A reverse osmosis concentrated water deep treatment and resource integration treatment system

Abstract

The present application relates to water depth processing technical field, especially to a kind of RO concentrated water depth processing and resource integration processing system, comprising: separation membrane concentration unit, shunt valve group, nanofiltration salt separation unit, post conditioning unit, MVR evaporation crystallization unit, switchable seed circulation branch, supersaturation detection module, silicon hardness ratio detection module, temperature detection module and system controller.System controller determines composite scale risk index according to membrane concentration liquid supersaturation, silicon hardness ratio and MVR heat exchange state variation parameter and divides scale risk grade, accordingly adjusts shunt valve group to adjust the concentration liquid proportion entering post conditioning unit, simultaneously adjusts membrane operating pressure and MVR operating load;While determining the initial value of seed source according to the main material type, and feedback correction is carried out according to the heat exchange state variation trend.The present application realizes the active control of scale risk through multi-parameter coupling sensing and hierarchical regulation.

Description

Technical Field

[0001] This invention relates to the field of advanced water treatment technology, and in particular to an integrated system for advanced treatment and resource recovery of RO concentrate. Background Technology

[0002] The typical treatment route for RO concentrate usually employs a combined process of pretreatment, membrane concentration, nanofiltration desalination, and evaporation crystallization. Some schemes use advanced oxidation or resin softening as pretreatment methods, followed by membrane concentration and nanofiltration desalination, and then evaporation crystallization of monovalent and polyvalent salts to achieve water reuse and salt recovery. However, in existing technologies, each process unit is usually controlled independently, with operating parameters set according to their own preset conditions, lacking a cross-unit linkage control mechanism based on real-time scaling risk. In the evaporation crystallization stage, scaling on the heat exchanger tube walls is one of the core issues affecting the long-term stable operation of the system, and existing technologies mainly rely on post-treatment methods such as adding scale inhibitors or shutting down for cleaning.

[0003] Chinese Patent Publication No. CN112110593B discloses a resource-based treatment system for TDI industrial wastewater. The outlet of the raw water feed pump is connected to the inlet of a weak acid resin adsorption bed. The outlet of the weak acid resin adsorption bed is connected to the inlet of a decarbonization tower via a decarbonization feed pump. The outlet of the decarbonization tower is connected to the inlet of an RO unit via an RO feed pump. The outlet of the RO unit is connected to an RO concentrate tank. The outlet of the RO concentrate tank is connected to the inlet of a first-stage nanofiltration unit via a first-stage nanofiltration high-pressure pump. The concentrated brine outlet of the first-stage nanofiltration unit is connected to the first-stage nanofiltration concentrate tank. The product water outlet of the first-stage nanofiltration unit is connected to the first-stage nanofiltration product water tank. Sodium sulfate separated from the concentrated primary nanofiltration water enters the freeze crystallization, hot melt crystallization and drying units to obtain sodium sulfate salt. Sodium chloride is first precipitated in the concentrated primary nanofiltration permeate, and sodium nitrate is precipitated in the evaporation crystallization unit. The separated mother liquor is then flash-cooled and cooled to crystallize, and then dried. It can be seen that the resource utilization treatment system for TDI industrial wastewater has the following problems: the lack of cross-unit linkage control based on the pre-concentration detection information of the membrane concentration stage makes it impossible for the evaporation crystallization unit to actively intervene before scaling occurs, affecting the long-term stable operation of the system. Summary of the Invention

[0004] To address this issue, the present invention provides an integrated system for deep treatment and resource recovery of RO concentrate, which overcomes the problem in the prior art of lacking cross-unit linkage control based on pre-concentration detection information, resulting in the evaporation and crystallization unit being unable to actively intervene before scaling occurs, thus affecting the long-term stable operation of the system.

[0005] To achieve the above objectives, the present invention provides an integrated treatment system for advanced RO concentrate treatment and resource recovery, comprising: The concentrate outlet of the separation membrane concentration unit is equipped with a diversion valve group, which is connected to the nanofiltration desalination unit and the post-conditioning unit respectively. The product water outlet of the nanofiltration desalination unit is connected to the monovalent salt feed end of the MVR evaporation crystallization unit, and the water outlet of the post-conditioning unit is connected to the mixed salt feed end of the MVR evaporation crystallization unit. The MVR evaporation crystallization unit is equipped with a switchable seed crystal circulation branch, which is connected to the crystal slurry outlet at the bottom of the crystallizer and the qualified salt crystal outlet at the centrifugal discharge end of the MVR evaporation crystallization unit, respectively, to switch the seed crystal source under different operating modes. The concentrated liquid outlet of the separation membrane concentration unit is equipped with a supersaturation detection module and a silicon hardness ratio detection module, and the MVR evaporation and crystallization unit is equipped with a temperature detection module for acquiring changes in its heat exchange state. The system controller is configured to: determine the composite fouling risk index based on the membrane concentrate supersaturation, silica hardness ratio, and MVR heat exchange state change parameters to determine the fouling risk level; adjust the diversion valve group according to the fouling risk level to adjust the proportion of concentrate entering the post-conditioning unit, and simultaneously adjust the operating pressure of the separation membrane concentration unit and the operating load of the MVR evaporation crystallization unit. Furthermore, the initial seed source of the switchable seed circulation branch is determined based on the dominant material type currently entering the MVR evaporation crystallization unit, and the concentration ratio, operating pressure, operating load, and seed source are corrected based on the MVR heat exchange state change trend.

[0006] As a preferred technical solution for an integrated treatment system for deep treatment and resource utilization of RO concentrate, the switchable seed crystal circulation branch includes a self-generated crystal slurry path and a qualified salt crystal path. The self-generated crystal slurry path is connected to the crystal slurry outlet at the bottom of the crystallizer of the MVR evaporation crystallization unit, and the qualified salt crystal path is connected to the qualified salt crystal outlet at the centrifugal discharge end.

[0007] As a preferred technical solution for an integrated treatment system for deep treatment and resource utilization of RO concentrate, the MVR evaporation and crystallization unit is configured such that, in response to the main inflow from the nanofiltration salt separation branch, the system controller controls the switching of the seed crystal circulation branch to open the qualified salt crystal path; and in response to the main inflow from the post-conditioning branch, the system controller controls the switching of the seed crystal circulation branch to open the self-produced crystal slurry path.

[0008] As a preferred technical solution for the RO concentrate deep treatment and resource utilization integrated treatment system, the supersaturation detection module and the silica hardness ratio detection module are set at the concentrate outlet of the separation membrane concentration unit to detect the supersaturation parameter and silica hardness ratio parameter of the concentrate. The temperature detection module is installed at the inlet and outlet of the heat exchange tube bundle of the MVR evaporation crystallization unit to acquire parameters of heat exchange state changes.

[0009] As a preferred technical solution for an integrated system for deep treatment and resource utilization of RO concentrate, the system controller is configured to: determine the risk membership degree of supersaturation based on the supersaturation degree of the membrane concentrate, determine the risk membership degree of silicon hardness ratio based on the silicon hardness ratio, and determine the risk membership degree of heat exchange state based on the heat exchange state change parameters of the MVR. The system controller performs an equal-weighted geometric average based on the complementary values ​​of the supersaturation risk membership degree, the silicon hardness ratio risk membership degree, and the heat transfer state risk membership degree, and determines the composite scale risk index based on the complementary values ​​of the results.

[0010] As a preferred technical solution for an integrated treatment system for deep treatment and resource utilization of RO concentrate, the system controller determines the scaling risk level based on the composite scaling risk index; Wherein, in response to the composite scale risk index being less than the low risk threshold, it is determined to be of low scale risk; If the composite scale risk index is greater than or equal to the low risk threshold and less than the high risk threshold, it is determined to be of medium scale risk. If the composite scale risk index is greater than or equal to the high-risk threshold, it is determined to be of high scale risk.

[0011] As a preferred technical solution for an integrated treatment system for deep treatment and resource recovery of RO concentrate, the system controller is configured to adjust the diversion valve group according to the scaling risk level; In response to an increased risk of scaling, the proportion of concentrate entering the post-conditioning unit is increased; In response to the reduced scaling risk level, the proportion of concentrate entering the post-conditioning unit is reduced.

[0012] As a preferred technical solution for the integrated treatment system of RO concentrate deep treatment and resource utilization, the system controller is also configured to synchronously adjust the operating pressure of the separation membrane concentration unit and the operating load of the MVR evaporation crystallization unit. In response to an increased risk of scaling, the operating pressure of the membrane concentration unit and the operating load of the MVR evaporation and crystallization unit are reduced. In response to the reduced risk of scaling, the operating pressure of the membrane concentration unit and the operating load of the MVR evaporation and crystallization unit are increased.

[0013] As a preferred technical solution for an integrated system for deep treatment and resource utilization of RO concentrate, the system controller determines the trend of MVR heat exchange state changes based on continuously acquired MVR heat exchange state change parameters, and performs feedback correction on the adjustment range of the proportion of concentrate entering the post-conditioning unit, the operating pressure of the separation membrane concentration unit, and the operating load of the MVR evaporation crystallization unit based on the trend of MVR heat exchange state changes.

[0014] As a preferred technical solution for an integrated treatment system for deep treatment and resource utilization of RO concentrate, in response to the continued decay of the MVR heat exchange state after increasing the adjustment range, the system controller controls the switchable seed circulation branch to connect the self-produced crystal slurry path. In response to the MVR heat exchange state changing from decay to recovery, the system controller redetermines the seed source of the switchable seed circulation branch based on the dominant material type currently entering the MVR evaporation crystallization unit.

[0015] Compared with existing technologies, the beneficial effects of this invention lie in constructing a composite fouling risk index that integrates membrane concentration supersaturation, silica hardness ratio, and MVR heat exchange temperature difference attenuation. This incorporates membrane-side fouling thermodynamic precursor information and evaporation-side actual heat exchange feedback into a unified evaluation system, enabling the system to implement graded early warning and proactive control based on risk levels before fouling occurs. The system synchronously adjusts the diversion valve group, membrane operating pressure, and MVR operating load according to the risk level, and automatically switches to the self-produced crystal slurry path to enhance fouling suppression after the adjustment reaches its upper limit. Simultaneously, a dual-source crystal seeding strategy, switching between qualified salt crystals and self-produced crystal slurry based on the dominant material type, balances the quality assurance of high-purity salt products under resource-based chemical conditions with scale prevention protection of the heat exchange surface under deep treatment conditions. Through multi-parameter coupled sensing, graded adaptive control, and cross-unit collaborative linkage, this invention achieves proactive full-process control of fouling risk during RO concentrate deep treatment and resource recovery, ensuring long-term stable system operation and establishing a dynamically adaptable operating mode between resource recovery and deep treatment. It is suitable for RO concentrate treatment needs under different water quality compositions and fluctuating operating conditions. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the integrated treatment system for deep treatment and resource recovery of RO concentrate according to an embodiment of the present invention. Detailed Implementation

[0017] To make the objectives and advantages of the present invention clearer, the present invention will be further described below with reference to embodiments; it should be understood that the specific embodiments described herein are merely for explaining the present invention and are not intended to limit the present invention.

[0018] Preferred embodiments of the present invention will now be described with reference to the accompanying drawings. Those skilled in the art should understand that these embodiments are merely illustrative of the technical principles of the present invention and are not intended to limit the scope of protection of the present invention.

[0019] It should be noted that in the description of this invention, the terms "upper", "lower", "left", "right", "inner", "outer", etc., which indicate directions or positional relationships, are based on the directions or positional relationships shown in the accompanying drawings. This is only for the convenience of description and is not intended to indicate or imply that the device or element must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, it should not be construed as a limitation of this invention.

[0020] Furthermore, it should be noted that, in the description of this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0021] Please see Figure 1 As shown, the present invention provides an integrated treatment system for advanced treatment and resource recovery of RO concentrate, comprising: The RO concentrate inlet pipeline is connected to the inlet of the separation membrane concentration unit. The concentrate outlet of the separation membrane concentration unit is equipped with a diversion valve group, which is connected to the nanofiltration desalination unit and the post-conditioning unit respectively. The product water outlet of the nanofiltration desalination unit is connected to the monovalent salt feed end of the MVR evaporation crystallization unit, and the water outlet of the post-conditioning unit is connected to the mixed salt feed end of the MVR evaporation crystallization unit. The MVR evaporation crystallization unit is equipped with a switchable seed crystal circulation branch, which is connected to the crystal slurry outlet at the bottom of the crystallizer and the qualified salt crystal outlet at the centrifugal discharge end of the MVR evaporation crystallization unit, respectively, to switch the seed crystal source under different operating modes. The concentrated liquid outlet of the separation membrane concentration unit is equipped with a supersaturation detection module and a silicon hardness ratio detection module, and the MVR evaporation and crystallization unit is equipped with a temperature detection module for acquiring changes in its heat exchange state. The system controller is configured to: determine the composite fouling risk index based on the membrane concentrate supersaturation, silica hardness ratio, and MVR heat exchange state change parameters to determine the fouling risk level; adjust the diversion valve group according to the fouling risk level to adjust the proportion of concentrate entering the post-conditioning unit, and simultaneously adjust the operating pressure of the separation membrane concentration unit and the operating load of the MVR evaporation crystallization unit. Furthermore, the initial seed source of the switchable seed circulation branch is determined based on the dominant material type currently entering the MVR evaporation crystallization unit, and the concentration ratio, operating pressure, operating load, and seed source are corrected based on the MVR heat exchange state change trend.

[0022] In this embodiment, RO stands for Reverse Osmosis, and MVR stands for Mechanical Vapor Recompression.

[0023] In implementation, the membrane concentration unit can employ high-pressure reverse osmosis membranes, DTRO (DiscTube Reverse Osmosis) membranes, or other pressure-driven membrane modules suitable for further concentration of high-salt concentrates. The specific membrane type and allowable operating pressure are determined based on the quality of the RO concentrate to be treated and the rated operating parameters of the membrane modules. The post-treatment conditioning unit uses chemical precipitation conditioning, including a conditioning reaction mechanism, a dosing mechanism, and a solid-liquid separation mechanism. By adjusting the reaction conditions, calcium, magnesium hardness components, and silicon components in the concentrate form precipitates or co-precipitates. After solid-liquid separation, the treated effluent is sent to the MVR evaporation and crystallization unit. This is existing technology; conventional methods used in water treatment can meet the treatment requirements, and will not be elaborated further.

[0024] The low-salt water produced by the membrane concentration unit is transported to the front-end RO permeate tank for reuse via freshwater; the concentrated water containing polyvalent salts retained by the nanofiltration desalination unit is returned to the front end of the post-conditioning unit for joint hardening and silica removal; the condensate generated by MVR evaporation and crystallization is supplied to the front-end membrane treatment process for reuse; the precipitated sludge generated by the post-conditioning unit is disposed of in compliance with regulations after conventional pressure filtration and dewatering. The above-mentioned clean water reuse, concentrated water return, and sludge dewatering facilities are all mature existing technologies in the industry, and the specific equipment selection and pipeline layout will not be described in detail.

[0025] The composite scale described in this invention mainly refers to the composite scale layer formed by the co-deposition, co-crystallization, or mutual coating of silicon components and calcium and magnesium hardness components during the RO concentrate concentration and evaporation crystallization process. It includes deposits formed by silicon-containing components together with carbonates, sulfates, and other hardness scale-forming components.

[0026] In practice, the self-generated crystal slurry channel is led out from the bottom of the crystallizer of the MVR evaporation crystallization unit. The crystal slurry material containing mixed salt crystals discharged from the crystal slurry outlet at the bottom of the crystallizer is directly extracted. This channel transports the crystal slurry material to the seed injection interface on the feed side of the heat exchange tube bundle, so that the circulating liquid containing crystal slurry flows through the heat exchange tube wall in a flushing manner, which plays a role in inhibiting the adhesion of microcrystals on the wall surface.

[0027] The qualified salt crystal channel is led out from the qualified salt crystal outlet at the centrifugal discharge end, and collects high-purity salt crystal material after centrifugal separation. This channel transports the qualified salt crystal material to the same seed crystal reinjection interface on the feed side of the heat exchange tube bundle, and uses high-purity crystals as circulating seed crystals to enter the evaporation circulation system.

[0028] The two pathways converge into the same reinjection pipeline through a switching valve group. The system controller controls the opening and closing of each valve in the switching valve group to enable either pathway to be turned on or off, thus providing the seed circulation branch with the structural basis to switch between the two seed sources according to the current operating mode.

[0029] The dominant material type is determined based on the currently set material distribution ratio of the diversion valve assembly. When the proportion of concentrate entering a certain branch exceeds 50% of the total diversion flow, the liquid entering that branch is determined to be the dominant material. When the proportions of the two branches are the same, the dominant material type corresponding to the previous operating state can be maintained.

[0030] It is understandable that "the main source of liquid in the nanofiltration salt separation branch" means that after the concentrate from the separation membrane concentration unit is distributed by the diversion valve group, most of it enters the nanofiltration salt separation unit for the separation of monovalent and polyvalent salts, and the nanofiltration permeate enters the monovalent salt feed end of the MVR evaporation and crystallization unit for evaporation and crystallization.

[0031] Under this operating condition, since nanofiltration has pre-separated the monovalent salts in the concentrate, the salt composition of the feed solution entering the MVR is relatively simple, and the crystallized salt product has high purity. At this time, the seed crystal circulation branch can be switched to open the qualified salt crystal path, and the high-purity industrial salt crystals after centrifugal separation can be used as circulating seed crystals to be reinjected into the MVR heat exchanger inlet. This avoids heterogeneous nucleation of impurities and contamination of the salt product. At the same time, the growth sites provided by the high-purity seed crystal surface help guide the solute to grow regularly on it, improving the purity and particle size uniformity of the final salt product.

[0032] The term "mainly supplied liquid in the post-conditioning branch" means that the diversion valve group distributes most of the concentrated liquid to the post-conditioning unit. After conditioning to remove hardness ions and silicate, the effluent enters the mixed salt feed end of the MVR evaporation and crystallization unit for evaporation and crystallization.

[0033] Under this operating condition, the feed liquid entering the MVR is a mixed system of polyvalent salts and residual monovalent salts, and the crystallized product is a mixed salt. At this time, the seed crystal circulation branch can be switched to connect the self-produced crystal slurry path, using the self-produced crystal slurry discharged from the crystal slurry outlet at the bottom of the MVR crystallizer as the circulating seed crystal. Its function is to utilize the large number of suspended fine crystal particles in the crystal slurry to provide a huge specific surface area, so that supersaturated ions preferentially precipitate on the seed crystal surface rather than forming scale on the heat exchange tube wall.

[0034] Both the supersaturation detection module and the silicon hardness ratio detection module are located at the concentrate outlet of the separation membrane concentration unit, and they share the same sampling point to maintain consistency in detection conditions.

[0035] The supersaturation detection module includes an ion-selective electrode array and a temperature sensor. The ion-selective electrode array includes calcium ion-selective electrodes, magnesium ion-selective electrodes, carbonate ion-selective electrodes, and sulfate ion-selective electrodes, used to measure the ion activities of calcium ions, magnesium ions, carbonate ions, and sulfate ions in the concentrate, respectively. The temperature sensor measures the current temperature of the concentrate. The millivolt signals from each electrode and the resistance signal from the temperature sensor are converted into 4–20 mA standard current signals by their respective transmitters and then connected to the analog input module of the system controller via shielded cables. The controller calculates the ratio of the activity product to the solubility product of each scaling salt based on the measured ion activity and the solubility product at the current temperature, which is taken as the supersaturation value.

[0036] The silica hardness ratio detection module includes a silicon ion selective electrode, a calcium ion selective electrode, and a magnesium ion selective electrode. The silicon ion selective electrode, in conjunction with a pH compensation electrode, measures the silicate concentration in the concentrate. The calcium ion selective electrode and the magnesium ion selective electrode, in combination, measure the total hardness of calcium and magnesium ions in the concentrate. The millivolt signals output from each electrode are converted into standard current signals by a transmitter and then input to the analog input module of the system controller. The controller calculates the silica hardness ratio based on the ratio of silicate concentration to total hardness.

[0037] Each ion-selective electrode is sequentially arranged along the flow direction in the same sampling flow cell on the concentrate outlet pipe. The sensing end of each electrode is immersed below the liquid surface of the flow cell. The inlet of the flow cell is connected to the concentrate outlet pipe via a sampling branch pipe, and the outlet is connected back to the downstream side of the concentrate outlet pipe to ensure that the concentrate flowing over the electrode surface maintains the same real-time state as the main pipe. The aforementioned ion-selective electrodes and thermocouples are all commercially available products commonly used in industrial online analysis. Their model selection is determined according to the concentration range and temperature range of the measured medium, based on the manufacturer's selection manual. This is existing technology and will not be elaborated further.

[0038] The temperature detection module includes an inlet thermocouple at the inlet of the heat exchange tube bundle of the MVR evaporation crystallization unit and an outlet thermocouple at the outlet. The thermoelectric potential signals collected by the two thermocouples are converted into standard current signals by temperature transmitters and then connected to the analog input module of the system controller. The controller reads the inlet and outlet temperatures in real time and calculates the temperature difference.

[0039] The system controller has a built-in analog input module, which contains multiple signal channels. Each channel is connected to the output of the corresponding strain gauge via a shielded cable. After analog-to-digital conversion, the module stores the acquired values ​​of each channel into the controller's internal register for use by the calculation program.

[0040] In implementation, each detection module is connected to its corresponding transmitter via signal lines. The transmitter conditions and converts the weak electrical signal output from the sensor into a 4–20mA standard current signal (or a 0–10V standard voltage signal), which is then connected to the analog input module of the system controller via a shielded cable. The analog input module contains an analog-to-digital converter circuit that converts the analog signal into a digital quantity and stores it in the controller's internal register for use by the controller's computational program. The signal connection between each detection module and the controller uses standard wired connections common in industrial settings, requiring no special modifications.

[0041] To ensure that the membrane-side detection parameters and the MVR heat exchange state correspond to the same material operating period, the system controller performs time alignment for both types of parameters. Specifically, the hydraulic lag time of each branch is determined based on the effective volume and corresponding flow rate of the concentrate delivered from the detection position of the separation membrane concentration unit to the MVR evaporation and crystallization unit via different processing branches, and the equivalent lag time is determined based on the proportion of material entering the MVR from each branch. When calculating the current complex fouling risk index, the supersaturation and silica hardness ratio of the membrane concentrate at the previous moment corresponding to the current MVR heat exchange state are used in the calculation, thereby reducing the time misalignment of upstream and downstream parameters caused by material transport lag.

[0042] In this embodiment, the silicon hardness ratio is expressed as a mass concentration ratio, that is, the ratio of the mass concentration of silicon component calculated as SiO2 to the total hardness mass concentration calculated as CaCO3, and both use the same concentration unit.

[0043] In cases where multiple fouling salts exist, the ratio of the ion activity product to the corresponding solubility product of each target fouling salt is calculated, and the maximum value is taken as the current membrane concentrate supersaturation parameter to characterize the fouling thermodynamic risk corresponding to the fouling salt most likely to precipitate.

[0044] In this embodiment, the composite scale risk index unifies the scaling thermodynamic tendency during the membrane concentration stage, the tendency of silicon and hardness components to form composite scale, and the heat transfer state changes during the MVR evaporation and crystallization stage into the same risk quantity, so as to avoid the inability to directly compare different parameters due to their different physical meanings and dimensions.

[0045] Understandably, the supersaturation risk membership degree is determined based on the supersaturation of the membrane concentrate. The supersaturation of the membrane concentrate characterizes the degree of deviation of the fouling salt components in the concentrate from their dissolution equilibrium state. When the supersaturation of the membrane concentrate is low, the fouling salts have a stronger ability to remain in a dissolved state, resulting in a lower supersaturation risk membership degree. Conversely, the thermodynamic driving force for the precipitation and formation of crystal nuclei by fouling salts is enhanced, leading to a higher supersaturation risk membership degree. Therefore, the supersaturation risk membership degree reflects the fouling tendency of the membrane concentrate itself before a significant decline in the heat transfer state of the MVR evaporation and crystallization unit. This allows the determination of complex fouling risk to include prior risk information, rather than relying solely on changes in the heat transfer state that have already occurred.

[0046] The risk membership of supersaturation can be determined based on the water quality composition of the RO concentrate to be treated. This can be achieved by setting up a limited group of concentration tests with different membrane concentrate supersaturation levels, keeping other major operating conditions consistent, recording the scaling state of the concentrate under each test condition, and determining the corresponding low-risk and high-risk benchmark values ​​based on the relationship between the membrane concentrate supersaturation and the degree of scaling.

[0047] Specifically, the supersaturation of the membrane concentrate, obtained by comparing the ion activity product with the scale salt solubility product at the current temperature, is calibrated using the target RO concentrate as a benchmark. At least five gradient points are set at equal intervals between the supersaturation value (from 1) and the maximum possible supersaturation value under design conditions, by adjusting the concentration factor. Temperature, pH, and operating time are kept consistent at each point, and the degree of scaling is characterized by the amount of scale deposited per unit area. A piecewise linear regression is performed between the supersaturation value and the degree of scaling. The supersaturation value corresponding to the point where the fitted curve begins to significantly deviate from zero is the low-risk benchmark, and the value corresponding to the inflection point of the growth rate is the high-risk benchmark.

[0048] Based on the experimental results, the membership relationship between the low-risk benchmark value and the high-risk benchmark value is determined by linear interpolation. When the parameter is lower than the low-risk benchmark value, the risk membership degree is 0, and when the parameter is higher than the high-risk benchmark value, the risk membership degree is 1. The intermediate region is calculated according to the ratio of the difference between the two.

[0049] The risk membership degree of the silica-hardness ratio is determined based on the silica-hardness ratio itself. The silica-hardness ratio reflects the relative compositional relationship between silica components and hardness ions in the concentrate, and its risk change differs from parameters that increase unidirectionally with concentration. Under certain water quality conditions, as the silica-hardness ratio gradually approaches the characteristic ratio of composite scale, the relative composition of silica components and hardness ions gradually enters a state favorable for composite scale formation, and the corresponding risk membership degree of the silica-hardness ratio gradually increases. When the silica-hardness ratio continues to deviate from the characteristic ratio of composite scale, because one type of component involved in composite scale formation is in a relatively insufficient or excessive state relative to the other type of component, the corresponding risk membership degree of the silica-hardness ratio gradually decreases. Therefore, the risk membership degree of the silica-hardness ratio is used to characterize the influence of the combination state of silica components and hardness ions on composite scale formation, rather than simply characterizing the content of silica components or hardness ions.

[0050] The characteristic ratio of composite scale can be determined by setting a finite set of crystallization tests with different silica-hardness ratios for the composition of the RO concentrate to be treated, while keeping other major operating conditions consistent. The formation state of composite scale under each test condition is recorded, and curve fitting is performed based on the relationship between the silica-hardness ratio and the degree of composite scale formation. The peak position corresponding to the tendency of composite scale formation is determined as the characteristic ratio of composite scale. For RO concentrate with a relatively stable composition, this characteristic ratio can be used as a calculation parameter under the corresponding water quality conditions after calibration.

[0051] During calibration, the interval between test points with different silicon-hardness ratios was controlled at 5%–10% by adjusting the dosage of silicon or hardness components to obtain a complete trend of change; the temperature, pH, and running time were kept consistent at each point. A quadratic polynomial fitting was performed with the silicon-hardness ratio as the abscissa and the scale deposition amount as the ordinate, and the silicon-hardness ratio corresponding to the peak value of the fitted curve was taken as the characteristic ratio of the composite scale.

[0052] The membership degree of heat transfer state risk is determined based on the MVR heat transfer state change parameters, which reflect the changes in the heat transfer state of the heat exchange tube bundle during the evaporation and crystallization process over time. When the deposition degree on the surface of the heat exchange tube bundle is low, its heat transfer state changes less relative to the baseline operating state, and the corresponding heat transfer state risk membership degree is low; conversely, it indicates that the heat transfer process of the heat exchange tube bundle is more affected by deposits, and the corresponding heat transfer state risk membership degree increases accordingly. Unlike the pre-fouling trend reflected by the membrane concentrate supersaturation, the heat transfer state risk membership degree is used to reflect the changes in heat transfer state already exhibited during the operation of the MVR evaporation and crystallization unit, thus serving as actual operational feedback for judging the front-end fouling trend.

[0053] The risk membership of heat exchange status can be determined by setting up a limited number of evaporation and crystallization tests under different operating conditions, keeping the feed composition consistent, recording the correspondence between the MVR heat exchange status change parameters and the actual scaling status under each operating condition, and determining the corresponding low-risk and high-risk benchmark values ​​based on the relationship between the degree of heat exchange temperature difference attenuation and the degree of scaling formation.

[0054] Specifically, during the system commissioning phase, under clean or stable conditions after maintenance of the heat exchanger tube bundle, stable heat exchange temperature differences were collected under different MVR operating loads, feed flow rates, and feed concentrations. A correspondence between operating parameters and baseline heat exchange temperature differences was established. The calibration conditions covered 30% to 100% of the MVR design load, 50% to 110% of the feed flow rate, and 80% to 120% of the feed TDS. Each operating condition combination was allowed to operate stably until the temperature difference fluctuation did not exceed ±0.5℃ / 30min, after which baseline values ​​were recorded. A correspondence was established using multiple linear regression or interpolation with feed flow rate and concentration as inputs and baseline temperature difference as output. Operating conditions not covered were obtained through linear interpolation.

[0055] During actual operation, the system controller determines the reference heat exchange temperature difference under the current operating condition based on the current MVR operating load, feed flow rate, and feed status, according to the above correspondence. It then determines the MVR heat exchange state change parameters based on the degree of deviation of the current measured heat exchange temperature difference from the reference heat exchange temperature difference. The obtained MVR heat exchange state change parameters are compared with the low-risk and high-risk reference values, and normalized according to their relative positions between the two reference values ​​to determine the heat exchange state risk membership degree.

[0056] In this embodiment, the degree of scaling is characterized by the amount of scale deposited per unit heat exchange area. Heat exchange surfaces with identical material, surface condition, and effective heat exchange area are used, and the test durations for each group are kept consistent. Unattached crystal particles are removed from the heat exchange surface, and the surface with attached scale is dried until its quality stabilizes. The amount of scale deposited per unit heat exchange area is determined based on the ratio of the mass difference before and after the test to the effective heat exchange area. A higher amount of scale deposited per unit heat exchange area indicates a higher degree of scaling. The aforementioned amount of scale deposited per unit heat exchange area is only used for calibrating the risk membership degree before system commissioning or during the commissioning phase.

[0057] Therefore, the risk membership degree of supersaturation, the risk membership degree of silicon hardness ratio, and the risk membership degree of heat transfer state characterize the risk of complex scale from three aspects: the thermodynamic driving force of scale formation and salt precipitation, the composite composition relationship between silicon components and hardness ions, and the actual changes in the heat transfer state of MVR. The value range of each risk membership degree is 0 to 1.

[0058] After determining the three risk membership degrees, complementary values ​​for each risk membership degree are obtained. These three complementary values ​​are then weighted geometrically and further processed to obtain the composite fouling risk index. In this approach, the three risk factors have equal weights; an increase in any one risk factor will increase the composite fouling risk index. When multiple risk factors increase simultaneously, the composite fouling risk index further increases, thus allowing the fouling trend on the membrane side, the composition characteristics of the composite fouling, and changes in the heat transfer state on the MVR side to all participate in the risk characterization. The equivalent meaning is: when all three parameters are at a low risk level, the index approaches zero; when any parameter deviates from the low risk range, the index increases significantly; and when all parameters are at a high risk level, the index approaches 1.

[0059] Regarding scaling risk levels, in one embodiment, a composite scale risk index of 0.30 is set as the low-risk threshold, and a composite scale risk index of 0.70 is set as the high-risk threshold. When the composite scale risk index is below 0.30, it is determined to be a low scaling risk level; when the composite scale risk index is not lower than 0.30 but lower than 0.70, it is determined to be a medium scaling risk level; and when the composite scale risk index is not lower than 0.70, it is determined to be a high scaling risk level. The above values ​​are used to illustrate a specific risk classification method and are not fixed limitations on the threshold values.

[0060] Low-risk and high-risk cutoff values ​​can be calibrated based on actual operating data corresponding to the RO concentrate to be treated. Specifically, during the system commissioning phase, a limited number of operating conditions covering different membrane concentrate supersaturation, silica hardness ratios, and MVR heat transfer state changes can be set up. The composite scale risk index corresponding to each operating condition is calculated and analyzed in relation to the scale state recorded under that condition. The test results are grouped according to the states of no obvious scale trend, the beginning of a continuous scale trend, and further development of the scale trend. The low-risk and high-risk cutoff values ​​are determined based on the distribution boundaries of the composite scale risk index corresponding to adjacent states. For example, a deposition amount below the detection limit of 0.1 g / m³ is considered low-risk. 2 No obvious scaling trend was observed; a value above the detection limit and rising three times consecutively indicates the beginning of a sustained scaling trend; reaching or exceeding the warning value of 1.0 g / m³ indicates a scaling trend has begun. 2 To further develop the trend, if historical operating data is available, the boundary value can also be corrected by using regression fitting based on the historical operating data.

[0061] During system operation, the corresponding risk membership degree is determined based on the current membrane concentrate supersaturation, silica hardness ratio, and MVR heat exchange state change parameters. The current composite scale risk index is obtained according to the above complementary treatment and equal weighted geometric mean relationship. The composite scale risk index is then compared with the low-risk and high-risk thresholds to determine the current low-scale-risk, medium-scale-risk, or high-scale-risk level.

[0062] Understandably, when the risk of scaling increases, it's crucial to simultaneously reduce the likelihood of continued high-scaling operating conditions by addressing three aspects: material composition, membrane-side concentration level, and MVR-side evaporation concentration intensity. Specifically, increasing the proportion of concentrate entering the post-conditioning unit allows more concentrate from the extreme separation membrane to enter for hardness ions and silicon components removal, reducing the amount of easily scaling components that directly enter the nanofiltration salt separation path and further enter the evaporation and crystallization stage. Reducing the operating pressure of the separation membrane concentration unit slows down further membrane-side concentration. Lowering the operating load of the MVR evaporation and crystallization unit reduces further concentration of the feed liquid during evaporation, creating a coordinated risk mitigation mechanism among the three control actions.

[0063] The operating load of the MVR evaporation and crystallization unit is characterized by the ratio of the actual evaporation rate to the designed evaporation rate. The system controller adjusts the evaporation rate by regulating the operating status of the MVR compressor and the feed rate, thereby achieving operating load regulation.

[0064] In practice, the system controller simultaneously outputs corresponding control commands to the pressure regulating actuators of the diversion valve group, the separation membrane concentration unit, and the load regulating actuators of the MVR evaporation crystallization unit, based on the current scaling risk level.

[0065] When the risk of scaling is determined to be low, the system operates under normal production conditions. The concentrate mainly enters the nanofiltration desalination unit for resource recovery, while the post-conditioning unit maintains basic operating conditions.

[0066] When a risk of scaling is identified, the system controller increases the proportion of concentrate entering the post-conditioning unit, allowing more concentrate to enter the post-conditioning unit to remove hardness ions and silicon components, thereby reducing the content of scaling precursors entering the MVR evaporation and crystallization unit. At the same time, the operating pressure of the separation membrane concentration unit and the operating load of the MVR evaporation and crystallization unit are reduced simultaneously, so that both the membrane concentration process and the evaporation and crystallization process are carried out under relatively mild operating conditions.

[0067] When a high risk of scaling is identified, the system controller further increases the proportion of concentrate entering the post-conditioning unit and further reduces the operating pressure of the membrane concentration unit and the operating load of the MVR evaporation crystallization unit to the preset operating values ​​corresponding to the high risk level, so as to suppress the development of scaling risk to the greatest extent.

[0068] When the scaling risk level decreases, the system controller performs a linkage adjustment in the opposite direction, gradually reducing the proportion of concentrate entering the post-conditioning unit, and simultaneously increasing the operating pressure of the separation membrane concentration unit and the operating load of the MVR evaporation crystallization unit, so that the system can gradually restore its processing capacity under the premise that the scaling risk is controllable.

[0069] The post-conditioning unit removes hardness ions and silicon components from the concentrate before it enters the MVR evaporation and crystallization unit, reducing the likelihood of complex scale formation in the feed liquid. The adjustment of the operating pressure of the separation membrane concentration unit controls the concentration level on the membrane side, preventing excessive accumulation of scale-forming salts due to excessive concentration. The adjustment of the operating load of the MVR evaporation and crystallization unit controls the evaporation intensity, reducing the possibility of localized supersaturation and scale formation on the heat exchanger tube walls. These three control variables act on different process stages, but all work synergistically to reduce the risk of system scaling.

[0070] In this invention, after determining the scaling risk level, the system controller simultaneously performs initial linkage control of concentrate distribution, membrane concentration operation, and evaporation crystallization operation. When the risk level increases, the system simultaneously adjusts the three control variables in the direction of reducing scaling conditions; when the risk level decreases, the system simultaneously adjusts the three control variables in the direction of restoring processing capacity. This ensures that the three adjustment actions of source conditioning, membrane-side scaling inhibition, and evaporation load reduction maintain a consistent control direction, establishing an initial operating state that matches the current scaling risk for the subsequent stable operation of the system. This avoids incoordination of operating conditions between pre- and post-treatment units due to adjusting only the operating state of a single device.

[0071] In this embodiment, after completing the initial linkage adjustment, the system controller continuously acquires the MVR heat exchange state change parameters and determines the MVR heat exchange state change trend based on the direction of change during continuous operation. Then, using this change trend as actual operation feedback, the controller corrects the adjustment range of the proportion of concentrate entering the post-conditioning unit, the operating pressure of the separation membrane concentration unit, and the operating load of the MVR evaporation crystallization unit. This allows the initial control quantity determined by the risk level to be further adjusted according to the actual heat exchange state of the MVR, avoiding reliance solely on pre-set risk level control parameters that cannot adapt to changes in actual operating conditions.

[0072] During the feedback adjustment process, when the MVR operating load, feed flow rate, or membrane concentration operating status is actively adjusted, the system controller synchronously updates the reference heat exchange temperature difference corresponding to the current operating conditions. Subsequent heat exchange status change parameters are all calculated based on the updated reference heat exchange temperature difference to eliminate the impact of active changes in operating parameters on the determination of scaling status.

[0073] The system controller continuously acquires multiple heat exchange state change parameters within a preset time range and determines the heat exchange state change trend based on the overall change direction of the parameters within that time range: when the heat exchange state change parameter changes in the direction of heat exchange decay for 6 consecutive sampling results within the preset time window, it is determined that the heat exchange state is continuously decaying; when the change amplitude of 6 consecutive sampling results is less than a set threshold or changes in the direction of heat exchange recovery, it is determined that the heat exchange state is stabilizing or recovering. The time range is set according to the thermal response characteristics and operational fluctuations of the MVR evaporation and crystallization unit to avoid control misjudgments caused by fluctuations in a single detection result.

[0074] Specifically, the preset time range is set to 30-60 minutes, and the heat exchange state change parameters are collected every 5 minutes; when the results of 6 consecutive samplings all change in the direction of heat exchange decay, a feedback correction is performed; when the results of 6 consecutive samplings return to stability, the correction amount is stopped.

[0075] The concentrate split ratio, membrane concentration unit operating pressure, and MVR evaporation and crystallization unit operating load corresponding to each scaling risk level can be used as baseline control parameters for feedback correction. During the system commissioning phase, several different combinations of split ratios, membrane operating pressures, and MVR operating loads are set for the same scaling risk level. These combinations are operated separately while maintaining basically consistent feed water composition and other main operating conditions, and the changing trends of the MVR heat exchange state corresponding to each parameter combination are recorded.

[0076] For the same risk level, exclude parameter combinations that cause the MVR heat exchange state to continuously decline, and then select a set of parameter combinations that can keep the heat exchange state stable. The set with a relatively low proportion of entering the post-conditioning unit and a relatively high membrane operating pressure and MVR operating load is selected as the benchmark control parameters corresponding to the risk level, so as to maintain a reasonable balance between scaling risk control and system processing capacity.

[0077] In actual operation, when the MVR heat exchange status continues to decline after the initial linkage adjustment, the system controller increases the adjustment range based on the baseline control parameters corresponding to the current risk level. This means further increasing the proportion of concentrate entering the post-conditioning unit and correspondingly increasing the reduction in the operating pressure of the separation membrane concentration unit and the operating load of the MVR evaporation and crystallization unit. When the MVR heat exchange status tends to stabilize or recover, the adjustment range is stopped, and the aforementioned additional correction amount can be gradually reduced to bring the operating parameters back to the baseline control parameters corresponding to the current risk level.

[0078] Feedback corrections for each regulation are performed independently by the controller based on the initial adjustment. While maintaining a constant feed composition, the controller applies step commands of known amplitude to the diverter valve assembly, membrane pressure regulating actuator, and MVR load regulating actuator, respectively. The time delay and overshoot from command issuance to actual action of each actuator are recorded. Based on this, a correction step size and correction period matching the response characteristics of each actuator are determined. Generally, the adjustment range of each regulation in a single instance does not exceed 1% to 5% of its total regulation range, in order to avoid over-adjustment while ensuring response speed.

[0079] The step command amplitude is set to 5% to 10% of the range of each actuator, and it is executed at least 3 times in both directions. The correction period is set to 2 to 3 times the lag time, and the step size is set to 1% to 5% of the range. A small step size is used when the overshoot is large, and a large step size is used when the overshoot is small. The time range is 3 to 5 times the correction period.

[0080] In this invention, the adjustment range of the control quantity is modified a second time by utilizing the actual heat exchange state change trend of the MVR, so that the concentrate distribution, membrane concentration intensity and evaporation crystallization intensity can be dynamically adjusted according to the actual heat exchange state, thereby improving the matching between the initial linkage control and the actual operating state.

[0081] In this embodiment, if the MVR heat exchange status continues to decline after the system makes feedback corrections to the concentrate ratio, membrane operating pressure and MVR operating load, the system controller adjusts the seed source according to the current operating status to further reduce the risk of scaling on the heat exchange tube wall.

[0082] Specifically, when the MVR heat exchange state change parameters continue to change in the decay direction within a preset time range, the system controller determines that the current operating parameters are not adjusted enough, and controls the switchable seed circulation branch to open the self-produced crystal slurry path, so that the self-produced crystal slurry containing a large number of fine crystal particles participates in the circulation, providing a preferential growth site for salt precipitation and reducing the adhesion of crystals on the surface of the heat exchange tube wall.

[0083] When the MVR heat exchange state is restored and it needs to return to the qualified salt crystal circulation mode, the system controller controls the switching crystal seed circulation branch to first stop the crystal slurry reinjection in the self-produced crystal slurry path, and then restore the operation of the qualified salt crystal path. This prevents the residual crystal slurry in the self-produced crystal slurry path from directly entering the high-purity salt evaporation and crystallization path, thereby avoiding the impact of mixed salt crystals on the high-purity salt product.

[0084] The technical solution of the present invention has been described above with reference to the preferred embodiments shown in the accompanying drawings. However, it will be readily understood by those skilled in the art that the scope of protection of the present invention is obviously not limited to these specific embodiments. Without departing from the principles of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after these changes or substitutions will all fall within the scope of protection of the present invention.

[0085] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. An integrated system for advanced treatment and resource recovery of RO concentrate, characterized in that, include: The concentrate outlet of the separation membrane concentration unit is equipped with a diversion valve group, which is connected to the nanofiltration desalination unit and the post-conditioning unit respectively. The product water outlet of the nanofiltration desalination unit is connected to the monovalent salt feed end of the MVR evaporation crystallization unit, and the water outlet of the post-conditioning unit is connected to the mixed salt feed end of the MVR evaporation crystallization unit. The MVR evaporation crystallization unit is equipped with a switchable seed crystal circulation branch, which is connected to the crystal slurry outlet at the bottom of the crystallizer and the qualified salt crystal outlet at the centrifugal discharge end of the MVR evaporation crystallization unit, respectively, to switch the seed crystal source under different operating modes. The concentrated liquid outlet of the separation membrane concentration unit is equipped with a supersaturation detection module and a silicon hardness ratio detection module, and the MVR evaporation and crystallization unit is equipped with a temperature detection module for acquiring changes in its heat exchange state. The system controller is configured to determine the composite fouling risk index based on the membrane concentrate supersaturation, silica hardness ratio, and MVR heat transfer state change parameters, in order to determine the fouling risk level. Adjust the diversion valve group according to the scaling risk level, adjust the proportion of concentrate entering the post-conditioning unit, and simultaneously adjust the operating pressure of the separation membrane concentration unit and the operating load of the MVR evaporation crystallization unit. Furthermore, the initial seed source of the switchable seed circulation branch is determined based on the dominant material type currently entering the MVR evaporation crystallization unit, and the concentration ratio, operating pressure, operating load, and seed source are corrected based on the MVR heat exchange state change trend.

2. The integrated treatment system for advanced RO concentrate treatment and resource recovery according to claim 1, characterized in that, The switchable seed crystal circulation branch includes a self-generated crystal slurry path and a qualified salt crystal path. The self-generated crystal slurry path is connected to the crystal slurry outlet at the bottom of the crystallizer of the MVR evaporation crystallization unit, and the qualified salt crystal path is connected to the qualified salt crystal outlet at the centrifugal discharge end.

3. The integrated treatment system for advanced RO concentrate treatment and resource recovery according to claim 2, characterized in that, The MVR evaporation crystallization unit is configured such that, in response to the main inflow from the nanofiltration salt separation branch, the system controller controls the switching of the seed crystal circulation branch to open the qualified salt crystal path; and in response to the main inflow from the post-conditioning branch, the system controller controls the switching of the seed crystal circulation branch to open the self-produced crystal slurry path.

4. The integrated treatment system for advanced RO concentrate treatment and resource recovery according to claim 1, characterized in that, The supersaturation detection module and the silicon hardness ratio detection module are located at the concentrate outlet of the separation membrane concentration unit to detect the supersaturation parameter and silicon hardness ratio parameter of the concentrate. The temperature detection module is installed at the inlet and outlet of the heat exchange tube bundle of the MVR evaporation crystallization unit to acquire parameters of heat exchange state changes.

5. The integrated treatment system for advanced RO concentrate treatment and resource recovery according to claim 4, characterized in that, The system controller is configured to: determine the supersaturation risk membership degree based on the membrane concentrate supersaturation, determine the silicon hardness ratio risk membership degree based on the silicon hardness ratio, and determine the heat transfer state risk membership degree based on the MVR heat transfer state change parameters; The system controller performs an equal-weighted geometric average based on the complementary values ​​of the supersaturation risk membership degree, the silicon hardness ratio risk membership degree, and the heat transfer state risk membership degree, and determines the composite scale risk index based on the complementary values ​​of the results.

6. The integrated treatment system for advanced RO concentrate treatment and resource recovery according to claim 5, characterized in that, The system controller determines the scaling risk level based on the composite scaling risk index; Wherein, in response to the composite scale risk index being less than the low risk threshold, it is determined to be of low scale risk; If the composite scale risk index is greater than or equal to the low risk threshold and less than the high risk threshold, it is determined to be of medium scale risk. If the composite scale risk index is greater than or equal to the high-risk threshold, it is determined to be of high scale risk.

7. The integrated treatment system for advanced RO concentrate treatment and resource recovery according to claim 6, characterized in that, The system controller is configured to adjust the diversion valve assembly according to the scaling risk level; In response to an increased risk of scaling, the proportion of concentrate entering the post-conditioning unit is increased; In response to the reduced scaling risk level, the proportion of concentrate entering the post-conditioning unit is reduced.

8. The integrated treatment system for advanced RO concentrate treatment and resource recovery according to claim 7, characterized in that, The system controller is also configured to synchronously adjust the operating pressure of the membrane concentration unit and the operating load of the MVR evaporation and crystallization unit; In response to an increased risk of scaling, the operating pressure of the membrane concentration unit and the operating load of the MVR evaporation and crystallization unit are reduced. In response to the reduced risk of scaling, the operating pressure of the membrane concentration unit and the operating load of the MVR evaporation and crystallization unit are increased.

9. The integrated treatment system for advanced RO concentrate treatment and resource recovery according to claim 8, characterized in that, The system controller determines the MVR heat exchange state change trend based on the continuously acquired MVR heat exchange state change parameters, and performs feedback correction on the adjustment range of the proportion of concentrate entering the post-conditioning unit, the operating pressure of the separation membrane concentration unit, and the operating load of the MVR evaporation crystallization unit based on the MVR heat exchange state change trend.

10. The integrated treatment system for advanced RO concentrate treatment and resource recovery according to claim 9, characterized in that, In response to the continued decay of the MVR heat exchange state after increasing the adjustment range, the system controller controls the switchable seed circulation branch to open the self-generated crystal slurry path. In response to the MVR heat exchange state changing from decay to recovery, the system controller redetermines the seed source of the switchable seed circulation branch based on the dominant material type currently entering the MVR evaporation crystallization unit.

Images