generated, the hydrophobic microzone inhibits continuous spreading of the crystals and promotes peeling of the microcrystals; the calcium carbonate microcrystals are separated and concentrated and then recycled to the chemical crystallization granulation unit for recycling. After treatment by the chemical crystallization granulation coupling membrane interface induced crystallization calcium removal system, the concentration of calcium ions in the wastewater is below 10 mg / L. The application realizes calcium removal by coupling of preliminary softening by chemical crystallization granulation and induced crystallization by a membrane, has the advantages of low reagent consumption, recyclable microcrystals and closed-loop operation.

Description

Technical Field

[0001] This invention belongs to the field of water treatment technology, and relates to wastewater calcium removal treatment, specifically to a chemical crystallization granulation coupled membrane interface induced crystallization calcium removal system and method. Background Technology

[0002] In recent years, with the tightening of environmental policies in heavy industries such as coal chemical, mining, and metallurgy, "zero discharge (ZLD)" of industrial high-hardness, high-salinity wastewater has become an irreversible industry trend. In a typical ZLD process, wastewater usually undergoes pretreatment, high-pressure reverse osmosis (RO) or electrodialysis (EDR) concentration, and finally enters a mechanical vapor recompression (MVR) or multi-effect evaporation (MED) system for crystallization and salt separation. However, these high-precision membrane separation and evaporation devices are extremely sensitive to the quality of the influent. Under high concentration ratios and high-temperature conditions, trace amounts of residual calcium ions in the water can easily form hard, dense scale on the heat exchanger tube walls or membrane surfaces, leading to a sharp drop in equipment efficiency or even physical damage. Therefore, for high-hardness, high-salinity wastewater, especially when used as pretreatment water for reverse osmosis, evaporation crystallization feed water, or boiler feed water for reuse, the industry places extremely high demands on effluent hardness control. Generally, it is required that the total hardness be reduced to a low level. The total hardness of the feed water in the reverse osmosis stage is generally required to be less than 1 mmol / L, and the requirements are even more stringent for applications such as boiler feedwater. If the residual calcium ion control does not meet the standards, it is very easy to form scale on the surface of subsequent membrane separation or heat exchange equipment, affecting the long-term stable operation of the system.

[0003] To further remove calcium from high-hardness water after primary softening, traditional technologies such as chemical precipitation, ion exchange, and membrane filtration are widely used in industry. However, all of these have inherent drawbacks. Patent CN120136357 A discloses a method for deep hardness removal from concentrated brine. This method eliminates interference from high-concentration scale inhibitors by adding scale-dissolving agents, and then utilizes sodium carbonate and sodium phosphate to react stepwise with calcium ions to generate precipitates, thereby deeply removing hardness from the concentrated brine and ultimately reducing the total hardness of the effluent to below 0.5 mmol / L. However, its core is based on coagulation and sedimentation technology. For scenarios requiring further reduction of effluent hardness to a lower level, chemical precipitation often requires significantly increasing the dosage of reagents and intensifying separation conditions. This not only significantly increases operating costs but also adds to the system's complexity and solid waste treatment costs due to the subsequent dewatering and disposal of chemically precipitated sludge. Invention patent CN120097446 A discloses a hardness removal device and method for high-hardness saline wastewater. It uses sodium-type ion exchange resin to adsorb and remove calcium and magnesium hardness ions from the wastewater, and innovatively uses a high-concentration sodium sulfate solution as a regeneration liquid to replace the hardness ions adsorbed on the resin and restore the resin's exchange capacity. However, this technology relies on expensive ion exchange resin and requires a complex multi-column series regeneration, waste liquid disposal, and resin transfer system.

[0004] Compared to traditional chemical precipitation and ion exchange methods, chemical crystallization circulating granulation fluidized beds, based on the principle of induced crystallization, utilize seed crystals within the fluidized bed to induce heterogeneous crystallization of calcium ions on the seed crystal surface. This offers advantages such as high operating load, small footprint, and the ability to recycle the crystallization products, making it suitable as a front-end hardness removal unit for treating high-hardness wastewater. Generally, crystallization granulation fluidized beds primarily undertake high-load hardness removal tasks at the front end, significantly reducing the calcium ion concentration in raw water from hundreds of mg / L to tens of mg / L, lowering the total hardness of the water to a lower level, thereby removing most hardness ions from the water and significantly reducing the scaling load on subsequent treatment units. Patent CN119912050B discloses a metal ion micro-interface induced crystallization separation device for high-salt wastewater, comprising a cylinder containing, from bottom to top, a fluid mixing zone, a circulating granulation zone, and a particle separation zone. The invention provides a metal ion micro-interface induced crystallization separation device for high-salt wastewater. With the help of a differentially distributed gas-liquid distributor, the high-salt wastewater enters the upper space of the gas-liquid distributor at a differential speed. At the same time, more crystal particles are sent into the circulating granulation zone. However, when this device treats coal gasification ash water, the concentration of calcium ions is 1352 mg / L before treatment and is still as high as 139 mg / L after treatment, although the concentration of calcium ions is greatly reduced.

[0005] For low-concentration calcium ions remaining after initial treatment, especially when further control of residual calcium ion concentration is required to achieve further calcium removal, relying solely on crystallization granulation fluidized beds is often insufficient for efficient completion. In the low-concentration residual calcium ion stage, the supersaturation driving force required for calcium carbonate nucleation and growth within the system is significantly weakened. If the method of directly adding softening agents is still used, it is difficult to ensure that calcium ions and carbonate ions combine at effective locations in a controllable manner. On the other hand, simply increasing the dosage of softening agents such as Na2CO3 or NaOH can easily lead to localized excessive supersaturation within the fluidized bed, inducing homogeneous nucleation and generating a large number of microcrystals that are difficult to settle and separate. This results in increased agent consumption, a heavier separation burden, and makes it difficult to achieve economical and effective further calcium removal.

[0006] To address the bottlenecks faced by traditional membrane technologies in specific application scenarios, current research trends are driving the development of membrane technology from single separation elements towards advanced functional materials that integrate multiple functions, selectively separate water, and customize for various applications. Patent CN120139328 A discloses a hydrophobic-hydrophilic Janus water-collecting membrane, which utilizes the wetting gradient between the hydrophobic and hydrophilic sides to generate capillary force differences, driving the directional transport of captured water droplets from the hydrophobic side to the hydrophilic side, thereby achieving efficient and rapid water collection. Patent CN117883991 A discloses a method for preparing highly stable mixed matrix membranes using an interface-induced strategy. Hydrophobic zeolite imidazole framework-8 nanoparticles are redistributed within the polymer matrix under interfacial force, tending to accumulate on the side furthest from the water surface, significantly improving the stability of the mixed matrix membrane during long-term use. However, existing membrane interface-induced crystallization technologies are insufficient for independently treating high-hardness wastewater, and for high-hardness water that has not undergone preliminary softening, the enormous crystallization load on the membrane surface can lead to irreversible membrane scaling and system failure.

[0007] In summary, existing technologies for further softening of high-hardness wastewater suffer from several drawbacks. High chemical consumption and wastewater generation are common problems. Crystallization fluidized beds cannot simultaneously achieve further softening and low chemical consumption, and overcoming the thermodynamic bottleneck of low-concentration calcium removal remains a challenge. Traditional membrane filtration methods are prone to irreversible scaling and failure, and membrane interface-induced crystallization technology cannot independently handle the treatment of high-hardness wastewater and the significant crystallization load on the membrane surface. Given these limitations, the high dosage, high cost, and secondary pollution associated with further calcium ion removal after softening high-hardness wastewater are pressing technical issues that need to be addressed. Summary of the Invention

[0008] To address the aforementioned technical problems, the present invention aims to provide a chemical crystallization granulation coupled membrane interface induced crystallization calcium removal system and method. This system employs chemical crystallization granulation coupled membrane interface induced crystallization technology, utilizing a dual-circulation system on both the aqueous and chemical sides to achieve further softening of high-hardness wastewater at low cost, with zero sludge and zero secondary pollution. The specific solution is as follows:

[0009] This invention provides a chemical crystallization granulation coupled membrane interface induced crystallization calcium removal system, which includes a chemical crystallization granulation unit 1, a membrane interface induced crystallization unit 2, and a microcrystal separation and recycling unit 3.

[0010] The chemical crystallization granulation unit 1 is used to perform primary softening treatment on the wastewater to be treated to obtain primary softened wastewater; the membrane interface induced crystallization unit 2 is used to induce crystallization of the primary softened wastewater from the chemical crystallization granulation unit 1; the membrane interface induced crystallization unit 2 includes a membrane interface induced crystallization component 201, an aqueous phase circulation system connected to the aqueous phase side of the membrane interface induced crystallization component 201, and a drug solution circulation system connected to the drug solution side of the membrane interface induced crystallization component 201.

[0011] The chemical crystallization granulation unit 1 is connected to the aqueous phase circulation system of the membrane interface induced crystallization unit 2, and receives the microcrystals returned by the microcrystal separation and reuse unit 3.

[0012] The microcrystal separation and reuse unit 3 is connected to the drug circulation system of the membrane interface induced crystallization unit 2, and is used to separate, concentrate and reuse the microcrystals generated by the membrane interface induced crystallization component 201.

[0013] The membrane interface induced crystallization assembly 201 is composed of a membrane element 202, which has an inner wall 205 and an outer wall 206.

[0014] The aqueous circulation system includes a circulating water tank 203 connected to the outlet of the primary softened wastewater obtained from the chemical crystallization granulation unit 1, an aqueous phase channel 2022 formed by the inner wall 205 of the membrane element, and a water circulation pipeline 204. The inner wall 205 of the membrane element is in contact with the aqueous phase from the circulating water tank 203. A first solenoid valve 218 is installed on the first outlet pipe 215 of the water circulation pipeline 204 to control the discharge of the effluent after crystallization induced by the membrane interface induced crystallization unit 2 to a clear water tank 217 connected to the rear end of the first solenoid valve 218. A second outlet pipe 216 of the water circulation pipeline 204 is connected to the circulating water tank 203 via a membrane module variable frequency return pump 214. A second solenoid valve 219 is installed at the front end of the membrane module variable frequency return pump 214 on the second outlet pipe 216 to control the return of the effluent after crystallization induced by the membrane interface induced crystallization unit 2 to the circulating water tank 203.

[0015] The drug circulation system includes a drug dosing system 208, a drug channel 2021 formed by the outer wall 206 of the membrane element and its surrounding outer cavity, and a drug circulation pipeline 207. Along the direction of drug circulation, the rear end of the drug dosing system 208 is connected to a variable frequency drug dosing pump 209, and the front end of the drug dosing system 208 is connected to a variable frequency drug return pump 210. The outer wall 206 of the membrane element contacts the drug solution added from the drug dosing system 208, forming an induced crystallization and microcrystal exfoliation region on the outer wall 206. The drug circulation pipeline 207 contains an induced crystallization agent 2026 from the drug dosing system 208.

[0016] The solution channel 2021 provides the solution environment required for inducing crystallization on the membrane surface. The solution channel 2021 and the aqueous phase channel 2022 are separated by a membrane substrate 2024. The membrane interface of the membrane substrate 2024 has hydrophilic microregions 2028 and hydrophobic microregions 2029. The hydrophilic microregions 2028 are used to enrich calcium ions 2025 and reduce the interfacial nucleation energy barrier. The hydrophobic microregions 2029 are used to inhibit the continuous spreading and growth of crystals on the membrane surface, thereby promoting the controllable generation and stripping of calcium carbonate microcrystals 2027 at the membrane interface. The membrane interface causes the calcium ions 2025 and the crystallization-inducing agent 2026 within the confined area of ​​the membrane interface to converge in a directional manner, and further removal of calcium ions 2025 from the primary softened wastewater is achieved through calcium carbonate-induced crystallization at the membrane interface.

[0017] The membrane interface induced crystallization component 201 is composed of one or more sets of parallel membrane elements 202, and the number of membrane elements 202 is adjustable; the membrane element 202 is one or more of tubular membrane elements, plate membrane elements or hollow fiber membrane elements.

[0018] The chemical crystallization granulation unit 1 includes a fluidized bed body 101, which is a variable diameter structure that is narrow at the bottom and wide at the top. From bottom to top, it is provided with a fluidized bed water inlet pipe 102, a chemical dosing pipe 103, a crystal particle discharge pipe 104, a seed crystal dosing pipe 105, and a water collection area 106. The fluidized bed inlet pipe 102 is located below the fluidized bed body 101, and the dosing pipe 103 is located above the fluidized bed inlet pipe 102; inside the fluidized bed body 101, at the same horizontal position as the dosing pipe 103, a drug distribution interlayer 107 is provided. The crystallization particle discharge pipe 104 is located below the diameter change of the fluidized bed body 101 and between the drug distribution jacket 107. The crystallization particle discharge pipe 104 discharges large mature calcium carbonate crystal particles generated by the reaction of the wastewater to be treated with the reagent on the seed surface in the fluidized bed body 101. The seed dosing pipe 105 is located above the diameter change of the fluidized bed body 101. The water collection area 106 discharges the primary softening wastewater from the fluidized bed body 101 and enters the membrane interface induced crystallization unit 2.

[0019] The microcrystal separation and reuse unit 3 includes a hydrocyclone 301, a seed tank 305, and a seed dosing pump 306 for concentrating and separating the calcium carbonate microcrystal 2027 drug solution mixture generated by the membrane interface induced crystallization unit 2.

[0020] The upper feed end and the top overflow outlet end of the hydrocyclone 301 are respectively connected to the liquid circulation pipeline 207 after the liquid circulation channel 2021 of the liquid circulation system of the membrane interface induced crystallization unit 2. The upper feed end of the hydrocyclone 301 is connected to the liquid circulation pipeline 207 through the first screw pump 303. The bottom discharge end of the hydrocyclone 301 is connected to the inlet of the seed tank 305 through the second screw pump 304. The outlet of the seed tank 305 is connected to the seed addition pipe 105 of the chemical crystallization granulation unit 1 through the seed addition pump 306.

[0021] The hydrocyclone 301 uses centrifugal force to concentrate and separate the stripped calcium carbonate microcrystal 2027 solution. The supernatant after separation overflows from the top of the hydrocyclone 301 and flows back to the solution circulation pipeline 207 for recycling. The concentrated calcium carbonate microcrystal 2027 slurry separated at the bottom serves as calcium carbonate seed crystals. After being pressurized by the first screw pump 303 and the second screw pump 304, it is first transported to the seed tank 305, and then transported back to the fluidized bed body 101 of the chemical crystallization granulation unit 1 by the seed addition pump 306. Furthermore, the upper feed end of the hydrocyclone 301 is connected to the solution circulation pipeline 207 through the first screw pump 303.

[0022] The bottom discharge end of the hydrocyclone 301 is connected to the inlet of the seed tank 305. Furthermore, the bottom discharge end of the hydrocyclone 301 is connected to the inlet of the seed tank 305 through the second screw pump 304.

[0023] The outlet of the seed tank 305 is connected to the seed addition pipe 105 of the chemical crystallization granulation unit 1; further, the outlet of the seed tank 305 is connected to the seed addition pipe 105 of the chemical crystallization granulation unit 1 through the seed addition pump 306.

[0024] The chemical crystallization granulation coupled membrane interface induced crystallization calcium removal system includes a control unit 4 for linkage and regulation, which is a signal collection and control center 401.

[0025] This invention also provides a calcium removal method using a chemical crystallization granulation coupled membrane interface-induced crystallization calcium removal system, the calcium removal method comprising the following steps: Step 1 is the primary softening of wastewater in the chemical crystallization granulation unit 1: the wastewater to be treated enters the fluidized bed body 101 through the fluidized bed inlet pipe 102, mixes with the softening agent injected from the dosing pipe 103, and heterogeneous crystallization occurs on the surface of the seed crystals injected from the seed crystal dosing pipe 105 to generate calcium carbonate crystals, thus obtaining primary softened wastewater; the generated calcium carbonate crystal particles are discharged from the crystal particle discharge pipe 104, and the primary softened wastewater is collected in the water collection area 106, flows out from the outlet of the water collection area 106 and enters the circulating water tank 203; Step 2 is the induction of crystallization by the membrane interface induced crystallization unit 2: the membrane module variable frequency reflux pump 214 is turned on to establish internal aqueous phase circulation, and the reagent variable frequency dosing pump 209 is turned on to establish external reagent circulation; the primary softened wastewater that entered the circulating water tank 203 in step 1 flows through the aqueous phase channel 2022 where the inner wall 205 of the membrane element is located. Under the action of the concentration difference driving force, the residual calcium ions 2025 in the primary softened wastewater penetrate from the aqueous phase channel 2022 to the outer wall 206 of the membrane element and are enriched in the hydrophilic microregion 2028; under the interface confinement conditions, with the help of the interface regulation effect of the hydrophilic microregion 2028 and the hydrophobic microregion 2029, under the synergistic induction of the crystallization induction agent 2026, the residual calcium ions 2025 in the primary softened wastewater and the carbonate ions in the crystallization induction agent 2026 are directionally combined at the membrane interface to generate calcium carbonate microcrystals 2027; The hydrophobic microregion 2029 inhibits the continuous spreading of induced calcium carbonate microcrystals 2027 and promotes microcrystal exfoliation. According to the change of transmembrane pressure difference at the membrane interface, the shear force generated by the tangential flow of the drug solution through the drug solution channel 2021 on the outer wall 206 of the membrane element will exfoliate the calcium carbonate microcrystals 2027 induced to crystallize on the outer wall 206 of the membrane element. Step 3 is the separation and reuse of microcrystals in the microcrystal separation and reuse unit 3: the second solenoid valve 219 is opened, and the drug solution mixture rich in calcium carbonate microcrystals 2027 mentioned in step 2 enters the hydrocyclone 301 tangentially through the upper feed end for centrifugal concentration; the supernatant after separation overflows through the top overflow outlet end of the hydrocyclone 301 and flows back to the drug solution circulation pipeline 207 loop for drug recycling; the concentrated calcium carbonate microcrystal 2027 slurry separated at the bottom is first transported to the seed tank 305 through the bottom discharge end of the hydrocyclone 301, and then transported back to the fluidized bed body 101 of the chemical crystallization granulation unit 1 as the inducing seed crystal of step 1 of the chemical crystallization granulation unit 1.

[0026] Further, in step 1, the total hardness concentration of the wastewater to be treated is 500~5000 mg / L, and the calcium ion concentration is 100~1500 mg / L; the flow rate of the wastewater to be treated entering the fluidized bed body 101 is 50~500 m³ / h, the fluid rising velocity inside the fluidized bed body 101 is 60~100 m / h, preferably 80 m / h; and the hydraulic retention time is 8~12 min, preferably 10 min.

[0027] The seed crystals with a particle size of 0.2~0.5mm and a seed bed height of 0.3~0.5m are added to the seed crystal feeding tube 105. The seed crystals can operate normally and achieve the same effect within the range of 0.3~0.5m, and are preferably 0.4m. The seed crystals are preferably calcite.

[0028] The softening agent is a pH adjuster and / or an agent that can provide carbonate ions. The pH adjuster is sodium hydroxide, and the agent that can provide carbonate ions is sodium carbonate. The dosage of the pH adjuster is based on adjusting the pH of the mixed liquid in the fluidized bed body 101 to 9.5-10.0. The dosage of the agent that can provide carbonate ions is controlled according to the molar ratio of carbonate ions to calcium ions to be removed being (1.0-1.5):1.

[0029] Further, in step 2, the flow rate of the aqueous phase in the aqueous phase channel 2022 is 0.5~2.0 m / s, and the flow rate of the drug solution in the drug solution channel 2021 is 0.3~1.5 m / s; the concentration of carbonate ions in the drug solution in the drug solution channel 2021 is 0.02~0.2 mol / L, and the pH value is between 8.5 and 9.5; the crystallization induction agent 2026 is one or both of a 0.05~0.1 mol / L sodium carbonate solution or potassium carbonate solution; the transmembrane pressure difference at the membrane interface of the membrane element 202 is in the range of 0.05~0.15 MPa; after treatment by the membrane interface induced crystallization unit 2, the calcium ion concentration in the wastewater is below 10 mg / L.

[0030] Furthermore, the inlet pressure of the drug solution mixture rich in calcium carbonate microcrystals 2027 described in step 3 for centrifugal concentration in hydrocyclone 301 is 0.10~0.40 MPa; the recycling rate of calcium carbonate microcrystals 2027 is 80%~90%.

[0031] Compared with the prior art, the present invention has the following technical effects: (1) To address the difficulty of removing low-concentration residual calcium ions through chemical reactions in a fluidized bed, this invention employs a membrane interface-induced crystallization membrane module. This module creates a local microenvironment at the membrane interface where calcium ions and carbonate ions bind directionally, allowing residual calcium ions in the primary softening wastewater to preferentially undergo induced heterogeneous nucleation at the interface and form calcium carbonate microcrystals. The core of this invention lies in overcoming the bottleneck of insufficient reaction driving force and difficulty in continuous and efficient calcium removal during the low-concentration stage of traditional further softening processes through local enrichment, directional migration, and controllable crystallization at the membrane interface.

[0032] (2) This invention organically couples the membrane interface induced crystallization component with the chemical crystallization granulation technology. The calcium carbonate microcrystals generated by the membrane interface induced crystallization and sheared can be recycled as seed crystals for the front-end chemical crystallization granulation unit. The front-end chemical crystallization granulation unit can also perform primary softening and removal of most of the calcium ions in the water, reducing the membrane load for further calcium removal at the subsequent membrane interface, thereby achieving the synergistic coupling of "front-end load reduction - back-end further removal - microcrystal reflux granulation".

[0033] (3) The present invention constructs a closed-loop process system of “crystallization granulation softening - membrane interface induced crystallization - microcrystal separation and reuse”. The calcium carbonate microcrystals formed at the membrane interface are separated and reused as inducing crystal seeds in the front-end chemical crystallization granulation unit, which avoids the generation of a large amount of wastewater and sludge in the traditional chemical precipitation process and realizes the recycling and resource-based operation of system materials.

[0034] (4) The chemical crystallization granulation coupled membrane interface induced crystallization calcium removal system and method provided by the present invention significantly reduces the calcium ion concentration in the effluent to below tens of mg / L after calcium removal from the wastewater to be treated, and can be further reduced to an even lower level under optimized operating conditions. According to the different requirements of subsequent treatment processes for influent water quality, the calcium ion concentration in the effluent can be controlled and adjusted by adjusting the system operating parameters, so as to meet the requirements of low hardness water quality for different application scenarios such as reverse osmosis, evaporation crystallization or boiler feedwater. Attached Figure Description

[0035] Figure 1 A schematic diagram of the modular combination of functional units in a chemical crystallization granulation coupling membrane interface-induced crystallization calcium removal system; Figure 2 Schematic diagram of a chemical crystallization granulation coupling membrane interface-induced crystallization calcium removal system; Figure 3 This is a magnified view of a portion of the membrane interface-induced crystallization.

[0036] Figure label: 1-Chemical crystallization granulation unit, 101-Fluidized bed body, 102-Fluidized bed inlet pipe, 103-Dosing pipe, 104-Crystallized particle discharge pipe, 105-Seed crystal addition pipe, 106-Water collection area, 107-Dosing layer; 2-Membrane interface induced crystallization unit, 201-Membrane interface induced crystallization component, 203-Circulating water tank, 204-Water circulation pipeline, 205-Inner wall of membrane element, 206-Outer wall of membrane element, 207-Chemical solution circulation pipeline, 208-Chemical dosing system, 209-Chemical frequency conversion dosing pump, 210-Chemical frequency conversion reflux pump, 211-Online pH meter, 212-Automatic dosing device, 213-Solenoid valve of automatic dosing device, 214-Membrane module frequency conversion reflux pump, 215-First outlet pipeline, 216-Second outlet pipeline, 217-Clear water tank, 218-First solenoid valve, 219-Second solenoid valve, 220-Online water quality analyzer, 221-Online pressure gauge; 202-Membrane element, 2021-Drug channel, 2022-Aqueous phase channel, 2023-Local magnified region, 2024-Membrane substrate, 2025-Calcium ion, 2026-Crystallization induction agent, 2027-Calcium carbonate microcrystals, 2028-Hydrophilic microregion, 2029-Hydrophobic microregion; 3-Microcrystalline separation and reuse unit, 301-Hydrocyclone, 302-Third solenoid valve, 303-First screw pump, 304-Second screw pump, 305-Seed tank, 306-Seed dosing pump; 4-Control unit, 401-Signal collection and control center. Detailed Implementation

[0037] The present invention will be further described in detail below with reference to the embodiments. However, the scope of protection of the present invention is not limited to tubular membrane elements. The membrane element 202 of the present invention can be a tubular membrane, a flat sheet membrane, a hollow fiber membrane, or other membrane elements that can construct an induced crystallization microenvironment at the membrane interface and realize the separation and circulation of the aqueous phase channel 2022 and the drug solution channel 2021.

[0038] Example 1 This embodiment provides a chemical crystallization granulation coupled membrane interface-induced crystallization calcium removal system. For example... Figure 1-3 As shown, the chemical crystallization granulation coupled membrane interface induced crystallization calcium removal system includes a chemical crystallization granulation unit 1, a membrane interface induced crystallization unit 2, and a microcrystal separation and recycling unit 3.

[0039] The chemical crystallization granulation unit 1 is used to perform primary softening treatment on the wastewater to be treated to obtain primary softened wastewater; the membrane interface induced crystallization unit 2 is used to induce crystallization of the primary softened wastewater from the chemical crystallization granulation unit 1; the membrane interface induced crystallization unit 2 includes a membrane interface induced crystallization component 201, an aqueous phase circulation system connected to the aqueous phase side of the membrane interface induced crystallization component 201, and a liquid circulation system connected to the liquid side of the membrane interface induced crystallization component 201.

[0040] The chemical crystallization granulation unit 1 is connected to the aqueous phase circulation system of the membrane interface induced crystallization unit 2, and receives the microcrystals returned by the microcrystal separation and reuse unit 3.

[0041] The microcrystal separation and reuse unit 3 is connected to the drug circulation system of the membrane interface induced crystallization unit 2, and is used to separate, concentrate and reuse the microcrystals generated by the membrane interface induced crystallization component 201.

[0042] The membrane interface induced crystallization assembly 201 is composed of a membrane element 202, which has an inner wall 205 and an outer wall 206.

[0043] The aqueous circulation system includes a circulating water tank 203 connected to the outlet of the primary softened wastewater obtained from the chemical crystallization granulation unit 1, an aqueous phase channel 2022 formed by the inner wall 205 of the membrane element, and a water circulation pipeline 204. The inner wall 205 of the membrane element is in contact with the aqueous phase from the circulating water tank 203. A first solenoid valve 218 is installed on the first outlet pipe 215 of the water circulation pipeline 204 to control the discharge of the effluent after crystallization induced by the membrane interface induced crystallization unit 2 to a clear water tank 217 connected to the rear end of the first solenoid valve 218. A second outlet pipe 216 of the water circulation pipeline 204 is connected to the circulating water tank 203 via a membrane module variable frequency return pump 214. A second solenoid valve 219 is installed at the front end of the membrane module variable frequency return pump 214 on the second outlet pipe 216 to control the return of the effluent after crystallization induced by the membrane interface induced crystallization unit 2 to the circulating water tank 203. When the residual calcium ion concentration in the water circulation pipe 204 is higher than the further softening threshold, the second solenoid valve 219 is opened and the first solenoid valve 218 is closed, driving the induced crystallized water to return to the circulating water tank 203 to continue internal circulation; when the residual calcium ion concentration in the water circulation pipe 204 drops below the threshold, the first solenoid valve 218 is opened and the second solenoid valve 219 is closed, and the induced crystallized water is discharged into the clear water tank 217.

[0044] The drug circulation system includes a drug dosing system 208, a drug channel 2021 consisting of the outer wall 206 of the membrane element and the outer cavity thereon, and a drug circulation pipeline 207. Along the direction of drug circulation, the rear end of the drug dosing system 208 is connected to the variable frequency drug dosing pump 209, and the front end of the drug dosing system 208 is connected to the variable frequency drug return pump 210. The outer wall 206 of the membrane element is in contact with the drug solution added from the drug dosing system 208, forming an induced crystallization and microcrystal exfoliation region on the outer wall 206 of the membrane element. The drug circulation pipeline 207 contains an induced crystallization agent 2026 from the drug dosing system 208. The induced crystallization agent 2026 is one or both of 0.05~0.1 mol / L sodium carbonate or potassium carbonate solution. Preferably, the induced crystallization agent 2026 further includes a crystallization regulator, which is one or more of polyaspartic acid, sodium polyacrylate, and sodium carboxymethyl cellulose, with a dosage concentration of 0.1~10 mg / L.

[0045] The solution channel 2021 provides the solution environment required for inducing crystallization on the membrane surface. The solution channel 2021 and the aqueous phase channel 2022 are separated by a membrane substrate 2024. The membrane interface of the membrane substrate 2024 has hydrophilic microregions 2028 and hydrophobic microregions 2029. The hydrophilic microregions 2028 are used to enrich calcium ions 2025 and reduce the interfacial nucleation energy barrier. The hydrophobic microregions 2029 are used to inhibit the continuous spreading and growth of crystals on the membrane surface, thereby promoting the controllable generation and stripping of calcium carbonate microcrystals 2027 at the membrane interface. The membrane interface causes the calcium ions 2025 and the crystallization-inducing agent 2026 within the confined area of ​​the membrane interface to converge in a directional manner, and further removal of calcium ions 2025 from the primary softened wastewater is achieved through calcium carbonate-induced crystallization at the membrane interface.

[0046] The membrane interface induced crystallization component 201 is composed of one or more sets of parallel membrane elements 202. The number of membrane elements 202 can be flexibly adjusted according to the actual water treatment volume and operating load of the system. Each set of membrane elements 202 is independently configured with corresponding inlet and outlet water pipes and valves. The membrane element 202 is one or more of tubular membrane elements, plate membrane elements or hollow fiber membrane elements.

[0047] The chemical crystallization granulation unit 1 includes a fluidized bed body 101, which is a variable diameter structure that is narrow at the bottom and wide at the top. From bottom to top, it is provided with a fluidized bed water inlet pipe 102, a chemical dosing pipe 103, a crystal particle discharge pipe 104, a seed crystal dosing pipe 105, and a water collection area 106. The fluidized bed inlet pipe 102 is located below the fluidized bed body 101, and the dosing pipe 103 is located above the fluidized bed inlet pipe 102. Inside the fluidized bed body 101, at the same horizontal position as the dosing pipe 103, a dosing layer 107 is provided. The dosing layer 107 is used to evenly distribute the softening agent entering from the dosing pipe 103 along the cross-section of the fluidized bed body 101, so that the softening agent can fully contact the wastewater to be treated and the seed crystals, thereby reducing the risk of homogeneous nucleation caused by local supersaturation. The crystallization particle discharge pipe 104 is located below the diameter change of the fluidized bed body 101 and between the drug distribution jacket 107. The crystallization particle discharge pipe 104 discharges large mature calcium carbonate crystal particles generated by the reaction of the wastewater to be treated with the reagent on the seed surface in the fluidized bed body 101. The seed dosing pipe 105 is located above the diameter change of the fluidized bed body 101. The water collection area 106 discharges the primary softening wastewater from the fluidized bed body 101 and enters the membrane interface induced crystallization unit 2.

[0048] When treating wastewater, the wastewater to be treated and the softening agent enter the fluidized bed body 101 through the fluidized bed inlet pipe 102 and the dosing pipe 103, respectively. The wastewater to be treated and the agent mix and react on the seed crystal surface inside the fluidized bed to generate large mature calcium carbonate crystal particles. After settling, the crystal particles are discharged through the crystal particle discharge pipe 104. The primary softened water is collected in the water collection area 106. The water effluent from the water collection area 106 is discharged into the circulating water tank 203 through the outlet, and then enters the membrane interface induced crystallization module 201.

[0049] The microcrystal separation and reuse unit 3 includes a hydrocyclone 301, a seed tank 305, and a seed dosing pump 306 for concentrating and separating the calcium carbonate microcrystal 2027 drug solution mixture generated by the membrane interface induced crystallization unit 2.

[0050] The upper feed end and the top overflow outlet end of the hydrocyclone 301 are respectively connected to the liquid circulation pipeline 207 after the liquid channel 2021 of the liquid circulation system of the membrane interface induced crystallization unit 2; further, the upper feed end of the hydrocyclone 301 is connected to the liquid circulation pipeline 207 through the first screw pump 303.

[0051] The bottom discharge end of the hydrocyclone 301 is connected to the inlet of the seed tank 305. Further, the bottom discharge end of the hydrocyclone 301 is connected to the inlet of the seed tank 305 via a second screw pump 304. The outlet of the seed tank 305 is connected to the seed addition pipe 105 of the chemical crystallization granulation unit 1. Further, the outlet of the seed tank 305 is connected to the seed addition pipe 105 of the chemical crystallization granulation unit 1 via a seed addition pump 306.

[0052] The hydrocyclone 301 uses centrifugal force to concentrate and separate the stripped calcium carbonate microcrystal 2027 drug solution mixture. The supernatant after separation overflows from the top overflow outlet of the hydrocyclone 301 and flows back to the drug solution circulation pipeline 207 for drug recycling. The concentrated calcium carbonate microcrystal 2027 slurry separated at the bottom is used as calcium carbonate seed crystals. After being pressurized by the first screw pump 303 and the second screw pump 304, it is first transported to the seed tank 305, and then transported back to the fluidized bed body 101 of the chemical crystallization granulation unit 1 by the seed addition pump 306.

[0053] Example 2 Based on Example 1, the chemical crystallization granulation coupling membrane interface induced crystallization calcium removal system is further equipped with a control unit 4 for linkage and regulation operation, and the control unit 4 is a signal collection and control center 401.

[0054] The membrane interface induced crystallization unit 2 is further equipped with an online pH meter 211, an online water quality analyzer 220, and an online pressure gauge 221.

[0055] The online pH meter 211 is installed between the reagent dosing system 208 and the reagent frequency conversion reflux pump 210 to monitor the consumption of the reagent solution on the outer wall 206 of the membrane element in real time. The front end of the reagent dosing system 208 is connected to the automatic replenishment device 212. The outlet of the automatic replenishment device 212 is equipped with an automatic replenishment device solenoid valve 213. When the pH value or carbonate ion concentration falls below the set lower limit, the signal collection and control center 401 controls the automatic replenishment device solenoid valve 213 to open, so that the reagent in the replenishment device 212 enters the reagent dosing system 208. Under the action of the reagent frequency conversion reflux pump 210, it is mixed with the circulating reagent solution and then transported to the outer wall 206 of the membrane element, thereby maintaining the crystallization driving force at the membrane interface.

[0056] The online water quality analyzer 220 is installed on the water circulation pipeline 204 after the outlet of the aqueous channel 2022 of the membrane interface induced crystallization component 201 and before the diversion of the first outlet pipeline 215 and the second outlet pipeline 216. It is used to monitor the concentration of residual calcium ions in the water after membrane interface induced crystallization treatment. When the online water quality analyzer 220 detects that the concentration of residual calcium ions in the water circulation pipeline 204 is higher than the further softening threshold, the signal collection and control center 401 controls the second solenoid valve 219 to open and the first solenoid valve 218 to close, driving the water back to the circulating water tank 203 to continue internal circulation. When the online water quality analyzer 220 detects that the concentration of residual calcium ions in the water circulation pipeline 204 drops below the threshold, the signal collection and control center 401 links to close the corresponding solenoid valve, open the first solenoid valve 218, and close the second solenoid valve 219, discharging the water after further calcium removal treatment into the clear water tank 217.

[0057] The online pressure gauge 221 includes an aqueous phase pressure detection point located on the aqueous phase channel 2022 side of the membrane element 202 and a drug solution pressure detection point located on the drug solution channel 2021 side. The signal collection and control center 401 calculates the transmembrane pressure (TMP) of the membrane element 202 based on the aqueous phase pressure and the drug solution pressure. When the online pressure gauge 221 detects that the transmembrane pressure of one or more groups of membrane elements 202 reaches the set cleaning critical threshold, the signal collection and control center 401 immediately starts the "online microcrystal stripping program" for that group of membranes, that is, increases the operating frequency of the variable frequency drug delivery pump 209 on the outer wall 206 of the corresponding membrane element, and uses the shear force generated by the tangential flow of the drug solution in the drug solution channel 2021 to strip and remove the calcium carbonate microcrystals 2027 on the outer wall 206 of the membrane element. During the stripping and cleaning of the aforementioned single membrane module, the signal collection and control center 401 automatically switches or distributes the influent load to the remaining membrane elements that are in normal operation. This prevents a system shutdown caused by the cleaning of membrane element 202 in the single membrane interface induced crystallization component 201, ensuring uninterrupted, continuous, and high-quality wastewater treatment by the membrane interface induced crystallization unit 2 as a whole. Once the membrane pressure differential of the stripped group returns to normal, it is reintegrated into the system.

[0058] The microcrystalline separation and reuse unit 3 is further equipped with a third solenoid valve 302. The third solenoid valve 302 is located between the drug circulation pipeline 207 loop after the outlet of the drug channel 2021 of the membrane interface induced crystallization unit 2 and the inlet of the first screw pump 303 at the upper feed end of the hydrocyclone 301 of the microcrystalline separation unit 3. It is used to control the intermittent or continuous entry of the drug mixture rich in exfoliated calcium carbonate microcrystals 2027 into the hydrocyclone 301 for separation. The signal collection and control center 401 system periodically opens the third solenoid valve 302 to introduce the mixture rich in exfoliated calcium carbonate microcrystals 2027 into the hydrocyclone 301 for centrifugal concentration. The supernatant after separation overflows from the top overflow outlet of the hydrocyclone 301 and flows back to the drug circulation pipeline 207 for drug recycling. The concentrated calcium carbonate microcrystal 2027 slurry separated at the bottom is first transported to the seed tank 305, and then transported back to the fluidized bed body 101 of the chemical crystallization granulation unit 1 by the seed addition pump 306.

[0059] Example 3 This embodiment provides a method for further calcium removal from the membrane element 202 of the membrane interface induced crystallization assembly 201.

[0060] like Figure 3As shown, during operation, the primary softened wastewater after primary softening by the chemical crystallization granulation unit 1 enters the aqueous phase channel 2022 of the membrane element 202 of the membrane interface induced crystallization unit 2 and circulates. The residual calcium ions 2025 in the primary softened water penetrate from the aqueous phase channel 2022 to the outer wall 206 of the membrane element under the driving force of the concentration difference and are enriched in the hydrophilic microregion 2028. With the help of the interface regulation effect of the hydrophilic microregion 2028 and the hydrophobic microregion 2029, under the synergistic induction of the crystallization inducing agent 2026, the residual calcium ions 2025 in the primary softened wastewater are induced to form calcium carbonate microcrystals 2027 in the outer wall 206 of the membrane element and the carbonate ions in the crystallization inducing agent 2026. The shear force generated by the tangential flow of the liquid through the liquid channel 2021 will peel off the calcium carbonate microcrystals 2027 induced to crystallize in the outer wall 206 of the membrane element.

[0061] At the same time, a crystallization-inducing agent 2026, including sodium carbonate or potassium carbonate, is continuously introduced into the drug solution channel 2021. The drug solution flows tangentially along the outer wall 206 of the membrane element within the drug solution channel 2021, so that the membrane surface is always maintained in a drug solution environment suitable for inducing crystallization.

[0062] The hydrophilic microregion 2028 is used to enrich calcium ions 2025 and reduce the interfacial nucleation energy barrier, while the hydrophobic microregion 2029 is used to inhibit the continuous spreading and growth of crystals on the membrane surface, thereby promoting the controllable generation and exfoliation of the calcium carbonate microcrystals 2027 on the membrane surface.

[0063] Within the magnified region 2023, calcium ions 2025 from the aqueous phase channel 2022 migrate to the outer wall 206 of the membrane element at the membrane interface. There, they combine with carbonate ions from the crystallizing agent 2026 in the drug solution channel 2021 in a localized area on the membrane surface, forming calcium carbonate microcrystals 2027 at the membrane interface. Because the crystallization process is confined to the vicinity of the membrane interface, the disordered precipitation of a large number of microcrystals caused by large-scale homogeneous nucleation in the bulk aqueous phase can be avoided, thus facilitating the targeted removal of low-concentration residual calcium ions 2025.

[0064] Furthermore, the tangential flow of the solution in the solution channel 2021 continuously replenishes the crystallizing agent 2026 and maintains the crystallization driving force at the membrane interface. On the other hand, the shear force generated by the tangential flow exerts a shearing effect on the calcium carbonate microcrystals 2027 already formed on the membrane surface, inhibiting their continuous accumulation and dense coverage on the membrane surface. This makes it easier for the generated microcrystals to detach from the membrane surface and enter the subsequent microcrystal separation and recycling unit 3. Therefore, the membrane interface induced crystallization component 201 can further remove residual calcium ions 2025 from the primary softened wastewater of the upstream chemical crystallization granulation unit 1 and provide reusable seed crystals for the chemical crystallization granulation unit 1.

[0065] Example 4 This embodiment provides a calcium removal method for the chemical crystallization granulation coupled membrane interface-induced crystallization calcium removal system described in Embodiment 1 or 2. The calcium removal method for the chemical crystallization granulation coupled membrane interface-induced crystallization calcium removal system includes the following steps: Step 1 is the primary softening of wastewater in the chemical crystallization granulation unit 1: the wastewater to be treated enters the fluidized bed body 101 through the fluidized bed inlet pipe 102, mixes with the softening agent injected from the dosing pipe 103, and heterogeneous crystallization occurs on the surface of the seed crystals injected from the seed crystal dosing pipe 105 to generate calcium carbonate crystals, thus obtaining primary softened wastewater; the generated calcium carbonate crystal particles are discharged from the crystal particle discharge pipe 104, and the primary softened wastewater is collected in the water collection area 106, flows out from the outlet of the water collection area 106 and enters the circulating water tank 203.

[0066] Further, in step 1, the total hardness concentration of the wastewater to be treated is 500–5000 mg / L, the calcium ion concentration is 100–1500 mg / L, the flow rate of the wastewater to be treated entering the fluidized bed body 101 is 50–500 m³ / h, the fluid rise velocity inside the fluidized bed body 101 is 60–100 m / h, and the hydraulic retention time is 8–12 min.

[0067] The seed crystals with a particle size of 0.2 to 0.5 mm and a seed bed height of 0.3 to 0.5 m are added to the seed crystal feeding tube 105.

[0068] The softening agent is a pH adjuster and / or an agent that can provide carbonate ions. The pH adjuster is sodium hydroxide, and the agent that can provide carbonate ions is sodium carbonate. The dosage of the pH adjuster is to adjust the pH of the mixed liquid in the fluidized bed body 101 to 9.5-10.0. The dosage of the agent that can provide carbonate ions is controlled according to the molar ratio of carbonate ions to calcium ions to be removed being (1.0-1.5):1.

[0069] Step 2 further removes calcium from the membrane interface induced crystallization unit 2: the membrane module variable frequency reflux pump 214 is turned on to establish internal aqueous phase circulation, and the reagent variable frequency dosing pump 209 is turned on to establish external reagent circulation; the primary softened wastewater that entered the circulating water tank 203 in step 1 flows through the aqueous phase channel 2022 where the inner wall 205 of the membrane element is located. Under the action of the concentration difference driving force, the residual calcium ions 2025 in the primary softened wastewater penetrate from the aqueous phase channel 2022 to the outer wall 206 of the membrane element and are enriched in the hydrophilic microregion 2028; under the interface confinement conditions, with the help of the interface regulation effect of the hydrophilic microregion 2028 and the hydrophobic microregion 2029, under the synergistic induction of the crystallization induction agent 2026, the residual calcium ions 2025 in the primary softened wastewater and the carbonate ions in the crystallization induction agent 2026 are directionally combined at the membrane interface to generate calcium carbonate microcrystals 2027; The hydrophobic microregion 2029 inhibits the continuous spreading of induced calcium carbonate microcrystals 2027 and promotes microcrystal exfoliation. According to the change of transmembrane pressure difference at the membrane interface, the shear force generated by the tangential flow of the drug solution through the drug solution channel 2021 on the outer wall 206 of the membrane element will exfoliate the calcium carbonate microcrystals 2027 induced to crystallize on the outer wall 206 of the membrane element.

[0070] Further, in step 2, the flow rate of the aqueous phase in the aqueous phase channel 2022 is 0.5~2.0 m / s, and the flow rate of the drug solution in the drug solution channel 2021 is 0.3~1.5 m / s; the carbonate ion concentration in the drug solution in the drug solution channel 2021 is 0.02~0.20, and the pH value is between 8.5 and 9.5; the crystallization induction agent 2026 is one or more of a 0.05~0.1 mol / L sodium carbonate solution or potassium carbonate solution; the transmembrane pressure difference at the membrane interface of the membrane element 202 is in the range of 0.05~0.15 MPa; after treatment by the membrane interface induced crystallization unit 2, the calcium ion concentration in the wastewater is below 10 mg / L.

[0071] Step 3 is the separation and reuse of microcrystals in the microcrystal separation and reuse unit 3: the second solenoid valve 219 is opened, and the drug solution mixture rich in calcium carbonate microcrystals 2027 mentioned in step 2 enters the hydrocyclone 301 tangentially through the upper feed end for centrifugal concentration; the supernatant after separation overflows through the top overflow outlet end of the hydrocyclone 301 and flows back to the drug solution circulation pipeline 207 loop for drug recycling, and the concentrated calcium carbonate microcrystal 2027 slurry separated at the bottom is first transported to the seed tank 305 through the bottom discharge end of the hydrocyclone 301, and then transported back to the fluidized bed body 101 of the chemical crystallization granulation unit 1.

[0072] Furthermore, in step 3, the pressure at which the drug solution mixture rich in calcium carbonate microcrystals 2027 enters the hydrocyclone 301 for centrifugal concentration is 0.10~0.40 MPa; the recycling rate of calcium carbonate microcrystals 2027 is 80%~90%.

[0073] Example 5 This embodiment provides a specific application of the calcium removal method of the chemical crystallization granulation coupled membrane interface induced crystallization calcium removal system.

[0074] In the treatment of coal gasification water produced by a certain coal gasification unit, a chemical crystallization granulation coupled membrane interface induced crystallization calcium removal system provided in Example 1 was used. Following the usage method of Example 4 above, coal gasification water containing a high concentration of calcium ions was used as the wastewater to be treated. The specific wastewater treatment process and effects are as follows: 1. Wastewater properties and related parameters The water quality of the gasification ash water from a coal chemical enterprise is shown in Table 1 below.

[0075] Table 1 Gasification Ash Water from a Coal Chemical Enterprise

[0076] Note: Total hardness is calculated as CaCO3. 2. Operation process Step 1 is the primary softening of the chemical crystallization granulation unit 1: In the fluidized bed body 101, calcite seeds with a particle size of 0.2~0.5 mm are added through the seed addition pipe 105, and the seed bed height is 0.4 m; the coal gasification wastewater to be treated enters the fluidized bed body 101 through the fluidized bed inlet pipe 102 at a flow rate of 300 m³ / h; sodium carbonate and sodium hydroxide solutions are simultaneously added to the dosing pipe 103 to adjust the pH to 10.0.

[0077] Wastewater is thoroughly mixed with the reagents within the fluidized bed 101, undergoing a heterogeneous crystallization reaction on the seed crystal surface. Most calcium ions in the wastewater are deposited as calcium carbonate on the seed crystal surface, forming granular crystals. The wastewater flows upwards, fluidizing and suspending the seed crystals and calcium carbonate crystal particles. Some of the water flows back along the inner wall to the lower reaction zone after reaching the upper part, forming an internal circulation flow to enhance the contact between the softening reagent, calcium ions, and the seed crystals, improving the heterogeneous crystallization efficiency and promoting crystal growth. The upward velocity of the fluid in the fluidized zone is controlled at 80 m / h, and the hydraulic retention time is 10 min. After treatment by the fluidized bed 101, the calcium ion concentration decreases from the initial 520 mg / L to 30 mg / L, yielding primary softened wastewater.

[0078] Step 2 is to further remove calcium in the membrane interface induced crystallization unit 2: The above-mentioned primary softened wastewater is introduced into the membrane interface induced crystallization unit 2, forming a circulating flow in the aqueous phase channel 2022 of the membrane element 202 with a flow rate of 1.0 m / s. At the same time, a sodium carbonate solution with a concentration of 0.1 mol / L is introduced into the drug channel 2021 outside the membrane as an inducing crystallization agent 2026, forming a tangential flow with a flow rate of 0.5 m / s. During operation, residual calcium ions 2025 in the primary softened wastewater penetrate from the aqueous phase channel 2022 to the outer wall 206 of the membrane element, where they accumulate in the hydrophilic microregions 2028. Under interfacial confinement conditions, and with the interfacial regulation effect of the hydrophilic microregions 2028 and hydrophobic microregions 2029, and under the synergistic induction of the crystallizing agent 2026, the residual calcium ions 2025 in the primary softened wastewater combine directionally with carbonate ions in the crystallizing agent 2026 at the membrane interface, forming calcium carbonate microcrystals 2027. The shear force generated by the tangential flow of the solution in the solution channel 2021 strips the calcium carbonate microcrystals 2027 induced on the outer wall 206 of the membrane element, with the transmembrane pressure difference at the membrane interface controlled at 0.10 MPa.

[0079] After treatment by the membrane interface induced crystallization unit 2, the calcium ion concentration in the water can be further reduced from 30 mg / L to about 5 mg / L.

[0080] Step 3 is the separation and reuse of microcrystals in the microcrystal separation and reuse unit 3: The drug solution mixture rich in calcium carbonate microcrystals 2027 generated in step 2 is introduced into the hydrocyclone 301 through the upper feed end of the hydrocyclone 301. Centrifugal separation is performed under an inlet pressure of about 0.2 MPa. The supernatant after separation overflows from the top overflow outlet end of the hydrocyclone 301 and flows back to the drug solution circulation pipeline 207 for drug recycling. The concentrated calcium carbonate microcrystal 2027 slurry separated at the bottom is first transported to the seed tank 305 through the bottom discharge end of the hydrocyclone 301, and then transported back to the fluidized bed 101 as seed for recycling by the seed addition pump 306. The separation efficiency of concentrated calcium carbonate microcrystals 2027 can reach more than 95%, and the reuse rate is 85%.

[0081] 3. Implementation Results The concentration of calcium ions in water samples was determined by EDTA complexometric titration, following the method specified in GB / T 7476-1987 "Determination of Calcium in Water - EDTA Titration Method". When the calcium ion concentration in the sample exceeded 100 mg / L, the sample was diluted before measurement. The calcium ion content in the wastewater before and after treatment is shown in Table 2 below.

[0082] Table 2 Comparison of calcium ion concentrations before and after treatment in Example 5

[0083] In the system of the present invention, by adjusting the operating parameters of the membrane interface induced crystallization unit 2, including but not limited to the carbonate ion concentration in the induced crystallization agent 2026, the flow rate of the agent, the transmembrane pressure difference (TMP) at the membrane interface, the type and dosage of the crystallization regulator, the local supersaturation and crystallization driving force at the membrane interface can be finely controlled, thereby achieving the graded control and removal of residual calcium ions.

[0084] Experimental results show that, under normal operating conditions, the system of the present invention can stably control the calcium ion concentration in the effluent below 10 mg / L; after further optimization of the operating parameters, the calcium ion concentration in the effluent can be stably reduced to 5 mg / L, while maintaining continuous and stable operation of the system.

[0085] Furthermore, the effluent quality of the system of the present invention can be directionally controlled according to the feed water requirements of subsequent process units. When used as feed water for reverse osmosis (RO), the calcium ion concentration is controlled to be below 20 mg / L; when used as feed water for evaporation crystallization (MVR / MED), the calcium ion concentration is controlled to be below 10 mg / L; and when used as feed water for high-pressure boilers or high-end reclaimed water, the calcium ion concentration can be further controlled to be below 5 mg / L.

[0086] Therefore, this invention not only achieves further calcium removal from primary softened wastewater, but also has the ability to adjust the hardness of the effluent as needed, significantly improving the engineering applicability and flexibility of the system.

[0087] Comparative Example 1 The same wastewater sample as in Example 5 was treated using a traditional chemical precipitation method. Specifically, sodium carbonate solution was added to the wastewater, and the pH of the system was adjusted to 10.0 using sodium hydroxide. After stirring for 30 minutes, the mixture was allowed to settle for 60 minutes. The supernatant was then collected to measure the calcium ion concentration, which was found to be 50 mg / L after treatment.

[0088] Compared to Example 5, the traditional chemical precipitation method can reduce the calcium ion concentration in wastewater. However, for the same concentration of wastewater, the calcium ion concentration of 50 mg / L after treatment by the traditional chemical precipitation method is significantly higher than the 5 mg / L after membrane interface induced crystallization treatment in Example 5. Furthermore, the traditional chemical precipitation method generates a large amount of chemically precipitated sludge, increasing the cost of calcium removal from wastewater.

[0089] The comparative results show that the calcium removal method using chemical crystallization granulation coupled membrane interface induced crystallization in Example 5 of this patent not only helps to further remove the calcium ion concentration in the wastewater to be treated, but also allows the generated calcium carbonate to be transported to the chemical crystallization granulation unit 1 as seed crystals for recycling through the microcrystal separation and reuse unit 3. This reduces water treatment costs and does not generate secondary pollution.

[0090] Comparative Example 2 This comparative example is basically the same as Example 5, except that the wastewater to be treated is only treated by the chemical crystallization granulation unit 1. The calcium ion content in the wastewater before and after treatment is shown in Table 3.

[0091] Compared with Example 5, since the wastewater to be treated was only treated by the chemical crystallization granulation system, the calcium ion concentration in the wastewater after treatment was still as high as 30 mg / L, which was significantly higher than the calcium ion concentration of 5 mg / L after membrane interface induced crystallization treatment in Example 5. Therefore, the calcium removal effect of the wastewater to be treated was worse than that of Example 5.

[0092] The comparative results show that the membrane-induced crystallization unit 2 in Example 5 is beneficial to the further removal of calcium ion concentration in the primary softened water, and plays an important role in further reducing the concentration of calcium ions in the wastewater to be treated.

[0093] Table 3 Comparison of calcium ion concentrations before and after treatment in Comparative Example 2

[0094] Comparative Example 3 This comparative example is basically the same as Example 5, except that the flow rate of the wastewater to be treated in the aqueous phase channel 2022 of the membrane interface induced crystallization unit 2 is increased from 1.0 m / s in Example 5 to 3.0 m / s, while the other operating conditions remain unchanged. The calcium ion content in the wastewater before and after treatment is shown in Table 4.

[0095] Compared with Example 5, due to the increased water flow rate in the aqueous phase channel 2022 of the membrane interface induced crystallization unit 2, the contact reaction time between the primary softened water in the aqueous phase channel 2022 and the induced crystallization solution in the solution channel 2021 is reduced, resulting in a calcium ion concentration of 15 mg / L in the wastewater after treatment by the membrane interface induced crystallization unit 2, which is higher than the calcium ion concentration of 5 mg / L after treatment in Example 5. Therefore, the further calcium removal effect of the wastewater to be treated is worse than that in Example 5.

[0096] The comparative results show that, in the further calcium removal process, controlling the flow rate of the wastewater to be treated within a reasonable range of operating process conditions is beneficial to improving the further calcium removal effect in membrane-induced crystallization unit 2.

[0097] Table 4 Comparison of calcium ion concentrations before and after treatment in Comparative Example 3

[0098] The specific embodiments described in the specification are merely explanations and further descriptions of this application and are not intended to limit this application. All equivalent modifications made based on the technical solutions of this application fall within the protection scope of this invention.

Claims

1. A chemical crystallization granulation coupled membrane interface induced crystallization calcium removal system, comprising a chemical crystallization granulation unit (1), characterized in that, The system also includes a membrane interface induced crystallization unit (2) and a microcrystal separation and recycling unit (3); The chemical crystallization granulation unit (1) is used to perform primary softening treatment on the wastewater to be treated, so as to obtain primary softened wastewater; The membrane interface induced crystallization unit (2) is used to induce crystallization of the primary softened wastewater from the chemical crystallization granulation unit (1); the membrane interface induced crystallization unit (2) includes a membrane interface induced crystallization component (201), an aqueous phase circulation system connected to the aqueous phase side of the membrane interface induced crystallization component (201), and a liquid circulation system connected to the liquid side of the membrane interface induced crystallization component (201); The chemical crystallization granulation unit (1) is connected to the aqueous phase circulation system of the membrane interface induced crystallization unit (2) and receives the microcrystals returned by the microcrystal separation and reuse unit (3). The microcrystal separation and reuse unit (3) is connected to the drug circulation system of the membrane interface induced crystallization unit (2) and is used to separate, concentrate and reuse the microcrystals generated by the membrane interface induced crystallization component (201). After the wastewater is treated by the chemical crystallization granulation coupled membrane interface induced crystallization calcium removal system, the calcium ion concentration in the wastewater is below 10 mg / L.

2. The chemical crystallization granulation coupled membrane interface induced crystallization calcium removal system according to claim 1, characterized in that, The membrane interface induced crystallization assembly (201) is composed of a membrane element (202), which has an inner wall (205) and an outer wall (206).

3. The chemical crystallization granulation coupled membrane interface-induced crystallization calcium removal system according to claim 2, characterized in that, The aqueous circulation system includes a circulating water tank (203) connected to the outlet of the primary softened wastewater obtained from the chemical crystallization granulation unit (1), an aqueous channel (2022) formed by the inner wall (205) of the membrane element, and a water circulation pipeline (204). The inner wall (205) of the membrane element is in contact with the water phase from the circulating water tank (203); The first outlet pipe (215) of the water circulation pipe (204) is equipped with a first solenoid valve (218) for controlling the discharge of the water after the membrane interface induced crystallization unit (2) induces crystallization to the clear water pool (217) connected to the rear end of the first solenoid valve (218); The second outlet pipe (216) of the water circulation pipe (204) is connected to the circulating water tank (203) through the membrane module variable frequency return pump (214). A second solenoid valve (219) is installed at the front end of the membrane module variable frequency return pump (214) on the second outlet pipe (216) to control the return of the water after crystallization induced by the membrane interface induced crystallization unit (2) to the circulating water tank (203).

4. The chemical crystallization granulation coupled membrane interface induced crystallization calcium removal system according to claim 3, characterized in that, The drug circulation system includes a drug dosing system (208), a drug channel (2021) formed by the outer wall (206) of the membrane element and the outer cavity where it is located, and a drug circulation pipeline (207). Along the direction of drug circulation, the rear end of the drug dosing system (208) is connected to the drug frequency conversion dosing pump (209), and the front end of the drug dosing system (208) is connected to the drug frequency conversion return pump (210). The outer wall (206) of the membrane element is in contact with the drug solution added from the drug dosing system (208); The drug circulation pipeline (207) contains a crystallizing agent (2026) from the drug dosing system (208). The liquid channel (2021) and the aqueous channel (2022) are separated by a membrane substrate (2024), and the membrane interface of the membrane substrate (2024) is provided with hydrophilic microregions (2028) and hydrophobic microregions (2029).

5. The chemical crystallization granulation coupled membrane interface-induced crystallization calcium removal system according to claim 4, characterized in that, The chemical crystallization granulation unit (1) includes a fluidized bed body (101), which is a variable diameter structure that is narrow at the bottom and wide at the top. From bottom to top, it is provided with a fluidized bed water inlet pipe (102), a dosing pipe (103), a crystal particle discharge pipe (104), a seed crystal dosing pipe (105), and a water collection area (106). The fluidized bed inlet pipe (102) is located below the fluidized bed body (101), and the dosing pipe (103) is located above the fluidized bed inlet pipe (102). Inside the fluidized bed body (101), at the same horizontal position as the dosing pipe (103), a drug distribution jacket (107) is provided. The crystallization particle discharge pipe (104) is located below the diameter change of the fluidized bed body (101) and between the drug delivery interlayer (107); The seed dosing tube (105) is located above the variable diameter of the fluidized bed body (101).

6. The chemical crystallization granulation coupled membrane interface-induced crystallization calcium removal system according to claim 5, characterized in that, The microcrystal separation and reuse unit (3) includes a hydrocyclone (301), a seed tank (305), and a seed dosing pump (306) for concentrating and separating the calcium carbonate microcrystals (2027) solution mixture generated by the membrane interface induced crystallization unit (2) through crystallization. The upper feed end and the top overflow outlet end of the hydrocyclone (301) are respectively connected to the liquid circulation pipeline (207) after the liquid circulation channel (2021) of the liquid circulation system of the membrane interface induced crystallization unit (2); The bottom discharge end of the hydrocyclone (301) is connected to the inlet of the seed tank (305), and the outlet of the seed tank (305) is connected to the seed feeding pipe (105) of the chemical crystallization granulation unit (1).

7. The chemical crystallization granulation coupled membrane interface induced crystallization calcium removal system according to claim 6, characterized in that, The system for removing calcium by chemical crystallization granulation coupled membrane interface induced crystallization includes a control unit (4) for linkage regulation and operation, and the control unit (4) is a signal collection and control center (401). The membrane interface induced crystallization unit (2) also includes an online pH meter (211), an online water quality analyzer (220), and an online pressure gauge (221). The online pH meter (211) is installed between the drug dosing system (208) and the drug frequency conversion reflux pump (210) to monitor the consumption of drug solution on the outer wall (206) of the membrane element in real time; The online water quality analyzer (220) is installed on the water circulation pipeline (204) after the outlet of the aqueous channel (2022) of the membrane interface induced crystallization component (201) and before the diversion of the first outlet pipeline (215) and the second outlet pipeline (216), and is used to monitor the concentration of residual calcium ions in the water after the membrane interface induced crystallization treatment. The online pressure gauge (221) includes an aqueous phase pressure detection point set on the aqueous phase channel (2022) side of the membrane element (202) and a drug solution pressure detection point set on the drug solution channel (2021) side. The signal collection and control center (401) calculates the transmembrane pressure difference at the membrane interface of the membrane element (202) based on the aqueous phase pressure and the drug solution pressure.

8. The chemical crystallization granulation coupled membrane interface-induced crystallization calcium removal system according to claim 7, characterized in that, The microcrystal separation and reuse unit (3) also includes a third solenoid valve (302). The third solenoid valve (302) is located between the drug circulation pipeline (207) after the outlet of the drug channel (2021) of the membrane interface induced crystallization unit (2) and the screw pump inlet at the upper feed end of the hydrocyclone (301) of the microcrystal separation unit (3). It is used to control the calcium carbonate microcrystal (2027) drug mixture generated by the induced crystallization of the membrane interface induced crystallization unit (2) to enter the hydrocyclone (301). The screw pump is the first screw pump (303).

9. A method for removing calcium using the chemical crystallization granulation coupled membrane interface-induced crystallization calcium removal system as described in claim 8, characterized in that, The calcium removal method of the chemical crystallization granulation coupled membrane interface induced crystallization calcium removal system includes the following steps: Step 1 is the chemical crystallization granulation unit (1) primary softening of the wastewater to be treated: the wastewater to be treated enters the fluidized bed body (101) through the fluidized bed inlet pipe (102) and is mixed with the softening agent injected from the dosing pipe (103). Heterogeneous crystallization occurs on the surface of the seed crystals injected from the seed crystal dosing pipe (105) to generate calcium carbonate crystals. The generated calcium carbonate crystal particles are discharged from the crystal particle discharge pipe (104). The primary softened wastewater is collected in the water collection area (106) and flows out from the outlet of the water collection area (106) and enters the circulating water tank (203). Step 2 is the induction of crystallization by the membrane interface induced crystallization unit (2): the membrane module variable frequency reflux pump (214) is turned on to establish internal water phase circulation, and the reagent variable frequency dosing pump (209) is turned on to establish external reagent circulation; the primary softened wastewater that entered the circulating water tank (203) in step 1 flows through the water phase channel (2022) where the inner wall (205) of the membrane element is located, and the residual calcium ions (2025) in the primary softened wastewater penetrate from the water phase channel (2022) to the outer wall of the membrane element ( 206), enriched in the hydrophilic micro-region (2028); residual calcium ions (2025) in the primary softened wastewater combine with carbonate ions in the crystallization-inducing agent (2026) at the membrane interface on the outer wall (206) of the membrane element to generate calcium carbonate microcrystals (2027); the shear force generated by the tangential flow of the liquid through the outer wall (206) of the membrane element in the liquid channel (2021) will peel off the calcium carbonate microcrystals (2027) induced by crystallization on the outer wall (206) of the membrane element; Step 3 is the separation and reuse of microcrystals in the microcrystal separation and reuse unit (3): the second solenoid valve (219) is opened, and the drug solution mixture rich in calcium carbonate microcrystals (2027) mentioned in step 2 enters the hydrocyclone (301) tangentially through the upper feed end of the hydrocyclone (301) for centrifugal concentration; the supernatant after separation is returned to the drug solution circulation system through the top overflow outlet end of the hydrocyclone (301) for continued use, and the concentrated calcium carbonate microcrystals (2027) slurry separated at the bottom is first transported to the seed tank (305) through the bottom discharge end of the hydrocyclone (301), and then transported back to the fluidized bed body (101) of the chemical crystallization granulation unit (1).

10. The calcium removal method of the chemical crystallization granulation coupled membrane interface-induced crystallization calcium removal system according to claim 9, characterized in that, In step 2, the flow rate of the aqueous phase in the aqueous phase channel (2022) is 0.5~2.0 m / s, and the flow rate of the drug solution in the drug solution channel (2021) is 0.3~1.5 m / s; the concentration of carbonate ions in the drug solution in the drug solution channel (2021) is 0.02~0.2 mol / L, and the pH value is between 8.5 and 9.

5. The crystallization-inducing agent (2026) is one or both of a 0.05~0.1 mol / L sodium carbonate solution or potassium carbonate solution; the membrane element (202) has a transmembrane pressure difference at the membrane interface ranging from 0.05 to 0.15 MPa; after treatment by the membrane interface induced crystallization unit (2), the calcium ion concentration in the wastewater is below 10 mg / L.

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