An intelligent control method and system for electrodialysis membrane fouling

Abstract

The application discloses an intelligent control method and system for electrodialysis membrane pollution, and the method steps are as follows: after the equipment is operated, the electrodialysis system starts to acquire system operation parameters at a fixed time; the first acquired Ai, PDi and PCi are valued as A0, PD0 and PC0, and the initial CX is valued as 0; the unit time processing capacity of the electrodialysis system is calculated according to the salt content Ci of the water; the water inlet pump frequency and the opening degree of the pneumatic valve group are adjusted according to the ratio of the unit time processing capacity to the full load design processing capacity through the control logic; the Ai, PDi and PCi are recorded during the system operation process, and are compared with the A0, PD0 and PC0; and according to the comparison result, the start of the reverse polarity program, the start of the flushing program or the start of the cleaning program is selected to be executed. The application can reduce the chemical cleaning frequency, save the cleaning agent consumption, improve the operation stability of the electrodialysis membrane system and prolong the service life of the electrodialysis membrane.

Description

Technical Field

[0001] This invention relates to the field of electrodialysis technology, and in particular to an intelligent control method and system for electrodialysis membrane fouling. Background Technology

[0002] Electrodialysis inevitably generates organic and inorganic membrane fouling during operation. Methods to control membrane fouling generally include frequent reversal, flushing, or cleaning. Current reversal, flushing, and cleaning cycles are typically set to fixed intervals, usually based on experience or subjective judgment by on-site operators based on operating conditions and parameters. However, these methods do not address how to implement automatic flushing functions, let alone how to automatically identify reversal, flushing, or cleaning operations. Furthermore, because wastewater treatment sites generally have complex influent conditions with significant fluctuations in water quality and quantity, if the electrodialysis treatment capacity is fixed, overloading under poor water quality conditions can lead to rapid membrane fouling. Conversely, under better water quality conditions, the faster treatment process can easily cause water polarization, further increasing the probability of membrane fouling.

[0003] The reversal program of existing electrodialysis systems is generally controlled by timer. A fixed reversal time is set in advance, and the reversal program is automatically started when the equipment runs for the set time. However, in reality, too frequent reversal will increase operating energy consumption and reduce treatment efficiency; if the reversal interval is too long, the membrane will operate under fouling conditions, resulting in more stubborn membrane fouling, damaging the membrane, and making it difficult to restore the membrane performance.

[0004] Flushing and cleaning procedures are generally determined by the experience of operators to determine when flushing or cleaning is necessary. On-site cleaning cycles are typically 15–30 days per cycle, while flushing cycles are typically 2–6 hours per cycle. Excessive flushing leads to increased energy consumption, dilutes the concentrate in the pipelines with flushing water, and affects recovery rates. Conversely, excessively long flushing intervals can cause membranes to operate under contaminated conditions, especially since some surface contaminants that could be removed by flushing can become embedded in the membrane over time, causing irreversible fouling. Too frequent cleaning can disrupt the interconnected operation of systems on-site, increase the amount of cleaning agents used, and thus raise operating costs. However, excessively long cleaning cycles can exacerbate membrane fouling and cause irreversible damage to membrane performance.

[0005] Because assembling electrodialysis membrane stacks is difficult, once the number of membrane sheets is fixed, it's hard to adjust them on-site unless the equipment is returned to the factory for maintenance. Wastewater treatment plant influent water quality and quantity fluctuate significantly, making it difficult to match these quantities by adjusting the membrane sheets. In poor water quality conditions, overloading can lead to rapid membrane fouling. Conversely, in better water quality conditions, the faster treatment process can cause water polarization, also increasing the probability of membrane fouling. Therefore, controlling the amount of water entering the electrodialysis membrane stack through theoretical calculations and automated adjustments based on actual water quality conditions is crucial for controlling membrane fouling.

[0006] Different electrodialysis membrane stacks treat different wastewaters, with varying degrees and types of fouling. It is impossible to accurately judge the operating status of the membrane stack and the recovery of membrane fouling after flushing or cleaning based on empirical values. Summary of the Invention

[0007] Purpose of the invention: The purpose of this invention is to provide an intelligent control method and system for electrodialysis membrane fouling, which can automatically determine the fouling status of the membrane, improve the operational stability of the electrodialysis membrane system, and extend the service life of the electrodialysis membrane.

[0008] Technical solution: A smart control method for electrodialysis membrane fouling, comprising the following steps:

[0009] S1, After the equipment is running, the electrodialysis system starts timing and acquiring system operating parameters;

[0010] S2, assign the values ​​A0, PD0, and PC0 to the first obtained Ai, PDi, and PCi, and assign the initial value 0 to CX;

[0011] S3, calculate the processing capacity per unit time of the electrodialysis system based on the salinity Ci of the influent;

[0012] S4, through control logic, adjusts the frequency of the inlet pump and the opening of the pneumatic valve group according to the ratio of the unit time processing capacity to the full load design processing capacity;

[0013] S5 continuously records Ai, PDi, and PCi during system operation and compares them with A0, PD0, and PC0:

[0014] When PDi ≥ 1.2PD0 or PCi ≥ 1.2PC0, the polarity reversal procedure is started. After the polarity reversal procedure is completed, the operation continues.

[0015] If the conditions PDi < 1.2PD0 or PCi < 1.2PC0 are not met, continue running;

[0016] When Ai≤0.7A0, start the flushing procedure.

[0017] Furthermore, the system operating parameters obtained include: influent salinity Ci, current Ai, freshwater pressure difference PDi, and concentrate pressure difference PCi.

[0018] Furthermore, CX=0 or 1 indicates the flushing status: CX=0 means no flushing, and CX=1 means flushing.

[0019] Furthermore, the expression for the processing volume per unit time is as follows:

[0020]

[0021] Among them, the membrane area, current efficiency, and current density are fixed parameters; Cout is a preset value; and F is the Faraday constant.

[0022] Furthermore, after rinsing, the current is restored to the initial A0 value or to Ai≥0.75A0;

[0023] If the current cannot be restored to Ai≥0.75A0, start the cleaning program; after cleaning, observe the Ai value again. If it is restored to Ai≥0.75A0, set CX to 0, turn on the power, and repeat steps S1-S5.

[0024] If the Ai value cannot be restored to Ai≥0.75A0 after cleaning, replace the membrane.

[0025] An intelligent control system for electrodialysis membrane fouling, executing the aforementioned intelligent control method, includes a PLC control system, a feed pump, a DC power supply, a pneumatic valve assembly, and a differential pressure transmitter assembly. The PLC control system controls the intelligent operation of the feed pump, DC power supply, pneumatic valve assembly, and differential pressure transmitter assembly. The feed pump adjusts its frequency according to program instructions. The DC power supply is used to supply power and read current. The pneumatic valve assembly adjusts its opening degree according to program instructions. The differential pressure transmitter assembly is used to read the freshwater differential pressure PDi and the concentrate differential pressure PCi.

[0026] Compared with the prior art, the significant advantages of this invention are as follows:

[0027] This invention utilizes assembly control logic stored on a logical storage medium, relying entirely on intelligent programs to automatically determine the membrane fouling status based on actual water quality and take corresponding solutions. It requires no manual operation, which can slow down the rate of membrane fouling during the operation of the electrodialysis system, reduce the frequency of chemical cleaning, save on cleaning agent consumption, improve the operational stability of the electrodialysis membrane system, and extend the service life of the electrodialysis membrane. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the control logic of the PLC system of the present invention;

[0029] Figure 2This is a schematic diagram of the intelligent control system of the present invention. Detailed Implementation

[0030] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0031] The technical terms used in this embodiment are as follows:

[0032] Electrodialysis (ED): Electrodialysis refers to the phenomenon where charged solute particles (such as ions) in a solution migrate through a membrane under the influence of an electric field. The technique of purifying and separating substances using electrodialysis is called electrodialysis.

[0033] Reverse electrode electrodialysis (EDR): Based on electrodialysis, this operation involves automatically switching the electrode polarity and simultaneously changing the flow direction of concentrate and desalinate water. This operation prevents membrane fouling caused by concentration polarization on the membrane surface, reduces the adhesion and accumulation of charged colloids or bacterial flocs on the membrane surface, provides operational stability for wastewater treatment using electrodialysis, and avoids or reduces the need for adding chemicals such as acids or scale inhibitors, thus lowering operating costs.

[0034] Electrodialysis membranes: Electrodialysis membranes are natural or artificial semi-permeable membranes that allow ions to pass through but not larger colloidal particles. They are divided into two categories: non-selective membranes and selective membranes. Non-selective membranes allow both anions and cations to pass through, making them ineffective at removing ions from aqueous solutions. Currently, selective membranes, also known as ion exchange membranes, are widely used in industry. Ion exchange membranes are further divided into anion exchange membranes and cation exchange membranes. Anion exchange membranes allow only anions to pass through, while cation exchange membranes allow only cations to pass through.

[0035] Rinsing: A method of restoring membrane performance by flushing the membrane surface with water at appropriate pressure and high flow rate. This removes pollutants and deposits that have adhered to the membrane surface in a short period of time.

[0036] like Figure 1As shown, an intelligent control method for electrodialysis membrane fouling is implemented by writing the intelligent control method into a logic storage medium. The method includes the following steps: Based on the influent water quality, controlling the frequency of the influent pump and the opening degree of the start-up valve group to regulate the system's throughput; periodically acquiring system operating parameters: influent salinity Ci, current Ai, freshwater pressure difference PDi, and concentrate pressure difference PCi, and assigning the initially acquired Ai, PDi, and PCi values ​​to A0, PD0, and PC0; automatically determining the start of the polarity reversal procedure by comparing PDi and PCi with PD0 and PC0; initiating the flushing procedure when comparing Ai with A0; and automatically determining the effectiveness of the flushing and whether a cleaning procedure is needed based on the Ai value after flushing. The program also automatically records the flushing status. Repeat the above steps without manual operation to ensure that the electrodialysis system, under intelligent control, automatically assesses membrane fouling based on actual water quality and takes corresponding measures: adjusting the treatment capacity, initiating polarity reversal, flushing, and cleaning programs to mitigate membrane fouling. This overcomes the drawbacks of existing electrodialysis systems that rely on manual judgment and experience-based cleaning cycles. Detailed implementation steps are as follows:

[0037] Step 1: After the equipment is running, turn on the power and the system will start acquiring system operating parameters at regular intervals: influent salinity Ci, current Ai, freshwater pressure difference PDi, and concentrated water pressure difference PCi.

[0038] Step 2: The system assigns the values ​​A0, PD0, and PC0 to the first obtained Ai, PDi, and PCi, and initially assigns the value 0 to the flushing status CX.

[0039] Step 3: The system performs the following calculation logic based on the influent salinity Ci:

[0040]

[0041] In the above calculation logic: membrane area, current efficiency, and current density are fixed parameters; Cout is a preset value, set according to the standards achieved by wastewater treatment; F is the Faraday constant.

[0042] Step 4: After calculating the processing capacity per unit time based on the calculation logic in Step 3, the frequency of the inlet pump and the opening degree of the pneumatic valve group are adjusted by the control logic according to the ratio of the processing capacity per unit time to the full-load design processing capacity.

[0043] Step 5: During system operation, Ai, PDi, and PCi are continuously recorded and compared with A0, PD0, and PC0, and the following calculation logic is performed:

[0044] When PDi ≥ 1.2PD0 or PCi ≥ 1.2PC0, the polarity reversal procedure is started. After the polarity reversal procedure is completed, the operation continues.

[0045] If the conditions PDi < 1.2PD0 or PCi < 1.2PC0 are not met, continue running;

[0046] When Ai ≤ 0.7A0, initiate the rinsing procedure. After rinsing, the current will recover somewhat due to reduced membrane fouling, returning to the initial A0 value or to Ai ≥ 0.75A0. However, after prolonged operation, some stubborn fouling embedded inside the membrane cannot be removed by rinsing. Even after multiple rinsings, the current recovery effect is still not significant. If the Ai value recovery is unsatisfactory, i.e., it cannot recover to Ai ≥ 0.75A0, initiate the cleaning procedure. After cleaning, observe the Ai value again. If it recovers to Ai ≥ 0.75A0, set CX to 0, turn on the power, and repeat steps 1-5. If, after cleaning, the Ai value cannot recover to Ai ≥ 0.75A0, consider replacing the membrane.

[0047] In the automatic control logic diagram, CX = 0 or 1 is used to determine the flushing status. CX = 0 means no flushing and CX = 1 means flushing. The initial value of CX is 0.

[0048] After performing the flushing procedure, it is not necessary to reinitialize A0, PD0, PC0, and CX. However, after performing the polarity reversal procedure and the cleaning procedure, it is necessary to reinitialize A0, PD0, PC0, and CX.

[0049] like Figure 2 As shown in this embodiment, an intelligent control system for electrodialysis membrane fouling includes a PLC control system, a feed pump, a DC power supply, a pneumatic valve assembly, and a differential pressure transmitter assembly. The PLC control system controls the intelligent operation of each device, including the feed pump, DC power supply, pneumatic valve assembly, and differential pressure transmitter assembly. The feed pump can adjust its frequency according to program instructions, the DC power supply is used to supply power and read the current, the pneumatic valve assembly can adjust its opening degree according to program instructions, and the differential pressure transmitter assembly reads the differential pressure.

Claims

1. A smart control method for electrodialysis membrane fouling, characterized in that, The steps include the following: S1. After the equipment is running, the electrodialysis system starts timing and acquiring system operating parameters; the system operating parameters include: influent salinity Ci, current Ai, freshwater side pressure difference PDi, and concentrate side pressure difference PCi. S2, assign values ​​A0, PD0, and PC0 to the first obtained Ai, PDi, and PCi, and initially assign 0 to CX; where CX=0 or 1 is used to determine the flushing status: CX=0 means no flushing, and CX=1 means flushing; S3, calculate the throughput of the electrodialysis system per unit time based on the influent salinity Ci; the expression for the throughput per unit time is as follows: ， Among them, the membrane area, current efficiency, and current density are fixed parameters; Cout is a preset value; and F is the Faraday constant. S4, through control logic, adjusts the frequency of the inlet pump and the opening of the pneumatic valve group according to the ratio of the unit time processing capacity to the full load design processing capacity; S5 continuously records Ai, PDi, and PCi during system operation and compares them with A0, PD0, and PC0: When PDi ≥ 1.2PD0 or PCi ≥ 1.2PC0, the polarity reversal procedure is started. After the polarity reversal procedure is completed, the operation continues. If the conditions PDi < 1.2PD0 or PCi < 1.2PC0 are not met, continue running; When Ai≤0.7A0, start the flushing procedure.

2. The intelligent control method for electrodialysis membrane fouling according to claim 1, characterized in that, After rinsing, the current returns to the initial A0 value or returns to Ai≥0.75A0; If the current cannot be restored to Ai≥0.75A0, start the cleaning program; after cleaning, observe the Ai value again. If it is restored to Ai≥0.75A0, set CX to 0, turn on the power, and repeat steps S1-S5. If the Ai value cannot be restored to Ai≥0.75A0 after cleaning, replace the membrane.

3. An intelligent control system for electrodialysis membrane fouling, executing the intelligent control method according to any one of claims 1-2, characterized in that, It includes a PLC control system, an inlet pump, a DC power supply, a pneumatic valve assembly, and a differential pressure transmitter assembly. The PLC control system controls the intelligent operation of the inlet pump, the DC power supply, the pneumatic valve assembly, and the differential pressure transmitter assembly. The inlet pump adjusts its frequency according to program instructions. The DC power supply is used to supply power and read current. The pneumatic valve assembly adjusts its opening degree according to program instructions. The differential pressure transmitter assembly is used to read the freshwater side differential pressure PDi and the concentrate side differential pressure PCi.

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