Secondary reverse osmosis alkali adding device and control method thereof

Abstract

This invention discloses a two-stage reverse osmosis alkali addition device and its control method. The device includes a two-stage inlet water pipeline, an alkali addition unit, a monitoring unit, a controller, and a static mixer. The alkali addition unit includes a chemical storage tank and a metering pump. The monitoring unit includes a flow meter, a pH meter, and a conductivity sensor. The controller determines the initial output of the metering pump based on the inlet water flow rate and adjusts the output of the metering pump based on the pH value and conductivity of the mixed inlet water. The control method includes flow feedforward control, pH feedback adjustment, and conductivity correction, and controls the reflux unit to perform reflux treatment when water quality is abnormal. This invention can improve the alkali addition response speed and mixing uniformity, reduce pH fluctuations, and improve the operational stability of the two-stage reverse osmosis system.

Description

Technical Field

[0001] This invention belongs to the field of high-purity water preparation technology, specifically a two-stage reverse osmosis alkali addition device and its control method. Background Technology

[0002] The secondary reverse osmosis system is a crucial step in the high-purity water production process. The permeate from the primary reverse osmosis system may still contain dissolved carbon dioxide, which, if directly introduced into the secondary reverse osmosis unit, can easily affect desalination and increase the conductivity of the permeate. Current technologies typically add NaOH solution to the feed water side of the secondary reverse osmosis system to adjust the feed water pH and improve the secondary reverse osmosis treatment effect.

[0003] Existing two-stage reverse osmosis alkali dosing systems mostly use a single pH feedback method to control the alkali dosage. When the influent flow rate or water quality changes, adjustment lag and pH fluctuations are likely to occur. Furthermore, insufficient mixing after alkali addition may result in excessively high local alkali concentrations, affecting detection accuracy and alkali dosing effectiveness. In addition, existing systems typically lack measures for adjusting the alkali dosage based on the influent conductivity and for reflux treatment in case of abnormal water quality. Their adaptability to different operating conditions and operational protection capabilities still need improvement. Summary of the Invention

[0004] To overcome the shortcomings of existing technologies and solve at least one of the problems mentioned in the background art, a two-stage reverse osmosis alkali addition device and its control method are proposed.

[0005] The technical solution adopted by the present invention to solve its technical problem is: a two-stage reverse osmosis alkali addition device, comprising: a two-stage inlet water pipe, an alkali addition unit, a monitoring unit, a controller, and a static mixer installed on the two-stage inlet water pipe;

[0006] The alkali addition unit includes a storage tank and a metering pump. The inlet of the metering pump is connected to the storage tank, and the outlet is connected to the secondary water inlet pipe upstream of the static mixer. The monitoring unit includes: a flow meter located upstream of the alkali addition unit and connected to the secondary inlet water pipeline, and a pH meter and conductivity sensor located downstream of the static mixer and connected to the secondary inlet water pipeline; The controller is connected to the flow meter, pH meter, conductivity sensor and metering pump respectively. The controller determines the initial output of the metering pump based on the detection value of the flow meter, and adjusts the output of the metering pump based on the detection values ​​of the pH meter and conductivity sensor.

[0007] Preferably, the storage tank is connected to a water inlet pipe and an alkali inlet pipe. The water inlet pipe is equipped with an electric valve and a manual valve for water inlet, and the alkali inlet pipe is equipped with an electric valve and a manual valve for alkali inlet. The storage tank is equipped with a stirrer and a liquid level sensor, and a drain valve is installed at the bottom.

[0008] Preferably, an alkali pipeline is connected between the storage tank and the secondary water inlet pipeline, and the alkali pipeline is provided with a metering pump inlet valve, a check valve, a metering pump, a metering pump outlet valve, a pressure gauge, a back pressure valve and a dosing valve in sequence along the alkali delivery direction.

[0009] Preferably, a pulse damper and a pressure relief valve are also installed on the alkali solution pipeline. The pulse damper is located downstream of the metering pump outlet valve and is connected to the alkali solution pipeline. A pulse damper inlet manual valve is also installed between the inlet side of the pulse damper and the alkali solution pipeline. The inlet of the pressure relief valve is connected to the alkali solution pipeline located between the metering pump and the metering pump outlet valve, and the outlet of the pressure relief valve is connected to the drug storage tank.

[0010] Preferably, the static mixer is an SV type static mixer; the static mixer is connected to a sewage discharge pipeline, and the sewage discharge pipeline is equipped with a manual sewage discharge valve and a power sewage discharge valve.

[0011] Preferably, it also includes: a primary reverse osmosis unit, a secondary inlet booster pump, a secondary reverse osmosis security filter, an intermediate water tank, a secondary high-pressure pump, a secondary reverse osmosis unit, and a reflux unit; The outlet of the primary reverse osmosis unit is connected to the intermediate water tank, which is connected in sequence to the secondary inlet pump, static mixer, secondary reverse osmosis security filter, secondary high-pressure pump and secondary reverse osmosis unit through the secondary inlet pipe; The secondary inlet pipeline is also equipped with a secondary reverse osmosis inlet manual valve, a secondary reverse osmosis inlet electric valve, a secondary reverse osmosis inlet thermometer, and a secondary reverse osmosis security filter inlet valve; the secondary reverse osmosis inlet manual valve and the secondary reverse osmosis inlet electric valve are located between the secondary high-pressure pump and the secondary reverse osmosis unit; the secondary reverse osmosis inlet thermometer is upstream of the alkali addition unit; the secondary reverse osmosis security filter inlet valve is located between the pH meter and the secondary reverse osmosis security filter; The reflux unit includes: a reflux pipeline and a reflux unit inlet manual valve and a reflux electric regulating valve installed on the reflux pipeline. One end of the reflux pipeline is connected to the secondary inlet pipeline between the secondary reverse osmosis inlet manual valve and the secondary reverse osmosis inlet electric valve, and the other end is connected to the intermediate water tank. The sewage discharge electric valve, the secondary inlet water lift pump, the secondary high-pressure pump, the secondary reverse osmosis inlet water electric valve, the reflux electric regulating valve, and the secondary reverse osmosis inlet water thermometer are all connected to the controller via communication.

[0012] A method for controlling alkali addition in a secondary reverse osmosis system includes the following steps: S1. Collect the secondary reverse osmosis feed water flow rate, determine the initial alkali addition amount based on the secondary reverse osmosis feed water flow rate and the preset alkali addition ratio coefficient, and control the metering pump according to the initial alkali addition amount; S2. Collect the pH value of the secondary reverse osmosis feed water after mixing by the static mixer, and adjust the output of the metering pump according to the deviation between the pH value of the secondary reverse osmosis feed water and the preset pH target range. S3. Collect the conductivity of the secondary reverse osmosis feed water, adjust the preset pH target range according to the conductivity of the secondary reverse osmosis feed water, and adjust the output of the metering pump according to the adjusted pH target range.

[0013] Preferably, in step S1, the preset alkali addition ratio coefficient is 0.05-0.10 mL / L, and the alkali solution added by the alkali addition unit is a 30% NaOH solution by mass.

[0014] Preferably, in step S2, the preset pH target range is 7.8-8.3, and the output of the metering pump is adjusted by PID control. The proportional parameter P of the PID control is 2.0, the integral time I is 120s, and the derivative time D is 5s. When the pH value of the secondary reverse osmosis feed water is lower than the lower limit of the current preset pH target range and greater than or equal to 7.5, increase the output of the metering pump; when the pH value of the secondary reverse osmosis feed water is in the range of 8.3 < pH ≤ 8.8, decrease the output of the metering pump; when the pH value of the secondary reverse osmosis feed water is higher than the upper limit of the current preset pH target range and less than or equal to 8.8, maintain the current output of the metering pump. When the pH of the secondary reverse osmosis feed water is <7.5 or >8.8, an alarm signal is output, the reflux electric regulating valve is opened, the secondary high-pressure pump is stopped and the secondary reverse osmosis feed water electric valve is closed, while the secondary feed water lift pump is kept running so that the water in the secondary feed water pipeline flows back to the intermediate water tank through the reflux pipeline. After refluxing for at least 10 minutes, retest the pH value and conductivity of the secondary reverse osmosis feed water. When the pH value of the secondary reverse osmosis feed water is within the current preset pH target range and the conductivity of the secondary reverse osmosis feed water is less than or equal to 50 μS / cm, close the reflux electric regulating valve, open the secondary reverse osmosis feed water electric valve, and start the secondary high-pressure pump.

[0015] Preferably, in step S3, when the conductivity of the secondary reverse osmosis feed water is greater than 50 μS / cm and not greater than 60 μS / cm, the upper and lower limits of the preset pH target range are increased by 0.2 respectively; when the conductivity of the secondary reverse osmosis feed water is less than or equal to 40 μS / cm, the upper and lower limits of the preset pH target range are decreased by 0.2 respectively. When the conductivity of the secondary reverse osmosis feed water is greater than 60 μS / cm, the upper and lower limits of the preset pH target range are increased by 0.2 respectively, and an alarm signal is output. The secondary feed water booster pump and the secondary high-pressure pump are kept running, the secondary reverse osmosis feed water electric valve is kept open, and the reflux electric regulating valve is opened according to the preset opening degree, so that part of the water in the secondary feed water pipeline flows back to the intermediate water tank through the reflux pipeline. When the conductivity of the secondary reverse osmosis feed water is less than or equal to 60 μS / cm, the opening degree of the reflux electric regulating valve is reduced until it is closed, and the output of the metering pump is continued to be adjusted according to the preset pH target range corresponding to the current conductivity of the secondary reverse osmosis feed water.

[0016] The beneficial effects of this invention are as follows: 1. The two-stage reverse osmosis alkali addition device of the present invention, by setting a flow meter upstream of the alkali addition point and setting a pH meter and conductivity sensor downstream of the static mixer, enables the controller to pre-determine the initial output of the metering pump based on the flow rate of the two-stage reverse osmosis feed water, and to correct the output of the metering pump based on the pH value and conductivity of the mixed water, thereby reducing the alkali addition lag caused by relying solely on pH feedback and improving the adaptability of the alkali addition amount to changes in feed water flow and water quality; at the same time, the static mixer can fully mix the alkali solution with the two-stage reverse osmosis feed water, reducing the situation of excessively high local alkali concentration, which is conducive to stabilizing the water quality of the two-stage reverse osmosis feed water and improving the utilization efficiency of the alkali solution.

[0017] 2. The secondary reverse osmosis alkali addition control method of the present invention first determines the initial alkali addition amount based on the secondary reverse osmosis feed water flow rate and the preset alkali addition ratio coefficient, then adjusts the output of the metering pump based on the pH value of the mixed feed water, and dynamically adjusts the pH target range based on the feed water conductivity, thereby forming a multi-parameter collaborative control mode that combines flow feedforward, pH feedback and conductivity correction. This method can adjust the alkali addition amount in a timely manner when the feed water flow rate or water quality changes, reduce the lag and fluctuation of pH adjustment, and make the alkali addition control adaptable to different feed water conductivity conditions, which is beneficial to improving the stability of the secondary reverse osmosis feed water pH and product water quality. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the structure of the two-stage reverse osmosis alkali addition device of the present invention; Figure 2 This is a schematic diagram of the alkali addition unit in this invention; Figure 3 This is a schematic flowchart of the secondary reverse osmosis alkali control method of the present invention.

[0019] Legend: 1. Primary reverse osmosis unit; 2. Intermediate water tank; 3. Secondary inlet pipe; 4. Alkali addition unit; 5. Monitoring unit; 6. Controller; 7. Static mixer; 8. Secondary high-pressure pump; 9. Secondary reverse osmosis unit; 10. Reflux unit; 11. Secondary reverse osmosis inlet manual valve; 12. Secondary reverse osmosis inlet electric valve; 13. Reflux unit inlet manual valve; 14. Reflux electric regulating valve; 15. Flow meter; 16. pH meter; 17. Secondary reverse osmosis inlet thermometer; 18. Secondary reverse osmosis security filter inlet valve; 19. Sewage manual valve; 20. Sewage electric valve; 2 1. Pulse damper inlet manual valve; 22. Chemical storage tank water inlet electric valve; 23. Chemical storage tank alkali inlet electric valve; 24. Chemical storage tank alkali inlet manual valve; 25. Chemical storage tank water inlet manual valve; 26. Agitator; 27. Liquid level sensor; 28. Drain valve; 29. ​​Chemical storage tank; 30. Metering pump inlet valve; 31. Check valve; 32. Metering pump; 33. Metering pump outlet valve; 34. Pressure gauge; 35. Pressure relief valve; 36. Pulse damper; 37. Back pressure valve; 38. Dosing valve; 39. Secondary water inlet booster pump; 40. Secondary reverse osmosis security filter; 41. Conductivity sensor. Detailed Implementation

[0020] To illustrate in detail the technical solutions adopted by the present invention to achieve the intended technical objectives, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Furthermore, the technical means or technical features in the embodiments of the present invention can be replaced without creative effort. The present invention will be described in detail below with reference to the accompanying drawings and embodiments.

[0021] Example 1 like Figure 1 As shown, this embodiment provides a two-stage reverse osmosis alkali addition device, including a two-stage inlet pipe 3, an alkali addition unit 4, a monitoring unit 5, a controller 6, and a static mixer 7. The static mixer 7 is installed on the two-stage inlet pipe 3 and is used to ensure that the alkali solution added to the two-stage inlet pipe 3 is fully mixed with the first-stage reverse osmosis permeate.

[0022] This embodiment also includes: a primary reverse osmosis unit 1, an intermediate water tank 2, a secondary inlet booster pump 39, a secondary reverse osmosis security filter 40, a secondary high-pressure pump 8, and a secondary reverse osmosis unit 9. The outlet of the primary reverse osmosis unit 1 is connected to the intermediate water tank 2, and the permeate from the primary reverse osmosis unit 1 enters the intermediate water tank 2 for temporary storage. The outlet of the intermediate water tank 2 is connected to the secondary inlet pipe 3. Along the secondary reverse osmosis inlet direction, the secondary inlet pipe 3 is sequentially connected to the secondary inlet booster pump 39, the static mixer 7, the secondary reverse osmosis security filter 40, the secondary high-pressure pump 8, and the secondary reverse osmosis unit 9.

[0023] The secondary feed water booster pump 39 is used to transport water from the intermediate water tank 2 to the secondary feed water pipe 3, and can provide power for the reflux circulation under abnormal reflux conditions. The secondary reverse osmosis security filter 40 is used to intercept particulate matter or other impurities before entering the secondary high-pressure pump 8 and the secondary reverse osmosis unit 9, so as to reduce the possibility of impurities entering the secondary reverse osmosis membrane module. The secondary high-pressure pump 8 is used to pressurize and transport the water after alkali addition, mixing and filtration to the secondary reverse osmosis unit 9.

[0024] The secondary inlet pipe 3 is equipped with a secondary reverse osmosis inlet manual valve 11, a secondary reverse osmosis inlet electric valve 12, a secondary reverse osmosis inlet thermometer 17, and a secondary reverse osmosis security filter inlet valve 18. The secondary reverse osmosis inlet manual valve 11 and the secondary reverse osmosis inlet electric valve 12 are located between the secondary high-pressure pump 8 and the secondary reverse osmosis unit 9. The secondary reverse osmosis inlet manual valve 11 is used for manual control of the corresponding pipe section's on / off state, while the secondary reverse osmosis inlet electric valve 12 is used to switch the on / off state of the main inlet pipe under the control of the controller 6.

[0025] During normal water production, the secondary reverse osmosis inlet electric valve 12 is open, allowing water output from the secondary high-pressure pump 8 to enter the secondary reverse osmosis unit 9. Under abnormal backflow conditions with severely excessive pH, the secondary reverse osmosis inlet electric valve 12 closes to prevent water that does not meet water quality requirements from continuing to enter the secondary reverse osmosis unit 9.

[0026] The secondary reverse osmosis feed water thermometer 17 is located upstream of the connection point between the alkali addition unit 4 and the secondary feed water pipe 3, and is used to detect the temperature of the secondary reverse osmosis feed water before alkali addition. The secondary reverse osmosis security filter inlet valve 18 is located between the pH meter 16 and the secondary reverse osmosis security filter 40, and is used to control the flow of water into the secondary reverse osmosis security filter 40.

[0027] like Figure 2 As shown, the alkali addition unit 4 includes: a chemical storage tank 29, a metering pump 32, and an alkali solution pipeline connecting the chemical storage tank 29 and the secondary inlet water pipeline 3. The inlet of the metering pump 32 is connected to the chemical storage tank 29 through the alkali solution pipeline, and the outlet of the metering pump 32 is connected to the secondary inlet water pipeline 3 located between the secondary reverse osmosis inlet water thermometer 17 and the static mixer 7 through the alkali solution pipeline, thereby quantitatively delivering the alkali solution in the chemical storage tank 29 to the secondary inlet water pipeline 3.

[0028] In this embodiment, the storage tank 29 stores a 30% NaOH solution. The storage tank 29 is connected to a water inlet pipe and an alkali inlet pipe. The water inlet pipe is used to add water for preparing the medicine to the storage tank 29, and the alkali inlet pipe is used to add the NaOH solution to the storage tank 29. The water inlet pipe is equipped with a power valve 22 and a manual valve 25 for water inlet, and the alkali inlet pipe is equipped with a power valve 23 and a manual valve 24 for alkali inlet.

[0029] The storage tank 29 is equipped with a stirrer 26 and a level sensor 27. The stirrer 26 is used to agitate the alkaline solution in the storage tank 29 to maintain a uniform concentration. The level sensor 27 is used to detect the liquid level in the storage tank 29 and can send the detection result to the controller 6. A drain valve 28 is provided at the bottom of the storage tank 29 to drain residual liquid or for cleaning and sludge removal.

[0030] Along the alkali delivery direction, the alkali pipeline is sequentially equipped with a metering pump inlet valve 30, a check valve 31, a metering pump 32, a metering pump outlet valve 33, a pressure gauge 34, a back pressure valve 37, and a dosing valve 38. The metering pump inlet valve 30 and metering pump outlet valve 33 are used to isolate the corresponding pipeline sections during metering pump 32 maintenance or replacement. The check valve 31 prevents backflow of liquid from the alkali pipeline towards the storage tank 29. The pressure gauge 34 detects the pipeline pressure at the outlet side of the metering pump 32. The back pressure valve 37 creates a stable back pressure at the outlet side of the metering pump 32 to improve the dosing stability of the metering pump 32. The dosing valve 38 controls the connection between the alkali pipeline and the secondary water inlet pipeline 3.

[0031] A pulse damper 36 and a pressure relief valve 35 are also installed on the alkali solution pipeline. The pulse damper 36 is located between the metering pump outlet valve 33 and the pressure gauge 34, and is connected to the alkali solution pipeline. A pulse damper inlet manual valve 21 is installed between the inlet side of the pulse damper 36 and the alkali solution pipeline. When the metering pump 32 is an electromagnetic diaphragm metering pump, its output alkali solution has periodic pulsations. The pulse damper 36 can absorb the pressure pulsations generated by the discharge of the metering pump 32, so that the flow rate and pressure in the alkali solution pipeline tend to be stable. The pulse damper inlet manual valve 21 can be closed when the pulse damper 36 is being maintained to isolate the pulse damper 36.

[0032] The inlet of the pressure relief valve 35 is connected to the alkali pipeline located between the metering pump 32 and the metering pump outlet valve 33, and the outlet of the pressure relief valve 35 is connected to the storage tank 29. When the pressure on the outlet side of the metering pump 32 exceeds the preset pressure, the pressure relief valve 35 opens, allowing some of the alkali to return to the storage tank 29, thereby reducing the pressure in the alkali pipeline and protecting the metering pump 32 and the valves and instruments on the alkali pipeline.

[0033] Monitoring unit 5 includes a flow meter 15, a pH meter 16, and a conductivity sensor 41. The flow meter 15 is located upstream of the connection point between the alkali addition unit 4 and the secondary inlet water pipe 3, and is used to detect the flow rate of the secondary reverse osmosis feed water before alkali addition. The pH meter 16 and the conductivity sensor 41 are located downstream of the static mixer 7 and are connected to the secondary inlet water pipe 3, and are used to detect the pH value and conductivity after the alkali solution is mixed with the feed water.

[0034] By placing the flow meter 15 upstream of the dosing point, the controller 6 can pre-determine the initial output of the metering pump 32 based on the influent flow rate before a significant change in pH occurs, thus achieving flow feedforward regulation. By placing the pH meter 16 and conductivity sensor 41 downstream of the static mixer 7, the detection results can reflect the actual water quality after the alkali solution and influent are fully mixed, reducing the impact of uneven local alkali concentration on the detection results.

[0035] The static mixer 7 is an SV-type static mixer. In a preferred embodiment, the length-to-diameter ratio of the static mixer 7 can be 8-10. When the water and alkali solution flow through the static mixer 7, they are separated, rotated, and recombined under the action of the mixing unit inside, thereby uniformly dispersing the alkali solution in the water and reducing the possibility of excessively high local pH.

[0036] The static mixer 7 is also connected to a drain pipe, which is equipped with a manual drain valve 19 and a power drain valve 20. The drain pipe can be used for venting, cleaning and draining the static mixer 7 and the corresponding pipe sections. During normal operation, the manual drain valve 19 and the power drain valve 20 are kept closed. When draining or cleaning is required, the corresponding valves are opened to discharge the residual liquid in the pipe.

[0037] The reflux unit 10 includes a reflux pipeline, a manual reflux unit inlet valve 13, and a power-operated reflux regulating valve 14. One end of the reflux pipeline is connected to the secondary inlet pipe 3 between the secondary reverse osmosis inlet manual valve 11 and the secondary reverse osmosis inlet power-operated valve 12, and the other end is connected to the intermediate water tank 2. The manual reflux unit inlet valve 13 remains open during normal system operation and closes when the reflux unit 10 is under maintenance. The power-operated reflux regulating valve 14 can adjust its opening degree under the control of the controller 6 to change the reflux water flow rate.

[0038] In this embodiment, the controller 6 can be a PLC control system, which is used to receive the detection data of each detection component and send control commands to the metering pump 32, the secondary water inlet booster pump 39, the secondary high pressure pump 8, the secondary reverse osmosis water inlet electric valve 12 and the reflux electric regulating valve 14 according to the preset control program.

[0039] The controller 6 is communicatively connected to the flow meter 15, pH meter 16, conductivity sensor 41, metering pump 32, secondary feed water booster pump 39, secondary high-pressure pump 8, secondary reverse osmosis feed water electric valve 12, reflux electric regulating valve 14, and secondary reverse osmosis feed water thermometer 17. The controller 6 receives flow rate, pH value, conductivity, and temperature detection data, and adjusts the output of metering pump 32 and the operating status of each pump and valve according to preset control logic.

[0040] Example 2 This embodiment provides a control method applied to the above-mentioned secondary reverse osmosis alkali addition device.

[0041] After the system starts up, the permeate from the first-stage reverse osmosis unit 1 enters the intermediate water tank 2, and the second-stage feed water booster pump 39 delivers the water in the intermediate water tank 2 to the second-stage feed water pipeline 3. The controller 6 controls the second-stage reverse osmosis feed water electric valve 12 to open and controls the second-stage high-pressure pump 8 to run, so that the second-stage feed water enters the second-stage reverse osmosis unit 9 after alkali addition, mixing and filtration.

[0042] In step S1, flow meter 15 collects the secondary reverse osmosis feed water flow rate in real time, and controller 6 determines the initial alkali addition amount based on the detected secondary reverse osmosis feed water flow rate and the preset alkali addition ratio coefficient. The initial alkali addition amount can be determined according to the following formula: Initial alkali addition = Secondary reverse osmosis feed water flow rate × Preset alkali addition ratio coefficient.

[0043] In this embodiment, the preset alkali addition ratio coefficient is 0.05-0.10 mL / L, and the added alkali solution is a 30% (w / w) NaOH solution. The controller 6 determines the initial operating frequency or initial output of the metering pump 32 based on the calculated initial alkali addition amount.

[0044] For example, when the instantaneous feed water flow rate of the secondary reverse osmosis system is 333.3 L / min, and the preset alkali addition ratio is 0.075 mL / L, the initial alkali addition amount is: 333.3L / min×0.075mL / L≈25mL / min.

[0045] After conversion, the initial alkali addition is approximately 1.5 L / h. In this embodiment, an electromagnetic diaphragm metering pump 32 with a flow rate of 0–100 L / h and an operating frequency range of 0–50 Hz is used. Under the above-mentioned influent flow rate and alkali addition ratio coefficient, the steady-state operating frequency of the metering pump 32 is 7.5 Hz. By determining the initial alkali addition in advance through flow feedforward, the output of the metering pump 32 can change synchronously with the influent flow rate, reducing the adjustment lag caused by relying solely on pH feedback.

[0046] In step S2, the alkaline solution enters the secondary inlet pipe 3 upstream of the static mixer 7 via the dosing valve 38, and is thoroughly mixed with the water in the static mixer 7. The pH meter 16 collects the pH value of the secondary reverse osmosis feed water downstream of the static mixer 7, and the controller 6 adjusts the output of the metering pump 32 using PID control based on the deviation between the detected pH value and the preset pH target range.

[0047] In this embodiment, the preset pH target range is 7.8-8.3, and the proportional parameter P of the PID control method is 2.0, the integral time I is 120s, and the derivative time D is 5s. The proportional parameter is used to determine the immediate adjustment range based on the current pH deviation, the integral time is used to eliminate long-term steady-state deviations, and the derivative time is used to suppress overshoot caused by rapid pH changes.

[0048] When the pH value of the secondary reverse osmosis feed water is lower than the lower limit of the current preset pH target range and is greater than or equal to 7.5, it indicates that the current alkali addition is too low, and the controller 6 increases the output of the metering pump 32; when the pH value of the secondary reverse osmosis feed water is within the current preset pH target range, the controller 6 maintains the current output of the metering pump 32; when the pH value of the secondary reverse osmosis feed water is higher than the upper limit of the current preset pH target range and is less than or equal to 8.8, it indicates that the current alkali addition is too high, and the controller 6 decreases the output of the metering pump 32.

[0049] When the pH value of the secondary reverse osmosis feed water is below 7.5 or above 8.8, it indicates that the water quality has exceeded the normal adjustment range. Controller 6 outputs an alarm signal and executes severe abnormal backflow control; controller 6 opens the backflow electric regulating valve 14, stops the secondary high-pressure pump 8 and closes the secondary reverse osmosis feed water electric valve 12, while keeping the secondary feed water booster pump 39 running.

[0050] At this time, the secondary reverse osmosis inlet electric valve 12 closes to prevent water that does not meet the water quality requirements from entering the secondary reverse osmosis unit 9; the secondary inlet booster pump 39 continues to operate, providing power for water reflux. In this embodiment, when the secondary high-pressure pump 8 stops operating, its internal flow channel remains connected. The water output from the secondary inlet booster pump 39 can sequentially pass through the static mixer 7, the secondary reverse osmosis security filter 40, and the internal flow channel of the secondary high-pressure pump 8 into the reflux pipeline, and then return to the intermediate water tank 2 via the reflux pipeline, thereby forming a reflux cycle.

[0051] After the reflux circulation is maintained for no less than 10 minutes, the controller 6 reacquires the detection data of the pH meter 16 and the conductivity sensor 41. When the pH value of the secondary reverse osmosis feed water is within the current preset pH target range and the conductivity of the secondary reverse osmosis feed water is less than or equal to 50 μS / cm, the controller 6 closes the reflux electric regulating valve 14, opens the secondary reverse osmosis feed water electric valve 12, and starts the secondary high-pressure pump 8, thereby restoring the water supply to the secondary reverse osmosis unit 9.

[0052] When the water supply is restored, the controller 6 can first control the secondary inlet water pressure by adjusting the operating frequency of the secondary inlet water booster pump 39. After opening the secondary reverse osmosis inlet water electric valve 12, the secondary high-pressure pump 8 is started, and the operating frequency of the secondary high-pressure pump 8 is gradually increased so that the secondary reverse osmosis inlet water pressure gradually rises to the normal operating pressure, thereby reducing the pressure shock to the secondary reverse osmosis membrane module caused by pump start-up and valve switching.

[0053] In step S3, the conductivity sensor 41 collects the conductivity of the secondary reverse osmosis feed water downstream of the static mixer 7. The controller 6 adjusts the preset pH target range according to the conductivity detection results and continues to adjust the output of the metering pump 32 according to the adjusted pH target range.

[0054] When the conductivity of the secondary reverse osmosis feed water is greater than 50 μS / cm but not greater than 60 μS / cm, the controller 6 will increase the upper and lower limits of the preset pH target range by 0.2. For example, the original preset pH target range of 7.8-8.3 will be adjusted to 8.0-8.5 to increase the amount of alkali added. By increasing the pH target range, dissolved carbon dioxide in the water can be converted into ionic forms that are more easily retained by the reverse osmosis membrane.

[0055] When the conductivity of the secondary reverse osmosis feed water is less than or equal to 40 μS / cm, the controller 6 will lower the upper and lower limits of the preset pH target range by 0.2. For example, the original preset pH target range of 7.8-8.3 will be adjusted to 7.6-8.1 to reduce the output of the metering pump 32 and reduce alkali consumption. When the conductivity is greater than 40 μS / cm but not greater than 50 μS / cm, the original preset pH target range can be maintained unchanged.

[0056] When the conductivity of the secondary reverse osmosis feed water is greater than 60 μS / cm, the controller 6 will increase the upper and lower limits of the preset pH target range by 0.2 respectively and output an alarm signal. At this time, it is a mild abnormal condition where the conductivity exceeds the limit but water production does not need to be stopped. The controller 6 keeps the secondary feed water booster pump 39 and the secondary high-pressure pump 8 running, keeps the secondary reverse osmosis feed water electric valve 12 open, and opens the reflux electric regulating valve 14 according to the preset opening degree.

[0057] In this state, a portion of the water continues to enter the secondary reverse osmosis unit 9 through the secondary reverse osmosis feed electric valve 12, while the other portion returns to the intermediate water tank 2 through the return pipeline, thus forming partial reflux. The controller 6 can adjust the opening of the reflux electric regulating valve 14 according to the conductivity deviation, so that the system can maintain the secondary reverse osmosis water supply while circulating and correcting the water quality in the intermediate water tank 2 and the secondary feed pipeline 3. When the conductivity of the secondary reverse osmosis feed water is less than or equal to 60 μS / cm, the controller 6 gradually reduces the opening of the reflux electric regulating valve 14 until it is closed, and continues to adjust the output of the metering pump 32 according to the preset pH target range corresponding to the current conductivity of the secondary reverse osmosis feed water.

[0058] Specifically, when the conductivity of the secondary reverse osmosis feed water decreases to greater than 50 μS / cm but not greater than 60 μS / cm, partial reflux is stopped and the adjusted pH target range is maintained; when the conductivity of the secondary reverse osmosis feed water further decreases to greater than 40 μS / cm but less than or equal to 50 μS / cm, the original preset pH target range is restored; when the conductivity of the secondary reverse osmosis feed water is less than or equal to 40 μS / cm, the upper and lower limits of the preset pH target range are lowered by 0.2 respectively.

[0059] Example 3 In the experimental group with high conductivity and high CO2 content, the conductivity of the secondary reverse osmosis feed water before adjustment was 53-56 μS / cm, and the original pH target range was 7.8-8.3. The controller 6 adjusted the pH target range to 8.0-8.5, and the operating frequency of the metering pump 32 was increased from 7.5Hz to 9.2Hz. After the adjustment was stabilized, the pH value of the secondary reverse osmosis feed water was maintained at 8.20-8.35, and the conductivity of the secondary reverse osmosis permeate was 0.10-0.19 μS / cm.

[0060] Example 4 In the experimental group with low conductivity and low CO2 content, the conductivity of the secondary reverse osmosis feed water before adjustment was 36-39 μS / cm. Controller 6 adjusted the pH target range from 7.8-8.3 to 7.6-8.1, and the operating frequency of metering pump 32 was reduced from 7.5 Hz to 5.8 Hz. After stabilization, the pH value of the secondary reverse osmosis feed water remained at 7.70-7.90, and the conductivity of the secondary reverse osmosis permeate was 0.06-0.08 μS / cm. The above operating data indicate that dynamically adjusting the pH target range based on the conductivity of the secondary reverse osmosis feed water allows the alkali dosage to adapt to changes in feed water quality, while also considering the quality of the secondary reverse osmosis permeate and alkali consumption.

[0061] In this embodiment, flow feedforward data is provided by flow meter 15, closed-loop feedback data is provided by pH meter 16, and pH target range is dynamically corrected by conductivity sensor 41, so that the output of metering pump 32 can be adjusted according to changes in influent flow and water quality. At the same time, through the cooperation of secondary influent booster pump 39, secondary reverse osmosis influent electric valve 12 and reflux electric regulating valve 14, forced reflux can be achieved when pH is seriously out of limit, and partial reflux can be achieved without stopping the machine when conductivity is out of limit, reducing the possibility of water that does not meet the water quality requirements entering the secondary reverse osmosis unit 9.

[0062] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent substitutions, and improvements made to the above embodiments without departing from the scope of the present invention, based on the technical essence of the present invention and within the spirit and principles of the present invention, shall still fall within the protection scope of the present invention.

Claims

1. A two-stage reverse osmosis alkali addition device, characterized in that, include: A secondary water inlet pipeline, an alkali addition unit, a monitoring unit, a controller, and a static mixer installed on the secondary water inlet pipeline; The alkali addition unit includes a storage tank and a metering pump. The inlet of the metering pump is connected to the storage tank, and the outlet is connected to the secondary water inlet pipe upstream of the static mixer. The monitoring unit includes: a flow meter located upstream of the alkali addition unit and connected to the secondary water inlet pipe; and a pH meter and a conductivity sensor located downstream of the static mixer and connected to the secondary water inlet pipe. The controller is communicatively connected to the flow meter, the pH meter, the conductivity sensor, and the metering pump. The controller determines the initial output of the metering pump based on the detection value of the flow meter, and adjusts the output of the metering pump based on the detection values ​​of the pH meter and the conductivity sensor.

2. The secondary reverse osmosis alkali addition device according to claim 1, characterized in that, The storage tank is connected to a water inlet pipe and an alkali inlet pipe. The water inlet pipe is equipped with an electric valve and a manual valve for water inlet, and the alkali inlet pipe is equipped with an electric valve and a manual valve for alkali inlet. The storage tank is equipped with a stirrer and a liquid level sensor, and a drain valve is installed at the bottom.

3. The two-stage reverse osmosis alkali addition device according to claim 1, characterized in that, An alkali solution pipeline is connected between the storage tank and the secondary water inlet pipeline. Along the alkali solution delivery direction, the alkali solution pipeline is sequentially equipped with a metering pump inlet valve, a check valve, the metering pump, a metering pump outlet valve, a pressure gauge, a back pressure valve, and a dosing valve.

4. The secondary reverse osmosis alkali addition device according to claim 3, characterized in that, The alkali solution pipeline is also equipped with a pulse damper and a pressure relief valve. The pulse damper is located downstream of the metering pump outlet valve and is connected to the alkali solution pipeline. A pulse damper inlet manual valve is also provided between the inlet side of the pulse damper and the alkali solution pipeline. The inlet of the pressure relief valve is connected to the alkali solution pipeline located between the metering pump and the metering pump outlet valve, and the outlet of the pressure relief valve is connected to the drug storage tank.

5. The two-stage reverse osmosis alkali addition device according to claim 1, characterized in that, The static mixer is an SV type static mixer; the static mixer is connected to a sewage discharge pipeline, and the sewage discharge pipeline is equipped with a manual sewage discharge valve and a power sewage discharge valve.

6. The secondary reverse osmosis alkali addition device according to claim 5, characterized in that, Also includes: The system consists of a primary reverse osmosis unit, a secondary feed water booster pump, a secondary reverse osmosis security filter, an intermediate water tank, a secondary high-pressure pump, a secondary reverse osmosis unit, and a reflux unit. The outlet of the primary reverse osmosis unit is connected to the intermediate water tank, and the intermediate water tank is connected in sequence to the secondary inlet pump, the static mixer, the secondary reverse osmosis security filter, the secondary high-pressure pump, and the secondary reverse osmosis unit through the secondary inlet pipe. The secondary inlet pipe is also equipped with a secondary reverse osmosis inlet manual valve, a secondary reverse osmosis inlet electric valve, a secondary reverse osmosis inlet thermometer, and a secondary reverse osmosis security filter inlet valve; the secondary reverse osmosis inlet manual valve and the secondary reverse osmosis inlet electric valve are located between the secondary high-pressure pump and the secondary reverse osmosis unit; The secondary reverse osmosis feed water thermometer is located upstream of the alkali addition unit; The inlet valve of the secondary reverse osmosis security filter is located between the pH meter and the secondary reverse osmosis security filter; The reflux unit includes: a reflux pipeline and a reflux unit inlet manual valve and a reflux electric regulating valve disposed on the reflux pipeline. One end of the reflux pipeline is connected to the secondary inlet pipeline between the secondary reverse osmosis inlet manual valve and the secondary reverse osmosis inlet electric valve, and the other end is connected to the intermediate water tank. The sewage discharge electric valve, the secondary inlet water lift pump, the secondary high-pressure pump, the secondary reverse osmosis inlet water electric valve, the reflux electric regulating valve, and the secondary reverse osmosis inlet water thermometer are all connected to the controller via communication.

7. A method for controlling the addition of alkali in a two-stage reverse osmosis system, characterized in that, Includes the following steps: S1. Collect the secondary reverse osmosis feed water flow rate, determine the initial alkali addition amount based on the secondary reverse osmosis feed water flow rate and the preset alkali addition ratio coefficient, and control the metering pump according to the initial alkali addition amount; S2. Collect the pH value of the secondary reverse osmosis feed water after mixing by the static mixer, and adjust the output of the metering pump according to the deviation between the pH value of the secondary reverse osmosis feed water and the preset pH target range; S3. Collect the conductivity of the secondary reverse osmosis feed water, adjust the preset pH target range according to the conductivity of the secondary reverse osmosis feed water, and adjust the output of the metering pump according to the adjusted pH target range.

8. The secondary reverse osmosis alkali addition control method according to claim 7, characterized in that, In step S1, the preset alkali addition ratio coefficient is 0.05-0.10 mL / L, and the alkali solution added by the alkali addition unit is a 30% NaOH solution by mass.

9. The secondary reverse osmosis alkali addition control method according to claim 7, characterized in that, In step S2, the preset pH target range is 7.8-8.

3. The output of the metering pump is adjusted by PID control, wherein the proportional parameter P of the PID control is 2.0, the integral time I is 120s, and the derivative time D is 5s. When the pH value of the secondary reverse osmosis feed water is lower than the lower limit of the current preset pH target range and greater than or equal to 7.5, the output of the metering pump is increased; when the pH value of the secondary reverse osmosis feed water is in the range of 8.3 < pH ≤ 8.8, the output of the metering pump is decreased; when the pH value of the secondary reverse osmosis feed water is higher than the upper limit of the current preset pH target range and less than or equal to 8.8, the current output of the metering pump is maintained. When the pH of the secondary reverse osmosis feed water is <7.5 or >8.8, an alarm signal is output, the reflux electric regulating valve is opened, the secondary high-pressure pump is stopped and the secondary reverse osmosis feed water electric valve is closed, while the secondary feed water lift pump is kept running, so that the water in the secondary feed water pipeline flows back to the intermediate water tank through the reflux pipeline. After refluxing for at least 10 minutes, the pH value and conductivity of the secondary reverse osmosis feed water are retested. When the pH value of the secondary reverse osmosis feed water is within the current preset pH target range and the conductivity of the secondary reverse osmosis feed water is less than or equal to 50 μS / cm, the reflux electric regulating valve is closed, the secondary reverse osmosis feed water electric valve is opened, and the secondary high-pressure pump is started.

10. The secondary reverse osmosis alkali control method according to claim 7, characterized in that, In step S3, when the conductivity of the secondary reverse osmosis feed water is greater than 50 μS / cm and not greater than 60 μS / cm, the upper and lower limits of the preset pH target range are increased by 0.2 respectively; when the conductivity of the secondary reverse osmosis feed water is less than or equal to 40 μS / cm, the upper and lower limits of the preset pH target range are decreased by 0.2 respectively. When the conductivity of the secondary reverse osmosis feed water is greater than 60 μS / cm, the upper and lower limits of the preset pH target range are increased by 0.2 respectively, and an alarm signal is output. The secondary feed water booster pump and the secondary high-pressure pump are kept running, the secondary reverse osmosis feed water electric valve is kept open, and the return electric regulating valve is opened according to the preset opening degree, so that part of the water in the secondary feed water pipeline flows back to the intermediate water tank through the return pipeline. When the conductivity of the secondary reverse osmosis feed water is less than or equal to 60 μS / cm, the opening of the reflux electric regulating valve is reduced until it is closed, and the output of the metering pump is adjusted according to the preset pH target range corresponding to the current conductivity of the secondary reverse osmosis feed water.

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