Precise control method and system for pH of light salt brine discharged from single cell in multiple groups of electrolytic cells

Abstract

The invention provides a method and a system for accurately controlling the pH value of single-tank outlet light salt brine in multiple groups of electrolytic tanks, comprising multiple groups of electrolytic tanks, a tank inlet brine branch pipe is connected with a diluted hydrochloric acid branch pipe, the diluted hydrochloric acid branch pipe is provided with a diluted hydrochloric acid flowmeter and a diluted hydrochloric acid regulating valve, and the tank outlet light salt brine branch pipe is connected with a light salt brine sampling branch pipe. Each light salt brine sampling branch pipe is provided with a light salt brine sampling program control valve and a simulation assignment module, the light salt brine sampling branch pipes are connected with a light salt brine sampling header pipe, and the light salt brine sampling header pipe is provided with a sampling adjusting valve, a sampling flow meter and a pH meter; the diluted hydrochloric acid flow meter, the diluted hydrochloric acid adjusting valve, the light salt brine sampling program control valve, the sampling adjusting valve, the sampling flow meter and the pH meter are all connected into a DCS system, and the diluted hydrochloric acid adjusting valve adjusts the opening degree according to the detection value of the pH meter. Precise adjustment and control of pH of light salt brine discharged from each single cell in multiple groups of electrolytic cells are realized through a pH meter and a control loop thereof, the anode efficiency and the quality of a liquid caustic soda product are improved, and the production stability is improved.

Description

Technical Field

[0001] This application relates to the field of ion-exchange membrane electrolysis technology, and more specifically, to a method and system for precise pH control of the brine output from a single cell in a multi-cell electrolysis process. Background Technology

[0002] During operation, the ion-exchange membrane electrolyzer in a caustic soda plant is susceptible to pinholes due to factors such as raw material quality, pressure, temperature, and load. At this time, hydroxide ions from the cathode side migrate back to the anode chamber through these pinholes, causing an increase in the pH value of the anode chamber. This leads to corrosion and detachment of the anode coating by the high-temperature sodium hydroxide solution, and even perforation of the ion-exchange membrane, significantly reducing the lifespan of the electrode and the ion-exchange membrane. Simultaneously, Cl2 reacts with the migrating OH-... - Side reactions occur, causing a decrease in the purity of Cl2, an increase in the oxygen content in chlorine, and an increase in the content of hypochlorite and chlorate in the anolyte, which corrodes the anode gasket.

[0003] Adding hydrochloric acid to the anode chamber of the electrolytic cell can neutralize the OH groups that migrate from the cathode chamber to the anode chamber. - This can reduce the solubility of Cl2 in brine, prevent the side reaction between chlorine and alkali in the anode chamber of the electrolytic cell, and effectively reduce ClO. - Dilute acid helps protect the lifespan of the electrolyzer and ion-exchange membrane, reducing equipment maintenance costs and safety risks. However, insufficient or excessive addition of dilute acid can cause serious and irreversible damage to the electrolyzer and ion-exchange membrane. Typically, the pH value of the brine discharged from the electrolyzer should be controlled between 3.0 and 3.5 during production. Therefore, extremely high requirements are placed on the stability of the acid flow rate and the accuracy of pH control in the electrolyzer.

[0004] Chinese invention patent CN106065484B, entitled "An Acid Addition Device and Method for the Anode of an Ion-Exchange Membrane Electrolyte," discloses that the device includes a dilute hydrochloric acid storage tank, a hydrochloric acid transfer pump, a brine circulation tank, a brine transfer pump, a high-level brine tank, and a pipeline mixer. One stream of dilute hydrochloric acid is added to the pipeline mixer on the brine inlet main pipe at the outlet of the high-level brine tank via a pH control loop, and then flows into the anode chamber of the ion-exchange membrane electrolyzer. Another stream of dilute hydrochloric acid can be directly sent to the anode inlet of the ion-exchange membrane electrolyzer to adjust the pH value of the outlet brine. Typically, a caustic soda plant consists of multiple electrolyzers. This technology requires two-stage acid addition and two pH control loops for each electrolyzer's inlet and outlet brine, controlling both the pH of the inlet brine main pipe and the pH of the outlet brine, resulting in numerous control loops. This makes it difficult to simultaneously adjust and control the pH of the outlet brine from multiple ion-exchange membrane electrolyzers, leading to high investment, frequent operation, and high maintenance costs. Summary of the Invention

[0005] The purpose of this application is to provide a method and system for precise pH control of the brine output from a single cell in a multi-group electrolytic cell, enabling the detection and adjustment control of the pH value of the brine output from each single cell in a multi-group electrolytic cell of a single electrolytic device, achieving self-protection and process safety of the electrolytic cell, with a simple control loop, saving investment and facilitating maintenance.

[0006] The embodiments of this application are implemented as follows:

[0007] This embodiment provides a precise pH control system for the brine outlet of a single cell in a multi-group electrolytic cell system. The system includes multiple groups of electrolytic cells arranged in parallel. The anolyte inlet of each group of electrolytic cells is connected to a brine inlet branch pipe, and the anolyte outlet of each group of electrolytic cells is connected to a brine outlet branch pipe. Each brine inlet branch pipe is connected to a dilute hydrochloric acid branch pipe, and each dilute hydrochloric acid branch pipe is sequentially equipped with a dilute hydrochloric acid flow meter and a dilute hydrochloric acid regulating valve. The first end of each dilute hydrochloric acid branch pipe is connected to a dilute hydrochloric acid main pipe. One end of the dilute hydrochloric acid main pipe is connected to the material outlet of a dilute hydrochloric acid storage tank, and the other end of the dilute hydrochloric acid main pipe is connected to the circulation inlet of the dilute hydrochloric acid storage tank to form a circulation loop. A dilute hydrochloric acid pump is installed on the dilute hydrochloric acid main pipe.

[0008] Each saline outlet branch pipe is connected to a saline sampling branch pipe. Each saline sampling branch pipe is equipped with a saline sampling programmable valve and a simulation assignment module. The saline sampling branch pipes are all connected to the head end of the saline sampling main pipe. The saline sampling main pipe is equipped with a sampling regulating valve, a sampling flow meter and a pH meter in sequence along the liquid flow direction. The end of the saline sampling main pipe is connected to the anolyte discharge tank.

[0009] The dilute hydrochloric acid flow meter, dilute hydrochloric acid regulating valve, saline sampling programmable valve, sampling regulating valve, sampling flow meter, and pH meter are all connected to the DCS system. The sampling regulating valve is controlled by the sampling flow meter loop; the dilute hydrochloric acid regulating valve and the analog assignment module are controlled by the pH meter loop. The dilute hydrochloric acid regulating valve can adjust its opening degree according to the pH meter reading.

[0010] Furthermore, it also includes a dilute hydrochloric acid preparation component, which includes a high-purity hydrochloric acid pipeline and a pure water pipeline. The high-purity hydrochloric acid pipeline is equipped with a high-purity hydrochloric acid regulating valve and a high-purity hydrochloric acid flow meter, and the pure water pipeline is equipped with a pure water regulating valve and a pure water flow meter. The high-purity hydrochloric acid pipeline and the pure water pipeline are connected to the inlet of a pipeline mixer, and the outlet of the pipeline mixer is connected to the material inlet of the dilute hydrochloric acid storage tank. The high-purity hydrochloric acid regulating valve, the high-purity hydrochloric acid flow meter, the pure water regulating valve, and the pure water flow meter are all connected to the DCS system and realize loop control.

[0011] Furthermore, it also includes a saline sampling temperature control component, which includes a sampling heat exchanger. The sampling heat exchanger is installed on the saline sampling main pipe and located between the sampling flow meter and the pH meter. The circulating water inlet of the sampling heat exchanger is connected to the circulating water input pipe, and the circulating water outlet of the sampling heat exchanger is connected to the circulating water tank through the circulating water output pipe. A circulating water regulating valve is installed on the circulating water input pipe. A saline thermometer is installed on the saline sampling main pipe between the sampling heat exchanger and the pH meter. Both the circulating water regulating valve and the saline thermometer are connected to the DCS system and realize loop control.

[0012] Furthermore, both the circulating water inlet pipe and the circulating water outlet pipe are equipped with circulating water manual valves, with the circulating water manual valve of the circulating water inlet pipe located on both sides of the circulating water regulating valve.

[0013] Furthermore, both sides of the brine sampling manifold of the sampling heat exchanger are equipped with brine heat exchange manual valves.

[0014] Furthermore, the dilute hydrochloric acid main pipe is also equipped with a pressure transmitter and a pressure regulating valve. Both the pressure transmitter and the pressure regulating valve are connected to the DCS system and realize loop control.

[0015] Furthermore, a dilute hydrochloric acid check valve is installed after the dilute hydrochloric acid pump in the dilute hydrochloric acid main pipe, and a dilute hydrochloric acid manual valve is also installed in the dilute hydrochloric acid main pipe, which is located in front of the dilute hydrochloric acid branch pipe connected to the dilute hydrochloric acid main pipe.

[0016] This embodiment also provides a method for precise pH control of single-tank effluent brine in multiple electrolytic cells, employing the aforementioned precise pH control system for single-tank effluent brine in multiple electrolytic cells. This method includes a manual mode and an automatic mode.

[0017] In manual mode, when the brine sampling control valve of one electrolyzer is opened, the DCS program will close the brine sampling control valves of the other electrolyzers. The pH meter reading on the corresponding electrolyzer will be equal to the brine sampling value. When the pH meter detects that the pH of the brine leaving the electrolyzer deviates from the standard value, the connected DCS system will control the opening of the corresponding dilute hydrochloric acid regulating valve to ensure that the pH of the brine at the electrolyzer outlet is controlled between 3.0 and 3.5. When the pH of the brine leaving the electrolyzer is less than or equal to 2.5, the dilute hydrochloric acid regulating valve will automatically close to stop adding acid to the electrolyzer.

[0018] In automatic mode, the DCS program uses a current sensor connected to the electrolytic cell to detect and determine the current in real time. # Does the electrolytic cell operating current meet the condition of reaching the set threshold? If the condition is not met, proceed to step 2. # Electrolytic cell, open 1 if conditions are met. # Electrolytic cell brine sampling control valve, 1 #The brine from the electrolytic cell enters the pH detection and analysis stage and a countdown timer (T1) is initiated. After a certain time (T2), the pH meter reading is assigned to step 1. # Electrolytic cell, at this time 1 # The dilute hydrochloric acid regulating valve of the electrolytic cell switched from holding to automatic adjustment and control. The pH output setting of the dilute hydrochloric acid regulating valve was 3.0–3.5, and the pH of the outlet brine was also 3.0–3.5. After the DCS timer was reset, 1 # The electrolytic cell brine sampling control valve is closed, and the dilute hydrochloric acid regulating valve position changes from automatic to hold, ending step 1. # pH detection and adjustment control of the electrolyzer; the DCS program proceeds to the next step, continuing to determine step 2. # Electrolytic cell operating current conditions; if not met, then determine step 3. # The operating current conditions of the electrolytic cells are then determined, and so on, until switching to the last electrolytic cell, and then starting again from 1. # The electrolytic cell judgment and program operation cycle repeatedly until the operator switches from automatic to manual, at which point the automatic program enters the initialization phase.

[0019] Compared with the prior art, the embodiments of this application have at least the following advantages or beneficial effects:

[0020] 1. This application provides a precise pH control system for the brine output from individual cells in multiple electrolytic cells. Through a single pH meter and its control loop, the pH of the brine output from each individual cell in multiple electrolytic cells can be precisely adjusted and controlled between 3.0 and 3.5. This saves investment, facilitates maintenance, further reduces manual operation intensity, and improves production stability. It also effectively suppresses side reactions in the anode chamber of the electrolytic cell and neutralizes OH- ions migrating back from the cathode chamber. - This reduces the pH value, chlorate and sodium hypochlorite content of the brine discharged from the electrolytic cell, effectively protecting the electrolytic cell and ion exchange membrane. It also reduces the oxygen content in the chlorine, improving anode efficiency and the quality of the liquid alkali product.

[0021] 2. The pH meter reading is assigned to the current detection object through the analog assignment module, marking the current pH state of the current detection object. This avoids parameter confusion when multiple electrolytic cells share the detection equipment, and realizes "group identification, independent control, and state memory", ensuring the accuracy and reliability of the entire acid addition control system.

[0022] 3. The pressure transmitter and pressure regulating valve on the dilute hydrochloric acid main pipe are both connected to the DCS system and controlled in a loop. When the pressure of the dilute hydrochloric acid main pipe is too high or too low, adjusting the flow rate of the dilute hydrochloric acid storage tank can maintain the pressure of the dilute hydrochloric acid main pipe, avoid the impact of pressure fluctuation on the acid addition accuracy, and improve the system stability.

[0023] 4. Through a closed loop of "automatic / manual mode selection → sequential current determination → sampling timing → pH feedback adjustment → cycle / end determination", the pH of the brine discharged from multiple electrolytic cells is automatically detected and precisely controlled, adapting to the needs of continuous industrial operation scenarios.

[0024] 5. The dilute hydrochloric acid preparation unit can automatically prepare dilute hydrochloric acid according to needs and ensure a stable concentration of dilute hydrochloric acid. The brine sampling temperature control unit is used to regulate and control the temperature of the brine exiting the heat exchanger to ensure that pH detection is not affected by temperature. Attached Figure Description

[0025] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 This is an overall schematic diagram of the pH precision control system for the single-cell outlet brine in multiple electrolytic cells in this application embodiment;

[0027] Figure 2 This is a schematic diagram of the saline water sampling temperature control component in an embodiment of this application;

[0028] Figure 3 This is a control flowchart of a method for precisely controlling the pH of the brine output from a single cell in multiple electrolytic cells in this application embodiment.

[0029] Icons: 11-Electrolytic cell, 12-Inlet brine branch pipe, 13-Outlet dilute brine branch pipe, 14-Dilute brine sampling branch pipe, 141-Dilute brine sampling programmable valve, 142-Analog assignment module, 15-Dilute brine sampling main pipe, 151-Sampling regulating valve, 152-Sampling flow meter, 153-pH meter, 21-Dilute hydrochloric acid branch pipe, 211-Dilute hydrochloric acid flow meter, 212-Dilute hydrochloric acid regulating valve, 22-Dilute hydrochloric acid main pipe, 221-Dilute hydrochloric acid pump, 222-Pressure transmitter, 223-Pressure regulating valve, 224-Dilute hydrochloric acid check valve, 225-Dilute hydrochloric acid manual valve, 3-Dilute hydrochloric acid preparation unit Components: 31-High-purity hydrochloric acid pipeline, 311-High-purity hydrochloric acid regulating valve, 312-High-purity hydrochloric acid flow meter, 32-Pure water pipeline, 321-Pure water regulating valve, 322-Pure water flow meter, 33-Pipeline mixer, 4-Dilute brine sampling temperature control component, 41-Sampling heat exchanger, 411-Circulating water input pipe, 4111-Circulating water regulating valve, 412-Circulating water output pipe, 413-Dilute brine thermometer, 414-Circulating water manual valve, 415-Dilute brine heat exchange manual valve, 5-Dilute hydrochloric acid storage tank, 51-Circulation inlet, 6-Anode liquid discharge tank, 7-Circulating water pool, 8-Current sensor. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, 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. The components of the embodiments of this application described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0031] Therefore, the following detailed description of the embodiments of this application provided in the accompanying drawings is not intended to limit the scope of the claimed application, but merely to illustrate selected embodiments of the application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

[0032] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0033] In the description of the embodiments of this application, "a plurality of" means at least two.

[0034] In the description of the embodiments of this application, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0035] Example

[0036] Please refer to Figure 1 , Figure 2 This embodiment discloses a precise pH control system for the brine output from a single cell in multiple electrolytic cells. This system is used for precise adjustment and control of the pH of the brine output from each cell in multiple electrolytic cells, ensuring electrolysis efficiency and ion-exchange membrane lifespan. It includes multiple sets of parallel-distributed ion-exchange membrane electrolytic cells 11. The anolyte inlet of each set of electrolytic cells 11 is connected to an inlet brine branch pipe 12, and the anolyte outlet is connected to an outlet brine branch pipe 13. Each inlet brine branch pipe 12 is connected to a dilute hydrochloric acid branch pipe 21. Each dilute hydrochloric acid branch pipe 21 is equipped with a dilute hydrochloric acid flow meter 211 and a dilute hydrochloric acid regulating valve 212. The first end of each dilute hydrochloric acid branch pipe 21 is connected to a dilute hydrochloric acid main pipe 22. One end of the dilute hydrochloric acid main pipe 22 is connected to the material outlet of a dilute hydrochloric acid storage tank 5, and the other end is connected to the circulation inlet 51 of the dilute hydrochloric acid storage tank 5 to form a circulation loop. The dilute hydrochloric acid storage tank 5 is made of fiberglass and is a vertical cylindrical storage tank. A dilute hydrochloric acid main pipe 22 is sequentially equipped with a dilute hydrochloric acid pump 221, a pressure transmitter 222, and a pressure regulating valve 223 along the liquid flow direction. The connection between the dilute hydrochloric acid branch pipe 21 and the dilute hydrochloric acid main pipe 22 is located between the dilute hydrochloric acid pump 221 and the pressure transmitter 222. A dilute hydrochloric acid check valve 224 is installed after the dilute hydrochloric acid pump 221 on the dilute hydrochloric acid main pipe 22 to prevent backflow of dilute hydrochloric acid and protect the dilute hydrochloric acid pump 221. The dilute hydrochloric acid main pipe 22 is also equipped with a dilute hydrochloric acid manual valve 225, which is located at the front end of the first dilute hydrochloric acid branch pipe 21 for easy disconnection of the pipeline as needed. With this structure, the dilute hydrochloric acid pump 221 pumps 17% of the dilute hydrochloric acid from the dilute hydrochloric acid storage tank 5 into the dilute hydrochloric acid main pipe 22. Part of it enters the inlet brine branch pipe 12 through the dilute hydrochloric acid branch pipe 21, and after passing through the dilute hydrochloric acid regulating valve 212, it merges with each inlet brine branch pipe 12 and enters the anode chamber of the electrolytic cell 11. The remainder circulates back to the dilute hydrochloric acid storage tank 5 through the dilute hydrochloric acid main pipe 22, which can avoid the retention of the medium in the pipeline. The dilute hydrochloric acid flow meter 211 is used for display and measurement.

[0037] Each saline outlet branch pipe 13 is connected to a saline sampling branch pipe 14, which flows into the anolyte discharge tank 6 (standard setup, specific connection method omitted in attached diagram). Each saline sampling branch pipe 14 is equipped with a saline sampling programmable valve 141 and a simulation assignment module 142. Each saline sampling branch pipe 14 is connected to the beginning of the saline sampling main pipe 15. The saline sampling main pipe 15 is equipped with a sampling regulating valve 151, a sampling flow meter 152, and a pH meter 153 in sequence along the liquid flow direction. The end of the saline sampling main pipe 15 is connected to the anolyte discharge tank 6.

[0038] The dilute hydrochloric acid flow meter 211, dilute hydrochloric acid regulating valve 212, saline solution sampling control valve 141, sampling regulating valve 151, sampling flow meter 152, and pH meter 153 are all connected to the DCS system. The loop control between sampling regulating valve 151 and sampling flow meter 152 maintains a stable sampling flow rate, preventing flow fluctuations from affecting pH detection accuracy. The loop control between dilute hydrochloric acid regulating valve 212, analog assignment module 142, and pH meter 153, according to the DCS system control logic, adjusts the opening of the corresponding dilute hydrochloric acid regulating valve 212 based on the pH meter 153 reading when acid addition to a single tank requires adjustment. In this embodiment, analog assignment module 142 is a virtual function module within the DCS system. DCS system, or Distributed Control System, is an automated control system that uses a computer as its core and integrates communication, control, and display technologies. This application uses a DCS system combined with control algorithms to achieve decentralized control and centralized management, enabling precise monitoring and efficient management of the production process. The DCS system is installed in a cabinet and has a power supply module and a communication module. The specific structure and connection method of the DCS system are omitted in the attached drawings, which does not affect the implementation of the overall technical solution.

[0039] This embodiment provides a precise pH control system for the brine outlet of a single electrolytic cell in multiple electrolytic cells. When the brine outlet enters the brine sampling main pipe 15 via the brine sampling branch pipe 14, the brine sampling programmable valve 141 controls the single-group sampling switch. That is, the corresponding sampling programmable valve 141 is opened when the brine outlet of an electrolytic cell 11 needs to be tested. When the pH meter 153 detects that the pH of the brine outlet deviates from the standard value, the connected DCS system controls the opening of the dilute hydrochloric acid regulating valve 212 to ensure that the pH of the brine outlet of the electrolytic cell 11 is controlled between 3.0 and 3.5. Through the DCS system's time-sharing control of the opening and closing of the sampling programmable valve and the control loop of the dilute hydrochloric acid regulating valve 212, when the pH of the brine outlet is less than or equal to 2.5, the dilute hydrochloric acid regulating valve 212 automatically closes to stop the acid addition to the electrolytic cell 11, thus realizing the detection and regulation control of the pH of the brine outlet of each electrolytic cell 11 in multiple electrolytic cells 11. The analog assignment module 142 assigns a value displayed by the pH meter 153, marking the current pH state of the object being detected. This avoids parameter confusion that can occur when multiple electrolytic cells share the same detection equipment, achieving "group identification, independent control, and state memory," thus ensuring the accuracy and reliability of the entire acid addition control system. Simultaneously, the pressure transmitter 222 and pressure regulating valve 223 are both connected to the DCS system and controlled in a loop. When the pressure in the dilute hydrochloric acid main pipe 22 is too high or too low, adjusting the flow rate of the dilute hydrochloric acid storage tank 5 can maintain a stable pressure in the dilute hydrochloric acid main pipe 22, preventing pressure fluctuations from affecting the acid addition accuracy and improving system stability.

[0040] The system also includes a saline sampling temperature control component 4, which includes a sampling heat exchanger 41. The sampling heat exchanger 41 is installed on the saline sampling main pipe 15 and located between the sampling flow meter 152 and the pH meter 153. The circulating water inlet of the sampling heat exchanger 41 is connected to the circulating water input pipe 411, and the circulating water outlet of the sampling heat exchanger 41 is connected to the circulating water tank 7 through the circulating water output pipe 412. A circulating water regulating valve 4111 is installed on the circulating water input pipe 411. A saline thermometer 413 is installed between the sampling heat exchanger 41 and the pH meter 153 on the saline sampling main pipe 15. Both the circulating water regulating valve 4111 and the saline thermometer 413 are connected to the DCS system and achieve loop control. The sampling heat exchanger 41 works in conjunction with the circulating water system, and the saline thermometer 413 detects the sampling temperature and controls the sampling temperature through the circulating water regulating valve 4111. By adjusting the circulating water flow, the sampling temperature is controlled to be no higher than 45℃, eliminating the interference of temperature on the detection accuracy of the pH meter 153 and providing a reliable basis for acid addition control. The circulating water inlet pipe 411 is equipped with a circulating water regulating valve 4111 and circulating water manual valves 414 on both sides. The circulating water outlet pipe 412 is equipped with a circulating water manual valve 414. The brine sampling main pipe 15 on both sides of the sampling heat exchanger 41 is equipped with a brine heat exchange manual valve 415, which facilitates the disconnection of the pipeline as needed.

[0041] The system also includes a dilute hydrochloric acid preparation component 3, which consists of a high-purity hydrochloric acid pipeline 31, a pure water pipeline 32, and a pipeline mixer 33. The high-purity hydrochloric acid pipeline 31 is equipped with a high-purity hydrochloric acid regulating valve 311 and a high-purity hydrochloric acid flow meter 312 in sequence along the liquid flow direction. The pure water pipeline 32 is equipped with a pure water regulating valve 321 and a pure water flow meter 322. Both are connected to the inlet of the pipeline mixer 33. The outlet of the pipeline mixer 33 is connected to the material inlet of the dilute hydrochloric acid storage tank 5. The high-purity hydrochloric acid regulating valve 311, the high-purity hydrochloric acid flow meter 312, the pure water regulating valve 321, and the pure water flow meter 322 are all connected to the DCS system and realize loop control. Through this design, the DCS system can automatically adjust the flow ratio of the two according to the set concentration, and after preparing 17% dilute hydrochloric acid, it enters the dilute hydrochloric acid storage tank 5, and then is sent to multiple electrolytic cells 11 by the dilute hydrochloric acid main pipe 22, reducing the dilute hydrochloric acid concentration deviation, solving the problem of large errors in manual preparation, and reducing labor intensity.

[0042] In this embodiment, the high-purity hydrochloric acid pipeline 31, the dilute hydrochloric acid main pipe 22, and the dilute hydrochloric acid branch pipe 21 are made of steel-framed PE material, the saline sampling branch pipe 14 and the saline sampling main pipe 15 are made of titanium, and the pure water pipeline 32 is made of stainless steel.

[0043] This embodiment provides a precise pH control system for the brine output from multiple electrolytic cells. Through a pH meter 153 and its control loop, the pH of the brine output from each individual cell in multiple electrolytic cells can be precisely adjusted and controlled between 3.0 and 3.5. This effectively suppresses side reactions in the anode chamber of electrolytic cell 11, neutralizes hydroxide ions migrating back from the cathode chamber, and reduces the pH, chlorate, and sodium hypochlorite content of the brine output. Currently, the chlorate content in the brine output from electrolytic cell 11 is less than 4 g / L, and the sodium hypochlorite content is less than 2 g / L. This alleviates corrosion of the electrolytic cell and gaskets, effectively protecting electrolytic cell 11 and the ion-exchange membrane. Furthermore, it reduces the oxygen content in the chlorine, improves anode efficiency and the quality of the liquid alkali product, further reduces manual operation intensity, and enhances production stability.

[0044] It should be noted that the sampling program in this embodiment includes manual and automatic modes, controlled by a DCS manual / automatic switch. In manual sampling mode: manually opening the sampling control valve of one electrolytic cell 11 will cause the program to close the remaining sampling control valves, and the pH value of the brine displayed on the corresponding electrolytic cell 11 will equal the sampled value. In automatic sampling mode: clicking the program's manual / automatic switch switches the sampling program from manual to automatic mode.

[0045] In automatic mode, one embodiment of the present invention is as follows: First, initialization is performed, all brine sampling control valves 141 are closed, and then the first step of the periodic sequential program is entered. The DCS program detects and judges the current in real time through the current sensor 8 connected to the electrolyzer. #Whether the operating current of electrolytic cell 11 meets the condition of reaching the set threshold. In this embodiment, the operating current threshold is set to 6.0 kA (operating current is a key indicator reflecting whether the electrolytic cell is in an effective operating state. When the operating current reaches the set threshold, such as 6.0 kA in this example, it indicates that the electrolytic cell is in an abnormal operating state and needs to be adjusted). # (The process involves testing electrolytic cell 11; if the conditions are not met, proceed to step 2.) # Electrolytic cell 11 (no special intervention required) # (Regular operation status of electrolytic cell 11), if the conditions are met, then open 1. # Electrolytic cell 11 brine sampling control valve 141, 1 # The brine discharged from electrolytic cell 11 enters the pH detection and analysis system and a countdown timer T1 (the detection time can be set according to production needs; in this embodiment, it is set to 120 minutes). After a certain period of time T2 (when the brine pipeline filling and stabilization processes are completed), the pH value displayed by the brine pH meter is assigned to cell 1 through the simulation assignment module 142. # Electrolytic cell 11, at this time 1 # The dilute hydrochloric acid inlet regulating valve 212 of electrolytic cell 11 has switched from a hold position to automatic adjustment and control. The pH output setting value of dilute hydrochloric acid regulating valve 212 is 3.1 (between 3.0 and 3.5). At this time, 1 # The flow meter 211 for dilute hydrochloric acid in electrolytic cell 11 shows a value of 853L, and the pH of the discharged brine is also 3.1 (between 3.0 and 3.5). Waiting for the DCS timer to be zeroed, 1 # Electrolytic cell 11, brine sampling control valve 141, program closed; inlet dilute hydrochloric acid regulating valve 212, valve position changed from automatic to hold; end 1. # Electrolyzer 11 pH detection and adjustment control. The DCS program proceeds to the next step, continuing to determine step 2. # If the operating current condition of electrolytic cell 11 is not met, then judgment 3 is made. # The operating current conditions for electrolytic cell 11 are then adjusted accordingly until the last cell is switched on, and then the process begins again from cell 1. # Electrolytic cell 11 makes judgments and runs the program, and this cycle continues until the operator switches from automatic to manual, at which point the automatic program enters the initialization phase.

[0046] like Figure 3As shown, the DCS system control logic in this embodiment includes: (1) parameter setting (such as key control parameters such as automatic sampling cycle, current threshold, timing duration T1 / T2, etc.); (2) enter mode selection and determine whether to put automatic sampling into operation: if “No” is selected, the manual sampling process is executed (the process can end or the mode can be reselected after completing a single sampling analysis); if “Yes” is selected, the automatic sampling loop control is entered. (3) Automatic sampling loop operation: according to the preset parameters (such as electrolytic cell polling order, sampling interval, etc.), the detection logic is executed on multiple groups of electrolytic cells in sequence: for the target electrolytic cell 11 of the current loop, its operating current is detected and it is determined whether the condition “>6.0KA” is met: if it is not met (current ≤6.0KA), the electrolytic cell is skipped and the next group of electrolytic cells is entered for loop judgment; if it is met (current >6.0KA), the subsequent sampling and control actions are executed. (4) Sampling and pH adjustment control: After the current condition is met: the action of "opening the brine sampling control valve 141 of the corresponding electrolytic cell 11" is triggered, and the timer T1 is started at the same time; after waiting for a period of time T2 (completing the brine pipeline filling, stabilization and other processes), pH data is collected by pH meter 153 and the value is assigned to the pH control logic of the brine outlet of the electrolytic cell; based on the pH detection value, the opening degree of the corresponding dilute hydrochloric acid regulating valve 212 is controlled in linkage to realize the pH adjustment of the brine. (5) Cycle and termination conditions: after completing the detection and adjustment of a single electrolytic cell, it is determined whether "T1 is greater than the set value and the automatic sampling mode is still in operation": if the condition is met, return to the "automatic sampling cycle operation" link and continue the next round of electrolytic cell detection; if the condition is not met (T1 is not up to standard or automatic sampling has been exited), the process ends. The core logic is as follows: through a closed loop of "automatic / manual mode selection → sequential current determination → sampling timing → pH feedback adjustment → cycle / end determination", the pH of the brine discharged from multiple electrolytic cells 11 is automatically detected and precisely controlled, adapting to the needs of continuous industrial operation scenarios.

[0047] The above are merely preferred embodiments of this application and are not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. 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.

Claims

1. A system for accurately controlling the pH of brine in a single cell of a plurality of electrolytic cells, comprising a plurality of electrolytic cells (11) arranged in parallel, an inlet of an anolyte of each electrolytic cell (11) being connected to a brine inlet branch pipe (12), an outlet of the anolyte of each electrolytic cell (11) being connected to a brine outlet branch pipe (13), and a current sensor (8) being arranged in each electrolytic cell (11), characterized in that each brine inlet branch pipe (12) is connected to a dilute hydrochloric acid branch pipe (21), each dilute hydrochloric acid branch pipe (21) being provided with a dilute hydrochloric acid flow meter (211) and a dilute hydrochloric acid regulating valve (212), and a first end of each dilute hydrochloric acid branch pipe (21) being connected to a dilute hydrochloric acid main pipe (22), one end of the dilute hydrochloric acid main pipe (22) being connected to a material outlet of a dilute hydrochloric acid storage tank (5), the other end of the dilute hydrochloric acid main pipe (22) being connected to a circulation inlet (51) of the dilute hydrochloric acid storage tank (5) to form a circulation loop, the dilute hydrochloric acid main pipe (22) being provided with a dilute hydrochloric acid pump (221), and the dilute hydrochloric acid main pipe (22) being further provided with a pressure transmitter (222) and a pressure regulating valve (223); each brine outlet branch pipe (13) is connected to a brine sampling branch pipe (14), each brine sampling branch pipe (14) being provided with a brine sampling program-controlled valve (141) and an analog assignment module (142), and each brine sampling branch pipe (14) being connected to a first end of a brine sampling main pipe (15), the brine sampling main pipe (15) being provided with a sampling regulating valve (151), a sampling flow meter (152) and a pH meter (153) in sequence along a liquid flow direction, and a last end of the brine sampling main pipe (15) being connected to an anolyte discharge tank (6); the current sensor (8), the dilute hydrochloric acid flow meter (211), the dilute hydrochloric acid regulating valve (212), the pressure transmitter (222), the pressure regulating valve (223), the brine sampling program-controlled valve (141), the sampling regulating valve (151), the sampling flow meter (152) and the pH meter (153) are connected to a DCS system, the pressure transmitter (222) and the pressure regulating valve (223) are loop-controlled, the sampling regulating valve (151) and the sampling flow meter (152) are loop-controlled, the dilute hydrochloric acid regulating valve (212), the analog assignment module (142) and the pH meter (153) are loop-controlled, and the dilute hydrochloric acid regulating valve (212) can adjust an opening degree according to a detection value of the pH meter (153). ​ ​ ​ 2. The system for accurately controlling the pH of the dilute brine discharged from a single cell of a plurality of cells according to claim 1, characterized in that: The system further comprises a dilute hydrochloric acid preparation assembly (3) including a high-purity hydrochloric acid pipeline (31) provided with a high-purity hydrochloric acid regulating valve (311) and a high-purity hydrochloric acid flowmeter (312), and a pure water pipeline (32) provided with a pure water regulating valve (321) and a pure water flowmeter (322), wherein the high-purity hydrochloric acid pipeline (31) and the pure water pipeline (32) are connected to an inlet of a pipeline mixer (33), an outlet of the pipeline mixer (33) is connected to a material inlet of the dilute hydrochloric acid storage tank (5), and the high-purity hydrochloric acid regulating valve (311), the high-purity hydrochloric acid flowmeter (312), the pure water regulating valve (321) and the pure water flowmeter (322) are connected to a DCS system and are loop-controlled.

3. The system for accurately controlling the pH of the dilute brine discharged from a single cell of a plurality of cells according to claim 1, characterized in that: The system further comprises a dilute hydrochloric acid preparation assembly (3) including a high-purity hydrochloric acid pipeline (31) provided with a high-purity hydrochloric acid regulating valve (311) and a high-purity hydrochloric acid flowmeter (312), and a pure water pipeline (32) provided with a pure water regulating valve (321) and a pure water flowmeter (322), wherein the high-purity hydrochloric acid pipeline (31) and the pure water pipeline (32) are connected to an inlet of a pipeline mixer (33), an outlet of the pipeline mixer (33) is connected to a material inlet of the dilute hydrochloric acid storage tank (5), and the high-purity hydrochloric acid regulating valve (311), the high-purity hydrochloric acid flowmeter (312), the pure water regulating valve (321) and the pure water flowmeter (322) are connected to a DCS system and are loop-controlled.

4. The system for accurately controlling the pH of the dilute brine discharged from a single cell of a plurality of cells according to claim 3, characterized in that: The system further comprises a dilute hydrochloric acid preparation assembly (3) including a high-purity hydrochloric acid pipeline (31) provided with a high-purity hydrochloric acid regulating valve (311) and a high-purity hydrochloric acid flowmeter (312), and a pure water pipeline (32) provided with a pure water regulating valve (321) and a pure water flowmeter (322), wherein the high-purity hydrochloric acid pipeline (31) and the pure water pipeline (32) are connected to an inlet of a pipeline mixer (33), an outlet of the pipeline mixer (33) is connected to a material inlet of the dilute hydrochloric acid storage tank (5), and the high-purity hydrochloric acid regulating valve (311), the high-purity hydrochloric acid flowmeter (312), the pure water regulating valve (321) and the pure water flowmeter (322) are connected to a DCS system and are loop-controlled.

5. The system for controlling the pH of the dilute brine according to claim 3, wherein: The system further comprises a dilute hydrochloric acid preparation assembly (3) including a high-purity hydrochloric acid pipeline (31) provided with a high-purity hydrochloric acid regulating valve (311) and a high-purity hydrochloric acid flowmeter (312), and a pure water pipeline (32) provided with a pure water regulating valve (321) and a pure water flowmeter (322), wherein the high-purity hydrochloric acid pipeline (31) and the pure water pipeline (32) are connected to an inlet of a pipeline mixer (33), an outlet of the pipeline mixer (33) is connected to a material inlet of the dilute hydrochloric acid storage tank (5), and the high-purity hydrochloric acid regulating valve (311), the high-purity hydrochloric acid flowmeter (312), the pure water regulating valve (321) and the pure water flowmeter (322) are connected to a DCS system and are loop-controlled.

6. The system for accurate control of pH of the brine leaving the individual cells of the multiple-bank electrolyzer of claim 1, characterized in that it further comprises: The system further comprises a dilute hydrochloric acid preparation assembly (3) including a high-purity hydrochloric acid pipeline (31) provided with a high-purity hydrochloric acid regulating valve (311) and a high-purity hydrochloric acid flowmeter (312), and a pure water pipeline (32) provided with a pure water regulating valve (321) and a pure water flowmeter (322), wherein the high-purity hydrochloric acid pipeline (31) and the pure water pipeline (32) are connected to an inlet of a pipeline mixer (33), an outlet of the pipeline mixer (33) is connected to a material inlet of the dilute hydrochloric acid storage tank (5), and the high-purity hydrochloric acid regulating valve (311), the high-purity hydrochloric acid flowmeter (312), the pure water regulating valve (321) and the pure water flowmeter (322) are connected to a DCS system and are loop-controlled.

7. A method for precise control of the pH of single-tank outlet dilute brine in a multi-group desalination tank, characterized in that, ​ In manual mode, open the brine sampling control valve (141) of one electrolytic cell (11), the DCS program will close the remaining brine sampling control valve (141), the pH meter (153) corresponding to the electrolytic cell (11) displays a value equal to the outlet brine sampling value, when the pH meter (153) detects that the outlet brine pH deviates from the standard value, the connected DCS system will control the opening degree of the corresponding dilute hydrochloric acid regulating valve (212) of the electrolytic cell (11) to ensure that the pH of the outlet brine of the electrolytic cell (11) is controlled at 3.0-3.5, when the outlet brine pH is less than or equal to 2.5, the dilute hydrochloric acid regulating valve (212) is automatically closed to stop the electrolytic cell (11) from adding acid; In automatic mode, the DCS program detects in real time through the current sensor (8) connected to the electrolytic cell (11) to determine 1 # whether the operating current of the electrolytic cell (11) meets the condition of reaching the set threshold, and if not, go to 2 # If the condition is met, open 1 # the sampling program control valve (141) of the electrolytic cell (11) 1 # The outlet dilute brine of the electrolytic cell (11) enters the pH detection analysis and countdown T1, and after waiting for a certain time T2, the pH meter (153) displays the value and assigns it to 1 # The electrolytic cell (11) at this time 1 # The valve position of the dilute hydrochloric acid regulating valve (212) of the electrolytic cell (11) is changed from holding to automatic adjustment and control, the pH output set value of the dilute hydrochloric acid regulating valve (212) is 3.0-3.5, and the outlet dilute brine pH is also 3.0-3.5; after the DCS timer is cleared, 1 # The sampling program control valve (141) of the electrolytic cell (11) is closed, and the valve position of the dilute hydrochloric acid regulating valve (212) is changed from automatic to holding, ending 1 # The pH detection and adjustment control of the electrolytic cell (11); the DCS program enters the next step and continues to determine 2 # The operating current condition of the electrolytic cell (11), if not met, determine 3 # The operating current condition of the electrolytic cell (11), and so on, until the last electrolytic cell (11) is switched, and then from 1 # The electrolytic cell (11) determines and the program runs, and so on, until the operator switches from automatic to manual, and the automatic running program enters initialization.

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