Control method for RO system and control program for water treatment system

Abstract

Provided is a method for controlling an RO system, said method being capable of reducing the amount of power consumption (i.e., CO2) and waste by reducing the amount of chemicals used or the number of times of membrane replacement, enabling stable operation, and contributing to a reduction in energy conservation and maintenance. A method for controlling an RO system provided with: a plurality of RO devices (41-44) arranged in parallel; a control unit that controls start / stop processing including operation processing and stop processing of the RO devices (41-44); and a chemical injection unit that injects a chemical that mitigates fouling when the treatment is stopped, in the method for controlling the RO system, control is performed such that the number of times of start / stop is increased as the RO device is in which the treatment capacity is easily recovered by start / stop, and the stop time is controlled in accordance with the recovery degree.

Description

Technical Field

[0001] The present invention relates to a control method of an RO system and a control program of a water treatment system, and in particular to a control method of an RO system having a plurality of RO devices arranged in parallel and a control program of a water treatment system. Background Art

[0002] If fouling occurs on the reverse osmosis (RO) membrane, the water supply pressure will rise and the power consumption of the water supply pump will increase. Therefore, chemical cleaning is sometimes performed to remove the fouling. However, chemical cleaning using acids / alkalis of common industrial chemicals is not only time-consuming and expensive, but also causes membrane deterioration due to frequent chemical cleaning, shortening the life of the membrane.

[0003] Chemical cleaning is effective for various types of fouling, among which alkaline chemicals are targeted at organic fouling and microbial (biological) fouling. On the other hand, RO membranes also produce physical fouling such as SS fouling caused by suspended solids (SS). SS fouling can also occur due to mixing with microbial fouling. In addition, acids / chelating agents are also effective for fouling caused by inorganic scale.

[0004] Therefore, it is ideal to minimize the number of chemical cleanings while using a simple structure to suppress the fouling of the RO membrane and ensure the treatment efficiency of the water treatment system.

[0005] As a method for preventing clogging of an RO device having an RO membrane, Patent Document 1 describes a method of blowing off (blowing) suspended matter concentrated wastewater generated in a reverse osmosis membrane section during filtration of water to be treated, based on the accumulated water flow time.

[0006] Patent Document 2 describes that the priority of a plurality of parallel filtration devices to be operated is set based on the degree of membrane clogging. Furthermore, paragraph

[0064] of Patent Document 2 describes that the membrane is cleaned with air.

[0007] Patent Document 1: Japanese Patent Application Publication No. 2005-279461.

[0008] Patent document 2: Japanese Patent Application Publication No. 2016-067968. Summary of the invention

[0009] The present invention aims to provide a control method of an RO system and a control program of a water treatment system, wherein the power consumption (i.e., CO) can be reduced by reducing the amount of chemicals used or the number of membrane replacements. 2) and the amount of waste, and can operate stably, and contribute to labor saving due to energy saving / reduction in maintenance.

[0010] In the control method of the RO system of the present invention, the RO system has a plurality of parallel RO devices and a control unit for controlling the start-stop processing of the RO devices including operation processing and stop processing, and is characterized in that the RO devices are controlled in such a way that the more easily the processing capacity is restored by start-stopping, the more times the start-stop is performed, and the stop time is controlled according to the recovery degree.

[0011] In one aspect of the present invention, a chemical that alleviates scaling is injected into the RO device that has been shut down for impregnation.

[0012] In one aspect of the present invention, the history of the start-stop process including the stop time of each RO device is stored, and the priority of the RO devices to be operated is determined based on the history of the start-stop process.

[0013] In one aspect of the present invention, the history of the membrane treatment performance of each RO device is associated with the history of the start-stop treatment of each RO device and is memorized. Based on the history of the start-stop treatment and the history of the membrane treatment performance, the degree of recovery of the membrane treatment performance expected through the start-stop treatment is estimated for each of the RO devices, and the RO device with a greater degree of recovery expected through the start-stop treatment and chemical immersion is prioritized.

[0014] In one aspect of the present invention, the outlet pressure or power consumption of a water supply pump for supplying water to the RO device is measured, and the RO device having a larger outlet pressure or power consumption is prioritized.

[0015] In one embodiment of the present invention, the number of start-stop processes during driving is determined based on an estimated result of the degree of recovery of the membrane treatment performance predicted by the start-stop process, and the number of start-stop processes within a specified time is determined in such a way that the effect becoming an indicator of the recovery efficiency of the membrane treatment performance becomes higher than the ratio of the start-stop number.

[0016] In one aspect of the present invention, the membrane treatment performance of each RO device at a current time point is measured, and the priority of the RO devices is determined based on the membrane treatment performance at the current time point.

[0017] A program according to one embodiment of the present invention is a control program for a water treatment system, which is a program for controlling a water treatment system having a plurality of parallel RO devices, wherein the program causes a computer to execute the following commands: a control command for controlling the start and stop processing of the RO devices including operation processing, stop processing and stop time; a memory command for memorizing the history of the start and stop processing of each RO device; and a priority determination command for determining the priority of the RO devices to be operated based on the history of the start and stop processing.

[0018] [Effects of the Invention]

[0019] According to the present invention, the processing efficiency of the RO system can be ensured by a simple structure. Even when chemical cleaning is not performed, the present invention can remove scale by stopping and operating the RO membrane device or adjusting the flow rate of each flow path. Therefore, even without adding a special hardware structure, scale removal can be performed by software, and the structure is simple. In addition, when chemical cleaning is performed, since the chemical injection is only performed for a very short time during the stop time of the RO membrane device, the amount of chemical used can be greatly reduced compared to continuous injection or cleaning. In addition, since no chemicals are added during the operation of the RO membrane device, there is no concern about leakage to the permeate side.

[0020] Furthermore, since fouling will also be removed during the start-stop actions included in the operation plan, by planning the start-stop treatment in consideration of the course of the start-stop actions performed in the operation plan, the number of treatments related to fouling removal can be suppressed, compared with patent document 1 which specifically performs emission treatment, thereby efficiently removing fouling. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a system diagram of an RO system to which the control method according to the embodiment is applied.

[0022] Figure 2 This is a flowchart showing the flow of determination based on the functional blocks.

[0023] Figure 3 This is a flowchart showing the flow of determination based on the functional blocks.

[0024] Figure 4 This is a flowchart showing the flow of determination based on the functional blocks.

[0025] Figure 5 Graph showing the change in differential pressure of the RO modules in Experimental Example 1 and Comparative Example 1.

[0026] Figure 6 Graph showing the change in differential pressure of the RO modules in Experimental Example 2 and Comparative Example 2. DETAILED DESCRIPTION

[0027] Hereinafter, embodiments will be described with reference to the drawings.

[0028] Figure 1 This is a system diagram of an RO system to which the control method according to the embodiment is applied.

[0029] Raw water is supplied from a raw water pipe 1 to a plurality of (four in the present embodiment) treatment systems (hereinafter sometimes referred to as series) A, B, C, and D to be subjected to RO treatment.

[0030] In each series A to D, raw water is transported from pipes 11 to 14 connected to the raw water pipe 1, pressurized by pumps 21 to 24, and then supplied (water supply) to cross-flow RO devices 41 to 44 from pipes 31 to 34.

[0031] The permeated water that permeates the RO membranes of the RO devices 41 to 44 is taken out as permeated water from the permeated water pipes 51 to 54 via the collecting permeated water pipe 55. Furthermore, a part of the permeated water is transported to the cleaning water tank 57 via the pipe 56 branched from the pipe 55 and stored. The water in the cleaning water tank 57 can be supplied to the water supply pipes 31 to 34 via the cleaning line 59 having the cleaning pump 58.

[0032] The concentrated water (brine) of the RO devices 41 to 44 is taken out as concentrated water from the concentrated water pipes 61 to 64 via the concentrated water collecting pipe 65 .

[0033] Each of the pipes 11 to 14 and 31 to 34 is provided with a sensor S1 and a sensor S2 for measuring flow rate, pressure, pH value, etc. Pipes 51 to 54 and pipes 61 to 64 are provided with a sensor S3 and a sensor S4 for measuring one or more characteristics such as flow rate, pressure, conductivity, etc. Pipes 51 to 54 and pipes 61 to 64 are provided with a valve V1 and a valve V2.

[0034] In addition, chemical injection parts 71 to 74 for injecting chemicals are connected to the pipes 11 to 14. For example, the injection point is on the upstream side of the pumps 21 to 24. The chemicals injected by the chemical injection parts 71 to 74 are chemicals for relieving scale, such as RO cleaning chemicals or slime control agents.

[0035] The detection data of each sensor is input to the control device (illustration omitted). In the control device, the operation planning data and the control program are stored in the memory. The pumps 21 to 24, 58, the valves V1, V2 and the injection pumps (illustration omitted) of the chemical injection parts 71 to 74 are controlled according to the signal from the control device.

[0036] In this embodiment, in addition to chemical cleaning, the cross-flow RO device is stopped and restarted for a short period of time for the purpose of physically removing scale, that is, "start-stop processing". The stop time in this start-stop processing can be arbitrarily changed.

[0037] The effects of the start-stop treatment in removing physical scale include: "releasing the compaction of membrane fouling substances caused by stopping the device, and flushing when starting the device (the change in the effective pressure on the membrane surface from stopping to starting is large, which makes it easy to promote the release of the compaction of the membrane surface)" or "suck back (reverse cleaning due to the osmotic pressure generated during stopping)". In addition, the start-stop treatment has by-products in the normal water flow treatment (for example, the change in the number of operating units due to the change in the permeate flow rate, etc.), so it is excellent in the following aspects: physical scale can be removed without stopping the water flow treatment and without using chemicals.

[0038] The execution of the start-stop process is determined based on whether the "recovery effect of the membrane performance brought about by the start-stop process (e.g., the reduction in power consumption)" is greater than 0, or exceeds the "cost incurred by the start-stop process (e.g., the increase in power consumption associated with the flushing process or the start-up of the pump)". When this condition is met, the start-stop process can be repeated as long as no abnormality in the desalination rate is detected.

[0039] Specifically, if Figure 2 to Figure 4 As shown, based on the relationship between the previous start-stop history of the RO device used and the history of the membrane treatment performance, the "estimated membrane treatment performance restored by start-stop treatment" in the change from "the membrane treatment performance after the most recent cleaning or replacement of the membrane" to "the membrane treatment performance at the current time point" is calculated, and then the "number of start-stops per unit specified time (for example, within the past 24 hours)" with high effectiveness is determined, and the "recovery effect of the membrane performance brought about by the start-stop treatment (for example, water supply pressure, power consumption)" is calculated at this time.

[0040] If a certain RO device is repeatedly started and stopped, the recovery effect gradually decreases. Therefore, the recovery effect of each device is calculated regularly (for example, every 3 hours), and the operation priority is allocated so that the system with high recovery effect is allocated as many start and stop times as possible.

[0041] In addition, physical fouling has the property of becoming more compacted as it accumulates on the membrane surface for a longer time, so the "recovery effect of membrane performance brought about by the start-stop treatment" gradually decreases. The power consumption of the membrane device increases as the "expected membrane treatment performance recovered by the start-stop treatment" remains, so the detection and execution of the start-stop treatment in the early stage can achieve a significant reduction in the power consumption per unit of permeate water and the number of cleaning times.

[0042] Start-stop and chemical treatment also have an effect on improving fouling to an extent that cannot be detected, so the number of starts and stops can also be optimized during machine learning.

[0043] In this embodiment, in a system where a plurality of RO devices are arranged in parallel as described above, the operation priority is determined, and in particular, the operation priority of the RO devices is determined based on the history of start and stop performed in the operation plan.

[0044] An upper limit is set for the number of changes in the operation priority. When the "number of starts and stops per specified time" of each RO device cannot be satisfied (for example, the operator is determined to perform an operation (operation) of the operation priority ranking twice a day), the operation priority is allocated in such a way that as many starts and stops as possible are allocated to the series with high recovery effect.

[0045] When the "number of starts and stops per specified time" of each RO device is satisfied, the "membrane treatment performance that can be restored by the start and stop process" is detected at an early stage, and the operation priority is allocated so that the start and stop process is executed at an early stage.

[0046] The time for stopping the operation of the RO device by the start-stop process is, for example, more than 5 minutes, and is preferably determined according to the recovery degree of the membrane treatment performance. By taking a certain degree of stop time, the recovery effect of the membrane treatment performance brought about by the differential pressure is improved. Furthermore, if the stop time is less than 5 minutes, the recovery effect of the membrane treatment performance of the RO device is sometimes insufficient.

[0047] Here, whether the membrane treatment performance has been fully restored is determined by whether the "energy required per unit permeate volume (power consumption, water supply pressure) after the start-up and shutdown" is lower than the "energy required per unit permeate volume (power consumption, water supply pressure) before the start-up and shutdown".

[0048] When the change from "membrane treatment performance after the most recent cleaning or replacement of the membrane" to "membrane treatment performance at the current time point" includes "membrane treatment performance that cannot be restored by start-stop treatment", it is dealt with by implementing other cleaning methods (such as chemical cleaning, flushing with chemicals or treated water, and chemical immersion during stop).

[0049] When the chemical is impregnated when the RO device is stopped during the start-stop process, the chemical concentration is arbitrary, but it is controlled within a range of 10 mg / L or more and below the concentration that does not cause chemical degradation of the membrane. The stop time and chemical concentration can be determined based on the outlet pressure and / or power consumption of the water supply pump 21 to the water supply pump 24 corresponding to the stopped RO device 41 to the RO device 44. The degree of recovery of the membrane treatment performance of the RO device can be calculated based on the history of the membrane treatment performance, and the stop time and chemical concentration can be determined. In addition, in the case of "membrane treatment performance that cannot be restored by the start-stop process", it is possible to automatically choose not to add chemicals.

[0050] The time for chemical injection can be extremely short, which can significantly reduce the amount of chemical used compared to continuous injection or chemical cleaning. In addition, since chemical injection is performed when the RO device is stopped, there is no worry about leakage to the permeate side.

[0051] By executing the start-stop processing planning in consideration of the history of the start-stop processing performed in the operation planning, the number of processing times related to the scale removal can be reduced compared to Patent Document 1 which specifically performs emission processing, and the scale can be removed efficiently.

[0052] In this RO system, the operation plan is determined based on the amount of water generated, etc. The operation plan includes information on the number of RO devices operating at each time point. The operation rate of the RO devices in other series is controlled so that the amount of permeate water during the period when the RO device is stopped during the start-stop process is as planned.

[0053] Furthermore, the control system has the following functional units.

[0054] <Control Department>

[0055] The operation and stop of the filtering device are controlled by controlling valves and pumps.

[0056] The start-stop process includes an operation of blocking the flow path on the permeated water side and an operation of reducing the flow rate of raw water.

[0057] <Measurement unit that measures water supply information>

[0058] For example, measuring pH value, raw water pressure, raw water flow, etc.

[0059] <Measurement unit for measuring membrane processing performance>

[0060] For example, it can measure the water supply pressure, permeate water pressure, brine pressure, water supply flow, permeate water flow, brine flow, water temperature, water supply conductivity, treated water conductivity, etc.

[0061] <Acquisition section for acquiring pump status>

[0062] For example, frequency, output current, output voltage, power consumption, and outlet pressure can be obtained.

[0063] <Recording section for recording device information>

[0064] For example, the memory membrane area, the number of membrane vessels, the structure of the membrane, etc.

[0065] <Memory section for memory maintenance history>

[0066] Memorize the membrane processing performance (such as water supply pressure, membrane pressure difference, flux) after the most recent cleaning or membrane replacement.

[0067] <Memory section for memorizing the start and stop history>

[0068] The system memorizes the start and stop history according to the water treatment operation plan and the start and stop history for the purpose of removing suspended solids (SS). It also memorizes the stop time during the start and stop process.

[0069] <Memory section for recording the history of priorities>

[0070] The history of the priority instructed from the control unit is memorized.

[0071] <Calculation section for calculating membrane treatment performance>

[0072] For example, calculate the pressure difference and flux between membranes.

[0073] <Power consumption estimation unit>

[0074] When power consumption is not measured continuously, power consumption is estimated based on measured values ​​(for example, water supply pressure and water supply flow rate).

[0075] <Fouling estimation unit>

[0076] Based on the treatment performance after the most recent cleaning or replacement of the membrane, the effect of operating conditions (such as inlet water pressure, treatment water flow rate, and temperature) is eliminated from the difference in treatment performance reduction due to continued operation, and the change in membrane treatment performance due to fouling is calculated.

[0077] The nature of fouling is classified. For example, the membrane treatment performance that is expected to be restored by the start-stop process is calculated from the change in membrane treatment performance due to fouling, thereby detecting the membrane treatment performance that cannot be restored by the start-stop process.

[0078] <Start-Stop Effectiveness Estimation Section>

[0079] The recovery effect of the membrane treatment performance expected by the start-stop process, that is, the start-stop effectiveness, is estimated for each RO device. This is because the effectiveness of the start-stop for recovery of the membrane treatment performance varies depending on the RO device.

[0080] The effectiveness of the start-stop of each RO device is estimated based on the relationship between the start-stop history and the membrane treatment performance history in the past (e.g., within 1 year). For example, the degree of recovery of the treatment performance caused by the start-stop is calculated by referring to the number of starts and stops within a specified period and the changes in the membrane treatment performance before and after the starts and stops.

[0081] <Start-Stop Planning Department>

[0082] Based on the start-stop history, the timing of future start-stop processing is planned. The RO device that has not been started or stopped within the specified period is started or stopped.

[0083] The number of starts and stops is determined based on the estimation result of the start-stop effectiveness estimation unit. The number of starts and stops is determined in such a way that the ratio of the effect, which is an indicator of recovery efficiency, to the number of starts and stops becomes higher (for example, when there is no difference in the degree of recovery between 5 starts and stops and 4 starts and stops within 24 hours, it is set to 4 times).

[0084] <Priority Determination Department>

[0085] Based on the start-stop history of each RO device, the priority of the RO devices to be started and stopped is determined.

[0086] The RO device with high start-stop efficiency is prioritized.

[0087] Furthermore, the RO devices with higher outlet pressure or power consumption of the high-pressure pump (water supply pump) acquired by the pump state acquisition unit are prioritized. In addition, the RO devices with higher recovery of membrane treatment performance expected by chemical immersion treatment are prioritized.

[0088] <Chemical injection control department>

[0089] A chemical injection unit is provided at the inlet of each RO device arranged in parallel (for example, in front of the water supply pump), and the chemical is injected before the RO device stops based on the control of the chemical injection control unit. The chemical concentration can be set high enough to not damage the membrane. Regarding the chemical injection pump, if a pump with a high discharge pressure such as a water supply pump is used, the flow rate becomes too large and it is difficult to maintain a high chemical concentration. Therefore, it is preferable to use a pump with a low discharge pressure such as a raw water pump to increase the chemical concentration at a constant flow rate.

[0090] In addition, the chemical injection control unit estimates the degree of recovery of the membrane treatment performance expected by the chemical immersion for each RO device.

[0091] <Experimental example>

[0092] The change in differential pressure (delta pressure / MPa) of the first RO module where biofouling is likely to occur in an RO device for seawater desalination equipped with a 4-inch module was measured.

[0093] Experimental Example 1

[0094] Figure 5 Between 12 / 21 and 1 / 4 shown in the figure, the machine was operated under the start-stop condition of 16.65 minutes of stop, 5 minutes of flushing process, and then 55 minutes of continuous operation. It was confirmed that the pressure difference had a smaller tendency to increase than the continuous operation without start-stop, and stable operation was possible.

[0095] Comparative Example 1

[0096] Figure 5 Between 12 / 7 and 12 / 19, the operation was performed under the start-stop condition of stopping for 5 minutes and then continuously operating for 55 minutes. It was confirmed that there was basically no difference from continuous operation without starting and stopping.

[0097] Experimental Example 2

[0098] Next, under the raw water conditions that are more prone to biofouling, after the differential pressure increased, 100 mg / L of slime control agent (Kuriverter IK-220, Kurita Industry Co., Ltd.) was added and the process was stopped for 24 hours, and the change in differential pressure at this time was measured. The measurement results are shown in Figure 6 middle.

[0099] Comparative Example 2

[0100] After the pressure difference increases, the pressure difference is measured for 24 hours without adding chemicals. The measurement results are shown in Figure 6 middle.

[0101] like Figure 6 As shown, it was confirmed that when the chemical was added, the differential pressure decreased, and when the chemical was not added, the differential pressure did not change. In addition, the optimal value of the chemical concentration differs depending on the state of biofouling.

[0102] Although the present invention has been described in detail using specific embodiments, it will be apparent to one skilled in the art that various modifications can be made without departing from the spirit and scope of the present invention.

[0103] This application is based on Japanese patent application No. 2022-111256 filed on Jul. 11, 2022, the entire contents of which are incorporated herein by reference.

[0104] Description of Reference Numerals

[0105] 21-24: Pump.

[0106] 41~44:RO device.

[0107] 57: Cleaning box.

[0108] 71~74: Chemical injection section.

Claims

1. A method for controlling a reverse osmosis system, wherein the reverse osmosis system comprises a plurality of reverse osmosis devices arranged in parallel, and a control unit for controlling a start-stop process including an operation process and a stop process of the reverse osmosis devices, wherein: The reverse osmosis device whose processing capacity is easily restored by start-stop is controlled so that the number of start-stops increases, and the stop time is controlled according to the degree of recovery.

2. The method for controlling a reverse osmosis system according to claim 1, wherein: The reverse osmosis device that has been shut down is injected with a scale-mitigating chemical and impregnated.

3. The control method of the reverse osmosis system according to claim 2, wherein: Memorize the start and stop process history of each reverse osmosis device including the stop time, The priority of the reverse osmosis devices to be operated is determined based on the history of the start-stop process.

4. The method for controlling a reverse osmosis system according to claim 3, wherein: The history of membrane treatment performance of each reverse osmosis device is associated with the history of start-stop treatment of each reverse osmosis device and memorized. Based on the history of the start-stop process and the history of the membrane treatment performance, the degree of recovery of the membrane treatment performance expected by the start-stop process is estimated for each of the reverse osmosis devices, The reverse osmosis device having a greater degree of recovery expected through the start-stop treatment and chemical immersion is prioritized.

5. The method for controlling a reverse osmosis system according to claim 4, wherein: measuring the outlet pressure or power consumption of a water supply pump that supplies water to the reverse osmosis device, The reverse osmosis device having a larger outlet pressure or a larger power consumption is prioritized.

6. The method for controlling a reverse osmosis system according to claim 5, wherein: The number of times of the start-stop processing during driving is determined based on an estimated result of the degree of recovery of the membrane treatment performance predicted by the start-stop processing, The number of starts and stops within a predetermined time is determined so that the ratio of the effect, which is an index of the recovery efficiency of the membrane treatment performance, to the number of starts and stops becomes high.

7. The method for controlling a reverse osmosis system according to any one of claims 1 to 6, wherein: Measure the membrane treatment performance of each reverse osmosis device at the current time point, The reverse osmosis devices are prioritized based on the membrane processing performance at the current point in time.

8. A water treatment system control program, which is a program for controlling a water treatment system having a plurality of reverse osmosis devices in parallel, wherein: The control program of the water treatment system causes the computer to execute the following commands: Control commands for controlling the reverse osmosis device including operation processing, stop processing and stop time start and stop processing; Memory commands, memorize the start and stop processing history of each reverse osmosis device; as well as The priority order determination command determines the priority order of the reverse osmosis devices to be operated based on the history of the start-stop process.

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