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

Abstract

To estimate a cause of performance deterioration in an anion exchange device based on time series data obtained from a system equipped with the anion exchange device.SOLUTION: In an anion exchange device in which a desalination process and a regeneration process are alternately performed, time-series data is acquired for at least one of a measurement value of a differential pressure and a measurement value of water quality (for example, conductivity) of treated water during the desalination process, each cycle is divided into a predetermined number of averaging periods ([1] to [5]) with a period of one desalination process performed from the execution of the regeneration process to the execution of the next regeneration process as one cycle, and an average value is calculated from each measurement value constituting the time-series data for each averaging period. For each cycle, the order counted from the head is assigned to the averaging period in the cycle, and the cause of the performance deterioration in the anion exchange device is estimated based on the transition of the average value when the cycle is repeated.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a method and device for managing the operation of an anion exchange device equipped with an anion exchanger such as an anion exchange resin, and in particular to a cause estimation method and device for detecting the occurrence of an abnormality or a sign of an abnormality in an anion exchange device and estimating the cause of the performance degradation of the anion exchanger. [Background technology]

[0002] Pure water production systems that produce pure water or ultrapure water from raw water such as city water, groundwater, or river water include an ion exchange device filled with ion exchangers such as ion exchange resins. Ion exchange devices are also sometimes used in wastewater treatment systems used to treat wastewater. The pure water production system includes, for example, an activated carbon tower filled with activated carbon, a cation exchange resin tower filled with cation exchange resin, an anion exchange resin tower filled with anion exchange resin, and a decarbonation tower that removes carbonate components from the water. In this pure water production system, raw water from which impurities have been removed using a filter is supplied to the activated carbon tower. The outlet water from the activated carbon tower is supplied to the cation exchange resin tower. The outlet water from the cation exchange resin tower is then supplied to the anion exchange resin tower via the decarbonation tower, and pure water flows out from the outlet of the anion exchange resin tower. Another cation exchange resin tower may be provided downstream of the anion exchange resin tower, and the outlet water from this cation exchange resin tower may be used as pure water.

[0003] In such a pure water production system, as pure water production continues, 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, resulting in the removal of ionic impurities from the water. The captured ionic impurities accumulate in the ion exchange resins (i.e., the cation exchange resin and the anion exchange resin). When the amount of accumulated ionic impurities exceeds a certain value, the ion exchange resin can no longer remove the ionic impurities. Therefore, before this occurs, the ion exchange resin must be replaced or regenerated. Because ion exchange resins also deteriorate with long-term use, they must be replaced at some point, even when repeated regeneration processes are performed. Therefore, various methods have been proposed for evaluating the performance of ion exchange resins and for predicting when to replace or regenerate them.

[0004] Patent Document 1 discloses a method for evaluating the performance of anion exchange resins packed in ion exchange resin towers. The method involves calculating the mass transfer coefficient of the anion exchange resin relative to inorganic carbonate from measured values ​​of inorganic carbonate concentrations in the inlet and outlet water of the ion exchange resin tower, and evaluating the dynamic characteristics and degree of deterioration of the anion exchange resin based on the mass transfer coefficient. This performance evaluation method allows the lifespan or replacement timing of the anion exchange resin to be estimated based on the evaluation results. Patent Document 2 discloses an ion exchange apparatus that repeatedly performs demineralization treatment of water to be treated using an ion exchange resin and regeneration treatment of the ion exchange resin. The method periodically measures the time from the end of regenerant flow until the water quality of the effluent from the ion exchange resin reaches a predetermined value, and predicts the replacement timing of the ion exchange resin 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 by determining in advance for each temperature the relationship between the temperature and the time required for the ion exchange capacity to decrease to a certain level when demineralization treatment is performed at that temperature, and then calculating and accumulating the decrease in ion exchange capacity from the currently detected temperature. Patent Document 4 discloses that when an ion exchange device is operated to repeatedly perform desalination treatment (ion exchange treatment) and regeneration treatment, the total ion load of the raw water is calculated from the electrical conductivity of the raw water and the concentration of specific ions, the resin composition of the ion exchange resin is predicted from the calculated value, the water quality of the outlet water of the ion exchange resin and the amount of raw water that can be treated are predicted based on the predicted value, and switching from desalination treatment to regeneration treatment is performed based on this prediction.

[0005] Patent Document 5 discloses a method for evaluating the performance of an ion exchange resin by mixing and contacting a salt solution of a predetermined concentration with a predetermined amount of ion exchange resin, and measuring the change in the electrical conductivity of the salt solution over time after the mixing and contact. In the method described in Patent Document 5, the change in electrical conductivity over time is converted into a time-dependent curve of ion concentration, and the overall mass transfer capacity coefficient and selectivity coefficient are calculated from this curve and the exchange capacity of the ion exchange resin. The timing for replacing the ion exchange resin can be determined from the product of the exchange capacity, the overall active mass transfer capacity coefficient, and the selectivity coefficient. Patent Document 6 discloses a method for evaluating the performance of an ion exchange resin in a mixed-bed ion exchange resin tower packed with a mixture of anion exchange resin and cation exchange resin. This method involves supplying purified water to regenerated ion exchange resin for washing, and determining the degree of deterioration of the ion exchange resin from the measured value of total organic carbon (TOC) in the wash wastewater. Patent Document 7 discloses a method for predicting the life of a cation exchange resin by repeating the following steps under different conditions: adding an oxidizing agent to a cation exchange resin to perform accelerated aging treatment, measuring the water content of the ion exchange resin, determining the degree of deterioration based on the water content, and conducting various evaluation tests on the deteriorated ion exchange resin to determine whether it passes or fails. Patent Document 8 discloses a method for evaluating the performance and diagnosing the deterioration of an anion exchange resin while taking into account the reaction rate, in which a silicic acid-containing solution is passed through an anion exchange resin contained in a microcolumn, the silicic acid concentration in the water effluent from the column is measured, and the performance of the anion exchange resin is evaluated based on the measurement results. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2002-48776 [Patent Document 2] Japanese Patent Application Publication No. 2019-76844 [Patent Document 3] Japanese Patent Application Laid-Open No. 2002-143694 [Patent Document 4] Japanese Patent Application Publication No. 6-55082 [Patent Document 5] Japanese Patent Application Laid-Open 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 [Problem to be solved by the invention]

[0007] The methods disclosed in Patent Documents 1-8 all evaluate the performance and predict the lifespan of ion exchange resins, but they are unable to predict the cause of any unexpected performance degradation of the ion exchange resins. When operating an ion exchange device, it is necessary not only to predict in advance when to replace or regenerate the ion exchange resins, but also to predict the cause of any unexpected performance degradation. In particular, since the performance of anion exchange resins tends to deteriorate due to the inflow of TOC components and silica (SiO2) components, it is highly desirable to identify the cause of the performance degradation of anion exchange resins and implement countermeasures.

[0008] An object of the present invention is to provide a method and apparatus for estimating the cause of performance degradation in an anion exchange device, such as an anion exchange resin tower packed with an anion exchange resin as an anion exchanger, based on time-series data obtained from a system equipped with the anion exchange device. [Means for solving the problem]

[0009] In an anion exchange device equipped with an anion exchanger, a desalination process, in which water to be treated is passed through the anion exchanger to desalinate the water, and a regeneration process, in which the anion exchanger is regenerated using a regenerant, are alternately performed. Such an anion exchanger is typically incorporated into a water treatment system. Examples of water treatment systems incorporating an anion exchanger include pure water production systems that produce pure water from raw water such as city water, well water, or river water. When measuring quantities related to the operation and status of the water treatment system (e.g., flow rate, pressure, water quality), changes occur in the measured values ​​in response to abnormalities in the anion exchanger that may cause performance degradation. Therefore, analyzing the trends in the measured values ​​may enable the identification of the cause of performance degradation that has occurred or may occur in the anion exchanger. However, the measured values ​​obtained from the water treatment system contain variations due to various factors, making it difficult to automatically identify the cause of performance degradation in the anion exchanger by simply mechanically processing the measured values.

[0010] Therefore, one aspect of the present invention provides a cause estimation method for estimating the cause of performance degradation in an anion exchanger that includes an anion exchanger and is configured to allow water to pass through the anion exchanger, and that alternates between a desalination process (desalination of the water) and a regeneration process (regeneration of the anion exchanger). During the desalination process, time series data is acquired for at least one of measurements of the differential pressure across the anion exchanger and measurements of the water quality of the treated water discharged from the anion exchanger. The period from one desalination process to the next is defined as one cycle, and each cycle is divided into a predetermined number of averaging periods. The averaging periods within each cycle are assigned an order counted from the beginning of the cycle. The cause estimation method then estimates the cause of performance degradation in the anion exchanger based on how the average values ​​calculated from the measurements constituting the time series data for a specific averaging period change over time as the cycle is repeated.

[0011] The desalination treatment period may include not only the water sampling period during which the treated water is actually passed through and desalinated, but also the stop period during which the flow of treated water is temporarily stopped due to lack of demand for treated water. The average value may be any value that can represent the data values ​​within the averaging period (i.e., a feature quantity). For example, the average value may be the center of gravity (i.e., arithmetic mean value) of the data values ​​within the averaging period, the geometric mean value, or the harmonic mean value. The average value may be the median, the maximum value, the minimum value, the deviation, or the Mahalanobis distance used in the Mahalanobis-Taguchi (MT) method. Furthermore, the average value may be calculated by taking the logarithm of each data value and then averaging the logarithmic values.

[0012] The cause estimation device of one embodiment of the present invention is a cause estimation device that estimates the cause of performance degradation in an anion exchanger that is equipped with an anion exchanger and configured to allow treated water to pass through the anion exchanger, and that alternately performs a desalination process to desalinate the treated water and a regeneration process to regenerate the anion exchanger. The cause estimation device includes: a measuring means that is provided in the anion exchanger and that measures at least one of the differential pressure across the anion exchanger and the water quality of the treated water discharged from the anion exchanger and outputs the data as time series data; an averaging period setting unit that divides each cycle into a predetermined number of averaging periods, and that sets the averaging periods for each cycle so that the averaging periods included in that cycle are assigned an order counted from the beginning of the cycle; an average value calculation unit that calculates the average value of each measurement value that constitutes the time series data for each averaging period of a specific order for each cycle; and an estimation unit that estimates the cause of performance degradation in the anion exchanger based on the progression of the average value as the cycle is repeated. [Effects of the Invention]

[0013] According to the present invention, with respect to an anion exchange device such as an anion exchange resin tower, the cause of performance degradation in the anion exchange device can be estimated based on time-series data obtained by measurements in a water treatment system or the like that includes the anion exchange device. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a diagram showing an example of the configuration of a water treatment system to which a cause estimation method according to an embodiment of the present invention is applied; [Figure 2] FIG. 2 is a diagram showing an example of the configuration of an ion exchange processing unit. [Figure 3] FIG. 10 is a diagram showing another example of the configuration of the ion exchange processing unit. [Figure 4] FIG. 10 is a diagram showing an example of a change in conductivity. [Figure 5] FIG. 10 is a diagram showing an example of a change in conductivity. [Figure 6] FIG. 10 is a diagram illustrating an example of a change in differential pressure. [Figure 7] FIG. 10 is a diagram showing an example of a change in conductivity. [Figure 8] 1 is a flowchart showing a procedure for estimating the cause of performance degradation in an anion exchange device. [Figure 9] FIG. 1 is a block diagram showing an example of the configuration of a cause estimation device. DETAILED DESCRIPTION OF THE INVENTION

[0015] Next, an embodiment of the present invention will be described with reference to the drawings. Fig. 1 shows an example of the configuration of a water treatment system to which a cause estimation method according to an embodiment of the present invention is applied. In this embodiment, in a water treatment system incorporating an anion exchange device, the cause of performance degradation that has occurred or may occur in the anion exchange device is estimated based on changes over time in measured values ​​obtained from the water treatment system.

[0016] The water treatment system shown in FIG. 1 is configured as a pure water production system that produces pure water from raw water such as city water, well water, or river water. A storage tank 21 is provided for storing the raw water. The raw water in storage tank 21 is transported by pump 22, and solids and other components are removed by filter 23. The outlet water from filter 23 is stored in storage tank 24. Recovered water recovered from equipment that uses the pure water is also supplied to storage tank 24. The water in storage tank 24 is transported by pump 25 to activated carbon tower 26, where it undergoes activated carbon treatment. The outlet water from activated carbon tower 26 is supplied to ion exchange treatment unit 30. The ion exchange treatment unit 30 uses the outlet water from activated carbon tower 26 as the water to be treated and performs a desalination process on this water. The outlet water from ion exchange treatment unit 30 is transported by pump 41 and supplied to reverse osmosis membrane device 42. Pure water is discharged from reverse osmosis membrane device 42.

[0017] FIG. 2 shows an example of the configuration of the ion exchange treatment unit 30. The ion exchange treatment unit 30 includes a cation exchange resin tower 31 filled with a 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 device to which the cause estimation method according to the present invention is applied. The anion exchange resin tower 33 alternately performs a desalination process in which the outlet water of the decarbonation tower 32 is supplied as the water to be treated and the water is desalted, and a regeneration process in which the anion exchange resin is regenerated using a regenerant. During the desalination process, the outlet water of the anion exchange resin tower 33 is supplied to a reverse osmosis membrane device 42 in the downstream stage. As a result of the cation exchange treatment in the cation exchange resin tower 31, the outlet water of the cation exchange resin tower 31 contains hydrogen ions (H + ) contained in the water supplied to the cation exchange resin tower 31, and becomes acidic. 2- ) and bicarbonate ions (HCO) are converted into free carbon dioxide. The decarbonation tower 32 is provided to remove this free carbon dioxide by blowing in air or by membrane deaeration. As a result of providing the decarbonation tower 32, water that does not contain carbon dioxide components is supplied to the anion exchange resin tower 33.

[0018] The cation exchange resin packed in the cation exchange resin tower 31 may be a strong acid cation exchange resin (SACER) or a weak acid cation exchange resin (WACER). Furthermore, the cation exchange resin tower 31 may be packed with a mixture of a strong acid cation exchange resin and a weak acid cation exchange resin (i.e., in a mixed bed form) or in a multiple-bed form. In the illustrated example, these cation exchange resins are packed in a multiple-bed form, with the weak acid cation exchange resin on the upstream side and the strong acid cation exchange resin on the downstream side. Similarly, the anion exchange resin packed in the anion exchange resin tower 33 may be a strong basic anion exchange resin (SBAER) or a weak basic anion exchange resin (WBAER). Furthermore, the anion exchange resin tower 33 may be packed with a mixture of a strong basic anion exchange resin and a weak basic anion exchange resin (i.e., in a mixed bed form) or in a multiple-bed form. Furthermore, a first packed tower packed with a weakly basic anion exchange resin and a second packed tower packed with a strongly basic anion exchange resin may be connected in series to form the anion exchange resin tower 33. In the example shown in the figure, these anion exchange resins are packed in a single packed tower in a multi-bed configuration, with the weakly basic anion exchange resin on the upstream side and the strongly basic anion exchange resin on the downstream side, to form the anion exchange resin tower 33.

[0019] The ion exchange treatment unit 30 is provided with two pressure gauges (PI) 36 and 37 to measure the differential pressure generated when the water to be treated is passed 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 the anion exchange resin tower 33 is easily affected by the inflow. Therefore, a pressure gauge 36 is attached to a pipe connected to the inlet of the anion exchange resin tower 33 so as to measure the differential pressure generated in the weakly basic anion exchange resin layer in the anion exchange resin tower 33, and a pressure gauge 37 is attached to the anion exchange resin tower 33 so as to measure the pressure inside the anion exchange resin tower 33 at the position where the layer of the weakly basic anion exchange resin and the layer of the strong basic anion exchange resin meet. Furthermore, in order to measure the quality of the outlet water 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 attached to the piping connected to the outlet of the anion exchange resin tower 33. Since conductivity (electrical conductivity) and resistivity (electrical specific resistance, electrical resistivity) are inversely related, a resistivity meter may be attached to the piping connected to the outlet of the anion exchange resin tower 33 instead of the conductivity meter 38.

[0020] FIG. 3 shows another example of the configuration of the ion exchange treatment unit 30. The ion exchange treatment unit 30 shown in FIG. 3 is similar to the ion exchange treatment unit 30 shown in FIG. 2, but differs from that shown in FIG. 2 in that a cation exchange resin tower 34 is further provided downstream of the anion exchange resin tower 33, and outlet water from the anion exchange resin tower 33 is supplied to the cation exchange resin tower 34. Furthermore, instead of providing a conductivity meter 38 for measuring the conductivity of the outlet water from the anion exchange resin tower 33, a resistivity meter (RI) 39 for measuring the resistivity of the outlet water from the cation exchange resin tower 34, i.e., the treated water from the ion exchange treatment unit 30, is attached to a pipe connected to the outlet of the cation exchange resin tower 34. A conductivity meter may be attached to the pipe connected to the outlet of the cation exchange resin tower 34 instead of the resistivity meter 39. The cation exchange resin tower 34 provided downstream of the anion exchange resin tower 33 is filled with, for example, a single bed of strongly acidic cation exchange resin.

[0021] Next, we will explain the performance degradation in the anion exchange resin tower 33 and the resulting phenomena. When TOC components flow into the anion exchange resin tower 33, the anion exchange resin in the anion exchange resin tower 33, particularly the weakly basic anion exchange resin, is easily affected. The impact on the anion exchange resin varies depending on the molecular weight of the TOC components. Hereinafter, TOC components with a molecular weight of 100 or more 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 eluted due to oxidative degradation of cation exchange resins (e.g., polystyrene sulfonates (PSS), which are components of cation exchange resins). Low-molecular-weight TOC components include organic acids, alcohols, aldehydes, and the like, which have relatively small molecular weights.

[0022] When high molecular weight TOC components such as humic substances and polystyrene sulfonic acid flow into the anion exchange resin tower 33 and accumulate, the quality of the treated water from the anion exchange resin tower 33 deteriorates when the regeneration process is switched to the desalination process, and the reaction rate of the anion exchange reaction decreases. These phenomena are particularly noticeable in the layer of weakly basic anion exchange resin. When the quality of the treated water does not improve, the initial conductivity, which is the conductivity of the treated water immediately after switching to the desalination process, increases (i.e., deteriorates). The reason why the quality of the treated water does not improve is mainly due to the increase in sodium ions (Na +This is thought to be due to leakage of sodium ions. The leaked sodium ions can be captured by the cation exchange resin, so in the ion exchange treatment unit 30 configured as shown in FIG. 3, the electrical 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 prevent a deterioration in the initial electrical conductivity, the time required for the regeneration treatment must be extended. A decrease in the reaction rate of the anion exchange reaction increases the leakage of anions from the anion exchange resin tower 33, resulting in a deterioration in the steady-state electrical conductivity, which is the electrical conductivity of the treated water during the period when the desalination treatment is steadily performed (i.e., the period excluding the period immediately after the start and the period immediately before the end of the desalination treatment). In the ion exchange treatment unit 30 shown in FIG. 3, the leaked anions are not captured by the subsequent cation exchange resin tower 34, so the electrical conductivity of the outlet water from the anion exchange resin tower 33 is approximately equal to that of the outlet water from the cation exchange resin tower 34.

[0023] When low-molecular-weight TOC components such as organic acids flow into and accumulate in the anion exchange resin column 33, the differential pressure in the anion exchange resin column 33 increases, particularly in the weakly basic anion exchange resin layer. A certain amount of anions leaks early during the desalination process. This increase in differential pressure is thought to be due to the high swelling rate of the anion exchange resin. For example, the differential pressure gradually increases over the course of the desalination process. A similar increase in differential pressure also occurs when weakly conductive substances with low ion selectivity, such as borate ions, flow into the anion exchange resin column 33. A "weakly conductive substance with low ion selectivity" is a substance whose acid dissociation constant in water satisfies pKa ≥ 4.0. While relatively strong acids such as formic acid and oxalic acid do not qualify as "weakly conductive substances with low ionic selectivity," common TOC components, including acetic acid and propionic acid, do qualify as "weakly conductive substances with low ionic selectivity." Although weakly conductive substances with low ion selectivity include inorganic substances such as borate ions, silica components behave differently from low-molecular-weight TOC components when accumulated in the anion exchange resin layer. Therefore, the term "weakly conductive substances with low ion selectivity" as used herein does not include silica components. Furthermore, if anion exchange resin fractures, the differential pressure increases uniformly depending on the amount of fracture. If a certain amount of anions leaks early, the time until the next regeneration treatment can be shortened accordingly.

[0024] When silica components flow into and accumulate in the anion exchange resin tower 33, the anion exchange resin, particularly the strong basic anion exchange resin, is affected. This affects the anion exchange resin in the anion exchange resin tower 33. When the anion exchange resin tower 33 is switched to desalination treatment, the water quality of the treated water from the anion exchange resin tower 33 deteriorates, the initial conductivity increases, and the ion exchange capacity of the anion exchange resin is consumed more quickly, resulting in an earlier breakthrough of the anion exchange resin. The deterioration in water quality is thought to be primarily due to sodium ion leakage. Even in this case, with the ion exchange treatment unit 30 configured as shown in FIG. 3 , the electrical conductivity of the water at the outlet of the anion exchange resin tower 33 is higher than that of the water at the outlet of the cation exchange resin tower 34. Because the silica components themselves are captured by the anion exchange resin, if the anion exchange resin is sufficiently regenerated by regeneration treatment, the flow of silica components into the anion exchange resin tower 33 does not result in a deterioration in the initial conductivity or an earlier breakthrough. In addition, since the regeneration of anion exchange resin that has captured silica components is promoted by heating, when there is a risk of silica components entering the anion exchange resin, it is common to perform a heating regeneration treatment to regenerate the anion exchange resin.

[0025] The cause estimation method of this embodiment, based on measurements obtained from pressure gauges 36 and 37 and a conductivity meter 38 (or resistivity meter 39) in the water treatment system shown in FIG. 2 or 3, identifies whether the cause of performance degradation in the anion exchange resin tower 33 is (1) the inflow and accumulation of low-molecular-weight TOC components (or weakly conductive substances with low ion selectivity and a molecular weight of less than 100, such as borate ions), (2) the inflow and accumulation of high-molecular-weight TOC components, or (3) the inflow and accumulation of silica components. This identification will be described in detail below. In this description, the term "low-molecular-weight TOC components" refers to weakly conductive substances with low ion selectivity and a molecular weight of less than 100, such as low-molecular-weight TOC components. Therefore, the term "low-molecular-weight TOC components" also includes borate ions.

[0026] In the anion exchange resin tower 33, which serves as an anion exchange device, a desalination process and a regeneration process for regenerating the anion exchange resin are alternately performed. Here, one desalination process period is referred to as one cycle. The pressure gauges 36 and 37 and the conductivity meter 38 (or resistivity meter 39) continuously measure the water at least during the desalination process period, and output the obtained measurements as time-series data. In this embodiment, each cycle is divided into a predetermined number of averaging periods. Each divided averaging period is assigned an order counted from the beginning of the cycle. Then, the cause of performance degradation in the anion exchange device is estimated based on how the average values ​​calculated from the measurements constituting the time-series data for a specific averaging period change over time as the cycle is repeated. The change in the average value over time as the cycle is repeated can be determined, for example, by examining how the average value changes depending on a time representative of each cycle, such as the start time of the cycle.

[0027] FIG. 4 illustrates the changes in the values ​​measured by the conductivity meter 38 when high-molecular-weight TOC components flow into the anion exchange resin tower 33 in the water treatment system shown in FIG. 2. (a) shows the time change in conductivity for each cycle, (b) shows the division of the cycle into averaging periods, and (c) shows the transition of the average value as the cycle is repeated. FIG. 4(a) shows the change in conductivity for each of the four desalination treatment periods from cycle 1 to cycle 4. In each cycle, the conductivity is relatively high at the start of the desalination treatment, and then the conductivity rapidly decreases and reaches a steady state. Comparing these changes in conductivity for each cycle reveals that both the initial conductivity and the steady state conductivity deteriorate as the cycle is repeated, as indicated by the arrows in the figure.

[0028] FIG. 4(b) shows an example in which each cycle is divided into five averaging periods based on a common criterion for the cycle, illustrating how the conductivity graph shown in FIG. 4(a) is divided into the averaging periods. The five averaging periods are represented in the figure by brackets, "[1]" through "[5]," which indicate the order of the cycle from the beginning. In particular, averaging period [1] includes the period immediately after the start of the desalination process, and averaging period [5] includes the period immediately before the end of the desalination process. One example of a criterion for dividing the cycle into five equal periods is dividing the cycle into five equal periods based on its duration. In the illustrated example, the length of each of averaging periods [1] and [5] is shorter than the lengths of the other averaging periods [2] through [4] so that the behavior of the period immediately after the start and the period immediately before the end can be separated from the other periods. In this embodiment, the arithmetic mean value (i.e., the center of gravity value) of the measured conductivity values ​​is calculated as the average value for each cycle and each averaging period. Once the average conductivity measurement values ​​for each cycle and averaging period have been calculated, we then focus on the average values ​​for the averaging periods in a specific order, counting from the beginning of each cycle, and examine how these average values ​​change as the cycle is repeated. Figure 4(c) shows how the average conductivity value for each averaging period changes as the cycle is repeated, focusing on the first averaging period [1] and the third averaging period [3] at the beginning of the cycle. Here, we refer to the start time of each cycle as the timestamp assigned to that cycle, and Figure 4(c) shows how the average values ​​for averaging periods [1] and [3] change as the time represented by the timestamp passes.

[0029] In the example shown here, as shown in Figure 4(c), the average value obtained from averaging period [1] tends to increase with each cycle. Because averaging period [1] corresponds to the period immediately after the start of the desalination process, the increase in the average conductivity as the cycles are repeated during this averaging period indicates a deterioration in the initial conductivity. Similarly, because averaging period [3] corresponds to the period during which the desalination process is in a steady state, the increase in the average conductivity as the cycles are repeated during this averaging period indicates a deterioration in the steady-state conductivity. As described above, when high-molecular-weight TOC components flow into and accumulate in the anion exchange resin tower 33, both the initial and steady-state conductivity deteriorate. Therefore, if it is confirmed that the average conductivity increases with each cycle during both averaging periods [1] and [3], it can be determined that high-molecular-weight TOC components may have flowed into and accumulated in the anion exchange resin tower 33. As will be described later, other factors may also cause the average value during the averaging periods [1] and [3] to gradually increase. Therefore, simply detecting a change in the average conductivity during the averaging periods [1] and [3] does not allow us to conclude that high-molecular-weight TOC components are flowing into and accumulating in the anion exchange resin tower 33.

[0030] The above explanation focuses on averaging period [1] and averaging period [3] with respect to the inflow of high molecular weight TOC components, but the averaging periods that can be used are not limited to these. For example, the transition of initial conductivity can be examined using the sum of the average values ​​obtained in averaging period [1] and averaging period [2], and the transition of steady-state conductivity can be examined using the sum of the average values ​​obtained in averaging period [3] and averaging period [4]. Furthermore, while each desalination cycle is divided into five averaging periods in the above example, the number of divisions into averaging periods is not limited to five and can be, for example, six, eight, or ten.

[0031] Figure 5 illustrates the changes in the conductivity measured by the conductivity meter 38 when low-molecular-weight TOC components flow into the anion exchange resin tower 33 in the water treatment system shown in Figure 2, similar to those shown in Figures 4(a) to 4(c). Figure 5(a) shows the time change in conductivity for each cycle from cycle 1 to cycle 4, Figure 5(b) shows the division of the cycles into averaging periods, and Figure 5(c) shows the transition of the average value as the cycles are repeated. In each cycle, the conductivity is relatively high at the start of the desalination process, then rapidly decreases to a steady value, and then increases again at the end of the desalination process. In particular, as the cycles are repeated, the terminal conductivity, which is the conductivity in the period immediately before the end of the desalination process, deteriorates further, as indicated by the arrows in the figure. Here, each cycle is divided into five averaging periods [1] to [5], as described above. Figure 5(b) shows how the conductivity graph shown in Figure 5(a) is divided into averaging periods. Then, as described above, for each cycle and for each averaging period, the arithmetic mean value (i.e., centroid value) of the measured conductivity values ​​is calculated as the average value.

[0032] Focusing on the averaging period [5], which corresponds to the period immediately before the end of the desalination process, as shown in Figure 5(c), the average conductivity obtained during the averaging period [5] increases with each cycle. This indicates a deterioration in the terminal conductivity. It is known that terminal conductivity deteriorates when low-molecular-weight TOC components flow into and accumulate in the anion exchange resin tower 33. Therefore, if the average value obtained during the averaging period [5] tends to increase with each cycle, it can be determined that low-molecular-weight TOC components are flowing into the anion exchange resin tower 33. However, at this stage, it is not possible to determine with certainty that low-molecular-weight TOC components are flowing into the anion exchange resin tower 33. In this case, too, it is possible to calculate the sum of the average values ​​during the averaging period [4] and the average values ​​during the averaging period [5] and examine how this sum changes as the cycle is repeated. It is also possible to divide the cycle into averaging periods other than five.

[0033] 6(a) to 6(c) illustrate the change in differential pressure calculated from the measurements of the pressure gauges 36 and 37 when low-molecular-weight TOC components flow into the anion exchange resin tower 33 in the water treatment system shown in FIG. 2, similar to those shown in FIGS. 6(a) to 6(c). FIG. 6(a) shows the time change in differential pressure in each cycle from the first to the fourth cycle, FIG. 6(b) shows the division of the cycle into averaging periods, and FIG. 6(c) shows the transition of the average value as the cycle is repeated. In the example shown here, there is a period during the desalination treatment in which treated water from the anion exchange resin tower 33 is not supplied to downstream equipment, i.e., an outage period. During the outage period, the flow of water to be treated through the anion exchange resin tower 33 is also stopped, so no differential pressure is generated. Therefore, the outage period is missing from the differential pressure graph shown in FIG. 6(a). The period sandwiched between the outage periods and actually plotted on the graph is the water sampling period. Furthermore, when a stopped pump is started, the differential pressure rises sharply after a certain time has elapsed during the water sampling period, as shown in figure A, and then returns to normal when the pump is stopped and started again. Looking at each water sampling period, the differential pressure changes in a single step. This is due to the mechanical structure of the water treatment system, including the pump and piping, and does not indicate any abnormality in the anion exchange resin tower 33 or deterioration of the anion exchange resin.

[0034] In the first cycle, the differential pressure remains nearly constant throughout the entire cycle, except for the step-like changes in differential pressure during each water sampling period. However, as the cycle repeats, even if we ignore the step-like changes in differential pressure during each water sampling period, the differential pressure at the end of each cycle increases compared to the differential pressure at the beginning of the cycle. As described above, each cycle is divided into five averaging periods [1] to [5]. Figure 6(b) shows how the differential pressure graph shown in Figure 6(a) is divided into averaging periods. Similarly, for each cycle and each averaging period, the arithmetic mean (i.e., the center of gravity) of the differential pressure is calculated as the average. When calculating the average, it is necessary to eliminate the effect of step-like changes in differential pressure caused by starting and stopping the pump. Since the time it takes for the differential pressure to increase stepwise after the pump starts is nearly constant, for example, for each averaging period, the average differential pressure from the start of the pump until the differential pressure increases stepwise is calculated.

[0035] As described above, when low-molecular-weight TOC components flow into and accumulate in the anion exchange resin tower 33, the differential pressure generated in the anion exchange resin tower 33 also changes. This change becomes more pronounced in the latter half of each cycle. Focusing on the averaging period [5], which corresponds to the period immediately before the end of the desalination process, as shown in Figure 6(c), the average differential pressure obtained during the averaging period [5] increases with each cycle. This indicates a change in the differential pressure. When this change occurs, it can be determined that low-molecular-weight TOC components may be flowing into the anion exchange resin tower 33. In this case, too, the sum of the average values ​​during the averaging period [4] and the average values ​​during the averaging period [5] can be calculated, and the change in this sum can be examined as the cycle is repeated. The number of divisions into the averaging period of the cycle can also be set to a number other than five.

[0036] Figure 7 illustrates, similarly to Figures 4(a) to (c), the changes in the conductivity measured by the conductivity meter 38 when silica components flow into the anion exchange resin tower 33 in the water treatment system shown in Figure 2. Figure 7(a) shows the time change in conductivity for each cycle from cycle 1 to cycle 4, Figure 7(b) shows the division of the cycles into averaging periods, and Figure 7(c) shows the transition of the average value as the cycles are repeated. In each cycle, the conductivity is relatively high at the start of the desalination process, then rapidly decreases to a steady state, and then increases again at the end of the desalination process. As the cycles are repeated, the conductivity deteriorates throughout each cycle, i.e., overall, as indicated by the arrows in the figure. Here, each cycle is divided into five averaging periods [1] to [5], as described above. Figure 7(b) shows how the conductivity graph shown in Figure 7(a) is divided into averaging periods. Then, as described above, for each cycle and for each averaging period, the arithmetic mean value (i.e., centroid value) of the measured conductivity values ​​is calculated as the average value.

[0037] It is known that when silica components flow into the anion exchange resin column 33, the initial conductivity deteriorates and the breakthrough point occurs earlier, as described above. The earlier breakthrough point ultimately leads to a deterioration in the final conductivity. This deterioration in both the initial and final conductivity leads to a deterioration in the steady-state conductivity. Therefore, focusing on the averaging period [3] corresponding to the steady-state period of the desalination process and the averaging period [5] corresponding to the period immediately prior to the end, as shown in Figure 7(c), the average conductivity increases in both averaging periods [3] and [5] as the cycle is repeated. This indicates a deterioration in the steady-state conductivity and the final conductivity. When this deterioration occurs, it can be concluded that silica components have flowed into and accumulated in the anion exchange resin column 33. In this case, too, it is possible to focus on averaging periods other than [3] and [5], or to divide the cycle into averaging periods other than five. For example, when silica components flow in and accumulate, the initial conductivity also deteriorates, so the average conductivity during the averaging period [1], which corresponds to the period immediately after the start of the desalination process, is also expected to increase as the cycle is repeated.

[0038] The above has described how the average value calculated in each averaging period changes as the cycle is repeated for each cause of performance degradation in the anion exchange resin tower 33. As is clear from the above description, the cause of performance degradation in the anion exchange resin tower 33 can be estimated from the transition of the average value in a specific order of averaging periods, and by combining such estimations, the cause of performance degradation can be estimated with higher accuracy. Figure 8 is a flowchart explaining such an estimation process.

[0039] First, in step 101, time-series data on conductivity and differential pressure are acquired. 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 terminal conductivity and the differential pressure at the end of the cycle also increase as the cycle is repeated. The increase in terminal conductivity can be determined, for example, by whether the average conductivity value over the averaging period [5] increases. The increase in differential pressure at the end of the cycle can also be determined, for example, by whether the average differential pressure value over the averaging period [5] increases. If it is determined that both the terminal conductivity and the differential pressure at the end of the cycle increase as the cycle is repeated, in step 104, it is determined that a weakly conductive substance with low ion selectivity, such as a low-molecular-weight TOC component, has flowed into the anion exchange resin column 33, and the cause estimation process is then terminated. Examples of weakly conductive substances with low ion selectivity include acetic acid, propionic acid, fluoride ions, and borate ions. Among the substances listed here, acetic acid and propionic acid both have molecular weights of less than 100 and therefore fall under the category of low-molecular-weight TOC components. If the raw water and recovered water do not contain fluoride ions or borate ions and it is clear that these ionic components are not present in the outlet water of the activated carbon tower 26, it can be determined in step 104 that low-molecular-weight TOC components have flowed into the anion exchange resin tower 33. On the other hand, if it is determined in step 103 that neither the terminal conductivity nor the differential pressure at the end of the cycle has increased, it is next determined in step 105 whether the overall conductivity has increased with each cycle as the cycle is repeated. This determination can be made, for example, by determining whether the conductivity during the averaging period [3] corresponding to the steady state in each cycle has increased as the cycle is repeated. If the overall conductivity has not increased, it is determined in step 106 that the anion exchange resin tower 33 is normal, or that any performance degradation, if any, is due to other causes, and the cause estimation process is terminated.

[0040] If it is determined in step 105 that the overall conductivity increases with each cycle as the cycle is repeated, it can be assumed that silica components or high-molecular-weight TOC components have flowed into the anion exchange resin tower 33. To distinguish whether the components that flowed into the anion exchange resin tower 33 are silica components or high-molecular-weight TOC components, a thermal regeneration process is performed in the regeneration process following the current cycle (i.e., desalination process), and the amount of regenerant used to regenerate the anion exchange resin tower 33 is increased. For example, the amount of regenerant is doubled. Then, in step 107, it is determined whether the overall conductivity in the cycle after the thermal regeneration process remains high or has improved to a lower value. In this case, it is also possible to determine whether the average conductivity over the averaging time {3] remains high or has decreased (improved). If the conductivity has improved, it is assumed in step 108 that silica components have flowed in, and the cause estimation process is then terminated. On the other hand, if it is determined in step 107 that the conductivity has not improved, it is assumed that high molecular weight TOC components have flowed in, and then the process of estimating the cause is terminated.

[0041] By performing the above process, it becomes possible to estimate whether the cause of the performance degradation 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 some other cause. Here, the differential pressure in the anion exchange resin tower 33 and the conductivity of the outlet water are measured. However, even without measuring the differential pressure, the cause can be roughly estimated from the results of conductivity measurements alone. In this case, for example, when the cycle is repeated, if the average conductivity during the averaging period [3] remains almost unchanged but the conductivity during the averaging period [5] increases, it can be determined that low-molecular-weight TOC components (or borate ions, etc.) have likely infiltrated. If the average conductivity during the averaging period [3] also increases, it can be determined that the inflow of silica components or high-molecular-weight TOC components has likely infiltrated.

[0042] 9 shows an example of the configuration of a cause estimation device 10 that implements the above-described cause estimation method. This cause estimation device 10 manages the operation of a water treatment system including the ion exchange treatment unit 30 shown in FIG. 2 and is used to estimate the cause of performance degradation in the anion exchange resin tower 33 in the ion exchange treatment unit 30. The anion exchange resin tower 33 alternately undergoes demineralization and regeneration treatment. In addition to the pressure gauges 36 and 37 and the conductivity meter 38 shown in FIG. 2, the ion exchange treatment unit 30 is also provided with a regenerant supply unit 40 that supplies a regenerant when regenerating the anion exchange resin tower 33. The pressure gauges 36 and 37 and the conductivity meter 38 are constantly measuring, and time-series data consisting of these measurements is output to the cause estimation device 10.

[0043] The cause estimation device 10 includes a differential pressure calculation unit 11 that calculates a differential pressure from the measurement values ​​of the pressure gauge 36 and the measurement values ​​of the pressure gauge 37 and outputs the calculated differential pressure as time-series data, an averaging period setting unit 12 that receives signals indicating the timing of starting the desalination treatment or the regeneration treatment from the ion exchange treatment unit 30 and sets an averaging period, an average value calculation unit 13 that calculates an average value from the time-series data of the differential pressure for each averaging period, an average value calculation unit 14 that calculates an average value from the time-series data of the conductivity for each averaging period, and an estimation unit 15 that estimates the cause of performance deterioration in the anion exchange resin tower 33 according to the above-mentioned procedure. The averaging period setting unit 12 sets the averaging period by dividing each cycle into a fixed number of averaging periods, with one desalination treatment period being regarded as one cycle, so that the averaging periods within each cycle are assigned an order counted from the beginning of the cycle. The estimation unit 15 estimates the cause of performance degradation in the anion exchange resin tower 33 based on how the average value over the averaging period of a specific order for each cycle changes as the cycle is repeated, and outputs the estimation result. In estimating the cause of performance degradation, the average value when the amount of regenerant in the regeneration treatment is increased may be used. In order to make such an estimation, the estimation unit 15 can control the regenerant supply unit 40 in the ion exchange treatment unit 30 to increase the amount of regenerant supplied to the anion exchange resin tower 33 during the regeneration treatment.

[0044] By using such a cause estimation device 10, it is possible to perform cause estimation according to the procedure shown in Fig. 8. When estimating the cause of the performance degradation of the anion exchange resin tower 33 in the ion exchange treatment unit 20 configured as shown in Fig. 3, the measured values ​​obtained by the resistivity meter 39, rather than the conductivity meter 38, should be provided as time-series data to the average value calculation unit 14 of the cause estimation device 10.

[0045] In the above explanation, a substance with an acid dissociation constant pKa of 4.0 or more is defined as a "weakly conductive substance with low ion selectivity." Instead of this definition, the selectivity for a strongly basic anion exchange resin whose ionic form is the OH form is defined as K x OH As, K x OH It is also possible to define a material that satisfies K≦4.0 as a "weakly conductive material with low ion selectivity." x OH If the definition is based on this, hydrofluoric acid or fluoride ions are also included in the category of "weakly conductive materials with low ion selectivity." [Explanation of symbols]

[0046] 10 Cause estimation device 11 Differential pressure calculation section 12 Averaging interval setting section 13,14 Average value calculation section 15 Estimation part 21,24 Storage tank 22, 25, 41 Pump 23 Filter 26 Activated carbon tower 30 Ion exchange processing section 31,34 Cation exchange resin tower 32 Decarboxylation tower 33 Anion exchange resin tower 36,37 Pressure gauge 38 Conductivity meter 39 Resistivity meter 40 Regenerant supply section

Claims

1. A method for estimating the cause of performance degradation in an anion exchange device that is provided with an anion exchanger and configured so that water to be treated can pass through the anion exchanger, and in which a desalination process for desalination of the water to be treated and a regeneration process for regenerating the anion exchanger are alternately performed, comprising: During the desalination treatment, time series data is acquired for at least one of a measured value of the differential pressure for the anion exchanger and a measured value of the water quality of the treated water discharged from the anion exchange device; The period of one desalination treatment performed from one execution of the regeneration treatment to the execution of the next regeneration treatment is defined as one cycle, each of the cycles is divided into a predetermined number of averaging periods, and for each cycle, the averaging periods included in the cycle are assigned an order counted from the beginning of the cycle, and the cause of the performance degradation in the anion exchange device is estimated based on the transition of the average value when the cycle is repeated; The cause estimation method, wherein the average value is an average value calculated from each measurement value constituting the time series data during the averaging period in a specific order for each cycle.

2. 2. The cause estimation method according to claim 1, wherein the measured value of the water quality of the treated water is a measured value obtained by measuring the electrical conductivity or resistivity of the water at the outlet of the anion exchange device.

3. 2. The cause estimation method according to claim 1, wherein a cation exchange device is provided downstream of the anion exchange device, and the measurement value of the water quality of the treated water is a measurement value obtained by performing a conductivity measurement or a resistivity measurement on the outlet water of the cation exchange device.

4. the anion exchange device is an anion exchange resin tower packed with a weakly basic anion exchange resin and a strongly basic anion exchange resin as the anion exchangers in a mixed bed form, with the weakly basic anion exchange resin located upstream and the strongly basic anion exchange resin located downstream; 2. The method for estimating the cause of a problem according to claim 1, wherein the measured value of the differential pressure is a measured value of the differential pressure occurring in the layer of the weakly basic anion exchange resin.

5. 5. The cause estimation method according to claim 1, wherein, for the averaging period corresponding to immediately before the end of each cycle, when the average value calculated from the water quality deteriorates and the average value calculated from the differential pressure increases as the cycle is repeated, it is determined that a component having a molecular weight of less than 100 and an acid dissociation constant of 4.0 or more, but which is not a silica component, has flowed into the anion exchange device.

6. A cause estimation method according to any one of claims 1 to 4, wherein TOC components with a molecular weight of 100 or more are considered to be high molecular weight TOC components, and when the average value calculated from the water quality deteriorates as the cycle is repeated for the averaging period corresponding to the steady state period of each cycle, it is determined that silica components or high molecular weight TOC components have flowed into the anion exchange device.

7. 7. The cause estimation method according to claim 6, wherein, after determining that silica components or high molecular weight TOC components have flowed into the anion exchange device, the amount of regenerant is increased and the regeneration treatment is performed, and if the average value calculated from the water quality for the averaging period corresponding to the steady state period of the cycle thereafter continues to deteriorate, it is determined that high molecular weight TOC components have flowed in, and if the average value does not continue to deteriorate but improves, it is determined that silica components have flowed in.

8. A cause estimation device for estimating the cause of performance degradation in an anion exchange device that is provided with an anion exchanger and configured so that water to be treated can pass through the anion exchanger, and in which a desalination process for desalination of the water to be treated and a regeneration process for regenerating the anion exchanger are alternately performed, a measuring means provided in the anion exchanger for measuring at least one of the differential pressure across the anion exchanger and the water quality of treated water discharged from the anion exchanger, and outputting the measured data as time-series data; an averaging period setting unit that sets the averaging periods for each cycle such that the period of one desalination treatment performed from the time the regeneration treatment is performed until the time the next regeneration treatment is performed is one cycle, each cycle is divided into a predetermined number of averaging periods, and the averaging periods included in each cycle are assigned an order counted from the beginning of the cycle; an average value calculation unit that calculates an average value of each measurement value constituting the time series data during the averaging period in a specific order for each cycle; an estimation unit that estimates a cause of performance degradation in the anion exchange device based on a transition of the average value when the cycle is repeated; A cause estimation device having the above.

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

10. a cation exchange device is provided downstream of the anion exchange device, 9. The cause estimation device according to claim 8, wherein the measuring means includes a sensor that measures the electrical conductivity or resistivity of the outlet water of the cation exchange device.

11. the anion exchange device is an anion exchange resin tower packed with a weakly basic anion exchange resin and a strongly basic anion exchange resin as the anion exchangers in a mixed bed form, with the weakly basic anion exchange resin located upstream and the strongly basic anion exchange resin located downstream; 11. The cause estimation device according to claim 8, wherein the measuring means includes a sensor that measures a differential pressure generated in the layer of the weakly basic anion exchange resin.

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