Rubber additive wastewater treatment system based on ozone oxidation and crystallization granulation

Abstract

The invention relates to the technical field of industrial wastewater treatment, and discloses a rubber additive wastewater treatment system based on ozone oxidation and crystallization granulation, which is characterized in that a mother liquor pool and a primary washing tank are connected with a first oxidation tower, and a liquid outlet is connected with a tubular membrane and a nanofiltration assembly in series; the nanofiltration concentrated solution is connected back to the first oxidation tower or is led to the MVR evaporator; the secondary washing tank and an MVR condensate are connected with a second oxidation tower, a liquid outlet is treated by a crystallization fluidized bed, and a supernatant enters a reverse osmosis assembly through a membrane assembly; and the two-stage oxidation tower and the ozone generator form a closed cycle through the tail gas purifier. According to the invention, oxidation and mineralization of refractory organics in the mother liquor are enhanced through high and low concentration staged treatment and nanofiltration interception reflux; the crystallization fluidized bed heterogeneous nucleation granulation technology is utilized to remove scale-causing ions in advance, so that the risk of scaling and sewage blockage of a subsequent membrane module is reduced, and long-term stable operation of the system and resource utilization of wastewater are realized.

Description

Technical Field

[0001] This invention relates to the field of industrial wastewater treatment technology, specifically to a rubber additive wastewater treatment system based on ozone oxidation and crystallization granulation. Background Technology

[0002] Rubber additives, as an important supporting raw material in the rubber industry, involve complex synthetic reactions in their production process. The resulting wastewater is typically characterized by high salinity, high chemical oxygen demand (COD), and the presence of recalcitrant organic compounds such as benzothiazoles and anilines. Direct discharge of this type of wastewater without effective treatment will pollute the environment, and its complex composition also inhibits conventional biological treatment.

[0003] In existing technologies, the treatment of this type of wastewater often employs a combination of physicochemical pretreatment, biological treatment, and advanced treatment. Mechanical vapor recompression (MVR) evaporation technology is widely used to remove high concentrations of salt from wastewater. However, due to the large amount of resinous macromolecular organic matter and colloids in the wastewater, direct evaporation easily leads to coking and carbon buildup on the heat exchanger surface, affecting heat transfer efficiency and equipment operating cycle. Therefore, before evaporation or membrane concentration, advanced oxidation technologies are usually required to break down the organic matter structure.

[0004] Currently, commonly used advanced oxidation methods include Fenton oxidation and ozone oxidation. While Fenton oxidation is rapid, it produces a large amount of iron-containing chemical sludge, increasing solid waste disposal costs. Ozone oxidation, although sludge-free, suffers from limited gas-liquid mass transfer efficiency and low single-pass oxidant utilization in practical engineering applications, leading to high operating energy consumption. Furthermore, rubber additive wastewater often contains high concentrations of hardness ions such as calcium and magnesium, as well as silicates. Traditional chemical precipitation softening methods require large dosages, and the resulting flocs have unstable settling properties. When wastewater enters subsequent ultrafiltration, nanofiltration, or reverse osmosis dual-membrane systems, residual micro-suspended solids, supersaturated inorganic salt ions, and incompletely mineralized organic macromolecules can easily create a synergistic fouling effect on the membrane surface. Inorganic scaling and organic adsorption not only cause rapid membrane flux decay and shorten chemical cleaning cycles, but can also cause irreversible damage to membrane elements in severe cases, limiting the long-term stable application of membrane separation technology in the resource recovery of high-salt, recalcitrant wastewater. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a rubber additive wastewater treatment system based on ozone oxidation and crystallization granulation. This system solves the problems of difficult degradation of high-concentration mother liquor, incomplete mineralization of organic pollutants, and rapid flux decline and poor operational stability of membrane modules in subsequent desalination systems due to inorganic scaling and organic fouling.

[0006] To achieve the above objectives, the present invention is implemented through the following technical solution: a rubber additive wastewater treatment system based on ozone oxidation and crystallization granulation. This system solves the problems of difficult degradation of high-salt mother liquor and easy fouling of membrane systems in rubber additive wastewater by using staged oxidation and coupled crystallization technology.

[0007] The rubber additive wastewater treatment system based on ozone oxidation and crystallization granulation described in this invention mainly consists of a high-concentration wastewater treatment flow path, a low-concentration wastewater treatment flow path, and an ozone gas circulation loop.

[0008] In the high-concentration wastewater treatment flow path, the outlets of the mother liquor tank and the primary washing tank are connected to the inlet of the first oxidation tower. The outlet of the first oxidation tower is connected in series with a tubular membrane module and a nanofiltration module; the concentrate outlet of the nanofiltration module is connected back to the inlet of the first oxidation tower, forming a circulating oxidation loop for macromolecular organic matter; the product water outlet of the nanofiltration module is connected to the feed inlet of the MVR evaporator.

[0009] In the low-concentration wastewater treatment flow path, the condensate outlets of the secondary scrubbing tank and the MVR evaporator are connected to the inlet of the second oxidation tower. The outlet of the second oxidation tower is connected to the bottom inlet of the crystallization fluidized bed; the supernatant outlet of the crystallization fluidized bed is connected to the feed end of the reverse osmosis module via the tubular membrane module and the nanofiltration module.

[0010] In the gas circulation loop, the gas outlet of the ozone generator is connected to the aeration device located at the bottom of the first oxidation tower and the second oxidation tower, respectively.

[0011] In this invention, each processing unit is specifically configured based on reaction kinetics and mass transfer principles.

[0012] Regarding the solid-liquid reaction principle, the crystallization fluidized bed is configured as a vertical flow solid-liquid reactor. Its structure, from bottom to top, is divided into an inlet water distribution zone, a fluidization reaction zone, and a sedimentation separation zone, connected to a seed dosing machine and a chemical dosing machine. This unit is based on the principle of supersaturation control in the metastable zone. By adjusting the inlet water flow rate, the upward flow velocity within the fluidized bed is kept lower than the terminal settling velocity of the crystals, maintaining the crystals in suspension and growth within the fluidization reaction zone. The system utilizes a seed-induced heterogeneous nucleation mechanism to eliminate the induction period, allowing inorganic salt ions and organic macromolecules in the water to be directionally adsorbed and stacked on the seed surface under van der Waals forces and chemical bonds, thereby reducing the scaling potential energy of the effluent.

[0013] Regarding the gas-liquid mass transfer principle, the first oxidation tower is configured as a vertical cylindrical gas-liquid reaction vessel, with a microporous aeration device at the bottom and a liquid distributor at the top. The second oxidation tower has several layers of porous flow guide baffles or is filled with ceramic Raschig ring packing along its height. This structure increases the contact surface area and turbulence between the gas and liquid phases, thereby improving the volumetric mass transfer coefficient of ozone in the liquid phase and delaying bubble coalescence. This, in turn, enhances ozone utilization and the oxidation reaction rate without increasing energy consumption.

[0014] In addition, the exhaust ports at the top of the first and second oxidation towers are connected to the inlet of the exhaust gas purifier, and the gas outlet of the exhaust gas purifier is connected back to the inlet of the ozone generator, forming a closed-loop oxygen circulation.

[0015] In terms of membrane system configuration, the tubular membrane module is configured as an external cross-flow ultrafiltration unit, consisting of a circulation tank, a high-flow circulation pump, and a series-parallel array of membrane modules. The membrane modules adopt a large-channel structure made of modified polyvinylidene fluoride or recrystallized silicon carbide. The nanofiltration module includes a security filter, a high-pressure pump, and spiral wound nanofiltration membrane elements connected in series. Its concentrate outlet is connected to the inlet of the first oxidation tower or the feed inlet of the MVR evaporator through a pipeline equipped with a switching valve, achieving the staged retention of organic matter with different molecular weights. The reverse osmosis module includes a high-pressure plunger pump, an isobaric energy recovery device, and a series of antifouling seawater desalination spiral wound reverse osmosis membrane elements. Its concentrate outlet is connected to the first-stage scrubbing tank, and the product water outlet is connected to the reclaimed water tank.

[0016] The MVR evaporator is configured as a mechanical vapor recompression forced circulation crystallization system, integrating a plate preheater, a vertical gas-liquid separator, a forced circulation pump, a shell-and-tube heat exchanger, a centrifugal steam compressor, and a thickening dehydration assembly.

[0017] This invention provides a rubber additive wastewater treatment system based on ozone oxidation and crystallization granulation. It has the following beneficial effects: 1. This invention employs a high- and low-concentration wastewater split treatment coupled with nanofiltration reflux technology. The high-concentration mother liquor forms a circulation loop between the first oxidation tower and the nanofiltration module. By utilizing the retention effect of the nanofiltration membrane on macromolecules, the recalcitrant organic matter is repeatedly oxidized and mineralized in the first oxidation tower, or concentrated and then enters the MVR evaporator. This avoids high-concentration pollutants directly entering the subsequent reverse osmosis system, which would cause membrane flux attenuation. The low-concentration washing water is treated with an independent flow path, matching the anti-fouling load of different treatment units and optimizing the overall energy efficiency ratio of the system.

[0018] 2. The system of this invention introduces a crystallizing fluidized bed as a pretreatment stage before the membrane separation unit. It uses the principle of induced crystallization to reduce water hardness and scaling potential. By controlling the supersaturation in the fluidized bed, scale-causing ions such as calcium and magnesium in the wastewater grow into dense particles on the surface of the seed crystals and are discharged from the bottom. Compared with the traditional flocculation process, this method reduces the generation of colloidal sludge and reduces the risk of inorganic scaling on the surface of subsequent tubular membranes and reverse osmosis membrane elements, thus extending the chemical cleaning cycle and service life of the membrane elements.

[0019] 3. This invention designs an oxygen closed-loop circulation circuit, which purifies the oxygen-containing tail gas at the top of the two-stage oxidation tower and reuses it in the ozone generation system. This structure directly recovers the oxygen that has not participated in the reaction, reducing the cost of liquid oxygen or oxygen production in the ozone preparation process. At the same time, the tail gas purifier eliminates residual ozone and volatile organic compounds, avoiding secondary pollution and realizing the efficient utilization of the oxidant. Attached Figure Description

[0020] Figure 1 This is a process flow diagram of the rubber additive wastewater treatment system according to an embodiment of the present invention; Figure 2 This is a schematic diagram of the response curves between influent load fluctuation and ozone addition in an embodiment of the present invention.

[0021] The components include: 1. Ozone generator; 2. First oxidation tower; 3. Second oxidation tower; 4. Crystallization fluidized bed; 5. Tubular membrane module; 6. Nanofiltration module; 7. Reverse osmosis module; 8. MVR evaporator; 9. Mother liquor tank; 10. Primary scrubbing tank; 11. Secondary scrubbing tank; 12. Tail gas purifier; 13. Seed dosing machine; and 14. Chemical dosing machine. Detailed Implementation

[0022] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] See attached document Figure 1 The present invention provides a rubber additive wastewater treatment system based on ozone oxidation and crystallization granulation. The system includes: an ozone generator 1, a first oxidation tower 2, a second oxidation tower 3, a crystallization fluidized bed 4, a tubular membrane module 5, a nanofiltration module 6, a reverse osmosis module 7, and an MVR evaporator 8.

[0024] All components are connected via fluid pipelines and transfer pumps. The inlet end is equipped with a mother liquor tank 9, a primary scrubbing tank 10, and a secondary scrubbing tank 11. The outlet of the mother liquor tank 9 and the outlet of the primary scrubbing tank 10 are connected to the inlet of the first oxidation tower 2. The outlet of the secondary scrubbing tank 11 and the condensate outlet of the MVR evaporator 8 are connected to the inlet of the second oxidation tower 3.

[0025] The gas outlet of ozone generator 1 is connected to the aeration device at the bottom of the first oxidation tower 2 and the second oxidation tower 3. The exhaust ports at the top of the first oxidation tower 2 and the second oxidation tower 3 are connected to the exhaust gas purifier 12. The gas outlet of the exhaust gas purifier 12 is connected back to the inlet of ozone generator 1.

[0026] The outlet of the first oxidation tower 2 is connected to the feed end of the tubular membrane module 5. The clarified liquid outlet of the tubular membrane module 5 is connected to the feed end of the nanofiltration module 6. The permeate outlet of the nanofiltration module 6 is connected to the feed inlet of the MVR evaporator 8, and the concentrate outlet of the nanofiltration module 6 is connected to the inlet of the first oxidation tower 2.

[0027] The outlet of the second oxidation tower 3 is connected to the bottom inlet of the crystallization fluidized bed 4. The supernatant outlet of the crystallization fluidized bed 4 is connected to the feed end of the reverse osmosis module 7 via a tubular membrane module 5 and a nanofiltration module 6 in sequence. In this embodiment, separate tubular membrane modules 5 and nanofiltration modules 6 are configured for the high-concentration flow path of the effluent from the first oxidation tower 2 and the low-concentration flow path of the effluent from the crystallization fluidized bed 4, respectively, or the same set of modules can be used for time-sharing treatment by switching valves.

[0028] The permeate outlet of reverse osmosis module 7 is connected to the recycled water tank, and the concentrate outlet of reverse osmosis module 7 is connected to the primary scrubbing tank 10.

[0029] The crystallization fluidized bed 4 is connected to a seed crystal dosing machine 13 and a chemical dosing machine 14. The MVR evaporator 8 is equipped with a solid salt outlet and a condensate outlet.

[0030] This invention also provides a method for treating rubber additive wastewater based on ozone oxidation and crystallization granulation, comprising the following steps: S10, the reaction mother liquor generated in the rubber additive production process is mixed with the primary washing water and then incorporated into the nanofiltration concentrate from the subsequent process to form a high-concentration mixed waste liquid; S20, high-concentration mixed waste liquid is transported to the first oxidation tower 2, and ozone gas generated by ozone generator 1 is introduced to carry out gas-liquid contact reaction to oxidize and degrade organic pollutants in the waste liquid; S30, the waste liquid after oxidation treatment is separated into solid and liquid by tubular membrane module 5 to remove suspended particulate matter, and the product water enters nanofiltration module 6 for graded separation; the concentrated liquid retained by nanofiltration module 6 is returned to step S10 or S20 for recycling treatment, and the permeate of nanofiltration module 6 enters MVR evaporator 8. S40, the nanofiltration permeate is evaporated and crystallized in MVR evaporator 8 to produce sodium chloride solid salt, and the resulting evaporation condensate is sent to the low concentration treatment process. S50: The secondary washing water generated during the rubber additive production process is mixed with the evaporation condensate generated in step S40 and then transported to the second oxidation tower 3 for secondary oxidation treatment. S60, the effluent from secondary oxidation enters the crystallization fluidized bed 4, seed crystals and alkaline agents are added into the bed, and the fluid state is controlled so that calcium and magnesium ions in the water crystallize and grow into calcium carbonate particles on the surface of the seed crystals and are discharged from the bottom, and the supernatant overflows and is discharged. The supernatant discharged from steps S70 and S60 is filtered sequentially through tubular membrane module 5 and nanofiltration module 6, and then enters reverse osmosis module 7 for deep desalination. S80, the freshwater produced by the reverse osmosis module 7 is reused for production washing or boiler feedwater, and the reverse osmosis concentrate is returned to the first-stage washing process; at the same time, the exhaust gas discharged from the first oxidation tower 2 and the second oxidation tower 3 is collected, and after dehumidification and impurity removal, oxygen is separated and sent back to the ozone generator 1 as a gas source.

[0031] See attached document Figure 1 In this embodiment, the ozone generator 1 and the exhaust gas purifier 12 are connected to form a closed-loop oxygen circulation circuit. This circuit regenerates the oxidized exhaust gas through physical and chemical methods to meet the intake requirements of the ozone generator, thereby reducing the consumption of liquid oxygen or bottled oxygen.

[0032] The gas outlet of ozone generator 1 is connected to the bottom aeration tray of the first oxidation tower 2 and the second oxidation tower 3 via corrosion-resistant pipes made of polytetrafluoroethylene (PTFE) or 316L stainless steel. The exhaust ports at the top of the first oxidation tower 2 and the second oxidation tower 3 converge and connect to the inlet of the exhaust gas purifier 12. The exhaust port of the exhaust gas purifier 12 is connected back to the raw material gas inlet of ozone generator 1 via a circulating booster fan, and a fresh oxygen replenishment port is provided on the return pipeline.

[0033] The operation control of this loop specifically includes the following steps: S101, Ozone Preparation and Dosing: Ozone generator 1 employs a dielectric barrier discharge device using high-purity oxygen (oxygen volume fraction ≥90%) as the gas source. Under the action of a high-frequency, high-voltage electric field, oxygen molecules absorb energy, break bonds, and recombine to form ozone. To ensure the driving force for gas-liquid mass transfer, the discharge parameters of ozone generator 1 are set to output ozone gas with a concentration between 100 mg / L and 160 mg / L.

[0034] The generated ozone gas is transported to the oxidation tower and dispersed into the liquid phase through microporous aeration or ejector.

[0035] S102, Exhaust Gas Dehumidification and Pretreatment: The exhaust gas discharged from the oxidation tower is saturated with water vapor. The exhaust gas first enters the gas-liquid separation section of the exhaust gas purifier 12 to remove free droplets, and then enters the dehumidification section. The dehumidification section employs a combination of freeze-drying and adsorption-drying processes to control the dew point of the circulating gas between -45℃ and -60℃. This deep dehumidification step is to prevent water molecules from ionizing in the discharge gap to generate hydroxyl radicals, which can poison the dielectric tube and produce nitric acid byproducts that corrode the electrodes.

[0036] S103, Impurity Gas Retention and Purification: The dehumidified gas enters the decarbonization section. Since the mineralization of organic matter in wastewater produces carbon dioxide, the accumulated carbon dioxide in the circulation leads to a decrease in the oxygen partial pressure of the raw material gas, reducing ozone production. The decarbonization section is filled with modified 13X molecular sieves or solid sodium hydroxide particles with high selective adsorption capacity for carbon dioxide, configured to maintain the volume concentration of carbon dioxide in the circulating gas below 1%.

[0037] In addition, residual impurities such as carbon monoxide and nitrogen oxides in the exhaust gas are also synergistically adsorbed or catalytically converted during this stage.

[0038] S104, Oxygen Circulation and Mass Balance Control: The system maintains gas volume balance through online monitoring and feedback adjustment. During operation, ozone oxidation essentially consumes oxygen atoms, while some ozone decomposes and is reduced back to oxygen. To maintain stable loop pressure, the amount of oxygen consumed in the reaction and lost during purification needs to be replenished.

[0039] The system controller calculates and adjusts the opening of the fresh oxygen supply valve based on the principle of mass conservation. At this time, the fresh oxygen supply amount... The determination is based on the following calculation model: First, define the total mass flow rate of the gas entering ozone generator 1 as: (This value is controlled by the frequency of the circulating fan, in kg / h), the oxygen mass fraction in the intake air is... (Usually maintained above 0.9).

[0040] The electro-optical conversion efficiency of ozone generator 1 determines the ozone yield per pass, defined as the conversion rate. Under the high concentration conditions of this embodiment, The value range is typically 10% to 16%.

[0041] ozone mass flow rate entering the oxidation tower It can be represented as: ; After the oxidation reaction, the oxygen mass flow rate of the exhaust gas after purification and recovery It depends on the degree of ozone decomposition. Ozone utilization rate is defined. The proportion of ozone participating in the oxidation reaction is determined by detecting the residual ozone concentration in the exhaust gas. and exhaust gas flow The calculation shows that, .

[0042] The amount of oxygen recovered is: ; in, The mass stoichiometric ratio of ozone decomposing into oxygen is taken as a constant of 0.67. In the formula, the first term represents the oxygen that was not converted in the generator, and the second term represents the ozone that did not participate in the oxidation reaction and decompose back into oxygen.

[0043] Ultimately, the system requires a replenishment of fresh pure oxygen flow rate. Must meet: ; in, This value represents the system leakage and the purge gas loss during the adsorbent regeneration process. It is typically set as a design margin of 1% to 3% of the total gas volume.

[0044] Through the above control logic, the system can automatically match changes in reaction load, ensuring oxidation effect while increasing oxygen utilization to the theoretical maximum value.

[0045] See attached document Figure 1 In this embodiment, the first oxidation tower 2 is configured as a vertical cylindrical gas-liquid reaction vessel. This unit utilizes the mass transfer and self-decomposition characteristics of ozone in the liquid phase to generate strong oxidizing substances to destroy the recalcitrant organic structures in the rubber additive wastewater.

[0046] The first oxidation tower 2 is made of 2205 duplex stainless steel or carbon steel lined with fiberglass to withstand high concentrations of chloride ions and ozone. In order to follow the two-film theory of gas-liquid mass transfer and maximize the gas-liquid contact surface area, the tower body is designed to be slender, and the ratio of its effective water depth to diameter (height-to-diameter ratio) is limited to between 3:1 and 5:1.

[0047] The bottom of the tower is uniformly equipped with microporous aeration devices, which use sintered titanium powder filter plates or corundum microporous aeration heads, with an average micropore diameter controlled between 5 and 30 micrometers. The small bubble diameter reduces the bubble rise velocity, thereby increasing the residence time of the gas phase in the liquid phase and improving the gas-liquid mass transfer coefficient. ).

[0048] The operating process and parameter control of the first oxidation tower 2 include the following steps: S201, Mixing and Flow Distribution: The reaction mother liquor from mother liquor tank 9, the wash water from primary scrubbing tank 10, and the nanofiltration concentrate returned from nanofiltration module 6 are mixed online in a static pipeline mixer. The COD concentration of the mixed influent is typically in the range of 5000 mg / L to 20000 mg / L. The mixed waste liquid is uniformly sprayed into the tower through a liquid distributor located at the top of the tower, forming a countercurrent contact mode with the upward ozone flow. Countercurrent operation can maintain the largest gas-liquid concentration gradient across the entire tower height, improving the mass transfer driving force.

[0049] S202, pH Environment Adjustment and Free Radical Induction: A pH adjustment dosing point is set up on the inlet pipeline. Based on the feedback signal from the online pH meter, sodium hydroxide solution is added via a metering pump to maintain the pH value of the mixed solution in the tower between 7.0 and 10.0. Under weakly alkaline conditions, hydroxide ions ( ) as an initiator to induce the decomposition of dissolved ozone, generating hydroxyl radicals with a redox potential as high as 2.8V ( This free radical has non-selective oxidation properties, and can effectively attack and break down stable organic molecules with conjugated structures, such as benzothiazoles and anilines, in wastewater.

[0050] S203, Load-based ozone dosing control: Ozone gas from the ozone generator is dispersed into the liquid phase through a bottom aeration device. To accurately match oxidation requirements and avoid oxygen waste due to overdosing or membrane fouling due to underdosing, the system employs a mass flow control model based on the target removal load.

[0051] The flow rate of the mixed waste liquid entering the first oxidation tower 2 is set as follows: (Unit: m) 3 / h), the measured COD concentration of the influent mixture was (Unit: mg / L). Based on the influent tolerance limit of the downstream tubular membrane and nanofiltration system, the target COD value of the effluent from the first oxidation tower 2 is set to be... (Unit: mg / L)

[0052] Required ozone gas mass flow rate for the system (Unit: kg / h) Determined according to the following formula: ; in: Unit conversion factor (to Convert to ).

[0053] Ozone oxidation coefficient (unit: The coefficient represents the mass of ozone required to remove a unit mass of COD. This coefficient is determined by conducting intermittent experiments with actual wastewater samples, continuously introducing ozone at pH 9.0, and recording the ratio of total ozone consumption to total COD removal when COD decreases to the target value. For rubber additive wastewater, this coefficient typically ranges from 0.8 to 2.5.

[0054] Ozone mass transfer efficiency (dimensionless) represents the proportion of ozone transferred from the gas phase to the liquid phase. Limited by Henry's law and bubble coalescence effect, this value ranges from 0.80 to 0.95 under the condition of an effective water depth of 6 to 8 meters.

[0055] S204, Discharge of reaction products: The hydraulic residence time of the waste liquid in the tower is controlled to be between 2 and 4 hours to ensure that the slow oxidation reaction is complete. The oxidized waste liquid is discharged from the lower outlet of the tower and enters the intermediate water tank; the reaction tail gas is discharged from the top of the tower and enters the tail gas purification system.

[0056] See attached document Figure 1 In this embodiment, the second oxidation tower 3 is configured as a deep polishing oxidation unit for low-concentration organic wastewater. This unit is located before the crystallization fluidized bed, and its core function is to remove trace organic impurities in the wastewater through oxidation, especially to destroy surface-active substances that hinder crystal growth.

[0057] The structure of the second oxidation tower 3 is optimized for low-concentration reaction kinetics based on that of the first oxidation tower. Several layers of porous baffles or ceramic Raschig ring packing are arranged along the height of the tower. This internal configuration divides the tower into multiple reaction zones in series, suppressing longitudinal backmixing of the liquid phase and making the hydraulic characteristics of the reactor approach those of a plug flow reactor. In plug flow mode, the reactant concentration gradually decreases along the flow path, which is beneficial for maintaining the reaction rate under low-concentration conditions.

[0058] The operation control and processing flow of the second oxidation tower 3 specifically includes the following steps: S301, Low-concentration flow path confluence: Dilute wash water from secondary scrubbing tank 11 and evaporative condensate from MVR evaporator 8 converge before entering the second oxidation tower 3. Both fluids share the characteristic of low salt content (conductivity typically less than 5000 μS / cm), but contain small amounts of unreacted rubber additive precursors, byproduct small molecules, and organic additives with dispersing effects.

[0059] S302, Oxidation Reaction Environment and Impurity Removal Mechanism: The mixed liquor enters the second oxidation tower 3. Due to the low concentration of organic matter in the influent (COD is usually less than 500 mg / L), the reaction rate is controlled by the liquid film mass transfer resistance. At this stage, the main purpose of ozone oxidation is to destroy surfactants and colloidal protective substances (such as lignin sulfonates or synthetic polymeric dispersants) in the wastewater. If these substances are not removed, they will coat the surface of the seed crystals in subsequent processes, changing the crystal surface energy and preventing calcium carbonate from heterogeneous nucleation and agglomeration on the seed crystal surface, resulting in the system generating a large amount of unusable fine sludge.

[0060] The reaction contact time is set to 1.0 to 2.0 hours to ensure that the long chain structure of the dispersant molecules is completely broken.

[0061] S303, Dosage control based on residual concentration gradient: In order to overcome the mass transfer bottleneck at low substrate concentrations and ensure sufficient chemical potential driving force, the ozone dosing of the second oxidation tower 3 is controlled by the excess coefficient method.

[0062] The influent flow rate of the second oxidation tower 3 is set as follows: (Unit: m) 3 / h), influent COD concentration is (Unit: mg / L)

[0063] The system's set ozone dosage (Unit: kg / h) Calculated according to the following formula: ; in: Unit conversion factor; The oxidation coefficient (dimensionless) represents the low-concentration polishing coefficient. At low concentrations, a high dissolved ozone concentration in the liquid phase must be maintained to increase the collision probability between ozone molecules and organic molecules in the dilute solution; therefore, this coefficient is significantly higher than the theoretical stoichiometry. In this embodiment... The value range is set to 2.0 to 4.0.

[0064] The real-time determination of the value is based on the following feedback logic: An online Oxidation Reduction Potential (ORP) meter is installed at the effluent end of the second oxidation tower 3. When trace amounts of dissolved ozone (0.1-0.5 mg / L) are present in the effluent, the ORP value will jump. The system closed-loop controller adjusts the ozone flow rate to stabilize the effluent ORP value between 650 mV and 800 mV. The ratio of the dosage to the influent COD load at this time is the current value. value.

[0065] S304, Oxidation Product Transportation: The effluent from the second oxidation tower 3 has undergone changes in its interfacial chemical properties, no longer inhibiting the crystallization process. The effluent is then transported to the crystallization fluidized bed 4 via a booster pump.

[0066] See attached document Figure 1 In this embodiment, the crystallization fluidized bed 4 is configured as a vertical flow solid-liquid reactor, and is equipped with a seed dosing machine 13 and a chemical dosing machine 14. This unit utilizes the huge specific surface area provided by the fluidized particle surface to induce calcium and magnesium ions in water to undergo heterogeneous crystallization, thereby achieving solid-state separation of hardness substances.

[0067] The structure of the crystallization fluidized bed 4 is divided into three zones from bottom to top: a water inlet distribution zone, a fluidization reaction zone, and a sedimentation separation zone. The water inlet distribution zone is equipped with swirling nozzles or resistance distribution plates to generate a uniform upward liquid flow and prevent the reagent from reaching extremely high concentrations locally. The height of the fluidization reaction zone is typically designed to be 4 to 8 meters to ensure sufficient crystallization contact time. The diameter of the sedimentation separation zone is increased to 1.5 to 2.0 times that of the reaction zone. The upward liquid velocity in this zone is significantly reduced, and gravity settling is used to trap and return entrained fine crystals to the reaction zone.

[0068] The operation control and process flow of this unit specifically include the following steps: S401, Construction of the particle-graded fluidized bed: Natural silica sand or garnet with a particle size of 0.2 mm to 0.5 mm is added to the tower as seed crystals via seed dosing machine 13. The influent flow rate drives the seed crystals to be suspended and fluidized in the reaction zone. Due to the uneven particle size distribution of solid particles in the fluidized bed, under the action of hydraulic classification, the bed exhibits a natural stratified distribution with finer particles at the top and coarser particles at the bottom: newly added fine seed crystals are distributed in the upper part of the bed, while coarse particles with existing crystalline coatings are distributed in the lower part of the bed.

[0069] To maintain a stable fluidization state and achieve fractionation, the upward flow rate in the reaction zone must be strictly controlled. The minimum fluidization rate for the seed crystals is set as follows: The settling velocity of the particle terminal is These two parameters are determined based on the Richardson-Zaki formula or through on-site hydraulic model experiments.

[0070] The actual operating flow rate of the system Must meet: ; Under normal operating conditions, for a density of 2.65 g / cm³ 3 Silica sand seed crystals, rising flow rate The flow rate is set between 20 m / h and 40 m / h to maintain the bed expansion rate between 20% and 50%. This flow rate range ensures both intense turbulent contact between the seed crystals and the water flow and prevents a large number of seed crystals from being carried out of the separation zone.

[0071] S402, Metastable Region Supersaturation Control and Nucleation: Chemical dosing unit 14 injects an alkaline reagent (sodium hydroxide or sodium carbonate) into the mixing zone at the bottom of the fluidized bed. After the reagent is added, the ion product in the liquid phase ( Exceeding the solubility product constant ( This leads to a supersaturated state. In this embodiment, the supersaturation of the solution is controlled by adjusting the dosage of the reagent and the mixing intensity. Strictly limited to the metastable region (i.e., the area between the solubility curve and the supersolubility curve).

[0072] Within the metastable region, supersaturated energy is insufficient to overcome the energy barrier for homogeneous nucleation. The solute cannot spontaneously generate new fine crystal nuclei and can only grow heterogeneously through surface adsorption and lattice integration, using existing seed crystal surfaces as growth points. This mechanism effectively inhibits the formation of amorphous flocculent sludge.

[0073] S403, a dosing model based on material balance: In order to maintain the metastable state of S402, the dosage of the reagent must be dynamically matched with the influent hardness load.

[0074] The influent flow rate of the crystallization fluidized bed is set as follows: (Unit: m) 3 / h), calcium hardness concentration in the influent is (Unit: mmol / L), magnesium hardness concentration is (Unit: mmol / L). The drug dosing flow rate is set as follows: (Unit: L / h), the molar concentration of the reagent is (Unit: mol / L)

[0075] The formula for controlling the dosage of the agent is as follows: ; in: This is the correction factor for coprecipitation of magnesium ions. Because magnesium ions tend to form colloidal magnesium hydroxide precipitates in environments with pH above 10.0, this interferes with the crystallization of calcium carbonate. This reflects the removal rate of magnesium ions and the consumption of alkalinity under specific pH conditions. When the operating pH is controlled between 9.5 and 10.5, The value should be between 0.8 and 1.0; when the pH is controlled above 10.5, The value ranges from 1.0 to 1.2.

[0076] This is the chemical precipitation redundancy coefficient. This coefficient directly determines the supersaturation level of the reaction system. To prevent excessively high local concentrations from triggering explosive homogeneous nucleation, this embodiment will... Strictly control it between 1.05 and 1.20.

[0077] S404, Granulation Product Discharge and Seed Regeneration: As the crystallization reaction proceeds, the seed particle size gradually increases and the mass increases. According to the classification principle of S401, mature particles (particle size 1.0mm to 3.0mm) will naturally settle and gather in the slag discharge zone at the bottom of the fluidized bed.

[0078] The system determines the timing of slag discharge by monitoring the differential pressure at the bottom of the bed or the cumulative operating time. When the differential pressure at the bottom exceeds a set threshold (e.g., 20 kPa), the bottom discharge valve is opened to discharge spherical calcium carbonate particles.

[0079] At the same time, the seed dosing machine 13 automatically replenishes an equal amount of fresh small-diameter seed crystals to maintain a constant total specific surface area of ​​crystals in the reactor, ensuring the continuous stability of hardening removal efficiency.

[0080] See attached document Figure 1 In this embodiment, the tubular membrane module 5 is configured as an external cross-flow ultrafiltration device. This unit is located after the crystallization fluidized bed 4 and mainly undertakes the solid-liquid separation task of high solid content liquids, intercepting the escaped micro-crystals and unsettled suspended matter in the preceding process, and protecting the subsequent nanofiltration and reverse osmosis systems from particulate fouling.

[0081] The hardware of the tubular membrane module 5 consists of a circulation tank, a high-flow-rate circulation pump, and a series-parallel array of membrane modules. The membrane tubing is made of modified polyvinylidene fluoride (PVDF) or recrystallized silicon carbide (SiC) to withstand cleaning environments with pH values ​​of 1-13 and the scouring of high-hardness particles. To accommodate high-concentration suspended solids, the inner diameter of the membrane tubing is specifically designed as a large-channel structure of 8mm to 12mm. This size is significantly larger than that of conventional hollow fiber membranes, allowing particles with a diameter less than 3mm to pass freely without channel blockage. The membrane pore size range is selected from 30nm to 50nm (i.e., a molecular weight cutoff of 100,000 to 200,000 Daltons), which can completely retain bacteria and colloids while ensuring low-resistance permeation of dissolved salts.

[0082] The operation control and filtration process of tubular membrane module 5 specifically includes the following steps: S501, Establishment of the high-shear cross-flow circulation loop: The supernatant from the crystallizing fluidized bed 4 first enters the tubular membrane circulation tank. The circulation pump pumps the feed liquid into the membrane tube, the concentrate returns to the circulation tank, and the permeate is discharged through the membrane wall, forming a closed-loop circulation of feed water, concentration, and reflux.

[0083] Unlike conventional filtration, the tubular membrane module 5 relies on high-speed turbulence to control membrane fouling. The system controls the cross-flow velocity of the fluid inside the tube to be between 3.0 m / s and 5.0 m / s. At this velocity, the Reynolds number of the fluid inside the tube is much greater than 4000, indicating a state of intense turbulence. The radial shear stress generated by the fluid on the membrane surface effectively disrupts the concentration polarization layer in the fluid boundary layer and removes the filter cake layer deposited on the membrane surface, thereby maintaining a high and stable membrane flux of 60 LMH to 100 LMH.

[0084] S502, a filter driven by transmembrane pressure difference: the filtration is driven by the static pressure provided by the circulating pump. The system monitors the transmembrane pressure difference in real time through pressure sensors installed at both ends of the membrane module.

[0085] ; in: The feed pressure is typically 0.4MPa-0.6MPa. For the concentrate end pressure, This refers to the back pressure on the water production side.

[0086] S503, Fouling Resistance Model and Cleaning Trigger: As filtration progresses, membrane pores are gradually filled or covered by fine particles. The system controller uses a modified version of Darcy's law to calculate the total filtration resistance in real time. : ; in: Total filtration resistance (unit: m) −1 ); Transmembrane pressure difference (unit: Pa); The measured membrane flux (unit: m / s, i.e., m 3 / (m 2 ·s)); The dynamic viscosity of the liquid is given by Pa·s. Since viscosity is significantly affected by temperature, the system uses the following empirical formula for real-time temperature compensation of viscosity: ,in The standard water viscosity at 20°C This is the actual measured water temperature.

[0087] When the calculation yields Rise to initial resistance When the flux is 1.5 to 2.0 times higher than the design value, or when the membrane flux decreases to 80% of the design value, the system automatically determines that the membrane module is in a fouled state and triggers the online chemical cleaning (CIP) procedure.

[0088] S504, Chemical Recovery Cleaning: The CIP procedure does not require disassembly of the membrane module; the cleaning solution is introduced directly through a switching valve. The cleaning steps are as follows: Pickling: Use 1.0% citric acid or 0.5% hydrochloric acid to circulate for 30 minutes to dissolve the calcium carbonate and metal hydroxide scale deposited in the membrane pores using hydrogen ions; Alkaline washing and oxidation: A mixture of 0.5% sodium hydroxide and 500 ppm sodium hypochlorite was circulated for 60 minutes to degrade the organic gel layer and microbial slime adsorbed on the membrane surface using strong oxidizing properties.

[0089] See attached document Figure 1 In this embodiment, the nanofiltration module 6 is configured as a high-pressure cross-flow membrane separation unit. This unit is located downstream of the tubular membrane module 5 and serves as a key step in salt separation and concentration. It utilizes the selective permeability of the nanofiltration membrane to ions of different valence states to separate wastewater into a permeate mainly composed of sodium chloride and a concentrate mainly composed of sodium sulfate and organic matter.

[0090] The main system of nanofiltration module 6 includes a security filter, a high-pressure pump, a scale inhibitor dosing device, and multiple spiral-wound nanofiltration membrane elements connected in series. The nanofiltration membrane is a negatively charged polypiperazine amide composite membrane with a molecular weight cutoff (MWCO) of 200 Da to 300 Da. This membrane material has a unique pore size distribution and charge characteristics, exhibiting chlorine permeability and sulfur removal separation characteristics at operating pressures from 0.5 MPa to 3.5 MPa.

[0091] The operating logic and process control of nanofiltration component 6 specifically include the following steps: S601, Pretreatment and Chemical Conditioning: Permeate from tubular membrane module 5 first enters a 5μm precision security filter. To prevent inorganic salt scaling on the membrane surface, a non-phosphorus polymeric scale inhibitor is added via an online metering pump before entering the high-pressure pump, with the dosage controlled between 3ppm and 5ppm. Simultaneously, the feed water pH is monitored to ensure it is within the nanofiltration membrane's tolerance and optimal separation range (typically pH 6.5-8.0).

[0092] S602, Charge Effect Separation and Salt Determination: The feed solution, pressurized by a high-pressure pump, enters the nanofiltration membrane channel tangentially. Based on the Donnan equilibrium principle, the fixed negatively charged groups on the membrane surface affect divalent and polyvalent anions in the solution (such as... It generates strong electrostatic repulsion, while it is attracted to monovalent anions (such as...). The repulsive effect of ) is relatively weak.

[0093] Under this mechanism, over 98% of sulfate ions, heavy metal ions, and organic macromolecules (COD) with a molecular weight greater than 200 Da in the influent are retained on the concentrate side; while 80% to 90% of chloride ions and water molecules permeate through the membrane to the permeate side. This step converts the mixed salt wastewater into two streams: a low-COD, high-purity sodium chloride permeate (sent to reverse osmosis and subsequent resource recovery), and a high-COD, high-sodium sulfate concentrate.

[0094] S603, Oxidation Reflux Strategy for Concentrated Solution: The resulting nanofiltration concentrate is enriched with recalcitrant organic matter that was not fully mineralized in the preceding process. In this embodiment, the concentrate is refluxed back to the inlet of the first oxidation tower 2.

[0095] The technical basis of this reflux path is that the organic matter retained by nanofiltration membranes is mostly intermediate products of oxidation reactions or large molecular weight resistant substances. By returning it to the oxidation tower and using high-concentration ozone for secondary digestion, the overall mineralization rate of the system can be significantly improved. When the system monitors that the sulfate concentration in the loop reaches the saturation threshold (e.g., When the concentration exceeds 15%, a portion of the concentrate is bypassed and transported to the MVR evaporator 8 by switching valves for final recovery of sodium sulfate, thereby maintaining the salt balance in the system.

[0096] S604, recovery rate control based on osmotic pressure and polarization modulus: In order to balance the water production rate and membrane flux stability, the system controller dynamically adjusts the operating parameters according to the dissolution and diffusion model and concentration polarization theory.

[0097] Set the solvent permeation flux of the nanofiltration membrane to be (Unit: m / s).

[0098] Its flux governing equation is: ; in: The membrane's hydraulic permeability coefficient (unit: m / (s·Pa)); This is the temperature correction factor.

[0099] For effective transmembrane driving pressure. This represents the average reflectance coefficient of the mixed solution. Due to the presence of sodium sulfate (with a high rejection rate) in the feed solution... ) and sodium chloride with low retention rate ( This value is a weighted empirical value of 0.5 to 0.7.

[0100] The effective osmotic pressure difference across the membrane is given by the formula, which is modified to account for concentration polarization at the membrane surface: ; in: The molar concentration of the bulk fluid (unit: mol / m³) was measured using a conductivity meter. 3 ); The molar concentration of the permeate; For concentration polarization modulus, where The boundary layer mass transfer coefficient is given by m / s.

[0101] Value and cross-flow velocity within the membrane channel and the hydraulic diameter of the flow channel In this embodiment, the calculation is based on the following correlation: ; in, It is a Sherwood number; The solute diffusion coefficient; The Reynolds number ( ); For the Schmidt number ( ).

[0102] The system controls the concentration polarization modulus by adjusting the high-pressure pump frequency and the opening of the concentrate discharge valve. When the calculated modulus value exceeds the limit, the system automatically reduces the recovery rate or increases the crossflow velocity to prevent calcium sulfate or calcium carbonate scaling on the membrane surface due to local supersaturation.

[0103] See attached document Figure 1 In this embodiment, the reverse osmosis component 7 is configured as a high-pressure membrane concentration unit. This unit is located after the nanofiltration component 6, and its core function is to overcome the osmotic pressure of the high-concentration salt solution and increase the sodium chloride concentration in the nanofiltration permeate from 1.5%-3.0% to 6.0%-8.0%, thereby reducing the amount of liquid to be treated in the subsequent MVR evaporation unit.

[0104] The reverse osmosis module 7 comprises a high-pressure plunger pump, an isobaric energy recovery unit, and multiple spiral-wound reverse osmosis membrane elements connected in series. Although the feed water salinity falls within the brackish water category, a fouling-resistant seawater desalination reverse osmosis membrane (SWRO) is specifically selected in this embodiment to achieve high concentration. This membrane element uses a dense aromatic polyamide composite material, with a maximum operating pressure rating of 8.3 MPa (1200 psi). If a conventional brackish water membrane (BWRO) were used, the membrane would be compacted and deformed when the osmotic pressure on the concentrate side exceeds 4.1 MPa, leading to irreversible flux degradation.

[0105] The operation control and concentration process of reverse osmosis module 7 specifically includes the following steps: S701, Oxidation Protection and Secondary Pressurization: Before the nanofiltration permeate enters the RO high-pressure pump, the system monitors the oxidation-reduction potential (ORP) online. The amide bonds (-NH-CO-) in the polyamide membrane material are highly susceptible to breakage by free chlorine, leading to a permanent decrease in desalination rate. Therefore, when the monitored ORP value exceeds 250mV, the dosing device automatically adds sodium bisulfite solution, utilizing its reducing properties to neutralize residual oxidizing substances until the ORP value drops below 200mV.

[0106] Subsequently, the high-pressure pump pressurizes the feed water and delivers it to the membrane module. To reduce energy consumption, the system is equipped with an isobaric energy recovery device. This device uses the discharged high-pressure concentrate to directly pressurize the feed water, so that the high-pressure pump only needs to provide the additional pressure head required to overcome pipeline resistance and osmotic pressure difference, reducing the overall system energy consumption by 30% to 40%.

[0107] S702, High-Pressure Dissolution and Diffusion Separation: Under high pressure, water molecules dissolve into the membrane surface and diffuse through the dense layer, forming permeate with low conductivity. Sodium chloride ions, due to their large hydration radius and repulsion from the membrane surface, are retained on the high-pressure side. Since the preceding nanofiltration unit has removed sulfate and hardness ions, the main solute on the RO concentrate side is sodium chloride, a single component. This single-salt system makes the concentration process less restricted by inorganic salt scaling, allowing the system to operate at extremely high supersaturation.

[0108] S703, Pressure and Recovery Coupling Control Based on Ultimate Osmotic Pressure: The concentration limit of an RO system depends on the pressure tolerance limit of the membrane element. As the recovery rate increases, the osmotic pressure on the concentrate side increases exponentially. The system uses the following model to calculate the operating pressure and control the recovery rate: Set the inlet flow rate to The influent osmotic pressure is The osmotic pressure of the target concentrate is... .

[0109] The system requires an inlet water operating pressure (Unit: MPa) The net driving force requirement of the terminal membrane element must be met: ; in: This is the flow pressure drop at the inlet and outlet of the membrane module (usually taken as 0.2 MPa). The minimum net driving pressure required to maintain end-membrane flux (set to 0.5 MPa to 1.0 MPa). The average osmotic pressure within the membrane channel is calculated using the following formula: ; in: The van der Hoff factor is 2.0 for the strong electrolyte NaCl; The molar mass of the solute is 58.44 g / mol. The logarithmic average concentration of the influent and the concentrate (unit: mg / L). It is the ideal gas constant (8.314 J / (mol·K)). Absolute temperature (unit: K); This represents the permeability coefficient of a non-ideal solution. In high concentration ranges where sodium chloride concentration exceeds 50,000 mg / L, the interactions between ions increase, causing the colligative properties of the solution to deviate from the ideal state. In this embodiment, The value is determined by the measured conductivity-osmotic pressure standard curve, and the value is usually in the range of 0.92 to 0.96.

[0110] The control logic is as follows: the system calculates the current... .when When the calculated value reaches the pressure alarm threshold of the high-pressure pump or membrane element (e.g., 7.5 MPa), the controller automatically adjusts the opening of the concentrate discharge valve to lock the current recovery rate and prevent it from increasing further, thus preventing overpressure damage to the equipment.

[0111] S704, Diversion and Resource Utilization: RO permeate is reused in the production process. The resulting high-concentration sodium chloride concentrate is sent to MVR evaporator 8. Since the concentrate has already had hardness and organic matter removed, and its concentration is close to the optimal feed concentration for the MVR, the evaporation and crystallization process can directly enter the isothermal crystallization zone without undergoing a high-energy-consuming heating and concentration stage, significantly reducing energy consumption per ton of salt.

[0112] See attached document Figure 1 In this embodiment, the MVR evaporator 8 is configured as a mechanical vapor recompression forced circulation crystallization system. This unit recovers the latent heat of secondary steam to evaporate the water in the reverse osmosis concentrate and convert the dissolved salts into crystalline solids, achieving zero liquid discharge from the system.

[0113] The hardware system of the MVR evaporator 8 includes: a plate preheater, a vertical gas-liquid separator, a forced circulation pump, a shell-and-tube heat exchanger, a centrifugal steam compressor, and a thickening dehydration assembly. To prevent stress corrosion cracking caused by high concentrations of chloride ions (above 20,000 mg / L), all circulation pipelines, pump bodies, and heat exchange tubes in contact with the feed liquid are made of duplex stainless steel 2205 or titanium (Gr.2).

[0114] The operation control and thermal circulation process of the MVR evaporator 8 specifically includes the following steps: S801, Feed Preheating and Exhaust: The high-salt concentrate from reverse osmosis module 7 first enters the plate preheater, where it undergoes countercurrent heat exchange with the distilled water (i.e., condensate) discharged from the system, raising the feed temperature to near the system boiling point (85°C to 90°C). The preheated feed then enters the degasser, where dissolved carbon dioxide and oxygen are removed by vacuum suction or thermal stripping to prevent the accumulation of non-condensable gases in the shell side of the subsequent heater, thus preventing the formation of thermal resistance.

[0115] During the cold start-up phase of the system, live steam is introduced into the shell side of the heater through the auxiliary steam pipeline until the amount of secondary steam generated by the system meets the heat balance and the exhaust temperature stabilizes, at which point the auxiliary steam is automatically cut off.

[0116] S802, Forced Circulation and Steam Purification: The forced circulation pump delivers the liquid feed at a high flow rate to the tube side of the shell-and-tube heat exchanger, with the flow velocity controlled between 2.0 m / s and 3.0 m / s to prevent salt crystals from depositing and forming scale on the heat exchange tube walls. The heated liquid feed then enters the vertical gas-liquid separator tangentially, where it flashes under vacuum to generate secondary steam.

[0117] To protect the downstream compressor, the secondary steam must pass through a wire mesh demister or baffle plate demister at the top before leaving the separator to trap and return any trace amounts of salt mist droplets entrained in the steam. The system controls the TDS (Total Dissolved Solids) of the outlet steam to be below 5 mg / L to prevent salt from entering the compressor impeller and causing dynamic imbalance or corrosion.

[0118] S803, Steam Recompression and Water Spray Desuperheating: The purified low-temperature, low-pressure secondary steam is drawn into the centrifugal steam compressor.

[0119] The compressor does work on the steam, increasing its pressure and temperature. The compressor's suction pressure is set to... Inhalation temperature is The discharge pressure is Compressor shaft power The calculation model is as follows: ; in: Steam mass flow rate (kg / s); The constant of water vapor; For variable efficiency (taken as 0.80); The variability index is 1.31.

[0120] It is worth noting that compressed steam is usually in a superheated state, resulting in a low heat transfer coefficient. Therefore, a desuperheater is installed on the compressor outlet pipe. By injecting a small amount of distilled water, the superheat of the steam is eliminated, transforming it into saturated steam before it is sent to the shell side of the shell-and-tube heat exchanger to release its latent heat.

[0121] S804, Temperature Difference Driven and Boiling Point Elevation Overcoming: The core control objective of the system is to maintain an effective heat transfer temperature difference. Due to the boiling point elevation (BPE) phenomenon in high-concentration salt solutions, the temperature rise provided by the compressor... Must meet: ; in: This refers to the saturated steam temperature after compression. This is the saturation temperature of the inhaled steam. This represents the difference between the boiling point of a saturated salt solution and the boiling point of pure water. For a near-saturated sodium chloride system, the BPE is approximately 9°C to 12°C. The effective temperature difference required to maintain efficient operation of the heat exchanger (design value is 5°C to 8°C).

[0122] Accordingly, the system adjusts the compressor speed via frequency conversion to increase the compression ratio. Maintaining the temperature between 1.8 and 2.0 ensures a saturation temperature rise of 18°C ​​to 22°C, thus ensuring that the heat exchanger has a continuous evaporation driving force after overcoming the heat loss from BPE and pipelines.

[0123] S805, Crystal slurry discharge and mother liquor balance: The system monitors the solid content (suspension density) of the crystal slurry in the circulation pipeline online. When the solid content reaches 25% to 30% (mass fraction), the discharge valve is opened to send the crystal slurry into the thickener and centrifuge for solid-liquid separation.

[0124] The separated solid salts are packaged and recycled. Most of the centrifuged mother liquor is returned to the evaporator, but this is to prevent the accumulation of impurity ions (such as...). , , The unlimited accumulation of waste in the circulating system leads to a sharp increase in boiling point. The system is equipped with a mother liquor discharge ratio. Typically, 3% to 5% of the feed is discharged as mother liquor and sent to a separate drying device or bypass treatment to maintain the material and chemical balance within the system. Application Example: Intelligent Oxidation Treatment of High-Salt Mother Liquor for Rubber Additives Project Overview: This embodiment applies to a rubber additive manufacturing enterprise located in Shandong Province, primarily treating the high-concentration, high-salt mother liquor generated during the production of accelerators CBS and MBT. This wastewater is characterized by high organic matter concentration, high salinity, and significant fluctuations in water quality.

[0125] Influent water quality parameters: High-concentration mother liquor (raw water): Flow rate 10m 3 / h, Chemical oxygen demand (COD) 25,000 mg / L, Total dissolved solids (TDS) 45,000 mg / L (main component is sodium chloride).

[0126] Level 1 washing water: Flow rate 5m 3 / h, chemical oxygen demand 4,000 mg / L.

[0127] Secondary washing water: Flow rate 8m 3 / h, chemical oxygen demand 400mg / L.

[0128] Process operation flow and effect analysis: Step S10: Mixing and blending wastewater from multiple sources See attached document Figure 1The high-concentration mother liquor, primary wash water, and reflux concentrate from subsequent processes are mixed in a regulating tank. The influent flow rate to the first oxidation tower after mixing is stabilized at... The design baseline value for the chemical oxygen demand (COD) of the mixed solution is 18,500 mg / L.

[0129] Step S20: Intelligent linkage control of the first oxidation tower This step aims to degrade the COD of the mixture to a level suitable for subsequent membrane filtration.

[0130] Control Model and Baseline Calculation: The system is set to a target effluent COD of 14,000 mg / L (i.e., a target removal load of 4,500 mg / L). The ozone dosage is calculated using the aforementioned mass flow control model of this invention: ; The parameters are set as follows: (Flow rate) = 18m 3 / h; (Right now =4,500 mg / L; (Oxidation coefficient) = 1.1 ; (Mass transfer efficiency) = 0.9.

[0131] Under ideal baseline conditions with stable influent water quality, the theoretically calculated required ozone dosage is: ; Dynamic operational empirical evidence and chart analysis: In actual continuous production, the quality of the influent fluctuates significantly due to intermittent material discharge from the upstream workshop. (See attached image) Figure 2 The system's continuous operation monitoring data over 24 hours was demonstrated, validating the effectiveness of the control system. Inflow load fluctuation ( Figure 2 (as shown by the solid line) Monitoring data shows that the influent chemical oxygen demand fluctuated wildly within the range of 16,200 to 21,200 mg / L (corresponding to the left vertical axis). The dense, tiny sawtooth pattern in the curve accurately reflects the signal noise generated by the online sensor due to fluid disturbance.

[0132] Intelligent response adjustment ( Figure 2 (As shown by the dashed line): The central controller dynamically adjusts the ozone generator power in real time based on the fluctuations in the incoming water (corresponding to the right vertical axis). Responding to shocks: When the influent concentration surges to a peak (approximately 21,000 mg / L) around the 11th hour of operation, the system automatically increases the ozone dosage to approximately 148 kg / h (dashed peak), ensuring a sufficient supply of oxidant and preventing the effluent water quality from exceeding the standard.

[0133] Energy saving and consumption reduction: When the influent concentration drops to the trough (approximately 16,500 mg / L) during the 14th to 15th hour of operation, the system quickly reduces the ozone dosage to 55~60 kg / h (dotted trough), effectively avoiding oxygen waste under low load conditions.

[0134] Control characteristics: Comparing the solid and dashed lines, it can be seen that the ozone dosage is highly positively correlated with the influent pollutant concentration. Meanwhile, the dashed line shows a lag of approximately 10-15 minutes compared to the solid line. This lag is a smoothing filter mechanism specifically designed to prevent frequent oscillations of the regulating valve due to signal noise, demonstrating the robustness of the control strategy.

[0135] Step S30: The effluent from the high-efficiency solid-liquid separation oxidation enters the tubular membrane system (cross-flow velocity 4.5 m / s, transmembrane pressure difference 0.25 MPa), with a permeate turbidity of less than 0.5 NTU. It then enters the nanofiltration (NF) unit, where divalent salts (sodium sulfate) are separated and refluxed at a pressure of 2.5 MPa, while the permeate (sodium chloride solution) enters the subsequent process.

[0136] Steps S40-S80: Brief Description of Subsequent Depth Processing MVR Evaporation: Nanofiltration permeate enters the Mechanical Vapor Recompression (MVR) system, with the vapor compression ratio controlled at 1.8~2.0 and an effective temperature rise greater than 12℃, producing sodium chloride crystals.

[0137] Reverse osmosis treatment: The evaporated condensate enters the reverse osmosis (RO) system after secondary oxidation. The system prevents the osmotic pressure of the concentrate from exceeding the high-pressure pump limit (7.5MPa) by locking the recovery rate (65%~70%), and the final product water is reused in the production line.

[0138] Summary of implementation results: After 24 hours of continuous operation, the system achieved a 100% effluent qualification rate when dealing with influent load fluctuations of up to 30%. Compared with the traditional constant flow dosing method, the overall ozone consumption was reduced by 25.4%, achieving stable and low-consumption treatment of high-concentration fluctuating mother liquor.

Claims

1. A rubber additive wastewater treatment system based on ozone oxidation and crystallization granulation, characterized in that, include: The mother liquor tank (9) and the primary washing tank (10) are connected to the inlet of the first oxidation tower (2) through their outlets. The outlet of the first oxidation tower (2) is connected in series with the tubular membrane module (5) and the nanofiltration module (6). The concentrate outlet of the nanofiltration module (6) is connected back to the inlet of the first oxidation tower (2), and the product water outlet of the nanofiltration module (6) is connected to the feed inlet of the MVR evaporator (8). The outlet of the secondary washing tank (11) and the condensate outlet of the MVR evaporator (8) are connected to the inlet of the second oxidation tower (3), and the outlet of the second oxidation tower (3) is connected to the bottom inlet of the crystallization fluidized bed (4); the supernatant outlet of the crystallization fluidized bed (4) is connected to the feed end of the reverse osmosis module (7) via the tubular membrane module (5) and the nanofiltration module (6); The ozone generator (1) has its gas outlet connected to an aeration device located at the bottom of the first oxidation tower (2) and the second oxidation tower (3).

2. The rubber additive wastewater treatment system based on ozone oxidation and crystallization granulation according to claim 1, characterized in that, The exhaust ports at the top of the first oxidation tower (2) and the second oxidation tower (3) are connected to the inlet of the exhaust gas purifier (12), and the gas outlet of the exhaust gas purifier (12) is connected back to the inlet of the ozone generator (1), forming a closed-loop oxygen circulation circuit.

3. The rubber additive wastewater treatment system based on ozone oxidation and crystallization granulation according to claim 1, characterized in that, The concentrated liquid outlet of the reverse osmosis component (7) and the concentrated liquid outlet generated by the nanofiltration component (6) when processing the supernatant of the crystallization fluidized bed (4) are both connected to the primary washing tank (10), and the product water outlet of the reverse osmosis component (7) is connected to the recycled water tank.

4. The rubber additive wastewater treatment system based on ozone oxidation and crystallization granulation according to claim 1, characterized in that, The crystallization fluidized bed (4) is configured as a vertical solid-liquid reactor. The crystallization fluidized bed (4) is connected to a seed dosing machine (13) and a chemical dosing machine (14). The internal structure of the crystallization fluidized bed (4) is divided into an inlet water distribution zone, a fluidization reaction zone and a sedimentation separation zone from bottom to top.

5. The rubber additive wastewater treatment system based on ozone oxidation and crystallization granulation according to claim 1, characterized in that, The first oxidation tower (2) is configured as a vertical cylindrical gas-liquid reaction vessel with a microporous aeration device at the bottom and a liquid distributor at the top.

6. The rubber additive wastewater treatment system based on ozone oxidation and crystallization granulation according to claim 1, characterized in that, The second oxidation tower (3) has several layers of porous flow guide baffles or is filled with ceramic Raschig ring packing along the height direction inside.

7. The rubber additive wastewater treatment system based on ozone oxidation and crystallization granulation according to claim 1, characterized in that, The tubular membrane module (5) is configured as an external cross-flow ultrafiltration device, consisting of a circulation tank, a high-flow circulation pump and a series-parallel array of membrane modules; the membrane module adopts a large-channel structure made of modified polyvinylidene fluoride or recrystallized silicon carbide.

8. The rubber additive wastewater treatment system based on ozone oxidation and crystallization granulation according to claim 1, characterized in that, The nanofiltration assembly (6) includes a security filter, a high-pressure pump and a spiral wound nanofiltration membrane element connected in series; the concentrate outlet of the nanofiltration assembly (6) is connected to the inlet of the first oxidation tower (2) or the first-stage washing tank (10) through a pipeline equipped with a switching valve.

9. The rubber additive wastewater treatment system based on ozone oxidation and crystallization granulation according to claim 1, characterized in that, The reverse osmosis assembly (7) includes a high-pressure plunger pump, an isobaric energy recovery device, and a series spiral wound reverse osmosis membrane element; the spiral wound reverse osmosis membrane element is a fouling-resistant seawater desalination reverse osmosis membrane.

10. The rubber additive wastewater treatment system based on ozone oxidation and crystallization granulation according to claim 1, characterized in that, The MVR evaporator (8) is configured as a mechanical vapor recompression forced circulation crystallization system, including a plate preheater, a vertical gas-liquid separator, a forced circulation pump, a shell-and-tube heat exchanger, a centrifugal steam compressor, and a thick dehydration assembly.

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