Vanadium industrial wastewater based on bipolar membrane sodium sulfate and ammonia nitrogen resource utilization collaborative treatment recovery system and method

Abstract

The application belongs to the technical field of resource recycling, and discloses a system and method for resourceful collaborative treatment and recovery of sodium sulfate and ammonia nitrogen in vanadium industrial wastewater based on a bipolar membrane; the system comprises the following steps: collecting vanadium industrial wastewater and performing diversion allocation to obtain bipolar membrane separation liquid supply and ammonia nitrogen treatment liquid; sodium sulfate is split to obtain a sulfuric acid solution and a sodium hydroxide solution; the ammonia nitrogen treatment liquid is subjected to alkalization treatment to output free ammonia; the alkalinity and the deposition state are detected in real time, and when the preset secondary deposition triggering condition is reached, the sodium hydroxide solution flow is reduced and loop switching is performed; the free ammonia is subjected to contact reaction with the sulfuric acid solution to obtain an ammonium sulfate product; the crystallization state is detected in real time, and the set acid distribution position and configuration parameters are updated synchronously; parameter differences are identified, and the operating current and the preset recovery distribution ratio are adjusted, and the remaining acid and base solutions and the ammonium sulfate product are output; the control accuracy of resourceful collaborative treatment and recovery of sodium sulfate and ammonia nitrogen in vanadium industrial wastewater is improved.

Description

Technical Field

[0001] This application relates to the field of resource recycling technology, and more specifically, to a system and method for the co-treatment and recovery of sodium sulfate and ammonia nitrogen from vanadium industrial wastewater based on a bipolar membrane. Background Technology

[0002] The co-treatment and recovery of sodium sulfate and ammonia nitrogen from vanadium industrial wastewater is a common problem in the field of vanadium industrial wastewater resource reuse, which directly affects the stable operation of wastewater treatment systems and resource recovery efficiency. Existing technologies and traditional co-treatment and recovery methods commonly used by enterprises can effectively treat ammonia nitrogen and salt products under normal operating conditions, but they cannot achieve the expected results in complex resource recovery scenarios where sodium sulfate and ammonia nitrogen coexist, and there are still many technical bottlenecks.

[0003] In practical applications, sodium sulfate in vanadium industrial wastewater can be converted into sulfuric acid and sodium hydroxide using bipolar membrane electrodialysis. However, if the ammonia nitrogen concentration in the wastewater fluctuates significantly, traditional co-treatment and recovery methods typically feed the pretreated wastewater directly into the bipolar membrane electrodialysis unit without a diversion and allocation process. This can easily lead to competition and migration of ammonium ions near the membrane stack, causing interference and further affecting the purity of the sulfuric acid and sodium hydroxide products. Furthermore, acids and alkalis are generated simultaneously in the bipolar membrane electrodialysis unit, while subsequent processes have different demands for alkali and acid solutions. Traditional co-treatment and recovery methods generally control acid and alkali output based solely on a fixed operating current or recovery ratio set in the process plan, failing to identify the dynamic mismatch between acid and alkali production and actual consumption. This can easily result in an oversupply of one product and a shortage of another. The phenomena are as follows: Simultaneously, when using the produced sodium hydroxide solution to alkalize and release ammonia from the ammonia nitrogen treatment solution, localized high-alkali areas are easily generated near certain injection points due to uneven mixing. This can easily induce the precipitation of by-products, leading to pipeline blockage. Traditional co-processing and recovery methods often neglect real-time detection of local alkalinity fluctuations and pressure differences, lacking means to address the occurrence of by-products in a timely manner. Furthermore, during the salt conversion reaction between free ammonia gas and sulfuric acid solution, some mass transfer areas experience crystallization due to supersaturation. Traditional co-processing and recovery methods generally treat crystallization merely as a result of product precipitation, without simultaneously adjusting the acid distribution and related parameters in the corresponding mass transfer areas, nor considering corrections for subsequent acid-base recovery and product output parameters. This results in both the ammonia absorption efficiency of the salt conversion process and the stability of crystal precipitation being affected.

[0004] In view of this, this application proposes a bipolar membrane-based system and method for the co-treatment and recovery of sodium sulfate and ammonia nitrogen in vanadium industrial wastewater to solve the above problems. Summary of the Invention

[0005] To overcome the aforementioned deficiencies of the prior art and to achieve the above objectives, this application provides the following technical solution: a method for the co-treatment and recovery of sodium sulfate and ammonia nitrogen from vanadium industrial wastewater based on a bipolar membrane, comprising: S1. Collect vanadium industrial wastewater and perform chemical pretreatment, identify the sodium sulfate concentration and initial ammonia nitrogen concentration, and perform diversion and distribution to ensure that the ammonia nitrogen content in the output solution is lower than the preset migration interference threshold, thereby obtaining bipolar membrane separation supply solution and ammonia nitrogen treatment solution respectively. S2. Input the bipolar membrane separation supply solution into the preset bipolar membrane electrodialysis unit to split the sodium sulfate in the bipolar membrane separation supply solution to obtain sulfuric acid solution and sodium hydroxide solution; S3. Draw sodium hydroxide solution into the preset ammonia release unit corresponding to the ammonia nitrogen treatment solution to perform alkalization treatment on the ammonia nitrogen treatment solution and output free ammonia; monitor the alkalinity and deposition status in the preset ammonia release unit in real time, and reduce the flow rate of sodium hydroxide solution and perform loop switching when the preset secondary deposition trigger condition is reached; S4. Free ammonia and sulfuric acid solution are fed into a preset salt conversion unit for contact reaction to obtain ammonium sulfate product; the crystallization state is monitored in real time during the contact reaction, and the set acid distribution position of the sulfuric acid solution and the configuration parameters of the preset salt conversion unit are updated and adjusted based on the crystallization state. S5. Obtain the real-time acid production and real-time alkali production of the preset bipolar membrane electrodialysis unit, obtain the alkali consumption requirement of the preset ammonia release unit and the acid consumption requirement of the preset salt conversion unit; identify the parameter differences between the real-time acid production and real-time alkali production and the alkali consumption requirement and acid consumption requirement, and adjust the operating current of the preset bipolar membrane electrodialysis unit and the preset recovery distribution ratio of sulfuric acid solution and sodium hydroxide solution based on the parameter differences, and output the remaining acid and alkali solutions and ammonium sulfate products that did not participate in the recovery.

[0006] Furthermore, the methods for implementing traffic diversion and allocation include: The upper limit of the tolerance of the ion exchange membrane to ammonium ions in the preset bipolar membrane electrodialysis unit is obtained, and this value is used as the preset migration interference threshold. The pretreated vanadium industrial wastewater is used as the pretreatment solution, and the real-time volumetric flow rate of the pretreatment solution is obtained in real time. The product of the real-time volumetric flow rate and the initial ammonia nitrogen concentration is calculated to obtain the actual ammonia nitrogen influent load value. If the actual ammonia nitrogen influent load is higher than the preset migration interference threshold, the ratio of the preset migration interference threshold to the initial ammonia nitrogen concentration is calculated, and the real-time volumetric flow rate is adjusted to meet the theoretical allowable flow rate using this ratio. The lower limit of sodium sulfate inlet flow rate is set based on the sodium sulfate concentration. When the theoretical allowable flow rate is greater than or equal to the lower limit of sodium sulfate inlet flow rate, the opening of the diversion valve is adjusted, and the pretreated solution is used as the bipolar membrane separation supply according to the theoretical allowable flow rate. The remaining pretreated solution is used as the ammonia nitrogen treatment solution.

[0007] Furthermore, the methods of splitting include: In the pre-designed bipolar membrane electrodialysis unit, bipolar membranes, anion exchange membranes, and cation exchange membranes are arranged alternately to sequentially separate acid chambers, salt chambers, and alkali chambers. The bipolar membrane separation supply solution is fed into the salt chamber, while the sulfuric acid solution that has been produced is returned to the acid chamber as the bottom liquid of the acid chamber through the preset acid circulation pipeline, and the sodium hydroxide solution that has been produced is returned to the alkali chamber as the bottom liquid of the alkali chamber through the preset alkali circulation pipeline. The driving DC electric field continuously dissociates water molecules in the region where the bipolar membrane is located, outputting hydrogen ions to migrate to the acid chamber and hydroxide ions to migrate to the alkali chamber. At the same time, sulfate ions in the salt chamber combine with hydrogen ions, and sodium ions combine with hydroxide ions. The operating current density of the preset bipolar membrane electrodialysis unit is matched with the inlet flow rate of the salt chamber, while sulfuric acid solution and sodium hydroxide solution are discharged from the overflow ports of the preset acid circulation pipeline and the preset alkali circulation pipeline, respectively.

[0008] Furthermore, the ammonia nitrogen treatment solution is alkalized to output free ammonia in the following ways: The ammonia nitrogen treatment solution is input into the pH adjustment tank of the preset ammonia release unit, and the initial pH and initial liquid level of the ammonia nitrogen treatment solution are identified in real time. Calculate the pH difference between the initial pH and the preset target pH, and match it with the initial liquid level value and the preset chemical parameter table to obtain the corresponding theoretical alkali dosage. The total amount of sodium hydroxide solution, which is the same as the theoretical amount of alkali solution to be added, is grouped according to a preset step distribution ratio to obtain the graded addition amount, and the corresponding drive command sequence of each alkali addition pump is generated. The driving command sequence controls the corresponding alkali pumps at each level to inject sodium hydroxide solution into the pH adjustment tank in batches; the internal gas pressure of the gas phase collection area in the preset ammonia release unit is acquired in real time, and when the internal gas pressure reaches the preset release threshold, the gas outlet valve is controlled to output free ammonia.

[0009] Furthermore, methods for reducing the sodium hydroxide solution flow rate and performing loop switching include: During the batch injection of sodium hydroxide solution, the pH value downstream of each injection point in the preset ammonia release unit is collected simultaneously to form a pH sequence, and the pressure difference data between the beginning and end of the pipeline where the injection point is located is obtained at the same time. The pressure difference increase rate is calculated within a preset reaction time window, and the standard deviation of the fluctuation of the corresponding acidity / alkalinity sequence within the preset reaction time window is also calculated. If the rate of increase of pressure difference at any injection point is higher than the preset blockage threshold, or the standard deviation of fluctuation is higher than the preset alkali content fluctuation threshold, then the pipeline where the injection point is located is determined to have reached the preset secondary deposition triggering condition. If the preset secondary deposition trigger condition is met, a flow suppression command is generated; the flow suppression command is used to control the alkali pump corresponding to the injection point to reduce its operating power; a loop switching command is generated simultaneously to control the injection valve of the injection point to close and open the corresponding circulation valve to buffer and balance the liquid in the pipeline where the injection point is located.

[0010] Furthermore, the methods for carrying out the contact reaction include: Free ammonia is input from the bottom of the preset salt conversion unit to ensure that the free ammonia can diffuse in the gas phase from bottom to top inside the preset salt conversion unit; Simultaneously, the sulfuric acid solution is transported to the designated acid distribution position above the preset salt conversion unit, and the sulfuric acid solution is distributed downwards using the liquid distribution element in the preset salt conversion unit, forming a liquid flow from top to bottom; Free ammonia is brought into contact with the liquid flow in the mass transfer zone of the preset salt conversion unit to generate an ammonium sulfate solution; the precipitated crystals of the ammonium sulfate solution are collected at the bottom of the preset salt conversion unit to obtain the ammonium sulfate product.

[0011] Furthermore, the methods for updating and adjusting the set acid distribution position of the sulfuric acid solution and the configuration parameters of the preset salt conversion unit include: During the contact reaction process, the pressure difference between each mass transfer region in the preset salt conversion unit is obtained, and the resistance growth gradient of the corresponding mass transfer region is calculated based on the time segment corresponding to the pressure difference. The resistance growth gradient of the corresponding mass transfer region is compared with the preset passivation threshold. If the resistance growth gradient of the mass transfer region is higher than the preset passivation threshold, it is determined that the mass transfer region has crystallization coverage, and the specific coordinates of the mass transfer region are obtained. Based on the specific coordinates, a switch command for the acid distribution is generated. Other preset acid distribution locations in the corresponding mass transfer region are obtained. The acid distribution locations that are not covered by crystals are selected and the new coordinates of these locations are used to replace the current set acid distribution location. Simultaneously, a parameter update command is generated and sent to the liquid distribution element to replace the original flow configuration parameters of the liquid distribution element with preset high flow configuration parameters.

[0012] Furthermore, methods for identifying the differences between real-time acid and alkali production and the parameters of alkali and acid consumption requirements include: The difference between real-time alkali production and alkali consumption demand is calculated to obtain the alkali equivalent deviation value; the difference between real-time acid production and acid consumption demand is calculated to obtain the acid equivalent deviation value; the alkali equivalent deviation value and the acid equivalent deviation value are combined to obtain the acid-alkali supply-demand deviation vector, which is used as the parameter difference.

[0013] Furthermore, the methods for adjusting the operating current of the preset bipolar membrane electrodialysis unit and the preset recovery and distribution ratio of sulfuric acid solution and sodium hydroxide solution include: If each equivalent deviation value in the parameter difference is positive, an energy-saving command is generated and the preset bipolar membrane electrodialysis unit is controlled to reduce the operating current until any equivalent deviation value returns to zero; at the same time, another equivalent deviation value that has not returned to zero is identified, and the corresponding preset recovery allocation ratio is reduced based on the remaining amount of that value. If the alkali equivalent deviation value is negative, then the alkali equivalent deviation value is treated as the main shortage item and the acid equivalent deviation value is treated as the additional impact item; if the alkali equivalent deviation value is positive and the acid equivalent deviation value is negative, then the acid equivalent deviation value is treated as the main shortage item and the alkali equivalent deviation value is treated as the additional impact item. The compensation current increment is calculated based on the absolute value of the main shortage term. This compensation current increment is then summed with the current operating current, ensuring that it does not exceed the safety limit current, to obtain a new current control command. The expected increment of the additional influence term is calculated based on the new current control command. The expected increment is then algebraically summed with the original equivalent deviation value to obtain the total excess increment. If the total excess increment is greater than zero, the preset recovery allocation ratio corresponding to the additional impact item will be reduced simultaneously, and the solution corresponding to the reduced ratio will be discharged as a solution that has not participated in the recovery; otherwise, if the total excess increment is not greater than zero, the current preset recovery allocation ratio will be maintained.

[0014] A bipolar membrane-based co-treatment and recovery system for sodium sulfate and ammonia nitrogen in vanadium industrial wastewater is described, comprising: The diversion and distribution module collects vanadium industrial wastewater and performs chemical pretreatment. It identifies the sodium sulfate concentration and initial ammonia nitrogen concentration and performs diversion and distribution to ensure that the ammonia nitrogen content in the output solution is lower than the preset migration interference threshold, thereby obtaining bipolar membrane separation supply solution and ammonia nitrogen treatment solution respectively. The liquid phase separation module inputs the bipolar membrane separation supply solution into a preset bipolar membrane electrodialysis unit to split the sodium sulfate in the bipolar membrane separation supply solution to obtain sulfuric acid solution and sodium hydroxide solution. The deposition treatment module directs sodium hydroxide solution into the preset ammonia release unit corresponding to the ammonia nitrogen treatment solution to perform alkalization treatment on the ammonia nitrogen treatment solution and outputs free ammonia; it monitors the alkalinity and deposition status in the preset ammonia release unit in real time, and reduces the flow rate of sodium hydroxide solution and performs loop switching when the preset secondary deposition trigger condition is reached; The crystallization conversion module feeds free ammonia and sulfuric acid solution into a preset salt conversion unit for contact reaction to obtain ammonium sulfate products. During the contact reaction, the crystallization state is monitored in real time, and the set acid distribution position of the sulfuric acid solution and the configuration parameters of the preset salt conversion unit are updated and adjusted based on the crystallization state. The product recovery module acquires the real-time acid and alkali production of the preset bipolar membrane electrodialysis unit, the alkali consumption requirements of the preset ammonia release unit, and the acid consumption requirements of the preset salt conversion unit; it identifies the parameter differences between the real-time acid and alkali production and the alkali and acid consumption requirements, and adjusts the operating current of the preset bipolar membrane electrodialysis unit and the preset recovery distribution ratio of sulfuric acid solution and sodium hydroxide solution based on these parameter differences; it outputs the remaining acid and alkali solutions and ammonium sulfate products that did not participate in the recovery; the modules are connected to each other via wired and / or wireless means.

[0015] The technical effects and advantages of the bipolar membrane-based co-treatment and recovery system and method for sodium sulfate and ammonia nitrogen in vanadium industrial wastewater are as follows: By acquiring real-time process data from vanadium industrial wastewater treatment, a bipolar membrane-based method for the co-treatment and recovery of sodium sulfate and ammonia nitrogen was constructed. Compared with existing technologies, this method implements diversion and distribution control to address ammonia nitrogen migration interference, improving the reduction in product purity caused by competitive migration of ammonium ions in the presence of sodium sulfate and ammonia nitrogen. It identifies and removes byproducts, ensuring the overall control system does not maintain the original dosing state simply because alkali addition is completed, thus preventing the formation of localized high-alkali areas and solid deposition blockage. Based on crystallization state identification and acid distribution adjustment, the method reduces the impact of crystallization precipitation during ammonia absorption and salt formation. The probability of interface passivation risk is reduced; the supply and demand deviation of acid and alkali is correlated and aligned with the real-time state variables of acid and alkali production, and targeted corrections are made to the operating current of the subsequent bipolar membrane and the acid and alkali recovery distribution ratio. This enables the overall control system to effectively identify the source of the mismatch situation where acid and alkali are generated synchronously but consumed asynchronously, and to continuously optimize the process parameters of subsequent batches. The overall technical solution improves the control accuracy of the co-processing and recovery of sodium sulfate and ammonia nitrogen in vanadium industrial wastewater, ensures the material balance in the overall process, improves the quality of acid and alkali recovery and the stability of ammonium sulfate product formation, and also improves the continuous operation reliability of the overall control system. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the method for the co-treatment and recovery of sodium sulfate and ammonia nitrogen in vanadium industrial wastewater based on bipolar membrane according to this application. Figure 2 This is a schematic diagram of the bipolar membrane-based synergistic treatment and recovery system for sodium sulfate and ammonia nitrogen in vanadium industrial wastewater, as described in this application. Detailed Implementation

[0017] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0018] Example 1 Please see Figure 1 As shown in this embodiment, the method for co-treatment and recovery of sodium sulfate and ammonia nitrogen from vanadium industrial wastewater based on bipolar membrane includes: S1. Collect vanadium industrial wastewater and perform chemical pretreatment, identify the sodium sulfate concentration and initial ammonia nitrogen concentration, and perform diversion and distribution to ensure that the ammonia nitrogen content in the output solution is lower than the preset migration interference threshold, thereby obtaining bipolar membrane separation supply solution and ammonia nitrogen treatment solution respectively. S2. Input the bipolar membrane separation supply solution into the preset bipolar membrane electrodialysis unit to split the sodium sulfate in the bipolar membrane separation supply solution to obtain sulfuric acid solution and sodium hydroxide solution; S3. Draw sodium hydroxide solution into the preset ammonia release unit corresponding to the ammonia nitrogen treatment solution to perform alkalization treatment on the ammonia nitrogen treatment solution and output free ammonia; monitor the alkalinity and deposition status in the preset ammonia release unit in real time, and reduce the flow rate of sodium hydroxide solution and perform loop switching when the preset secondary deposition trigger condition is reached; S4. Free ammonia and sulfuric acid solution are fed into a preset salt conversion unit for contact reaction to obtain ammonium sulfate product; the crystallization state is monitored in real time during the contact reaction, and the set acid distribution position of the sulfuric acid solution and the configuration parameters of the preset salt conversion unit are updated and adjusted based on the crystallization state. S5. Obtain the real-time acid production and real-time alkali production of the preset bipolar membrane electrodialysis unit, obtain the alkali consumption requirement of the preset ammonia release unit and the acid consumption requirement of the preset salt conversion unit; identify the parameter differences between the real-time acid production and real-time alkali production and the alkali consumption requirement and acid consumption requirement, and adjust the operating current of the preset bipolar membrane electrodialysis unit and the preset recovery distribution ratio of sulfuric acid solution and sodium hydroxide solution based on the parameter differences, and output the remaining acid and alkali solutions and ammonium sulfate products that did not participate in the recovery.

[0019] The vanadium industry generates a large amount of high-salinity wastewater rich in sodium sulfate and ammonia nitrogen. Traditional processes use high-temperature evaporation and crystallization to treat this wastewater, which is energy-intensive and has a complex and lengthy process. In this embodiment, bipolar membrane electrodialysis technology is used to treat vanadium industrial wastewater, and all sulfuric acid solutions, sodium hydroxide solutions, and ammonium sulfate products generated by this technology are effectively recycled and reused, thereby improving process efficiency and resource utilization.

[0020] The methods for implementing traffic diversion and allocation include: Obtain the upper limit of tolerance of the ion exchange membrane to ammonium ions in the preset bipolar membrane electrodialysis unit, and use this value as the preset migration interference threshold.

[0021] The tolerance upper limit refers to the maximum permeate flux of ammonium ions that the cation exchange membrane can allow under the DC electric field operation conditions set by the process requirements. Within this value range, ammonium ions will not cause destructive interference to the main migration of sodium ions. Therefore, this value is used as the preset migration interference threshold.

[0022] The pretreated vanadium industrial wastewater was used as the pretreatment solution. The real-time volumetric flow rate of the pretreatment solution was obtained, and the product of the real-time volumetric flow rate and the initial ammonia nitrogen concentration was calculated to obtain the actual ammonia nitrogen influent load value.

[0023] In the specific process execution pipeline, electromagnetic flowmeters or ultrasonic flowmeters are used to collect the real-time volumetric flow rate of the pretreatment solution at high frequency. By calculating the product of the real-time volumetric flow rate of the pretreatment solution and the initial ammonia nitrogen concentration, a load parameter that reflects the input amount of ammonia nitrogen per unit time, i.e., the actual ammonia nitrogen influent load value, is obtained.

[0024] If the actual ammonia nitrogen influent load is higher than the preset migration interference threshold, the ratio of the preset migration interference threshold to the initial ammonia nitrogen concentration is calculated, and the real-time volumetric flow rate is adjusted to meet the theoretical allowable flow rate using this ratio.

[0025] If the actual ammonia nitrogen influent load is higher than the preset migration interference threshold, it indicates that the influent load is excessive and may seriously affect the migration process of ions. Therefore, by calculating the ratio of the preset migration interference threshold to the initial ammonia nitrogen concentration, a dimensionless ratio is obtained. This ratio refers to the proportion by which the original real-time volumetric flow rate needs to be reduced so that the total ammonia nitrogen load entering the bipolar membrane electrodialysis unit can be compressed within the safe threshold under the current ammonia nitrogen concentration, water quality conditions, and liquid flow state.

[0026] The real-time volumetric flow rate is proportionally reduced using this ratio to obtain the target flow rate that meets safety conditions, i.e., the theoretical allowable flow rate. In this embodiment, the theoretical allowable flow rate refers to the maximum main feed volume that is allowed to enter the bipolar membrane electrodialysis unit under the current operating conditions without triggering the risk of ion migration crosstalk, and is the adjustment target of the real-time volumetric flow rate.

[0027] The lower limit of sodium sulfate inlet flow rate is set based on the sodium sulfate concentration. When the theoretical allowable flow rate is greater than or equal to the lower limit of sodium sulfate inlet flow rate, the opening of the diversion valve is adjusted, and the pretreated solution is used as the bipolar membrane separation supply according to the theoretical allowable flow rate. The remaining pretreated solution is used as the ammonia nitrogen treatment solution.

[0028] The lower limit of sodium sulfate influent flow rate refers to the minimum influent flow rate allowed to enter the bipolar membrane electrodialysis unit under a certain sodium sulfate concentration to ensure the minimum effective conductivity in the salt chamber of the bipolar membrane electrodialysis unit and the minimum salt load required for continuous acid and alkali production. It needs to be set based on the actual sodium sulfate concentration and the minimum salt consumption requirement corresponding to the bipolar membrane electrodialysis unit.

[0029] When the theoretically permissible flow rate is greater than or equal to the lower limit of the sodium sulfate influent flow rate, it indicates that after limiting the ammonia nitrogen flow, the liquid entering the bipolar membrane electrodialysis unit can still provide sufficient sodium sulfate load for the exchange membrane, thereby ensuring the continued stable production of acid and alkali.

[0030] At this point, by controlling the diversion valve, a component located at the bifurcation point between the process pipeline and the main and bypass lines, the valve core opening is controlled, thereby distributing the solution flow into the main line of the bipolar membrane electrodialysis unit and the bypass line of the ammonia release unit. By converting the theoretical allowable flow rate into the inlet flow rate of the main line as the bipolar membrane separation supply solution, the remaining pretreatment solution is introduced into the bypass line as the ammonia nitrogen treatment solution input into the subsequent ammonia release unit.

[0031] Methods for splitting sodium sulfate in bipolar membrane separation feed solution include: In the pre-designed bipolar membrane electrodialysis unit, bipolar membranes, anion exchange membranes, and cation exchange membranes are arranged alternately to sequentially separate acid chambers, salt chambers, and alkali chambers.

[0032] In this embodiment, the bipolar membrane electrodialysis unit is composed of bipolar membranes, anion exchange membranes, and cation exchange membranes arranged and assembled in a fixed order. The bipolar membrane is a special ion exchange membrane composed of a cation exchange layer, a catalytic interface layer, and an anion exchange layer. Under the action of a DC electric field, it can dissociate water molecules into hydrogen ions and hydroxide ions at the catalytic interface layer. Three chambers are sequentially separated between adjacent membranes: the acid chamber is used to receive and enrich hydrogen ions and sulfate ions to generate sulfuric acid solution; the salt chamber is used to receive the bipolar membrane separation supply and provide source solution for ion migration; and the alkali chamber is used to receive and enrich hydroxide ions and sodium ions to generate sodium hydroxide solution.

[0033] The bipolar membrane separation solution is fed into the salt chamber, while the produced sulfuric acid solution is returned to the acid chamber as the bottom solution of the acid chamber through a preset acid circulation pipeline, and the produced sodium hydroxide solution is returned to the alkali chamber as the bottom solution of the alkali chamber through a preset alkali circulation pipeline.

[0034] The bipolar membrane separation solution is continuously pumped into the salt chamber as the source solution for ion migration. The preset acid circulation pipeline and preset alkali circulation pipeline refer to the circulation loops set in the bipolar membrane electrodialysis process, which are used to return a portion of the sulfuric acid solution and sodium hydroxide solution produced at the outlet of the acid chamber and the outlet of the alkali chamber to the inlet of the acid chamber and the alkali chamber to form a product self-circulation and continuously maintain the basic conductive environment inside the acid chamber and the alkali chamber.

[0035] The driving DC electric field continuously dissociates water molecules in the region where the bipolar membrane is located, outputting hydrogen ions that migrate to the acid chamber and hydroxide ions that migrate to the alkali chamber. At the same time, sulfate ions in the salt chamber combine with hydrogen ions, and sodium ions combine with hydroxide ions.

[0036] In this embodiment, after applying a DC electric field to the electrode plates on both sides of the bipolar membrane stack, the water molecules in the bipolar membrane catalytic interface layer continuously dissociate into hydrogen ions and hydroxide ions under the driving force of the electric field. Under the action of the electric field, hydrogen ions migrate towards the cathode and enter the acid chamber, while hydroxide ions enter the alkali chamber. At the same time, sulfate ions migrate from the salt chamber to the acid chamber through the anion exchange membrane and form sulfuric acid. Sodium ions pass through the cation exchange membrane and enter the alkali chamber to form sodium hydroxide.

[0037] The operating current density of the preset bipolar membrane electrodialysis unit is matched with the inlet flow rate of the salt chamber, while sulfuric acid solution and sodium hydroxide solution are discharged from the overflow ports of the preset acid circulation pipeline and the preset alkali circulation pipeline, respectively.

[0038] The operating current density refers to the current intensity applied to a unit effective membrane area of ​​the membrane stack. This value determines the dissociation rate of water molecules and the transmembrane migration rate of ions per unit time, which in turn determines the generation rate of acid and alkali. The feed flow rate of the salt chamber refers to the linear flow rate of the bipolar membrane separation supply solution passing through the salt chamber. This value determines how many sulfate and sodium ions can be delivered from the salt chamber to the acid and alkali chambers per unit time.

[0039] Based on relevant process theories and experience, it is necessary to ensure that the operating current density corresponds to the feed liquid flow rate. If the operating current density is too high and the feed liquid flow rate is low, the ions in the salt chamber will be rapidly removed but not replenished in time, resulting in insufficient ions in the salt chamber, which may lead to concentration gradient polarization or even membrane hydrolysis and burning. If the operating current density is too low and the feed liquid flow rate is too high, a large amount of salt-containing liquid will flow through the salt chamber rapidly, but the ions will not have time to be driven to migrate by the electric field, resulting in low splitting conversion rate and wasted energy. Therefore, it is necessary to match the operating current density with the real-time feed liquid flow rate to ensure that the membrane stack achieves efficient splitting within the safe operating range.

[0040] The methods for alkalizing ammonia nitrogen treatment solutions to output free ammonia include: The ammonia nitrogen treatment solution is input into the pH adjustment tank of the preset ammonia release unit, and the initial pH and initial liquid level of the ammonia nitrogen treatment solution are identified in real time.

[0041] In this embodiment, the pre-set ammonia release unit refers to a closed reaction space, including a pH adjustment tank, a gas phase collection area, and an inlet, a reflux port, and a drain port. The ammonia nitrogen treatment liquid is discharged from the bypass channel of the diversion valve and then input into the pH adjustment tank through the inlet. The initial pH refers to the pH value detected in real time by the online pH electrode installed in the tank when the ammonia nitrogen treatment liquid just enters the pH adjustment tank. The initial liquid level value refers to the liquid level height detected in real time by the sensor in the tank, which is used to reflect the actual volume of the ammonia nitrogen treatment liquid in the tank.

[0042] Calculate the pH difference between the initial pH and the preset target pH, and match it with the initial liquid level value and the preset chemical parameter table to obtain the corresponding theoretical alkali dosage.

[0043] The preset target pH value refers to the target pH value that needs to be achieved in order to fully convert ammonium nitrogen in the ammonia nitrogen treatment solution into free ammonia. This value is determined based on the chemical equilibrium relationship between ammonium nitrogen and free ammonia, and is generally set between 10.5 and 11.5. Within this range, more than 95% of the ammonium nitrogen in the wastewater can be converted into volatile free ammonia molecules.

[0044] The preset chemical parameter table is a lookup table constructed based on different initial liquid level values ​​and different pH differences, through prior calibration experiments or chemical theory calculations. The table records the volume of sodium hydroxide solution required to raise the liquid from the current pH condition to the preset target pH under various combinations of liquid level and pH difference conditions. Therefore, by using the pH difference and initial liquid level value as indexes, the corresponding theoretical alkali solution dosage can be matched from the preset chemical parameter table.

[0045] The total amount of sodium hydroxide solution, which is the same as the theoretical amount of alkali solution to be added, is grouped according to a preset step distribution ratio to obtain the graded addition amount, and the corresponding drive command sequence of each alkali addition pump is generated.

[0046] In this embodiment, the theoretical amount of alkali solution is not directly injected into the pH adjustment tank. Instead, it is divided into multiple stages according to a preset stepped distribution ratio. The preset stepped distribution ratio refers to a progressively decreasing distribution ratio sequence pre-set based on the process experience of the alkali reaction. For example, the first stage is 40% of the total amount, the second stage is 30%, the third stage is 20%, and the fourth stage is 10%. Since the pH of the liquid is low in the early stage of the alkali reaction, the buffer capacity is large, so it can withstand a large amount of alkali solution. As the pH gradually increases and approaches the target value, the buffer capacity of the liquid gradually decreases. If a large amount is still injected, a high-alkali area can easily form near the injection point, leading to the precipitation of by-products such as silicates. The distribution of each stage is encoded into a drive command that the corresponding alkali pump can recognize.

[0047] The sodium hydroxide solution is injected into the pH adjustment tank in batches by controlling the corresponding alkali pumps at each stage using a sequence of drive commands.

[0048] In this embodiment, the ammonia release unit is equipped with multiple alkali pumps. Each alkali pump is connected to an injection point at a different location in the pH adjustment tank through an independent injection pipeline. The main control system starts the corresponding alkali pumps in sequence according to the order and corresponding parameters in the drive command sequence, injecting sodium hydroxide solution into the pH adjustment tank in batches from different injection points. First, the pH level is rapidly increased with a larger flow rate, and then the flow rate is gradually reduced to make the pH slowly approach the target value, so that the alkalinity distribution in the pH adjustment tank is uniform.

[0049] The internal gas pressure in the gas phase collection zone of the preset ammonia release unit is acquired in real time. When the internal gas pressure reaches the preset release threshold, the outlet valve is controlled to output free ammonia.

[0050] As free ammonia is generated and rises to the gas phase collection area, the gas pressure increases. The preset release threshold is the safe upper limit that the internal gas pressure in the gas phase collection area can reach. The specific value is set based on the structural pressure bearing capacity of the gas phase collection area. When the internal gas pressure reaches the preset release threshold, the main control system generates an exhaust command and controls the exhaust valve to open, releasing the free ammonia gas accumulated in the gas phase collection area and exporting it to the subsequent preset salt conversion unit.

[0051] Real-time monitoring of alkalinity and deposition status in the preset ammonia release unit; when the preset secondary deposition trigger condition is reached, methods for reducing the sodium hydroxide solution flow rate and performing loop switching include: During the batch injection of sodium hydroxide solution, the pH value downstream of each injection point in the preset ammonia release unit is collected simultaneously to form a pH sequence, and the pressure difference data between the beginning and end of the pipeline where the injection point is located is also obtained.

[0052] In this embodiment, a pH sensor and a pipeline pressure sensor are installed in the downstream pipeline section of each injection point of the ammonia release unit. The pH sensor continuously collects the instantaneous acidity and alkalinity values ​​of the liquid phase in the downstream pipeline section at a fixed sampling period. Multiple continuous sampling values ​​within a preset reaction time window are sorted to obtain the acidity and alkalinity sequence of the corresponding injection point, which is used to reflect the change in the acidity and alkalinity of the liquid in the downstream pipeline section after the alkaline solution is injected. At the same time, the fluid pressure difference between the beginning and end of the pipeline where each injection point is located is obtained to reflect the flow resistance in the pipeline.

[0053] The pressure difference increase rate is calculated within a preset reaction time window, and the standard deviation of the corresponding acidity / alkalinity sequence fluctuation within the same preset reaction time window is also calculated.

[0054] The preset reaction time window refers to the time interval set to assess the condition of the pipeline section downstream of the injection point. The specific duration is based on the reaction time required for the alkali solution to be fully mixed from injection. The pressure difference increase rate refers to the increase in pressure difference per unit time from the start to the end within the preset reaction time window. The larger this value, the faster the accumulation of deposits on the inner wall of the pipeline section and the more obvious the pipeline blockage trend. The fluctuation standard deviation refers to the value obtained by calculating the standard deviation of the values ​​of each sampling point in the pH sequence within the same time window. The larger this value, the more drastic the pH fluctuations downstream of the injection point are in a short period of time, meaning that the alkali solution has not been uniformly mixed near the injection point.

[0055] If the rate of increase of the pressure difference at any injection point is higher than the preset blockage threshold, or the standard deviation of the fluctuation is higher than the preset alkali content fluctuation threshold, then the pipeline where the injection point is located is determined to have reached the preset secondary deposition trigger condition.

[0056] The preset blockage threshold refers to the maximum safe value allowed for the pipeline pressure difference increase rate under normal operating conditions. It is specifically set based on the pipeline inner diameter and the deposition resistance characteristics of the pipe wall material. When the actual pressure difference increase rate is higher than the preset blockage threshold, it indicates that a relatively obvious solid deposit has begun to adhere to the pipeline inner wall. The preset alkali content fluctuation threshold refers to the maximum value allowed for the standard deviation of the acid-base sequence fluctuation under normal alkali addition and mixing conditions. It is specifically set based on the stirring and mixing efficiency of the acid-base adjustment tank, the pipeline length, and the alkali injection rate.

[0057] If the pressure difference increase rate or fluctuation standard deviation of any injection point is higher than the corresponding threshold, it indicates that secondary deposits have already occurred or are about to occur in the pipeline section where the injection point is located. It should be noted that the preset secondary deposit triggering condition is that either the pressure difference increase rate or the fluctuation standard deviation is higher than the corresponding threshold, which means that the condition is met.

[0058] If the preset secondary deposition triggering condition is determined to be met, a flow suppression command is generated; the flow suppression command is used to control the alkali pump corresponding to the injection point to reduce its operating power.

[0059] If the preset secondary deposition triggering conditions have been met, a flow suppression command is sent to the pipeline where the corresponding injection point is located. This command is used to control the corresponding alkali pump to reduce its operating power to reduce the output flow, thereby reducing the instantaneous injection rate of sodium hydroxide solution at the injection point. By reducing the injection rate, the rate of increase in local alkalinity in the downstream pipeline section of the injection point is slowed down, allowing the already formed local high-alkali area to have more time to mix and dilute with the surrounding liquid, thus inhibiting the continued precipitation of secondary deposits.

[0060] Synchronously generate a loop switching command to control the injection valve at the injection point to close and open the corresponding circulation valve to buffer and balance the liquid in the pipeline where the injection point is located.

[0061] In this embodiment, the loop switching command includes two parts. The first part is used to close the injection valve of the injection point where the abnormality occurred, so that the injection point stops receiving new sodium hydroxide solution and completely cuts off the alkali supply source at that location, preventing the continued injection of high-alkalinity solution from aggravating sedimentation. The second part is to simultaneously open the circulation valve of the pipeline section where the injection point is located, isolating the pipeline section from the main alkali addition loop, so that the high-alkalinity liquid retained in the pipeline section enters the bypass circulation pipeline to achieve buffer balance. The bypass circulation pipeline is connected to the low-alkalinity liquid area of ​​the pH adjustment tank, so that the high-alkalinity liquid is mixed and diluted with the low-alkalinity liquid, thereby lowering the local alkalinity level of the pipeline section to a safe range where no secondary sediments will precipitate.

[0062] It should be noted that after the circulation pipeline has been running for a period of time, the pH of the liquid in the corresponding pipeline section will return to normal. The circulation valve can be closed again and the injection valve opened to restore the normal alkali addition function of the injection point.

[0063] The ways in which a contact reaction can occur include: Free ammonia is input from the bottom of the preset salt conversion unit to ensure that the free ammonia can diffuse from bottom to top inside the preset salt conversion unit.

[0064] In this embodiment, the salt conversion unit is a vertically arranged closed tower structure, which is divided into multiple mass transfer zones along the vertical direction. A gas inlet is set at the bottom and a tail gas outlet is set at the top. Free ammonia gas exported from the ammonia release unit enters from the bottom gas inlet of the salt conversion unit and diffuses through each mass transfer zone from bottom to top. By adopting the bottom gas inlet and top gas outlet method, the rising direction of the free ammonia gas is opposite to the direction of the sulfuric acid solution sprayed down from above, forming a gas-liquid counter-current contact state.

[0065] Simultaneously, the sulfuric acid solution is transported to the designated acid distribution position above the preset salt conversion unit, and the sulfuric acid solution is distributed downwards using the liquid distribution element in the preset salt conversion unit, forming a liquid flow from top to bottom.

[0066] The designated sulfuric acid inlet position refers to the pre-set inlet position of the sulfuric acid solution at the top of the tower of the salt conversion unit. This position is set based on specific process requirements and is usually located above the uppermost mass transfer zone, allowing the sulfuric acid solution to pass through each mass transfer zone sequentially from top to bottom. The liquid distribution element refers to the liquid distribution device installed at the designated sulfuric acid inlet position, which is used to disperse the sulfuric acid solution into multiple fine streams, allowing the sulfuric acid solution to flow downward along the surface of the mass transfer zone in the form of fine water streams or droplets. After the sulfuric acid solution is evenly distributed by the liquid distribution element, the effective contact area between the sulfuric acid solution and the rising free ammonia gas is increased, avoiding the situation where some mass transfer zones are not covered by liquid due to uneven distribution of sulfuric acid solution, thus improving the ammonia absorption efficiency.

[0067] Free ammonia comes into contact with the liquid flow in the mass transfer region of the preset salt conversion unit to generate an ammonium sulfate solution.

[0068] In this embodiment, the mass transfer zone refers to the functional section inside the tower of the salt conversion unit used to carry the gas-liquid contact reaction. It can be filled with structured packing or random packing, or it can be set as a plate tray structure to increase the gas-liquid contact area and contact residence time. When the free ammonia gas rising from the bottom passes through the mass transfer zone, it comes into counter-current contact with the sulfuric acid solution flowing downward from above. Ammonium sulfate or ammonium bisulfate is generated in the contact reaction, that is, an ammonium sulfate solution. The solution continues to flow downward and eventually collects in the liquid collection zone at the bottom of the salt conversion unit.

[0069] The ammonium sulfate solution is collected at the bottom of the pre-designed salt conversion unit to precipitate crystals, thus obtaining the ammonium sulfate product.

[0070] Because the ammonium sulfate solution continues to react after entering the collection zone, as the concentration of ammonium sulfate increases, it reaches supersaturation when the concentration exceeds the solubility at the corresponding temperature, and solid crystals gradually precipitate out, which are the ammonium sulfate products.

[0071] The methods for updating and adjusting the set acid distribution position of the sulfuric acid solution and the configuration parameters of the preset salt conversion unit include: During the contact reaction process, the pressure difference between each mass transfer region in the preset salt conversion unit is obtained, and the resistance growth gradient of the corresponding mass transfer region is calculated based on the time segment corresponding to the pressure difference.

[0072] The pressure difference between the intervals refers to the difference between the maximum and minimum pressures in each corresponding mass transfer region. This value reflects the magnitude of the flow resistance encountered by the gas when passing through the mass transfer region. The resistance growth gradient refers to the ratio of the change in the pressure difference from the initial value to the final value to the length of the corresponding time interval during a period of reaction in the corresponding mass transfer region. The pressure difference growth rate per unit time is the resistance growth gradient.

[0073] The resistance growth gradient of the corresponding mass transfer region is compared with a preset passivation threshold. If the resistance growth gradient of the mass transfer region is higher than the preset passivation threshold, it is determined that the mass transfer region has crystallization coverage, and the specific coordinates of the mass transfer region are obtained.

[0074] The preset passivation threshold refers to the maximum safe value allowed by the resistance growth gradient under normal operating conditions. It is specifically set based on the natural adhesion rate of ammonium sulfate on the surface of the mass transfer region under normal reaction conditions. When the resistance growth gradient of a certain layer of the mass transfer region exceeds this threshold, it indicates that a crystalline covering layer affecting the normal gas-liquid contact mass transfer has been formed on the surface of the corresponding mass transfer region. The ammonia absorption efficiency of the mass transfer region is rapidly decreasing. Therefore, the specific coordinate position of the mass transfer region is recorded, including the corresponding layer number and vertical height coordinate.

[0075] Based on the specific coordinates, a borate switching command is generated, the remaining preset borate positions in the corresponding mass transfer region are obtained, the borate positions that are not covered by crystals are filtered out, and the current preset borate position is replaced with the new coordinates of the position.

[0076] In this embodiment, multiple acid distribution positions are set at different heights of the tower body. Each acid distribution position is equipped with an independent liquid supply valve and liquid distribution element. During normal operation, only one acid distribution position is activated to distribute liquid downwards. When crystallization occurs in a certain mass transfer area, an acid distribution switching command is generated and the acid distribution positions located above the crystallized mass transfer area are excluded. From the remaining acid distribution positions, the corresponding mass transfer area where crystallization has not yet occurred is selected, and the original set acid distribution position is replaced by this position.

[0077] A parameter update command is generated synchronously and sent to the liquid distribution element, replacing the original flow configuration parameters of the liquid distribution element with the preset high flow configuration parameters.

[0078] The parameter update command is a control signal issued synchronously with the ammonia switching command, acting on the liquid distribution element corresponding to the mass transfer area where crystallization has occurred. The original flow configuration parameter refers to the standard spray flow parameter executed by the corresponding liquid distribution element under normal ammonia absorption conditions. The preset high flow configuration parameter refers to the high flow operating parameter pre-set specifically for flushing away the covered crystals. The specific value is generally a multiple of the original flow configuration parameter. The specific value can be set based on relevant process theory and process experience to ensure that the covered crystals can be peeled off and flushed down to the bottom collection area through a larger flow rate and velocity. The configuration parameters of the liquid distribution element in the corresponding mass transfer area are restored to the original flow configuration parameter only after the pressure difference in the subsequent intervals returns to the normal level.

[0079] Methods for identifying the differences between real-time acid and alkali production and the parameters of alkali and acid consumption requirements include: The difference between real-time alkali production and alkali consumption demand is calculated to obtain the alkali equivalent deviation value; the difference between real-time acid production and acid consumption demand is calculated to obtain the acid equivalent deviation value.

[0080] In this embodiment, the real-time alkali production and real-time acid production are both identified by sensors configured in the alkali chamber and acid chamber. The alkali consumption demand and acid consumption demand refer to the expected consumption values ​​per unit time set in the original process plan for the corresponding ammonia release unit and salt conversion unit. The alkali equivalent deviation value and acid equivalent deviation value are obtained by calculating the difference between the real-time alkali production and the alkali consumption demand, and the difference between the real-time acid production and the acid consumption demand, respectively.

[0081] The acid-base supply and demand deviation vector is obtained by combining the alkali equivalent deviation value and the acid equivalent deviation value, which serves as the parameter difference. The alkali equivalent deviation value and the acid equivalent deviation value are combined in a fixed order to form a two-dimensional vector, namely the acid-base supply and demand deviation vector, which is used to express the parameter difference.

[0082] The methods for adjusting the operating current of the preset bipolar membrane electrodialysis unit and the preset recovery and distribution ratio of sulfuric acid solution and sodium hydroxide solution include: If each equivalent deviation value in the parameter difference is positive, an energy-saving command is generated and the preset bipolar membrane electrodialysis unit is controlled to reduce the operating current until any equivalent deviation value returns to zero.

[0083] In this embodiment, when the algebraic signs corresponding to both the alkali equivalent deviation value and the acid equivalent deviation value are positive, it indicates that the sulfuric acid and sodium hydroxide produced by the current bipolar membrane electrodialysis unit exceed the actual consumption requirements of the downstream ammonia release unit and salt conversion unit, and are in an excess state. If the current operating current is maintained in this state, it will lead to unnecessary energy consumption and excessive production of acid and alkali. Therefore, an energy-saving command is generated to control the bipolar membrane electrodialysis unit to gradually reduce the operating current, so that the alkali production rate and acid production rate decrease simultaneously. Since the consumption requirements of the ammonia release unit and the salt conversion unit are independent and unequal, the rate of decrease of the acid-alkali equivalent deviation value is not consistent. One of them must drop to zero first. When any equivalent deviation value drops to zero, the reduction of the operating current is stopped.

[0084] Simultaneously identify another non-zero equivalent deviation value and adjust the corresponding preset recovery allocation ratio based on the remaining amount of that value.

[0085] When one equivalent deviation value returns to zero, the other equivalent deviation value that has not yet returned to zero remains in an excess state. The remaining value of the equivalent deviation value that has not yet returned to zero is obtained in real time. The preset recovery distribution ratio refers to the percentage of flow distribution of the product solution between the circulation pipeline and the discharge pipeline. It is specifically set based on the ratio of output to recovery and circulation requirements of the process. When there is excess, the preset recovery distribution ratio of the corresponding product solution is adjusted synchronously based on the proportion of excess excess to the total output. This ensures that the excess solution of the corresponding proportion no longer enters the circulation pipeline but is directly discharged, guaranteeing that the output discharged can meet the output requirements of the process.

[0086] If the alkali equivalent deviation value is negative, then the alkali equivalent deviation value is treated as the main shortage item, and the acid equivalent deviation value is treated as the additional impact item.

[0087] When the alkali equivalent deviation value is negative, it indicates that the current sodium hydroxide production rate of the bipolar membrane electrodialysis unit is lower than the consumption rate of the ammonia release unit. Therefore, the ammonia release unit may face the risk of insufficient alkali supply. At the same time, the ammonia release unit is a pre-process in the entire ammonia absorption and salt formation process. Insufficient alkali will directly lead to the inability of ammonia nitrogen to be fully released from the liquid phase into free ammonia, which in turn will reduce the actual acid consumption demand of the subsequent salt conversion unit. Therefore, regardless of the algebraic sign and value of the acid equivalent deviation value, as long as the alkali equivalent deviation value is negative, the alkali equivalent deviation value will be forcibly identified as the main shortage item, and the acid equivalent deviation value will be identified as an additional impact item.

[0088] The main shortage item refers to the most pressing source of resource shortage under the current operating conditions, while the additional impact item refers to another equivalent that is passively affected by changes in acid and alkali production after compensating for the main shortage item with current.

[0089] If the alkali equivalent deviation is positive and the acid equivalent deviation is negative, the acid equivalent deviation will be treated as the main shortage item and the alkali equivalent deviation as the additional impact item.

[0090] When the alkali equivalent deviation is positive and the acid equivalent deviation is negative, it indicates that the alkali supply in the ammonia release unit is sufficient, but the sulfuric acid supply in the salt conversion unit is insufficient to completely absorb the released free ammonia. This indicates that the real resource gap at this time is acid. Therefore, the acid equivalent deviation is taken as the main shortage item, and the alkali equivalent deviation is taken as an additional impact item.

[0091] The compensation current increment is calculated based on the absolute value of the main shortage term. This compensation current increment is then summed with the current operating current, ensuring that it does not exceed the safety limit current, to obtain a new current control command.

[0092] The formula for calculating the increment of the compensation current is as follows: The above formula is derived from Faraday's law of electrolysis. Indicates the increment of compensation current; Denotes Faraday's constant; Indicates the value of the missing item in the main body; This represents the current efficiency of the bipolar membrane electrodialysis unit. This value is used to express the ratio between the actual amount of sulfuric acid or sodium hydroxide equivalent formed per unit time under the current operating conditions and the amount of acid or alkali equivalent that should have been formed according to the theoretical input charge. 3600 refers to the conversion factor between hours and seconds. This compensation current increment represents the additional current intensity required under the current membrane stack conditions to produce an additional target product equal to the main shortage value per unit time.

[0093] The new operating current is obtained by summing the incremental compensation current with the currently running current, while ensuring that it does not exceed the value of the safety limit current. If it does, the value of the safety limit current is used by default. The safety limit current refers to the maximum continuous operating current that the membrane stack of the bipolar membrane electrodialysis unit can withstand without overheating damage or other conditions that shorten the membrane life.

[0094] The expected increment of the additional influence term is calculated based on the new current control command. The expected increment is then algebraically summed with the original equivalent deviation value to obtain the total excess increment.

[0095] Since the operating current is increased from its original value, not only will the output of the product corresponding to the main shortage item increase, but the output of the product corresponding to the additional impact item will also increase simultaneously. Based on the current difference between the new operating current and the original operating current, and using Faraday's law of electrolysis to calculate the expected increment of the additional impact item, the expected increment is added to the original equivalent deviation value with a sign to obtain the total excess increment.

[0096] If the total excess increment is greater than zero, the preset recovery allocation ratio corresponding to the additional impact item will be adjusted accordingly, and the solution corresponding to the adjusted ratio will be discharged as a solution that did not participate in the recovery.

[0097] When the total excess increment is greater than 0, it indicates that the product corresponding to the additional impact item has a surplus after the current is increased. If all of it is used for recycling, it will lead to problems such as excessively high influent concentration or overflow in downstream processes. Therefore, based on the ratio of the total excess increment to the total output of the product corresponding to the additional impact item, the preset recycling allocation ratio of the corresponding product is reduced simultaneously, and the corresponding proportion of sodium hydroxide solution or sulfuric acid solution is discharged.

[0098] It should be noted that the solutions not involved in recycling include sulfuric acid solution, sodium hydroxide solution, and ammonium sulfate products. Even if these products are not added to the current batch for recycling, they can be recycled in subsequent batches. The sulfuric acid solution and sodium hydroxide solution can be recovered and returned to the front end of the vanadium industry production process to participate in the vanadium leaching and impurity neutralization processes, thereby reducing the amount of sulfuric acid and sodium hydroxide solution used as auxiliary materials in these processes. As for the ammonium sulfate products, they can be returned to the vanadium precipitation process in the vanadium industry production process to reduce the amount of ammonium sulfate used as an auxiliary material.

[0099] Conversely, if the total surplus increment is not greater than zero, the current preset recycling and allocation ratio will be maintained.

[0100] If the total excess increment is not greater than 0, it means that although the operating current was increased to compensate for the main shortage, the output of the product corresponding to the additional impact item is still insufficient or just meets the consumption needs of the downstream process after the increase in current, and there is no excess that needs to be discharged. In this case, the current preset recycling and distribution ratio of the product corresponding to the additional impact item is maintained unchanged, and all the corresponding products produced continue to be recycled to the corresponding downstream process according to the original ratio. No diversion and drainage operations are carried out, which ensures that the product is utilized to the maximum extent when the overall capacity cannot meet the needs of both acid and alkali at the same time, and avoids waste in the case of insufficient resources.

[0101] By recycling all sulfuric acid solutions, sodium hydroxide solutions, and ammonium sulfate products produced in each batch, the resource utilization rate of the bipolar membrane system in this embodiment is ensured, the environmental impact of vanadium industrial wastewater is reduced, and the overall production cost of the process is also reduced, thus ensuring both economic and environmental benefits.

[0102] This embodiment constructs a bipolar membrane-based method for the co-treatment and recovery of sodium sulfate and ammonia nitrogen resources by acquiring real-time process data in vanadium industrial wastewater treatment. Compared with existing technologies, it implements diversion and distribution control to address ammonia nitrogen migration interference, thus improving the reduction in product purity caused by competitive migration of ammonium ions in the presence of sodium sulfate and ammonia nitrogen. It identifies and removes by-deposited products, ensuring that the overall control system does not continuously maintain the original dosing state simply because the alkali addition action is completed, thereby preventing the formation of localized high-alkali areas and solid deposition blockage. Based on crystallization state identification and acid distribution position adjustment, it reduces the impact of crystallization precipitation during ammonia absorption and salt formation. The probability of interface passivation risk caused by the cap is reduced; the supply and demand deviation of acid and alkali is correlated and aligned with the real-time state quantities of acid and alkali production, and targeted corrections are performed on the operating current of the subsequent bipolar membrane and the acid and alkali recovery distribution ratio. This enables the overall control system to effectively identify the source of the mismatch situation of synchronous generation and asynchronous consumption of acid and alkali, and continuously optimize the process parameters of subsequent batches. The overall technical solution improves the control accuracy of the co-processing and recovery of sodium sulfate and ammonia nitrogen in vanadium industrial wastewater, ensures the material balance in the overall process, improves the quality of acid and alkali recovery and the stability of ammonium sulfate product formation, and also improves the continuous operation reliability of the overall control system.

[0103] Example 2 Please see Figure 2 As shown, parts not described in detail in this embodiment are described in Embodiment 1. A bipolar membrane-based co-treatment and recovery system for sodium sulfate and ammonia nitrogen in vanadium industrial wastewater is provided, comprising: The diversion and distribution module collects vanadium industrial wastewater and performs chemical pretreatment. It identifies the sodium sulfate concentration and initial ammonia nitrogen concentration and performs diversion and distribution to ensure that the ammonia nitrogen content in the output solution is lower than the preset migration interference threshold, thereby obtaining bipolar membrane separation supply solution and ammonia nitrogen treatment solution respectively. The liquid phase separation module inputs the bipolar membrane separation supply solution into a preset bipolar membrane electrodialysis unit to split the sodium sulfate in the bipolar membrane separation supply solution to obtain sulfuric acid solution and sodium hydroxide solution. The deposition treatment module directs sodium hydroxide solution into the preset ammonia release unit corresponding to the ammonia nitrogen treatment solution to perform alkalization treatment on the ammonia nitrogen treatment solution and outputs free ammonia; it monitors the alkalinity and deposition status in the preset ammonia release unit in real time, and reduces the flow rate of sodium hydroxide solution and performs loop switching when the preset secondary deposition trigger condition is reached; The crystallization conversion module feeds free ammonia and sulfuric acid solution into a preset salt conversion unit for contact reaction to obtain ammonium sulfate products. During the contact reaction, the crystallization state is monitored in real time, and the set acid distribution position of the sulfuric acid solution and the configuration parameters of the preset salt conversion unit are updated and adjusted based on the crystallization state. The product recovery module acquires the real-time acid and alkali production of the preset bipolar membrane electrodialysis unit, the alkali consumption requirements of the preset ammonia release unit, and the acid consumption requirements of the preset salt conversion unit; it identifies the parameter differences between the real-time acid and alkali production and the alkali and acid consumption requirements, and adjusts the operating current of the preset bipolar membrane electrodialysis unit and the preset recovery distribution ratio of sulfuric acid solution and sodium hydroxide solution based on these parameter differences; it outputs the remaining acid and alkali solutions and ammonium sulfate products that did not participate in the recovery; the modules are connected to each other via wired and / or wireless means.

[0104] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

[0105] All formulas in this manual are dimensionless and calculated numerically. The formulas are derived from software simulations based on a large amount of collected data to obtain the most recent real-world results. The preset parameters and thresholds in the formulas are set by those skilled in the art according to the actual situation.

[0106] Although embodiments of this application have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of this application, the scope of which is defined by the claims and their equivalents.

Claims

1. A method for the co-treatment and recovery of sodium sulfate and ammonia nitrogen from vanadium industrial wastewater based on a bipolar membrane, characterized in that, include: S1. Collect vanadium industrial wastewater and perform chemical pretreatment, identify the sodium sulfate concentration and initial ammonia nitrogen concentration, and perform diversion and distribution to ensure that the ammonia nitrogen content in the output solution is lower than the preset migration interference threshold, thereby obtaining bipolar membrane separation supply solution and ammonia nitrogen treatment solution respectively. S2. Input the bipolar membrane separation supply solution into the preset bipolar membrane electrodialysis unit to split the sodium sulfate in the bipolar membrane separation supply solution to obtain sulfuric acid solution and sodium hydroxide solution; S3. Draw the sodium hydroxide solution into the preset ammonia release unit corresponding to the ammonia nitrogen treatment solution to perform alkalization treatment on the ammonia nitrogen treatment solution and output free ammonia; The alkalinity and deposition status in the preset ammonia release unit are monitored in real time. When the preset secondary deposition trigger condition is reached, the flow rate of sodium hydroxide solution is reduced and the loop is switched. S4. Free ammonia and sulfuric acid solution are fed into a preset salt conversion unit for contact reaction to obtain ammonium sulfate product; the crystallization state is monitored in real time during the contact reaction, and the set acid distribution position of the sulfuric acid solution and the configuration parameters of the preset salt conversion unit are updated and adjusted based on the crystallization state. S5. Obtain the real-time acid production and real-time alkali production of the preset bipolar membrane electrodialysis unit, obtain the alkali consumption requirement of the preset ammonia release unit and the acid consumption requirement of the preset salt conversion unit; identify the parameter differences between the real-time acid production and real-time alkali production and the alkali consumption requirement and acid consumption requirement, and adjust the operating current of the preset bipolar membrane electrodialysis unit and the preset recovery distribution ratio of sulfuric acid solution and sodium hydroxide solution based on the parameter differences, and output the remaining acid and alkali solutions and ammonium sulfate products that did not participate in the recovery.

2. The method for co-treatment and recovery of sodium sulfate and ammonia nitrogen from vanadium industrial wastewater based on bipolar membrane according to claim 1, characterized in that, The methods for performing traffic allocation include: The upper limit of the tolerance of the ion exchange membrane to ammonium ions in the preset bipolar membrane electrodialysis unit is obtained, and this value is used as the preset migration interference threshold. The pretreated vanadium industrial wastewater is used as the pretreatment solution, and the real-time volumetric flow rate of the pretreatment solution is obtained in real time. The product of the real-time volumetric flow rate and the initial ammonia nitrogen concentration is calculated to obtain the actual ammonia nitrogen influent load value. If the actual ammonia nitrogen influent load is higher than the preset migration interference threshold, the ratio of the preset migration interference threshold to the initial ammonia nitrogen concentration is calculated, and the real-time volumetric flow rate is adjusted to meet the theoretical allowable flow rate using this ratio. The lower limit of sodium sulfate inlet flow rate is set based on the sodium sulfate concentration. When the theoretical allowable flow rate is greater than or equal to the lower limit of sodium sulfate inlet flow rate, the opening of the diversion valve is adjusted, and the pretreated solution is used as the bipolar membrane separation supply according to the theoretical allowable flow rate. The remaining pretreated solution is used as the ammonia nitrogen treatment solution.

3. The method for co-treatment and recovery of sodium sulfate and ammonia nitrogen from vanadium industrial wastewater based on a bipolar membrane according to claim 2, characterized in that, The methods for performing the splitting include: In the pre-designed bipolar membrane electrodialysis unit, bipolar membranes, anion exchange membranes, and cation exchange membranes are arranged alternately to sequentially separate acid chambers, salt chambers, and alkali chambers. The bipolar membrane separation supply solution is fed into the salt chamber, while the produced sulfuric acid solution is returned to the acid chamber as the bottom liquid of the acid chamber through the preset acid circulation pipeline, and the produced sodium hydroxide solution is returned to the alkali chamber as the bottom liquid of the alkali chamber through the preset alkali circulation pipeline. The driving DC electric field continuously dissociates water molecules in the region where the bipolar membrane is located, outputting hydrogen ions to migrate to the acid chamber and hydroxide ions to migrate to the alkali chamber. At the same time, sulfate ions in the salt chamber combine with hydrogen ions, and sodium ions combine with hydroxide ions. The operating current density of the preset bipolar membrane electrodialysis unit is matched with the inlet flow rate of the salt chamber, while sulfuric acid solution and sodium hydroxide solution are discharged from the overflow ports of the preset acid circulation pipeline and the preset alkali circulation pipeline, respectively.

4. The method for co-treatment and recovery of sodium sulfate and ammonia nitrogen from vanadium industrial wastewater based on a bipolar membrane according to claim 3, characterized in that, The method of alkalizing the ammonia nitrogen treatment solution to output free ammonia includes: The ammonia nitrogen treatment solution is input into the pH adjustment tank of the preset ammonia release unit, and the initial pH and initial liquid level of the ammonia nitrogen treatment solution are identified in real time. Calculate the pH difference between the initial pH and the preset target pH, and match it with the initial liquid level value and the preset chemical parameter table to obtain the corresponding theoretical alkali dosage. The total amount of sodium hydroxide solution, which is the same as the theoretical amount of alkali solution to be added, is grouped according to a preset step distribution ratio to obtain the graded addition amount, and the corresponding drive command sequence of each alkali addition pump is generated. The driving command sequence controls the corresponding alkali pumps at each level to inject sodium hydroxide solution into the pH adjustment tank in batches; the internal gas pressure of the gas phase collection area in the preset ammonia release unit is acquired in real time, and when the internal gas pressure reaches the preset release threshold, the gas outlet valve is controlled to output free ammonia.

5. The method for co-treatment and recovery of sodium sulfate and ammonia nitrogen from vanadium industrial wastewater based on a bipolar membrane according to claim 4, characterized in that, The methods for reducing the flow rate of sodium hydroxide solution and performing loop switching include: During the batch injection of sodium hydroxide solution, the pH value downstream of each injection point in the preset ammonia release unit is collected simultaneously to form a pH sequence, and the pressure difference data between the beginning and end of the pipeline where the injection point is located is obtained at the same time. The pressure difference increase rate is calculated within a preset reaction time window, and the standard deviation of the fluctuation of the corresponding acidity / alkalinity sequence within the preset reaction time window is also calculated. If the rate of increase of pressure difference at any injection point is higher than the preset blockage threshold, or the standard deviation of fluctuation is higher than the preset alkali content fluctuation threshold, then the pipeline where the injection point is located is determined to have reached the preset secondary deposition triggering condition. If the preset secondary deposition trigger condition is met, a flow suppression command is generated; the flow suppression command is used to control the alkali pump corresponding to the injection point to reduce its operating power; a loop switching command is generated simultaneously to control the injection valve of the injection point to close and open the corresponding circulation valve to buffer and balance the liquid in the pipeline where the injection point is located.

6. The method for co-treatment and recovery of sodium sulfate and ammonia nitrogen from vanadium industrial wastewater based on a bipolar membrane according to claim 5, characterized in that, The methods for carrying out the contact reaction include: Free ammonia is input from the bottom of the preset salt conversion unit to ensure that the free ammonia can diffuse in the gas phase from bottom to top inside the preset salt conversion unit; Simultaneously, the sulfuric acid solution is transported to the designated acid distribution position above the preset salt conversion unit, and the sulfuric acid solution is distributed downwards using the liquid distribution element in the preset salt conversion unit, forming a liquid flow from top to bottom; Free ammonia is brought into contact with the liquid flow in the mass transfer zone of the preset salt conversion unit to generate an ammonium sulfate solution; the precipitated crystals of the ammonium sulfate solution are collected at the bottom of the preset salt conversion unit to obtain the ammonium sulfate product.

7. The method for co-treatment and recovery of sodium sulfate and ammonia nitrogen from vanadium industrial wastewater based on a bipolar membrane according to claim 6, characterized in that, The methods for updating and adjusting the set acid distribution position of the sulfuric acid solution and the configuration parameters of the preset salt conversion unit include: During the contact reaction process, the pressure difference between each mass transfer region in the preset salt conversion unit is obtained, and the resistance growth gradient of the corresponding mass transfer region is calculated based on the time segment corresponding to the pressure difference. The resistance growth gradient of the corresponding mass transfer region is compared with the preset passivation threshold. If the resistance growth gradient of the mass transfer region is higher than the preset passivation threshold, it is determined that the mass transfer region has crystallization coverage, and the specific coordinates of the mass transfer region are obtained. Based on the specific coordinates, a switch command for the acid distribution is generated. Other preset acid distribution locations in the corresponding mass transfer region are obtained. The acid distribution locations that are not covered by crystals are selected and the new coordinates of these locations are used to replace the current set acid distribution location. Simultaneously, a parameter update command is generated and sent to the liquid distribution element to replace the original flow configuration parameters of the liquid distribution element with preset high flow configuration parameters.

8. The method for co-treatment and recovery of sodium sulfate and ammonia nitrogen from vanadium industrial wastewater based on a bipolar membrane according to claim 7, characterized in that, The methods for identifying the differences between real-time acid and alkali production and the parameters of alkali and acid consumption requirements include: The difference between real-time alkali production and alkali consumption demand is calculated to obtain the alkali equivalent deviation value; the difference between real-time acid production and acid consumption demand is calculated to obtain the acid equivalent deviation value; the alkali equivalent deviation value and the acid equivalent deviation value are combined to obtain the acid-alkali supply-demand deviation vector, which is used as the parameter difference.

9. The method for co-treatment and recovery of sodium sulfate and ammonia nitrogen from vanadium industrial wastewater based on a bipolar membrane according to claim 8, characterized in that, The method for adjusting the operating current of the preset bipolar membrane electrodialysis unit and the preset recovery and distribution ratio of sulfuric acid solution and sodium hydroxide solution includes: If each equivalent deviation value in the parameter difference is positive, an energy-saving command is generated and the preset bipolar membrane electrodialysis unit is controlled to reduce the operating current until any equivalent deviation value returns to zero; at the same time, another equivalent deviation value that has not returned to zero is identified, and the corresponding preset recovery allocation ratio is reduced based on the remaining amount of that value. If the alkali equivalent deviation value is negative, then the alkali equivalent deviation value is treated as the main shortage item and the acid equivalent deviation value is treated as the additional impact item; if the alkali equivalent deviation value is positive and the acid equivalent deviation value is negative, then the acid equivalent deviation value is treated as the main shortage item and the alkali equivalent deviation value is treated as the additional impact item. The compensation current increment is calculated based on the absolute value of the main shortage term. This compensation current increment is then summed with the current operating current, ensuring that it does not exceed the safety limit current, to obtain a new current control command. The expected increment of the additional influence term is calculated based on the new current control command. The expected increment is then algebraically summed with the original equivalent deviation value to obtain the total excess increment. If the total excess increment is greater than zero, the preset recovery allocation ratio corresponding to the additional impact item will be reduced simultaneously, and the solution corresponding to the reduced ratio will be discharged as a solution that has not participated in the recovery; otherwise, if the total excess increment is not greater than zero, the current preset recovery allocation ratio will be maintained.

10. A bipolar membrane-based co-treatment and recovery system for sodium sulfate and ammonia nitrogen in vanadium industrial wastewater, used to implement the bipolar membrane-based co-treatment and recovery method for sodium sulfate and ammonia nitrogen in vanadium industrial wastewater as described in any one of claims 1-9, characterized in that, include: The diversion and distribution module collects vanadium industrial wastewater and performs chemical pretreatment. It identifies the sodium sulfate concentration and initial ammonia nitrogen concentration and performs diversion and distribution to ensure that the ammonia nitrogen content in the output solution is lower than the preset migration interference threshold, thereby obtaining bipolar membrane separation supply solution and ammonia nitrogen treatment solution respectively. The liquid phase separation module inputs the bipolar membrane separation supply solution into a preset bipolar membrane electrodialysis unit to split the sodium sulfate in the bipolar membrane separation supply solution to obtain sulfuric acid solution and sodium hydroxide solution. The deposition treatment module directs the sodium hydroxide solution into the preset ammonia release unit corresponding to the ammonia nitrogen treatment solution, alkalizes the ammonia nitrogen treatment solution, and outputs free ammonia. The alkalinity and deposition status in the preset ammonia release unit are monitored in real time. When the preset secondary deposition trigger condition is reached, the flow rate of sodium hydroxide solution is reduced and the loop is switched. The crystallization conversion module feeds free ammonia and sulfuric acid solution into a preset salt conversion unit for contact reaction to obtain ammonium sulfate products. During the contact reaction, the crystallization state is monitored in real time, and the set acid distribution position of the sulfuric acid solution and the configuration parameters of the preset salt conversion unit are updated and adjusted based on the crystallization state. The product recovery module acquires the real-time acid and alkali production of the preset bipolar membrane electrodialysis unit, the alkali consumption requirements of the preset ammonia release unit, and the acid consumption requirements of the preset salt conversion unit; it identifies the parameter differences between the real-time acid and alkali production and the alkali and acid consumption requirements, and adjusts the operating current of the preset bipolar membrane electrodialysis unit and the preset recovery distribution ratio of sulfuric acid solution and sodium hydroxide solution based on these parameter differences; it outputs the remaining acid and alkali solutions and ammonium sulfate products that did not participate in the recovery; the modules are connected to each other via wired and / or wireless means.

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