Method and device for estimating cause of performance degradation in anion exchange device

Abstract

Provided are a method and device for estimating the cause of performance degradation in an anion exchange device. The present invention pertains to a cause estimation method for estimating the cause of a decrease in performance in an anion exchange device that alternately performs desalination treatment and regeneration treatment, the method comprising: a step for acquiring time-series data for at least one of a measured value for a pressure difference and a measured value for the quality of treated water during the implementation of the desalination treatment; and a step for dividing each cycle into a predetermined number of averaging periods, with the period from the execution of the regeneration process to the execution of the next regeneration process being one cycle, and calculating an average value for each averaging period on the basis of each measurement value constituting the time-series data. In each cycle, a sequence number counted from the beginning is assigned to the averaging period in the cycle, and the cause of a decrease in performance in the anion exchange device is estimated on the basis of the transition of the average value at the time of repeating the cycle.

Description

Technical Field

[0001] This invention relates to a method and apparatus for managing the operation of anion exchange devices equipped with anion exchange resins or other anion exchangers, and more particularly to a method and apparatus for estimating the cause of performance degradation of anion exchangers by detecting the occurrence of abnormalities or their precursors in the anion exchange device. Background Technology

[0002] Pure water production systems that generate pure and ultrapure water from raw water sources such as municipal water, groundwater, and river water include ion exchange devices filled with ion exchange resins. Ion exchange resins include anion exchange resins and cation exchange resins. Ion exchange devices are sometimes also used in wastewater treatment systems used for wastewater treatment. Pure water production systems may include, for example, activated carbon towers filled with activated carbon, cation exchange resin towers filled with cation exchange resins, anion exchange resin towers filled with anion exchange resins, and decarbonation towers to remove carbonic acid from the water. In this pure water production system, raw water that has been filtered to remove waste and other contaminants is supplied to the activated carbon tower. The outlet water from the activated carbon tower is supplied to the cation exchange resin tower, and the outlet water from the cation exchange resin tower is supplied to the anion exchange resin tower via the decarbonation tower. Pure water flows out from the outlet of the anion exchange resin tower. Alternatively, another cation exchange resin tower can be installed downstream of the anion exchange resin tower, and the outlet water from that cation exchange resin tower can be used as pure water.

[0003] In such a pure water production system, if pure water production continues, the ionic impurities contained in the raw water are captured by the cation exchange resin in the cation exchange resin tower and the anion exchange resin in the anion exchange resin tower, thus removing the ionic impurities from the water. The captured ionic impurities accumulate in the ion exchange resins. If the amount of accumulated ionic impurities in the ion exchange resin exceeds a certain value, it becomes impossible to remove the impurities further. Therefore, the ion exchange resin needs to be replaced or regenerated before this happens. Since ion exchange resins also deteriorate with long-term use, they also need to be replaced at any time during repeated regeneration processes. Therefore, various methods have been proposed to evaluate the performance of ion exchange resins and thus predict their replacement or regeneration time.

[0004] Patent Document 1 discloses a method for evaluating the performance of anion exchange resin packed in an ion exchange resin tower. It calculates the mass transfer coefficient of the anion exchange resin relative to inorganic carbonic acid by measuring the concentration of inorganic carbonic acid at the inlet and outlet water of the ion exchange resin tower, and evaluates the dynamic characteristics and degree of degradation of the anion exchange resin based on this mass transfer coefficient. According to this performance evaluation method, the lifespan or replacement time of the anion exchange resin can be predicted based on the evaluation results. Patent Document 2 discloses a method for periodically measuring the time from the end of the regenerator flow to the point where the water quality of the effluent from the ion exchange resin reaches a specified value in an ion exchange device that repeatedly performs desalination treatment (ion exchange treatment) and regeneration treatment of the ion exchange resin. The replacement time of the ion exchange resin is predicted based on the measured time. Patent Document 3 discloses a method for predicting the lifespan of an ion exchange resin used in high-temperature environments. For each of a plurality of temperatures, the relationship between the temperature and the time until the ion exchange capacity decreases to a certain degree during desalination treatment at that temperature is pre-determined. The amount of decrease in ion exchange capacity is calculated based on the current detection temperature and accumulated, thereby predicting the lifespan of the ion exchange resin. Patent document 4 discloses a method for operating an ion exchange device by repeatedly performing desalination and regeneration treatments. The total ion load of the raw water is calculated based on the conductivity and specific ion concentration in the raw water. The resin composition of the ion exchange resin is predicted based on the calculated value. The water quality of the effluent from the ion exchange resin and the amount of raw water that can be treated are predicted based on the predicted value. The switching from desalination treatment to regeneration treatment is performed based on the prediction.

[0005] Patent Document 5 discloses a method for evaluating the performance of ion exchange resin by mixing and contacting a salt aqueous solution of a specified concentration with a specified amount of ion exchange resin, and measuring the change in conductivity of the mixed salt aqueous solution over time. In the method described in Patent Document 5, the change in conductivity over time is converted into a curve showing the change in ion concentration over time. The total capacity mass transfer coefficient and selectivity are calculated based on the exchange capacity with the ion exchange resin. The replacement time of the ion exchange resin can be determined by the product of the exchange capacity, the total capacity mass transfer coefficient, and the selectivity. Patent Document 6 discloses a method for evaluating the performance of ion exchange resin in a mixed-bed ion exchange resin tower filled with both anion and cation exchange resins. It discloses supplying pure water to the regenerated ion exchange resin for cleaning, and determining the degree of degradation of the ion exchange resin based on the measured value of the total organic carbon (TOC) concentration in the cleaning effluent. Patent Document 7 discloses a method that involves changing the conditions of accelerated degradation treatment, repeatedly adding an oxidant to a cation exchange resin and performing accelerated degradation treatment to measure the water content of the ion exchange resin, determining the degree of degradation based on the water content, and conducting various evaluation tests on the degraded ion exchange resin to determine its pass / fail status, thereby predicting the lifespan of the cation exchange resin. Patent Document 8 discloses a method for evaluating the performance and diagnosing the degradation of anion exchange resin considering reaction rate. This method involves passing a silica-containing solution through anion exchange resin housed in a microcolumn, measuring the silica concentration in the effluent from the column, and evaluating the performance of the anion exchange resin based on the measurement results.

[0006] Existing technical documents Patent documents Patent Document 1: Japanese Patent Application Publication No. 2002-48776 Patent Document 2: Japanese Patent Application Publication No. 2019-76844 Patent Document 3: Japanese Patent Application Publication No. 2002-143694 Patent Document 4: Japanese Patent Application Publication No. 6-55082 Patent Document 5: Japanese Patent Application Publication No. 2015-13276 Patent Document 6: Japanese Patent Application Publication No. 11-237370 Patent Document 7: Japanese Patent Application Publication No. 5-104000 Patent Document 8: Japanese Patent Application Publication No. 2020-131130 Summary of the Invention

[0007] The technical problem that the invention aims to solve The methods disclosed in Patent Documents 1-8 all evaluate the performance or predict the lifespan of ion exchange resins, but they cannot predict the causes of unexpected performance degradation in ion exchange resins. When operating ion exchange devices, it is necessary not only to predict in advance the timing of ion exchange resin replacement and regeneration, but also to predict the causes of unexpected performance degradation. In particular, anion exchange resins are prone to performance degradation due to the inflow of TOC and silica (SiO2) components; therefore, it is strongly required to identify the causes of anion exchange resin performance degradation and implement countermeasures.

[0008] The object of the present invention is to provide a method and apparatus for estimating the cause of performance degradation in anion exchange devices, such as anion exchange resin towers filled with anion exchange resin as an anion exchanger, based on time series data obtained from a system equipped with the anion exchange device.

[0009] Technical solutions for solving technical problems In anion exchangers equipped with anion exchangers, desalination treatment, in which the water to be treated is passed through the anion exchangers for desalination, and regeneration treatment, in which the anion exchangers are regenerated using a regenerant, are performed alternately. Typically, such anion exchangers are assembled into water treatment systems. An example of a water treatment system equipped with anion exchangers is a pure water production system that produces pure water from municipal water, well water, river water, etc. When measuring quantities related to the operation and state of a water treatment system, such as flow rate, pressure, and water quality, these measured values ​​change as anomalies that may cause performance degradation in the anion exchanger occur. Therefore, it is believed that by analyzing the trends in these changes, the cause of performance degradation that has occurred or may occur in the anion exchanger can be deduced. However, the measured values ​​obtained from a water treatment system contain deviations based on various factors, making it difficult to automatically deduce the cause of performance degradation in the anion exchanger simply by mechanically processing the measured values.

[0010] Therefore, one aspect of the cause estimation method of the present invention is a method for estimating the cause of performance degradation in an anion exchanger, the anion exchanger being configured to have anion exchangers and to allow treated water to pass through the anion exchangers, alternating between desalination and regeneration processes, wherein the desalination process desalinates the treated water and the regeneration process regenerates the anion exchangers. In this cause estimation method, during the implementation of the desalination process, time-series data are obtained from at least one of the measured values ​​of the pressure difference of the anion exchangers and the water quality of the treated water discharged from the anion exchanger. One cycle is defined as the period from the start of the regeneration process to the next regeneration process of one desalination process; each cycle is divided into a predetermined number of averaging periods, and each averaging period contained in the cycle is assigned a sequential number starting from the beginning of the cycle. Based on this, in one aspect of the cause estimation method, the cause of performance degradation in the anion exchanger is estimated based on how the average value calculated from the various measured values ​​constituting the time-series data shifts during repeated cycles in the averaging periods with specific sequential numbers.

[0011] During the desalination process, in addition to the water intake period during which the treated water is introduced and desalination is actually carried out, there may also be a stop period where the water intake is temporarily stopped so that the treated water is no longer needed. As for the average value, any value that can represent the data values ​​within the averaging period, i.e., the characteristic quantity, can be used. For example, the average value can be the centroid of the data values ​​within the averaging period, i.e., the arithmetic mean, the geometric mean, or the harmonic mean. The average value can be the median, the maximum value, the minimum value, the deviation, or the Mahalanobis distance used in the MT (Maharanobis-Taguchi) method. Furthermore, the average value can also be the average calculated from the logarithms of the data values.

[0012] One aspect of the present invention is a cause estimation device for estimating the cause of performance degradation in an anion exchanger. The anion exchanger is configured to include anion exchangers and allow treated water to pass through them, and alternately performs desalination and regeneration treatments. The desalination treatment desalinates the treated water, and the regeneration treatment regenerates the anion exchangers. The cause estimation device includes: a measurement unit disposed in the anion exchanger that measures at least one of the pressure difference with respect to the anion exchangers and the water quality of the treated water discharged from the anion exchanger, and outputs this as time-series data; and an average... The averaging period setting unit sets the averaging period in such a way that the period from the start of the regeneration process to the start of the next regeneration process is taken as one cycle, such that each cycle is divided into a predetermined number of averaging periods, and in each cycle, the averaging periods contained in the cycle are assigned sequential numbers starting from the beginning of the cycle; the average value calculation unit calculates the average value of each measured value constituting the time series data in the averaging periods with specific sequential numbers for each cycle; and the estimation unit estimates the cause of performance degradation in the anion exchanger based on the shift of the average value during repeated cycles.

[0013] Invention Effects According to the present invention, regarding anion exchange devices such as anion exchange resin towers, the cause of performance degradation in the anion exchange device can be inferred based on time series data obtained by measurements in water treatment systems or the like equipped with the anion exchange device. Attached Figure Description

[0014] Figure 1 This is a diagram illustrating an example of the structure of a water treatment system using a cause estimation method according to an embodiment of the present invention.

[0015] Figure 2 This is a diagram illustrating an example of the structure of an ion exchange treatment unit.

[0016] Figure 3 This is another example of the structure of an ion exchange treatment unit.

[0017] Figure 4 This is a graph illustrating an example of changes in electrical conductivity.

[0018] Figure 5 This is a graph illustrating an example of changes in electrical conductivity.

[0019] Figure 6 This is a graph illustrating an example of pressure differential change.

[0020] Figure 7 This is a graph illustrating an example of changes in electrical conductivity.

[0021] Figure 8 This is a flowchart illustrating the steps to determine the cause of performance degradation in an anion exchanger.

[0022] Figure 9 This is a block diagram illustrating an example of the structure of a cause-prediction device. Detailed Implementation

[0023] Next, the method for carrying out the present invention will be described with reference to the accompanying drawings. Figure 1 This example illustrates the structure of a water treatment system using a cause estimation method according to one embodiment of the present invention. In this embodiment, in a water treatment system equipped with an anion exchange device, the cause of performance degradation that has occurred or may occur in the anion exchange device is estimated based on the time-dependent changes in measured values ​​obtained from the water treatment system.

[0024] Figure 1 The water treatment system shown is configured as a pure water production system that produces pure water from raw water sources such as municipal water, well water, and river water. A storage tank 21 is provided for storing the supplied raw water. The raw water in the storage tank 21 is pumped by a pump 22 and passes through a filter 23 to remove solid components. The outlet water of the filter 23 is stored in a storage tank 24. Recycled water recovered from equipment that uses pure water is also supplied to the storage tank 24. The water in the storage tank 24 is pumped by a pump 25 to an activated carbon tower 26 for activated carbon treatment. The outlet water of the activated carbon tower 26 is supplied to an ion exchange treatment unit 30. The ion exchange treatment unit 30 uses the outlet water of the activated carbon tower 26 as treated water and performs desalination treatment on it. The outlet water of the ion exchange treatment unit 30 is pumped by a pump 41 and supplied to a reverse osmosis membrane unit 42. Pure water is discharged from the reverse osmosis membrane unit 42.

[0025] Figure 2 This illustrates an example of the structure of the ion exchange treatment unit 30. The ion exchange treatment unit 30 includes: a cation exchange resin tower 31 filled with cation exchange resin and supplied with the outlet water of the activated carbon tower 26; a decarbonation tower 32 supplied with the outlet water of the cation exchange resin tower 31; and an anion exchange resin tower 33 filled with anion exchange resin and supplied with the outlet water of the decarbonation tower 32. The anion exchange resin tower 33 is an anion exchange apparatus applicable to the cause-prediction method based on the present invention. In the anion exchange resin tower 33, desalination treatment, in which the outlet water of the decarbonation tower 32 is supplied as the treated water for desalination, and regeneration treatment, in which the anion exchange resin is regenerated using a regenerant, are alternately performed. During desalination treatment, the outlet water of the anion exchange resin tower 33 is supplied to the downstream reverse osmosis membrane unit 42. As a result of the cation exchange treatment performed in the cation exchange resin tower 31, the outlet water of the cation exchange resin tower 31 becomes containing hydrogen ions (H+). +The water supplied to the cation exchange resin tower 31 contains carbonate ions (CO3-), which makes it acidic. 2- ), bicarbonate ions (HCO3) - The carbon dioxide is converted into free carbonic acid. The decarbonation tower 32 is provided to remove this free carbonic acid by air blowing or membrane degassing. As a result of providing the decarbonation tower 32, water free of carbonic acid is supplied to the anion exchange resin tower 33.

[0026] The cation exchange resin packed in the cation exchange resin tower 31 can be a strongly acidic cation exchange resin (SACER) or a weakly acidic cation exchange resin (WACER). Furthermore, for the cation exchange resin tower 31, the strongly acidic and weakly acidic cation exchange resins can be mixed and packed in a mixed bed configuration, or they can be packed in a dual-bed configuration. In the illustrated example, these cation exchange resins are packed in a dual-bed configuration with the upstream side being a weakly acidic cation exchange resin and the downstream side being a strongly acidic cation exchange resin. Similarly, the anion exchange resin packed in the anion exchange resin tower 33 can be a strongly basic anion exchange resin (SBAER) or a weakly basic anion exchange resin (WBAER). Furthermore, for the anion exchange resin tower 33, the strongly basic and weakly basic anion exchange resins can be mixed and packed in a mixed bed configuration, or they can be packed in a dual-bed configuration. Furthermore, the anion exchange resin tower 33 can be constructed by connecting a first packed tower packed with weakly basic anion exchange resin and a second packed tower packed with strongly basic anion exchange resin in series. In the illustrated example, an anion exchange resin tower 33 is constructed by filling a single packed tower with the upstream side being a weakly basic anion exchange resin and the downstream side being a strongly basic anion exchange resin in a multi-bed configuration.

[0027] In the ion exchange treatment unit 30, two pressure gauges (PI) 36 and 37 are installed to measure the pressure difference generated when the treated water passes through the anion exchange resin tower 33 during desalination treatment. In this embodiment, when TOC components flow into the anion exchange resin tower 33, the weakly basic anion exchange resin located upstream of it in the anion exchange resin tower 33 is easily affected by the inflow of TOC components. Therefore, in order to be able to measure the pressure difference generated in the layer of weakly basic anion exchange resin in the anion exchange resin tower 33, a pressure gauge 36 is installed on the pipe connected to the inlet of the anion exchange resin tower 33, and a pressure gauge 37 is installed in the anion exchange resin tower 33 to measure the pressure inside the anion exchange resin tower 33 at the position where the layer of weakly basic anion exchange resin contacts the layer of strong basic anion exchange resin. Furthermore, in order to measure the water quality of the effluent from the anion exchange resin tower 33, i.e., the treated water discharged from the anion exchange resin tower 33, a conductivity meter (CI) 38 is installed on the piping connected to the outlet of the anion exchange resin tower 33. Since conductivity (electrical conductivity) is inversely related to resistivity (specific resistance, resistivity coefficient), a resistivity meter can also be installed on the piping connected to the outlet of the anion exchange resin tower 33 instead of the conductivity meter 38.

[0028] Figure 3 Another example showing the structure of the ion exchange treatment unit 30. Figure 3 The ion exchange treatment unit 30 shown is Figure 2 The ion exchange treatment unit 30 shown is the same, but a cation exchange resin tower 34 is further provided downstream of the anion exchange resin tower 33. The outlet water of the anion exchange resin tower 33 is supplied to the cation exchange resin tower 34, which is the same as... Figure 2 The structures shown are different. Furthermore, instead of installing a conductivity meter 38 to measure the conductivity of the outlet water of the anion exchange resin tower 33, a resistivity meter (RI) 39 to measure the resistivity of the outlet water of the cation exchange resin tower 34, i.e., the treated water from the ion exchange treatment unit 30, is installed on the piping connected to the outlet of the cation exchange resin tower 34. Alternatively, a conductivity meter can be installed on the piping connected to the outlet of the cation exchange resin tower 34 instead of the resistivity meter 39. In the cation exchange resin tower 34, located downstream of the anion exchange resin tower 33, a strongly acidic cation exchange resin is, for example, packed in a single bed.

[0029] Next, the performance degradation in the anion exchange resin tower 33 and the resulting phenomena will be explained. When TOC components flow into the anion exchange resin tower 33, the anion exchange resins within the tower, especially weakly basic anion exchange resins, are easily affected. The impact on the anion exchange resins varies depending on the molecular weight of the TOC components. Hereinafter, TOC components with a molecular weight of 100 or higher will be referred to as high molecular weight TOC components, and TOC components with a molecular weight of less than 100 will be referred to as low molecular weight TOC components. High molecular weight TOC components include humic substances and components dissolved due to oxidative degradation of the cation exchange resin. Among the components dissolved due to oxidative degradation are, for example, polystyrene sulfonic acid (PSS), a component of the cation exchange resin. Low molecular weight TOC components include organic acids, alcohols, aldehydes, etc., with smaller molecular weights.

[0030] If high molecular weight TOC components such as humic substances and polystyrene sulfonic acid flow into and accumulate in the anion exchange resin tower 33, the water quality from the anion exchange resin tower 33 will deteriorate during the switch from regeneration to desalination. Furthermore, the reaction rate in the anion exchange reaction will decrease. These phenomena are particularly pronounced in the weakly basic anion exchange resin layer. If the water quality deteriorates, the conductivity of the treated water immediately after switching to desalination will be higher, i.e., the initial conductivity, indicating water quality deterioration. It is believed that the deterioration in water quality is mainly due to sodium ions (Na+). + The leaked sodium ions can be captured by the cation exchange resin, therefore, if it is Figure 3 In the ion exchange treatment unit 30 shown, the conductivity of the outlet water from the anion exchange resin tower 33 is higher than that of the outlet water from the cation exchange resin tower 34. To suppress the deterioration of the initial conductivity, the regeneration time needs to be extended. If the reaction rate in the anion exchange reaction decreases, the leakage of anions from the anion exchange resin tower 33 increases, deteriorating the stable conductivity of the treated water during the period of stable desalination. Here, the period of stable desalination refers to the period excluding the initial period after desalination begins and the period immediately before its end. Figure 3 In the ion exchange treatment unit 30 shown, the leaked anions are not captured in the downstream cation exchange resin tower 34. Therefore, the conductivity of the outlet water of the anion exchange resin tower 33 is approximately equal to that of the outlet water of the cation exchange resin tower 34.

[0031] If low-molecular-weight TOC components such as organic acids flow into and accumulate in the anion exchange resin tower 33, the pressure differential of the anion exchange resin tower 33, especially in the layer of weakly basic anion exchange resin, will increase. Furthermore, a certain amount of anions will leak prematurely during desalination. The increase in pressure differential is attributed to the high swelling rate of the anion exchange resin. The pressure differential may gradually increase during desalination, for example. A similar increase in pressure differential will also occur when weakly conductive substances with low ion selectivity, such as borate ions, flow into the anion exchange resin tower 33. "Weakly conductive substances with low ion selectivity" refers to substances whose acid dissociation constant in water, pKa, satisfies pKa ≥ 4.0. Strong acids such as formic acid and oxalic acid are not considered "weakly conductive substances with low ion selectivity," but common TOC components, including acetic acid and propionic acid, are. While weakly conductive materials with low ion selectivity also contain inorganic substances such as borate ions, the behavior of silica components when accumulating in the anion exchange resin layer differs from that of low molecular weight TOC components. Therefore, the term "weakly conductive materials with low ion selectivity" in this specification does not include silica components. It should be noted that in the event of anion exchange resin breakage, the pressure differential increases uniformly depending on the amount of breakage. If a certain amount of anions leaks early on, the period until the next regeneration process may be correspondingly shorter.

[0032] If silica flows into and accumulates in the anion exchange resin tower 33, the anion exchange resins within tower 33, especially the strongly basic anion exchange resins, will be affected. This will lead to a decline in the quality of the treated water from tower 33 during desalination, with a higher initial conductivity and faster depletion of the anion exchange resin's ion exchange capacity, causing the anion exchange resin to reach its breakthrough point earlier. It is believed that the decline in water quality is mainly due to sodium ion leakage. In this case, if... Figure 3 In the ion exchange treatment unit 30 shown, the conductivity of the outlet water of the anion exchange resin tower 33 is also higher than that of the outlet water of the cation exchange resin tower 34. It should be noted that silica itself can be captured by the anion exchange resin; therefore, if the anion exchange resin is sufficiently regenerated through a regeneration process, even if silica flows into the anion exchange resin tower 33, it will not cause a deterioration in the initial conductivity or premature breakthrough. It should also be noted that the regeneration of the anion exchange resin that has captured silica is promoted by heating; therefore, when there is a possibility of silica flowing in, a heating regeneration process is usually performed during the regeneration of the anion exchange resin.

[0033] In the cause estimation method of this embodiment, Figure 2 or Figure 3In the water treatment system shown, based on the measurements obtained from pressure gauges 36 and 37 and conductivity meter 38 (or resistivity meter 39), determine whether the performance degradation of the anion exchange resin tower 33 is due to: (1) Low molecular weight TOC components, or weakly conductive substances with molecular weight less than 100 such as borate ions, flow in and accumulate. (2) High molecular weight TOC components flow in and accumulate; or (3) Silica components flow in and accumulate. This identification will be explained in detail below. In this explanation, when referring to low molecular weight TOC components, it refers to weakly conductive substances with a molecular weight less than 100 and low ion selectivity, represented by low molecular weight TOC components. Therefore, the low molecular weight TOC components mentioned here also contain borate ions.

[0034] In the anion exchange resin tower 33, which serves as an anion exchange device, desalination and regeneration processes are performed alternately, with one desalination process referred to as one cycle. Pressure gauges 36 and 37 and a conductivity meter 38 (or resistivity meter 39) continuously measure at least during the desalination process, and the resulting measurements are output as time-series data. In this embodiment, each cycle is divided into a predetermined number of averaging periods. Each cycle is assigned a sequential number starting from the beginning of that cycle for these averaging periods. Then, based on how the average value calculated from the various measurements constituting the time-series data shifts during repeated cycles in the averaging periods with specific sequential numbers, the cause of performance degradation in the anion exchange device is estimated. The shift in the average value during repeated cycles can be determined, for example, by investigating how the average value changes according to the times representing the cycles, such as the start time of the cycle.

[0035] Figure 4 This means that in Figure 2 The graph shown illustrates the changes in conductivity measured by conductivity meter 38 as high molecular weight TOC components flow into anion exchange resin tower 33 in the water treatment system. (a) represents the time variation of conductivity for each cycle, (b) represents the cycle being divided into averaging periods, and (c) represents the shift of the average value during repeated cycles. Figure 4 In (a), the changes in conductivity are shown for each of the four desalination cycles, from the first to the fourth. In each cycle, the conductivity is relatively high at the beginning of the desalination process, and then decreases rapidly to a stable value. If the changes in conductivity for each cycle are compared, both the initial and stable conductivity deteriorate with repeated cycles, as indicated by the arrows in the diagram.

[0036] Figure 4(b) shows an example of dividing each cycle into 5 averaged periods based on a common benchmark, illustrating... Figure 4 The conductivity curve shown in (a) is divided into averaged periods. In the figure, the five averaging periods are represented by “[1]” to “[5]” enclosed in square brackets, indicating the sequential numbering from the beginning of the cycle. In particular, averaging period [1] includes the period after the start of the desalination process, and averaging period [5] includes the period before the end of the desalination process. As a basis for dividing into averaging periods, for example, dividing the cycle into 5 equal parts for its duration can be taken. In the example shown, in order to separate the behavior in the period after the start and the period before the end from the other periods, the lengths of averaging periods [1] and [5] are shorter than the lengths of the other averaging periods [2] to [4]. Moreover, in this embodiment, for each cycle and for each averaging period, the arithmetic mean of the measured conductivity values ​​is calculated as the average value. The arithmetic mean is also called the centroid value. After calculating the average value of the measured conductivity values ​​for each cycle and for each averaging period, the average value of the averaging periods in the prescribed sequential numbering is then examined, starting from the beginning of each cycle, to investigate how the average value changes with repeated cycles. Figure 4 (c) focuses on the beginning of the cycle, namely the first averaging period [1] and the third averaging period [3], indicating how the average conductivity changes during each averaging period as the cycle repeats. Here, the start time of each cycle is referred to as the timestamp assigned to that cycle. Figure 4 (c) indicates how the average values ​​of [1] and [3] change during the averaging period as the timestamps are elapsed.

[0037] In the example shown here, such as Figure 4As shown in (c), the average value obtained from the averaging period [1] tends to increase with repeated cycles. The averaging period [1] is the averaging period corresponding to the beginning of the desalination process, so the increase in the average conductivity with repeated cycles during this averaging period indicates a deterioration in the initial conductivity. Similarly, the averaging period [3] is the averaging period corresponding to the period when the desalination process reaches a stable state, so the increase in the average conductivity with repeated cycles during this averaging period indicates a deterioration in the stable conductivity. As mentioned above, when high molecular weight TOC components flow into and accumulate in the anion exchange resin tower 33, both the initial conductivity and the stable conductivity deteriorate. Therefore, as long as it can be confirmed that the average conductivity increases with repeated cycles during either the averaging period [1] or [3], it can be determined that there is a possibility that high molecular weight TOC components flow into and accumulate in the anion exchange resin tower 33. As will be described later, due to other factors, the average values ​​during the averaging period [1] and [3] sometimes gradually increase. Therefore, by simply detecting the change in the average conductivity during the averaging period [1] and [3], it is impossible to determine whether the high molecular weight TOC component flows into and accumulates in the anion exchange resin tower 33.

[0038] In the above explanation, regarding the inflow of high molecular weight TOC components, although the focus is on the averaging period [1] and the averaging period [3], the averaging period that can be used is not limited to these. For example, the sum of the average value obtained in the averaging period [1] and the average value obtained in the averaging period [2] can be used to investigate the shift of the initial conductivity, and the sum of the average value obtained in the averaging period [3] and the average value obtained in the averaging period [4] can be used to investigate the shift of the stable conductivity. In addition, in the above, each cycle of desalination is divided into 5 averaging periods, but the number of divisions when dividing the cycle into averaging periods is not limited to 5. For example, it can be divided into 6, 8, 10, etc.

[0039] Figure 5 and Figure 4 The figures shown in (a) to (c) similarly illustrate that in Figure 2 The water treatment system shown depicts the change in the measured value based on conductivity meter 38 when low molecular weight TOC components flow into anion exchange resin tower 33. Figure 5 (a) represents the time variation of conductivity in each cycle from the first to the fourth cycle. Figure 5 (b) indicates that the cycle is divided into averaging periods. Figure 5(c) represents the shift of the average value during repeated cycles. In any cycle, the conductivity is relatively high at the beginning of the desalination process, then the conductivity decreases rapidly to a stable value, and then increases again at the end of the desalination process. In particular, as shown by the arrow in the figure, the conductivity further deteriorates in the period before the end of the desalination process with repeated cycles. Here, each cycle is divided into 5 averaging periods as described above[1] to [5]. Figure 5 (b) indicates Figure 5 The conductivity curve shown in (a) is divided into averaging periods. Moreover, as above, for each cycle and for each averaging period, the arithmetic mean (i.e., the centroid value) of the measured conductivity values ​​is calculated as the average.

[0040] When considering the averaging period corresponding to the period before the end of the desalination process [5], such as Figure 5 As shown in (c), the average conductivity obtained during the averaging period [5] increases with repeated cycles. This indicates that the conductivity deteriorates at the end. It is known that the conductivity deteriorates at the end when low molecular weight TOC components flow into and accumulate in the anion exchange resin column 33. Therefore, when the average value obtained during the averaging period [5] tends to increase with repeated cycles, it can be determined that there is a possibility of low molecular weight TOC components flowing into the anion exchange resin column 33. However, at this stage, it cannot be determined that low molecular weight TOC components have flowed in. In this case, the sum of the average value in the averaging period [4] and the average value in the averaging period [5] can also be calculated, and how this sum changes with repeated cycles can be investigated. Alternatively, the number of cycles to the averaging period can be set to any number other than 5.

[0041] Figure 6 Is with Figure 4 The figures shown in (a) to (c) similarly illustrate that in Figure 2 The graph shows the change in pressure difference in the water treatment system, calculated from the measurements taken by pressure gauges 36 and 37 when the low molecular weight TOC component flows into the anion exchange resin tower 33. Figure 6 (a) represents the time variation of the pressure difference in each cycle from the first to the fourth cycle. Figure 6 (b) indicates that the cycle is divided into averaging periods. Figure 6 (c) represents the shift in the average value during repeated cycles. In the example shown here, there is a stop period during the desalination process where treated water from the anion exchange resin column 33 is not supplied to the downstream equipment. During the stop period, the flow of treated water in the anion exchange resin column 33 also stops, and therefore no pressure differential is generated. Therefore, in Figure 6The pressure differential curve shown in (a) is missing the portion during the shutdown period. The period that is separated from the shutdown period but actually plotted in the curve is the water intake period. Furthermore, it was observed that when a stopped pump is started, after startup, at a certain point during the water intake period, as shown in Figure A, the pressure differential rises rapidly, and then returns to its original state when the pump stops and restarts. From each water intake period, the pressure differential exhibits a step-like change of one level. This originates from the mechanical structure of the water treatment system, including pumps and piping, and does not indicate any abnormality in the anion exchange resin tower 33 or deterioration of the anion exchange resin.

[0042] In the first cycle, the pressure difference remained almost constant throughout the cycle, except for the stepwise changes in pressure difference during each water intake period. However, as the cycle was repeated, even ignoring the stepwise changes in pressure difference during each water intake period, the pressure difference at the end of each cycle increased compared to the pressure difference in the early stages of the cycle. Here, as described above, each cycle was divided into 5 averaged periods[1] to [5]. Figure 6 (b) indicates Figure 6 The pressure differential curve shown in (a) is divided into averaging periods. Furthermore, similarly to the above, for each cycle and for each averaging period, the arithmetic mean (i.e., the centroid value) of the pressure differential values ​​is calculated as the average. In calculating the average, the effects of the step-like changes in pressure differential caused by pump start-up and shutdown need to be removed. After pump start-up, the time until the pressure differential rises step-like is approximately constant, so for example, for each averaging period, the average pressure differential is calculated from pump start-up until the pressure differential rises step-like.

[0043] As described above, when the low molecular weight TOC component flows into and accumulates in the anion exchange resin column 33, the pressure difference generated in the anion exchange resin column 33 also changes, and this change becomes significant in the latter half of each cycle. Therefore, when considering the averaging period corresponding to the period before the end of the desalination process [5], as Figure 6 As shown in (c), with repeated cycles, the average pressure difference obtained during the averaging period [5] increases. This indicates that the pressure difference has changed, and when such a change occurs, it can be determined that there is a possibility of low molecular weight TOC components flowing into the anion exchange resin tower 33. In this case, the sum of the average value in the averaging period [4] and the average value in the averaging period [5] can also be calculated, and how this sum changes with repeated cycles can be investigated. Alternatively, the number of cycles to the averaging period can be set to any number other than 5.

[0044] Figure 7 Is with Figure 4 The figures shown in (a) to (c) similarly illustrate that in Figure 2 The graph shows the change in the measured value based on the conductivity meter 38 when silica components flow into the anion exchange resin tower 33 in the water treatment system shown. Figure 7 (a) represents the time variation of conductivity in each cycle from the first to the fourth cycle. Figure 7 (b) indicates that the cycle is divided into averaging periods. Figure 7 (c) represents the shift of the average value during repeated cycles. In any cycle, the conductivity is relatively high at the beginning of the desalination process, then the conductivity decreases rapidly to a stable value, and then increases again at the end of the desalination process. Moreover, as shown by the arrows in the figure, the conductivity deteriorates with each repeated cycle, i.e., the overall conductivity. Here, as described above, each cycle is divided into 5 averaging periods [1] to [5]. Figure 7 (b) indicates Figure 7 The conductivity curve shown in (a) is divided into averaging periods. Moreover, as above, for each cycle and for each averaging period, the arithmetic mean of the measured conductivity values ​​is calculated as the average.

[0045] As is known, when silica flows into anion exchange resin tower 33, as described above, the initial conductivity deteriorates and the breakthrough point occurs earlier. The earlier breakthrough point ultimately leads to a deterioration in the final conductivity, both the initial and final conductivity deteriorate, and thus the stable conductivity also deteriorates. Therefore, when considering the averaging period [3] corresponding to the steady state period and the averaging period [5] corresponding to the period before the end of the desalination process, as Figure 7 As shown in (c), with repeated cycles, the average conductivity during either of the averaging periods [3] and [5] increases. This indicates a deterioration in both the stable conductivity and the final conductivity. When such a deterioration occurs, it can be determined that there is a possibility that silica components are flowing into and accumulating in the anion exchange resin tower 33. In this case, we can also focus on averaging periods other than averaging periods [3] and [5], and we can also set the number of cycles to averaging periods to be other than 5. For example, when silica components flow in and accumulate, the initial conductivity also deteriorates, so it is assumed that the average conductivity during the averaging period [1] corresponding to the period after the start of the desalination process also increases with repeated cycles.

[0046] The above explains how the average values ​​calculated during each averaging period change during repeated cycles for each cause of performance degradation in the anion exchange resin tower 33. As can be seen from the above explanation, the cause of performance degradation in the anion exchange resin tower 33 can be inferred based on the shift in the average values ​​during averaging periods with specific sequential numbers. By combining such inferences, the cause of performance degradation can be inferred with greater accuracy. Figure 8 This is a flowchart illustrating the process of making such a presumption.

[0047] First, in step 101, time series data related to conductivity and pressure difference are obtained. In step 102, the time series data is divided into averaging periods for each cycle, and the average value of each time series data is calculated for each averaging period. Then, in step 103, it is determined whether the conductivity at the end of the cycle increases with repeated cycles, and whether the pressure difference at the end of the cycle also increases. The increase in conductivity at the end of the cycle can be determined, for example, by whether the average conductivity value during the averaging period [5] increases, and the increase in pressure difference at the end of the cycle can also be determined, for example, by whether the average pressure difference value during the averaging period [5] increases. When it is determined that both the conductivity at the end of the cycle and the pressure difference at the end of the cycle increase with repeated cycles, in step 104, it is determined that a weakly conductive substance with low ion selectivity, such as low molecular weight TOC component, flows into the anion exchange resin tower 33, and then the cause estimation process ends. Examples of weakly conductive substances with low ion selectivity include acetic acid, propionic acid, fluoride ions, borate ions, etc. Among the substances listed here, acetic acid and propionic acid have molecular weights less than 100, and therefore belong to low molecular weight TOC components. In the case that the raw water and recycled water do not contain fluoride ions and borate ions, and the outlet water of activated carbon tower 26 does not contain these ion components, in step 104, it can be determined that low molecular weight TOC components flow into anion exchange resin tower 33. On the other hand, if it is not determined in step 103 that the conductivity at the end of the cycle and the pressure difference at the end of the cycle both increase, then in step 105, it is determined whether the conductivity in each cycle increases as a whole with repeated cycles. This determination can be made, for example, by whether the conductivity during the averaging period [3] corresponding to the steady state in each cycle increases during repeated cycles. Here, if the conductivity does not increase as a whole, in step 106, it is presumed that the anion exchange resin tower 33 was originally normal, or even if there is performance degradation, it is for other reasons, and the cause presumption process ends.

[0048] If, in step 105, it is determined that the conductivity in each cycle increases overall with repeated cycles, it can be presumed that either silica or high molecular weight TOC components flow into the anion exchange resin tower 33. To distinguish whether the component flowing into the anion exchange resin tower 33 is silica or high molecular weight TOC, a heating regeneration process is performed in the regeneration process after the current cycle, which is a desalination process, and the amount of regenerant used for the regeneration of the anion exchange resin tower 33 is increased. For example, the amount of regenerant is set to twice the usual amount. Then, in step 107, it is determined whether the conductivity in the cycle after the heating regeneration process remains high overall or improves to a lower value. At this time, for example, it is only necessary to determine whether the average conductivity during the averaging period [3] remains high as before or decreases, i.e., improves. Here, if the conductivity improves, in step 108, it is presumed that silica components flow in, and then the process of presuming the cause ends. On the other hand, if it is determined in step 107 that the conductivity has not improved, it is presumed that high molecular weight TOC components flow in, and then the process of presuming the cause ends.

[0049] By performing the above processing, it can be deduced that the cause of the reduced performance of the anion exchange resin tower 33, which is an anion exchange device, is the inflow of low molecular weight TOC components, including borate ions, the inflow of high molecular weight TOC components, the inflow of silica components, or other reasons. Here, the pressure difference in the anion exchange resin tower 33 and the conductivity of the outlet water were measured, but even without measuring the pressure difference, a general cause can be deduced based solely on the conductivity measurement results. In this case, for example, when the average conductivity during the averaging period [3] remains almost unchanged during repeated cycles but the conductivity during the averaging period [5] increases, it can be judged that the inflow of low molecular weight TOC components (or borate ions, etc.) is high. When the average conductivity during the averaging period [3] also increases, it can be judged that the inflow of silica components or high molecular weight TOC components is high.

[0050] Figure 9 This illustrates an example of the structure of a cause estimation device 10 that implements the above-described cause estimation method. This cause estimation device 10 manages... Figure 2 The operation of the water treatment system in the ion exchange treatment unit 30 shown is used to estimate the cause of performance degradation in the anion exchange resin tower 33 within the ion exchange treatment unit 30. Desalination and regeneration processes are alternately performed in the anion exchange resin tower 33, but in the ion exchange treatment unit 30, except... Figure 2In addition to the pressure gauges 36, 37 and conductivity meter 38 shown, a regenerant supply unit 40 is also provided to supply regenerant during the regeneration process of the anion exchange resin tower 33. The pressure gauges 36, 37 and conductivity meter 38 continuously measure and output time series data containing these measurements to the cause estimation device 10.

[0051] The cause estimation device 10 includes: a differential pressure calculation unit 11, which calculates the differential pressure based on the measured values ​​in pressure gauge 36 and pressure gauge 37 and outputs it as time series data; an averaging period setting unit 12, which receives signals from the ion exchange treatment unit 30 indicating the timing of the start of desalination treatment and the timing of the start of regeneration treatment and sets the averaging period accordingly; an average value calculation unit 13, which calculates the average value for each averaging period based on the time series data of the differential pressure; an average value calculation unit 14, which calculates the average value for each averaging period based on the time series data of conductivity; and an estimation unit 15, which estimates the cause of performance degradation in the anion exchange resin tower 33 according to the above steps. The averaging period setting unit 12 divides each cycle into a predetermined number of averaging periods by assigning sequential numbers, starting from the beginning of the cycle, to the averaging period within each cycle, treating one desalination treatment period as one cycle. The estimation unit 15 estimates the cause of performance degradation in the anion exchange resin tower 33 based on how the average value during the averaging period of a specific sequential number of each cycle shifts during repeated cycles, and outputs the estimation result. In estimating the cause of performance degradation, the average value when the amount of regenerant in the regeneration process is increased is sometimes used. To make such an estimation, the estimation unit 15 can control the regenerant supply unit 40 in the ion exchange processing unit 30 to increase the amount of regenerant supplied to the anion exchange resin tower 33 during the regeneration process.

[0052] By using such a cause estimation device 10, it is possible to perform... Figure 8 The steps shown are presumed to provide a cause. Additionally, in the presumption... Figure 3 When the performance of the anion exchange resin tower 33 in the ion exchange treatment unit 20 of the structure shown decreases, it is sufficient to provide the measured value in the resistivity meter 39 instead of the conductivity meter 38 as time series data to the average value calculation unit 14 of the cause estimation device 10.

[0053] In the above explanation, substances with an acid dissociation constant pKa of 4.0 or higher are defined as "weakly conductive substances with low ion selectivity". Alternatively, the selectivity for strongly basic anion exchange resins with an ionic form of OH can be denoted as K. x OH This will satisfy K x OHSubstances with a K-value ≤ 4.0 are defined as "weakly conductive substances with low ion selectivity". This is based on the selectivity K-value. x OH When defined, hydrofluoric acid or fluoride ions are also included in the category of "weakly conductive substances with low ion selectivity".

[0054] Explanation of reference numerals in the attached figures 10 Cause Prediction Device 11 Differential Pressure Calculation Department 12. Averaging Period Setting Department 13, 14 Average Calculation Section 15. Presumption Department Storage tanks 21 and 24 Pumps 22, 25, and 41 23 Filters 26 Activated Carbon Tower 30 Ion Exchange Processing Unit 31, 34 Cation Exchange Resin Towers 32 Decarbonation Tower 33 Anion Exchange Resin Tower Pressure gauges 36 and 37 38 Conductivity Meter 39 Resistivity Meter 40. Recycling Agent Supply Department.

Claims

1. A method for presuming a cause, characterized in that, The presumed cause of performance degradation in the anion exchanger is that the anion exchanger is configured to include anion exchangers and allow treated water to pass through them, and alternately performs desalination and regeneration treatments, wherein the desalination treatment desalinates the treated water and the regeneration treatment regenerates the anion exchangers. The cause estimation method has the following characteristics: In the implementation of the desalination process, a step is taken to obtain time series data of at least one of the measured values ​​of the pressure difference of the anion exchanger and the measured values ​​of the water quality of the treated water discharged from the anion exchange device. and The process of defining one desalination process as a cycle, from the start of the regeneration process to the start of the next regeneration process, is further divided into a predetermined number of averaging periods. Within each cycle, the averaging periods are assigned sequential numbers starting from the beginning of the cycle. Based on the shift in the average value over repeated cycles, the process of determining the cause of performance degradation in the anion exchanger is then described. The average value is calculated for each cycle based on the individual measurements constituting the time series data during the averaging period numbered in a specific sequence.

2. The cause estimation method according to claim 1, wherein, The water quality measurements of the treated water are obtained by measuring the conductivity or resistivity of the outlet water of the anion exchange device.

3. The cause estimation method according to claim 1, wherein, A cation exchange device is installed downstream of the anion exchange device. The water quality measurement values ​​of the treated water are obtained by measuring the conductivity or resistivity of the outlet water of the cation exchange device.

4. The cause estimation method according to claim 1, wherein, The anion exchange device is an anion exchange resin tower formed by filling a mixed bed of weakly basic anion exchange resin and strongly basic anion exchange resin as the anion exchangers, with the weakly basic anion exchange resin on the upstream side and the strongly basic anion exchange resin on the downstream side. The measured value of the pressure difference is the measured value of the pressure difference generated in the layer of the weakly basic anion exchange resin.

5. The cause estimation method according to any one of claims 1 to 4, wherein, Regarding the averaging period corresponding to the end of each cycle, when the average value calculated from the water quality deteriorates and the average value calculated from the pressure difference increases as the cycle repeats, it is determined that components with a molecular weight less than 100, an acid dissociation constant of 4.0 or higher, and not silica components flow into the anion exchange device.

6. The cause estimation method according to any one of claims 1 to 4, wherein, TOC components with a molecular weight of 100 or higher are considered high molecular weight TOC components. During the averaging period corresponding to the period of stable state of each cycle, if the average value calculated from the water quality deteriorates as the cycle is repeated, it is determined that silica components or high molecular weight TOC components flow into the anion exchange device.

7. The cause estimation method according to claim 6, wherein, After determining that silica or high molecular weight TOC components have flowed into the anion exchange device, the amount of regenerant is increased to perform the regeneration process. If the average value calculated from the water quality during the averaging period corresponding to the period of stable state of the subsequent cycle remains in a deteriorated state, it is determined that high molecular weight TOC components have flowed in; if the deteriorated state is no longer maintained but improved, it is determined that silica components have flowed in.

8. A cause estimation device, characterized in that, The presumed cause of performance degradation in the anion exchanger is that the anion exchanger is configured to include anion exchangers and allow treated water to pass through them, and alternately performs desalination and regeneration treatments, wherein the desalination treatment desalinates the treated water and the regeneration treatment regenerates the anion exchangers. The cause estimation device has: A measuring unit, which is installed in the anion exchange device, measures at least one of the pressure difference with respect to the anion exchanger and the water quality of the treated water discharged from the anion exchange device, and outputs it as time series data. The averaging period setting unit sets the averaging period in the following manner: the period from the execution of the regeneration process to the execution of the next regeneration process is taken as one cycle, each cycle is divided into a predetermined number of averaging periods, and in each cycle, the averaging periods contained in the cycle are assigned sequential numbers starting from the beginning of the cycle. The average calculation unit calculates, for each of the cycles, the average of the various measurements constituting the time series data during the averaging period of a specific sequential number; and The estimation section estimates the cause of performance degradation in the anion exchanger based on the shift in the average value during repeated cycles.

9. The cause estimation device according to claim 8, wherein, The measuring unit includes a sensor for measuring the conductivity or resistivity of the outlet water of the anion exchange device.

10. The cause estimation device according to claim 8, wherein, A cation exchange device is provided downstream of the anion exchange device. The measuring unit includes a sensor for measuring the conductivity or resistivity of the outlet water of the cation exchange device.

11. The cause estimation device according to any one of claims 8 to 10, wherein, The anion exchange device is an anion exchange resin tower formed by filling a mixed bed of weakly basic anion exchange resin and strongly basic anion exchange resin as the anion exchangers, with the weakly basic anion exchange resin on the upstream side and the strongly basic anion exchange resin on the downstream side. The measuring unit includes a sensor for measuring the pressure difference generated in the layer of the weakly basic anion exchange resin.

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