JP7200874B2 - Method for predicting operating voltage of electrodeionization device and method for controlling pure water production device - Google Patents

Description

The present invention relates to a method of predicting the operating voltage of an electrodeionization apparatus, and a method of controlling a pure water production apparatus using this predicted value of the operating voltage.

In recent years, the use of ultrapure water has become popular in the electronics industry field such as semiconductor manufacturing factories and liquid crystal manufacturing factories, and in the research and development field. A secondary pure water system (subsystem) is commonly used. The use of an electrodeionization apparatus for this primary pure water apparatus is becoming established.

In producing primary pure water using the primary pure water apparatus as described above, the operating current value for the inflowing ion load is determined by taking into consideration the desalination performance, that is, the current efficiency, etc., in order to remove ions. is generally determined and constant current operation is performed. At this time, the silica concentration of the water supplied to the electrodeionization apparatus is limited. This is because when the silica concentration of the water supplied to the electrodeionization equipment is high, silica scale is generated and the electrical resistance increases. It is because it will invite (patent document 1).

As a countermeasure against the silica concentration of the water supplied to the electrodeionization apparatus, conventionally, two stages of reverse osmosis membranes are provided in front of the electrodeionization apparatus to remove silica.

Moreover, in order to cope with the case where the silica concentration is high, pretreatment is also performed by provisionally providing an anion exchange means for the purpose of removing silica.

Furthermore, as shown in FIG. 1, for example, a primary water purifier (pure water production device) using an RO membrane and a degassing membrane is also used. A raw water tank 11 for storing pretreated water W obtained by treating well water W0 in 2, a first water pump 12, a heat exchanger 13, a safety filter 14, a second water pump 15, It comprises a reverse osmosis membrane (RO membrane) 16, a degassing membrane 17, and an electrodeionization device 18. The water to be treated whose silica concentration has been reduced by the reverse osmosis membrane (RO membrane) 16 is treated by the electrodeionization device. 18 and the primary pure water W1 produced by the primary pure water apparatus 1 is stored in the sub-tank 3.

Japanese Patent No. 6040789

In the conventional primary pure water apparatus as described above, if reverse osmosis membranes are provided in two stages in the preceding stage of the electrodeionization apparatus, the apparatus configuration becomes very large, and if silica is below a predetermined standard value, Although there is no problem, not only is it removed more than necessary, but the system configuration is excessive, so there is a problem that it cannot be applied when the installation space is limited.

In addition, if an anion exchange means is provisionally provided for the purpose of removing silica, not only will the equipment be expensive, but if the switching to the anion exchange means is not properly controlled, electrodeionization will occur. There is a problem that water to be treated having a high silica concentration may be supplied to the apparatus.

Furthermore, in the case of using a primary pure water apparatus using an RO membrane and a degassing membrane as shown in FIG. There is a problem that the water to be treated may be supplied.

If it is possible to predict the deterioration of treated water quality from the silica concentration and operating voltage of the water to be treated flowing into the electrodeionization device 18 and control the primary pure water production device, the treated water of the electrodeionization device, and further This is desirable because the water quality of the primary pure water W1 to be produced can be maintained well.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for predicting the operating voltage of an electrodeionization apparatus in order to maintain good quality of treated water of the electrodeionization apparatus. Another object of the present invention is to provide a method of controlling a water purifying apparatus using the predicted operating voltage.

In order to achieve the above objects, the present invention firstly provides a cathode and an anode, a cation exchange membrane and an anion exchange membrane disposed between the cathode and the anode, and a compartment formed by the cation exchange membrane and the anion exchange membrane. The desalting chambers and the concentrating chambers are filled with an ion exchange resin, and the concentrated water passing means for passing the concentrated water to the concentrating chambers and the desalting chambers are connected to each other. means for passing the water to be treated to extract deionized water, and the concentrated water passing means passes the deionized water passed through the desalting chamber as concentrated water. A method for predicting the voltage, wherein the future operating voltage of the electrodeionization apparatus is calculated from the initial voltage and the initial silica concentration of the feed water when the electrodeionization apparatus is in operation, and the voltage and the silica concentration of the feed water after a predetermined time has elapsed. A method for predicting the operating voltage of an electrodeionization apparatus is provided (Invention 1).

According to this invention (Invention 1), the rate of increase in voltage is calculated from the transition of the feed water silica concentration and voltage when the electrodeionization apparatus is operated, and the future time course when the operation of the electrodeionization apparatus is continued is calculated. By predicting the fluctuation of the target voltage, it is possible to predict whether the quality of the water to be treated flowing into the electrodeionization apparatus is appropriate and to take appropriate measures in advance.

In the above invention (Invention 1), the future operating voltage of the electrodeionization apparatus is determined by the following formula: Vn = V(n-1) + m x (Sin - Se) x D
(In the formula, Vn is the predicted operating voltage (V), V(n-1) is the voltage (V) after the elapse of a predetermined time, D is the predetermined time after the elapse (days), and Sin is is the feed silica concentration (μg/L), Se is the limit silica concentration (μg/L), and m is a coefficient specific to the electrodeionization apparatus)
It is preferable to predict by (Invention 2).

According to this invention (Invention 2), from the transition of the feedwater silica concentration and voltage when the electrodeionization apparatus is operated at the initial stage and the feedwater silica concentration and voltage when the electrodeionization apparatus is operated after a predetermined period of time has passed, , the coefficient specific to the electrodeionization apparatus is calculated, the rate of voltage increase is calculated by the above formula, and future temporal voltage fluctuations when the operation of the electrodeionization apparatus is continued are predicted. Then, based on this predicted voltage, it is possible to predict whether the quality of the water to be treated that flows into the electrodeionization apparatus is appropriate, and to take appropriate measures in advance.

Secondly, the present invention is a method of operating a water purifying apparatus having an electrodeionization apparatus and at least constituent elements other than the electrodeionization apparatus, wherein the initial voltage and the initial voltage during operation of the electrodeionization apparatus. The future operating voltage of the electrodeionization apparatus is predicted from the feed-water silica concentration, the voltage after the lapse of a predetermined time, and the feed-water silica concentration, and the electrodeionization is performed based on the predicted future operation voltage of the electrodeionization apparatus. Provided is a method for controlling a water purifying apparatus that controls constituent elements other than the ion apparatus (Invention 3).

According to this invention (Invention 3), future fluctuations in voltage over time when the operation of the electrodeionization apparatus is continued are predicted, thereby predicting the future treatment of the elements arranged upstream of the electrodeionization apparatus. It is possible to predict the suitability of , and take appropriate measures in advance, thereby stabilizing the operation of the pure water production apparatus and the quality of the produced pure water.

In the above invention (invention 3), the component other than the electrodeionization device is preferably a reverse osmosis membrane separation device (invention 4).

According to this invention (Invention 4), by predicting future voltage fluctuations over time when the operation of the electrodeionization apparatus is continued, treatment with the reverse osmosis membrane arranged in the preceding stage of the electrodeionization apparatus can be performed. It is possible to predict the future suitability of the system and plan in advance the replacement and maintenance of the reverse osmosis membrane for optimization. be able to.

According to the present invention, the future operating voltage of the electrodeionization apparatus is calculated from the initial voltage and the initial silica concentration of the feed water when the electrodeionization apparatus is in operation, and the voltage and the silica concentration of the feed water measured after a predetermined time has elapsed. As a result, it is possible to predict the appropriateness of the treatment in the element arranged in the front stage of the pure water production apparatus equipped with the electrodeionization device, and to take measures for optimization in advance. operation and the quality of pure water produced can be stabilized.

1 is a flow diagram showing a primary pure water production system to which a method for controlling a pure water production system according to an embodiment of the present invention can be applied; FIG. 1 is a schematic diagram showing an electrodeionization apparatus to which a method for predicting an operating voltage of an electrodeionization apparatus according to an embodiment of the present invention can be applied; FIG. FIG. 3 is a schematic diagram showing a water flow state of the electrodeionization apparatus; 4 is a graph showing changes in voltage of the electrodeionization apparatus. 4 is a graph showing the voltage of the electrodeionization apparatus and the assumed silica concentration; 4 is a graph showing calculated values of the voltage of the electrodeionization device;

Hereinafter, a method for predicting the operating voltage of an electrodeionization apparatus and a method for controlling a pure water production apparatus to which the method is applied according to an embodiment of the present invention will be described with reference to the accompanying drawings.

(pure water production equipment)
The pure water production apparatus that can be applied in the present embodiment is not particularly limited as long as it is equipped with an electrodeionization apparatus. For example, as shown in FIG. can be applied particularly preferably.

(Electrodeionization device)
In this embodiment, the electrodeionization device is not particularly limited, and for example, an electrodeionization device as shown in FIG. 2 can be used. In FIG. 2, the electrodeionization apparatus 21 alternately arranges a plurality of anion exchange membranes 24 and cation exchange membranes 25 between electrodes (anode 22 and cathode 23) to alternately arrange concentration compartments 26 and deionization compartments 27. The desalting chamber 27 is filled with ion exchange resins (anion exchange resin and cation exchange resin) in a mixed or multi-layered manner. Concentrating compartment 26, anode compartment 28 and cathode compartment 29 are also filled with ion exchange resin.

The electrodeionization apparatus 21 includes water passage means (not shown) for passing the water W to be treated, which is pretreated water, through the deionization chamber 27 to take out primary pure water (deionized water) W1, and concentrating water. Concentrated water passing means (not shown) for passing the concentrated water W2 through the chamber 26 is provided. Condensed water W2 is introduced into the concentration chamber 26 from the side and flows out from the side near the entrance of the deionization chamber 27, that is, from the direction opposite to the flow direction of the water W to be treated in the deionization chamber 27. Then, concentrated waste water W3 is discharged.

Specifically, as shown in FIG. 3, a portion of the primary pure water W1 obtained from the demineralization chamber 27 is introduced into the concentration chamber 26 and the anode chamber 28 . In this way, the primary pure water W1 is used as the concentrated water W2, and the concentrated water W2 with the reduced ion concentration is circulated.

In such an electrodeionization apparatus, the volume ratio of the anion exchange resin to the cation exchange resin in the ion exchange resin filled in the desalting chamber 27 is 80:20 to 60:40, preferably 80:20 to 70: 30. When the volume ratio of the anion exchange resin exceeds 80%, the elution of the PSA component derived from the cation exchange resin is reduced, but the removal rate of the cation component in the primary pure water W1 is lowered. On the other hand, when the proportion of the anion exchange resin is less than 60% by volume, the elution of the PSA component derived from the cation exchange resin increases, the electrical resistance of the electrodeionization apparatus increases, and the voltage required for operation increases. , the service life of the electrodeionization apparatus 1 tends to be shortened. The ratio of the ion exchange resin may be different between the upper side (inlet side) and the lower side (outlet side) of the demineralization chamber 7. For example, the proportion of the anion exchange resin may be increased.

(Method for Predicting Operating Voltage of Electrodeionization Apparatus)
In the primary pure water production apparatus 1 shown in FIG. 1, after pretreated water W obtained by treating well water W0 in the activated carbon tower 2 is stored in the raw water tank 11, the first water pump 12 and the second water pump 15 is started, and this pretreated water W is sequentially treated with a heat exchanger 13, a safety filter 14, and a reverse osmosis membrane (RO membrane) 16 to remove silica and organic matter. Subsequently, after removing oxygen and carbon dioxide with the degassing membrane 17 , it is treated with the electrodeionization device 18 . Primary pure water W<b>1 obtained by removing ionic impurities in the electrodeionization device 18 is stored in the subtank 3 .

In this electrodeionization apparatus 18, if the reverse osmosis membrane (RO membrane) 16 deteriorates over time or the water quality of the well water W0 fluctuates, the concentration of silica in the water supply of the electrodeionization apparatus 18 increases, reaching the limit. Exceed value. Along with this, the amount of silica accumulated in the ion exchange resin in the electrodeionization device 18 increases. Since the voltage is reversibly lowered at this time, silica does not become scale. However, part of the accumulated silica gradually becomes less mobile and remains in the electrodeionization device 18, which increases the operating voltage as the electrical resistance of the electrodeionization device 18 increases. Then, when the limit voltage is reached, the current value decreases, the desalination performance of the electrodeionization device 18 decreases, and the quality of the primary pure water W1 deteriorates.

Accordingly, the present inventor investigated the voltage of the electrodeionization apparatus when the silica concentration in the feed water of the electrodeionization apparatus 18 becomes higher than the specified value. As a result, the following formula was found.

Vn=V(n-1)+m×(Sin−Se)×D
(In the formula, Vn is the predicted operating voltage (V), V(n-1) is the voltage (V) after the elapse of a predetermined time, D is the predetermined time after the elapse (days), and Sin is is the feed silica concentration (μg/L), Se is the limit silica concentration (μg/L), and m is a coefficient specific to the electrodeionization apparatus)

That is, the operating voltage value Vn (V) is determined by the concentration difference between the silica concentration (Sin: μg/L) of the water supply to the electrodeionization apparatus and the limit silica concentration (Se: for example, 900 μg/L), and the elapsed time It can be calculated by adding the value obtained by multiplying D days by the coefficient m value to the operating voltage value V(n-1) (V) after D days. The silica concentration of the feed water (Sin: μg/L) may be measured, but the tendency of silica concentration increase due to deterioration of the reverse osmosis membrane (RO membrane) 16 etc. is measured in advance, and the elapsed time You may use the assumed silica concentration which predicted the silica concentration by. At this time, it is preferable to measure the silica concentration after replacement of the reverse osmosis membrane (RO membrane) 16 in advance.

For example, in an electrodeionization apparatus (KCDI-UPz-250H) manufactured by Kurita Water Industries, at a constant water flow rate of 25 m ³ /h and a constant current of 6 A, the m value is calculated to be 0.08. The initial value V0 of Vn is assumed to be 200 (V).

The voltage rises to the ultimate voltage value at the voltage rising rate described above, and the ultimate voltage Ve is calculated by the following formula from the assumed feed water silica concentration Sin (μg/L) of the electrodeionization apparatus 18 .
Ve = E x (Sin - Se)

Here, the E value is calculated to be 1.0 when Sin is in the range of 900 to 2000 ppb, under the operating conditions of the above-described water amount and current in this electrodeionization. However, when Sin<Se, Ve=200 (V). The value of this coefficient m varies depending on the model of the electrodeionization apparatus and the steady-state operating conditions (flow rate, current value) of the electrodeionization apparatus 18. When the operating current value changes, Vn (V) is the current value I It is obtained by multiplying (A) by I/6. Further, when the flow rate Q (m ³ /h) of the electrodeionization apparatus 18 is set by the number of desalting cells and fluctuates depending on the model, Vn (V) is Q/25 times (when Q>10), Alternatively, an approximate value can be calculated by multiplying Q/12.5 (when Q≤10).

In addition, the coefficient m is determined by setting the limit silica concentration (Se) in advance, and the predetermined time (days) It can be calculated in advance from the operating voltage (Vn) of the electrodeionization device 18 measured after the passage of time and the assumed feed water silica concentration (Sin). In this way, the coefficients such as the m value may be obtained in advance by the silica loading test for each model of the electrodeionization apparatus and calculated.

After calculating the operating voltage value (Vn) in this way, the calculated operating voltage value (Vn) is used to further calculate the subsequent Vn. It can be predicted intermittently along the day. In addition, if necessary, the operating voltage value is measured appropriately according to changes in conditions such as fluctuations in raw water quality and operating conditions, and by correcting the calculated value based on this, the calculated operating voltage value (Vn) expected value) can be improved.

(Control method for pure water production device)
Next, a method for controlling the pure water production apparatus of this embodiment using the predicted operating voltage of the electrodeionization apparatus 18 will be described.

By predicting the day-to-day change in the rise in the operating voltage of the electrodeionization device 18 as described above, the time until the treated water quality of the electrodeionization device 18 declines due to an increase in the silica concentration of the primary pure water W1, etc. can be predicted. Therefore, based on this predicted decrease time, a maintenance plan such as replacement of the reverse osmosis membrane (RO membrane) 16 in the preceding stage of the electrodeionization device 18 is planned, or feedback is given to the operating conditions. , the water supply silica concentration (Sin: μg/L) of the electrodeionization device 18 is lowered to stabilize the water quality of the primary pure water W1 produced by the primary pure water device 1 as a pure water production device. It is possible to prevent the occurrence of troubles caused by

Further, not only is the operating voltage of the electrodeionization device 18 increased, but also, for example, after the presumed feed water silica concentration (Sin) of the electrodeionization device 18 becomes normal after the reverse osmosis membrane (RO membrane) 16 in the preceding stage is replaced, Since it is also possible to calculate the rate of decrease in operating voltage, it can also be used to check the effectiveness of countermeasures. In this case, the feed water silica concentration (Sin) after replacement of the reverse osmosis membrane (RO membrane) 16 may be measured in advance or measured sequentially.

An embodiment of the present invention has been described above with reference to the accompanying drawings. The present invention is characterized in that element control in the preceding stage is performed based on prediction of an increase in the operating voltage of the electrodeionization apparatus 18. , and various modifications are possible without being limited to the above embodiment. For example, the configuration of the primary pure water production device (pure water production device) 1 is not particularly limited, and in addition to the reverse osmosis membrane (RO membrane) 16, it may have a regenerative ion exchange device, boron removal means, and the like. , the predicted value of the operating voltage of the electrodeionization device 18 may be used to control such maintenance.

EXAMPLES The present invention will be more specifically described below based on examples, but the present invention is not limited to the following examples.

[Example 1]
As shown in FIG. 1, using a primary pure water production apparatus 1 (water volume 25 m ³ /h) equipped with an activated carbon tower 2, a reverse osmosis membrane (RO membrane) 16, a degassing membrane 17 and an electrodeionization device 18, electricity A verification test was conducted on the prediction of the operating voltage of the deionizer and the control method of the water purifier using this prediction. "KCDI-UPz" manufactured by Kurita Water Industries Ltd. was used as the electrodeionization device 18, and was operated at a treated water volume of 25 m ³ /h and an operating current of 6 A (constant current operation). The operating voltage at this time was measured for 90 days. The results are shown in FIG.

As is clear from FIG. 4, when the elapsed time at which the voltage began to rise was defined as 0 days, the voltage continued to rise for 46 days thereafter. Then, when the operating voltage exceeded 350 V on the 46th day, when the reverse osmosis membrane (RO membrane) 16 in the front stage was replaced, the voltage decreased and returned to the initial voltage value (200 V) on the 70th to 80th day. rice field.

FIG. 5 shows the assumed silica concentration of the water supply of the electrodeionization device 18 at this time. In FIG. 5, only the assumed silica concentration on the 30th day is the measured value. As for the assumed silica concentration after replacement of the reverse osmosis membrane (RO membrane) 16, a value calculated from the tendency measured in advance was applied.

(Simulation based on formula for voltage rise rate)
We studied how to formulate the rise and fall of the operating voltage using the following formulas.
Vn=V(n-1)+m×(Sin−Se)×D
(where Vn is the predicted operating voltage (V), D is the previous voltage measurement time (days) for the elapsed time of the predicted operating voltage, and V(n-1) is calculated based on the initial voltage. is the applied voltage (V), S is the assumed feed water silica concentration (μg/L), Se is the critical silica concentration (μg/L), and m is a coefficient specific to the electrodeionization apparatus).

Operation is performed for D (days) at a voltage value of V(n-1) (V), the concentration of silica feedwater at that time is Sin (μg/L), and the permissible concentration of silica to the electrodeionization device 18 is Se (μg/L). , the voltage is Vn (V). Here, (Sin-Se) is the driving force (Dri-Force), and the voltage rise speed is determined by the coefficient m value, meaning that the voltage rises as the number of elapsed days increases. In other words, if the assumed feed water silica concentration exceeds the allowable limit, the amount of equilibrium accumulation in the ion exchange resin is determined in proportion to that amount, and as the adsorption amount increases, the voltage value rises (electric resistance increases). is.

Sequential calculation is performed from the number of days of water flow, the assumed silica concentration (Sin), the allowable silica concentration (limit concentration (Sin); 900 μg / L), and the difference (Dri-Force), and the calculated voltage value matches the field voltage value. When the m value was calculated so that the m value was 0.008, it was found to be possible. At this time, the assumed silica concentration is an assumed value calculated in advance based on the properties of the reverse osmosis membrane (RO membrane) 16 . Table 1 shows the calculation results based on these when m value=0.008.

(Comparison between calculated and measured values)
FIG. 6 shows the voltage at the calculated value when m value=0.008 compared with the measured value shown above. As can be seen from a comparison between FIG. 6 and FIG. 4, the calculation results can almost reproduce the measured values. Moreover, it was found that not only the voltage rise but also the voltage drop situation matched the results calculated with the same m value. This suggests that the increase and decrease in silica accumulation on the ion-exchange resin, whether the difference in silica equilibrium accumulation is positive or negative, is the driving force that determines the rate of voltage rise and fall. This is considered to indicate that

From these facts, the present invention makes it possible to predict the operating voltage of the electrodeionization apparatus. The silica concentration of the treated water can be calculated by predicting it with reference to the current value and entering it. It is also possible to calculate from the result of automatic measurement by a silica densitometer. From these calculations, for example, it is possible to determine whether the time until replacement of the reverse osmosis membrane (RO membrane) 16 is arranged and whether the voltage rise is within the allowable range of the power supply. It is possible to determine whether to drive with the vehicle lowered. Furthermore, when the assumed feed water silica concentration drops below the specified value due to the replacement of the reverse osmosis membrane (RO membrane) 16 or the change of the water source, etc., it is predicted how long it will take for the voltage value to return to normal. By comparing with the situation, it is possible to quickly check whether the voltage value is recovered as intended or not, and to consider countermeasures in case it is not.

1 Primary pure water device (pure water production device)
2 activated carbon tower 3 subtank 11 raw water tank 12 first water pump 13 heat exchanger 14 safety filter 15 second water pump 16 reverse osmosis membrane (RO membrane)
17 degassing membrane W0 well water W pretreated water W1 primary pure water (pure water, deionized water)

Claims (4)

a cathode and an anode; a cation exchange membrane and an anion exchange membrane arranged between the cathode and the anode; Concentrated water passage means for passing concentrated water through the concentration chambers and means for passing water to be treated through the demineralization chambers to extract deionized water, wherein the chambers and the concentration chambers are filled with an ion exchange resin. and a method for predicting the operating voltage of an electrodeionization apparatus in which the concentrated water passing means passes the deionized water passed through the deionization chamber as concentrated water,
predicting the future operating voltage of the electrodeionization apparatus from the initial voltage and initial feed-water silica concentration during operation of the electrodeionization apparatus and the voltage and feed-water silica concentration after a predetermined time has elapsed; How to predict operating voltage. The future operating voltage of the electrodeionization apparatus is calculated by the following formula Vn = V(n-1) + m x (Sin - Se) x D
(In the formula, Vn is the predicted operating voltage (V), V(n-1) is the voltage (V) after the elapse of a predetermined time, D is the predetermined time after the elapse (days), and Sin is is the feed silica concentration (μg/L), Se is the limit silica concentration (μg/L), and m is a coefficient specific to the electrodeionization apparatus)
The method for predicting the operating voltage of the electrodeionization apparatus according to claim 1, wherein the prediction is made by A method for operating a pure water production apparatus having an electrodeionization apparatus and at least constituent elements other than the electrodeionization apparatus,
Predicting the future operating voltage of the electrodeionization device from the initial voltage and initial feed silica concentration during operation of the electrodeionization device and the voltage and feed silica concentration after a predetermined time has elapsed,
A method of controlling a water purifying apparatus, comprising controlling constituent elements other than the electrodeionization apparatus based on the predicted future operating voltage of the electrodeionization apparatus. 4. The method of controlling a pure water production apparatus according to claim 3, wherein the component other than the electrodeionization apparatus is a reverse osmosis membrane separation apparatus.

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