JP2789404B2 - Reverse osmosis membrane exchange rate setting method and apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention comprises a plurality of unit reverse osmosis membranes arranged in parallel or in series to form feed water having a low conductivity by passing feed water having a high conductivity through a reverse osmosis membrane. The present invention relates to a method and an apparatus for setting a reverse osmosis membrane exchange rate used in a freshwater producing apparatus.

[0002]

2. Description of the Related Art In a fresh water producing apparatus in which a number of unit reverse osmosis membranes are connected in parallel or in series, the performance of the reverse osmosis membrane deteriorates with time. Need to change the membrane periodically. The membrane exchange rate can be obtained from the membrane deterioration rate coefficient and the initial performance, but is usually determined by the membrane maker. Conventionally, in actual membrane exchange, membrane exchange has been performed using a membrane exchange rate specified by a membrane maker, or using a rough and poorly established membrane exchange rate for each apparatus.

[0003] However, since the numerical value of the film maker is generalized so as to be applicable to any plant, the numerical value of the film maker is high and the safety is excessive. If the membrane exchange rate is excessive as described above, the membrane having a remaining life will be discarded. Since the membrane is expensive, not only the maintenance and management costs become enormous, but also resources are wasted. For this reason, especially in a medium-sized or large-scale apparatus, an increase in the maintenance cost due to an excessive membrane exchange rate has been a problem. On the other hand, if a value with a poor basis is used as the membrane exchange rate, if the value is lower than the appropriate value, a problem occurs that the performance of the apparatus cannot be maintained. Conventionally, a method of evaluating the membrane exchange rate based on the overall performance of the apparatus may be used, but in such a method, the replaced membrane performance affects the overall performance of the plant, and the evaluation is gradually inaccurate. There is a problem of becoming something.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems in the prior art and to provide a method and an apparatus for setting a reverse osmosis membrane exchange rate capable of setting an appropriate membrane exchange rate. I do.

[0005]

According to the present invention, in order to solve the above-mentioned problems, the present invention is applied to a fresh water producing apparatus in which a large number of unit reverse osmosis membranes are provided in parallel or in series to constitute an aggregate. In the reverse osmosis membrane exchange rate setting method, the conductivity of permeated water is measured for each unit reverse osmosis membrane, and the conductivity and the conductivity are measured.
The use period of the unit reverse osmosis membrane at the time of measuring the electric power is input to the processing means, and the degradation rate coefficient of the reverse osmosis membrane is determined by the inputted data and the consolidation coefficient of the reverse osmosis membrane, The consolidation coefficient and the deterioration rate coefficient, so that the quality of the permeated water predicted as the freshwater production device does not always exceed a predetermined value, with respect to the total number of reverse osmosis membranes constituting the freshwater production device. determining a film exchange rate per unit time is the ratio of the units reverse osmosis membrane the number of exchanging the unit period Te, it is characterized by an invention of claim 2 is provided in parallel or in series a number of units reverse osmosis membrane A reverse osmosis membrane exchange rate setting device for use in a fresh water producing apparatus configured as an aggregate, wherein a conductivity measuring means for measuring the conductivity of permeated water for each unit reverse osmosis membrane; and the measured conductivity and the conductivity. Measure
Means for inputting a use period of the unit reverse osmosis membrane at a time when the processing is performed, and determining the degradation rate coefficient of the reverse osmosis membrane based on the input data and a consolidation coefficient for consolidating the reverse osmosis membrane. Means, the whole of the freshwater producing apparatus is configured such that the quality of the permeated water predicted as the freshwater producing apparatus calculated from the consolidation coefficient and the deterioration rate coefficient does not always exceed a predetermined value. single against reverse osmosis membrane number is the ratio of the units reverse osmosis membrane the number of exchanging the unit period
And a means for calculating a membrane exchange rate per unit period .

[0006]

According to the first or second aspect of the present invention, since the above-described configuration is employed, the following operation is produced. First, the conductivity of the permeated water is measured for each unit reverse osmosis membrane. In this case, the conductivity measuring means may be a device for automatically measuring periodically, or a device for measuring sequentially or individually by human operation. Next, since the measured conductivity and the service period of the film are input to the processing means, these data are processed here. At this time, the name of the measured unit reverse osmosis membrane is also input to locate these data. In this case, the input means may be in a form in which a person inputs each measured value together with the period of use or the start time of using the reverse osmosis membrane in advance and the measurement date. Or automatic input means. The processing means calculates the film deterioration rate coefficient. For the calculation, it is desirable that the input group of measured values is statistically processed into data. Since this data is used for accurately predicting water quality in consideration of safety when finally calculating the membrane exchange rate, for example, a maximum value, a minimum value, an average value, and a standard deviation. In this case, a value obtained by adding several times the standard deviation to the average value, a maximum value, and the like can be used for the subsequent calculation. On the other hand, when the reverse osmosis membrane is used under a high pressure, it is generally compacted in accordance with its use period , the salt permeability is reduced, and the conductivity of the passing water is reduced. As a consolidation coefficient which is an index of such a decrease in salt permeability, for example, a value recommended by a membrane manufacturer is used, and the value is input to the processing means by human operation. Thereby, the effect of the consolidation of the reverse osmosis membrane on the conductivity of the permeated water can be corrected. However, a consolidation coefficient input means is provided, and a table or curve of the recommended values or the consolidation coefficient for the membrane use period obtained in advance by experiments or the like is input to the processing means, and the value is calculated from the membrane use period. Such a method may be used.
In this case, the input of the membrane use period may be directly input by the input means, or the reverse osmosis membrane exchange date may be input in advance to calculate the membrane use period from the measurement time. Is also good. In the processing means, further, by incorporating a relational expression between the film use period and the film deterioration rate coefficient, etc.,
A film deterioration rate coefficient is calculated from the consolidation coefficient, the input data, and the film use period. Such calculation of the membrane deterioration rate coefficient may be performed for each unit reverse osmosis membrane. However, from the viewpoint of the performance of the processing means, a group of measured data is statistically processed into one data as described above. It is preferable to carry out a group of reverse osmosis membranes as a unit. At a stage where data accumulation is small, a constant numerical value initially given as the film performance may be used. And finally, the membrane exchange rate calculation means, from the consolidation coefficient and the membrane degradation rate coefficient, such that the water quality after membrane exchange predicted as a freshwater production device does not always exceed a predetermined value determined from the required performance of the device The membrane exchange rate can be calculated. The membrane deterioration rate coefficient used here is a value calculated for each unit reverse osmosis membrane or a value calculated from statistically processed data, but when measuring the conductivity a plurality of times before performing water quality prediction, for example, It becomes the average of those values at the time of each measurement. In calculating the membrane exchange rate,
The calculation may be performed with the period of the membrane exchange being fixed, or the period may be changed to determine the optimum membrane exchange rate and the exchange time from the relationship between the membrane exchange rate and the exchange period.
Further, the optimum membrane exchange rate can be determined within a specific period, or the optimal membrane exchange rate can be determined so that the membrane exchange rate is always constant.

[0007] If the membrane is exchanged by the method or the apparatus for setting the exchange rate of reverse osmosis according to the first or second aspect, the membrane exchange rate does not become excessive even if necessary margin is taken into consideration. As the processing means, the consolidation coefficient input means (when the consolidation coefficient is calculated), and the membrane exchange rate calculation means, for example, a program incorporated in a microcomputer can be used.

Although the quality of the permeated water actually obtained is affected by the operating conditions of the apparatus, the operating conditions and the permeated water quality have a certain relationship. If the operating condition input means to be input and the correcting means for comparing the input operating condition with the design condition of the fresh water producing apparatus and correcting the measured conductivity corresponding to the difference are provided, Even when the operating conditions of the above are different from the design conditions, the accuracy of calculating the membrane exchange rate can be maintained by using these means.

[0009]

FIG. 1 shows a schematic configuration of an apparatus capable of executing a reverse osmosis membrane exchange rate setting method according to an embodiment, and FIG. 2 shows a reverse configuration as a fresh water producing apparatus which can use the present method and apparatus. 1 shows a configuration example of a reverse osmosis membrane unit of an osmosis membrane type seawater desalination apparatus. The configuration of the present apparatus will be described with reference to these drawings.

In FIG. 2, the seawater desalination apparatus is constituted by an assembly having a large number of unit reverse osmosis membranes which permeate seawater through a reverse osmosis membrane to convert the water into low-conductivity permeated water. , A, and B, an assembly of the unit reverse osmosis membranes in two series is configured in two stages, and in the first stage, 1F (F means the water supply side) to 65F and 1Br (Br means the brine side), respectively. A total of 130 unit reverse osmosis membranes consisting of a series A to a series B are composed of two rows of series A and series B. In the second stage, 1F '(F' means the water supply side) to 30F 'and 1Br' A total of 60 unit reverse osmosis membranes consisting of (Br ′ means the brine side) to 30Br ′ are formed as an aggregate of two rows of A series and B series.
In the seawater desalination apparatus having such a configuration, in the first stage, seawater is supplied from the direction shown by arrow A as supply water pressurized by a high-pressure pump (not shown), and the permeated water having reduced conductivity from the direction shown by arrow B. Certain first stage demineralized water is delivered. Then, the first-stage demineralized water becomes supply water, is pressurized again and supplied to the second stage from the direction of arrow C, is further desalted in the second stage, and is permeated as permeate in the direction of arrow II. Is sent out. After the second demineralized water is further processed by a device not shown, fresh water is finally obtained. In addition,
In the seawater desalination apparatus of the embodiment, the feedwater is directly supplied to the reverse osmosis membrane module on the water supply side (F, F ′ side) in each of the first and second stages, but is supplied on the brine side (Br, Br ′). Side) is supplied with supply water concentrated in the module.

The reverse osmosis membrane exchange rate setting device used in such a seawater desalination device has the following devices. FIG.
In the first-stage and second-stage unit reverse osmosis membrane devices 1F to
65F, 1Br-65Br and 1F'-30F ', 1B
Sampling racks 101 and 102 and instrument racks 103 and 104 are provided as conductivity measuring means capable of measuring the conductivity of the water passing through each of r ′ to 30Br ′.

In the sampling racks 101 and 102,
The manual valves 101-1 and the like and 102-1 and the like are provided in a group. Then, when measuring the conductivity, the measurer sequentially opens and closes these valves, whereby the first and second unit reverse osmosis membranes 1F, 1Br, etc. and 1F ′,
The first-stage demineralized water and the second-stage demineralized water on the water supply side and the brine side that have passed through them from 1Br ′ and the like are supplied as sample water. However, an automatic valve such as a solenoid valve is used in place of the manual valves 101-1 and 102-1 and the like, and is automatically opened and closed at a predetermined time or is sequentially opened and closed by a human operation to save the labor of conductivity measurement. You may make it aim. The sample base valves 1F-1 and 1F'-1 on the machine side are normally opened.

The meter racks 103 and 104 have the conductivity meter 1
Reference numerals 03a and 104a are provided to measure the conductivity of the demineralized water introduced through the respective reverse osmosis membranes on the water supply side and the brine side.

As input means, local operation panels 105, 10
In this embodiment, the measurer inputs the name of the reverse osmosis membrane and the measured individual electrical conductivity together with the date to the personal computer control device 107 described below. However, the input means may be a device which can be automatically input from the on-site operation panels 105 and 106 to the personal computer control device 107 or the personal computer control device 1
07 CRT 107a display screen and keyboard 107b
The device may be configured to perform input using the following.

In the reverse osmosis membrane exchange rate setting device of this embodiment, the operating conditions include feed water pressure, desalted and concentrated concentrated water pressure, demineralized water pressure, feed water flow rate, demineralized water flow rate, water temperature, and the like. Operation data such as feedwater conductivity, feedwater salt concentration, etc.
It is obtained from each measuring device installed in the seawater desalination device. Then, these data are input to the main body of the personal computer control device using the CRT 107a and the keyboard 107b of the personal computer control device 107 which is an example of the operation condition input means. However, a computer or the like provided in the seawater desalination apparatus may be used as the operating condition input means, and the operation condition input means may be automatically input to the personal computer control apparatus body.

The personal computer control unit 107 includes a CRT 107
a, a keyboard 107b, a printer 107c, and a processing unit, a membrane exchange rate determining unit, and, in the present embodiment, a correcting unit for operating conditions.

The correction means compares the measured and input supply water pressure, concentrated water pressure, demineralized water pressure, supplied water flow rate, demineralized water flow rate, water temperature, supplied water conductivity, and supplied water salinity concentration with design conditions. If there is a difference, the measured individual conductivity is corrected from the difference and a correction coefficient predetermined for each operating condition. This correction is performed in order to obtain the conductivity when the plant is operated according to the design conditions when the actual operation conditions are different from the design conditions. As a result, it is possible to correctly evaluate individual film performance. However, there is a case where such a correction means need not be provided for a plant that is always operated under conditions close to the design conditions.

In the processing means, the individual thus corrected
From the data of
Determine the value, mean and standard deviation. In this embodiment, CR
Initial membrane replacement using T107a and keyboard 107b
The consolidation coefficient of 1.0, the consolidation coefficient after one to three years
0.65, and enter this value into the main unit of the control unit 107.
Power. However, such conditions are set in the control device body in advance.
By taking into account the time when conductivity is measured,
Use of membraneperiodThe consolidation coefficient may be calculated from
No. In the processing means, for example, the initial salt transmittance may be Spo,
Up to the time of measurementUse of membranePeriod(Unit is time), T time
The salt permeability after passage is Spt, and the membrane degradation rate coefficient is Ksp.
Then, Log (Spt / Spo) = Ksp · t^0.65  By using the following empirical formula, the film deterioration rate coefficient Ksp is calculated.
You. In this case, the initial andUsage period t (hours)Salt after passing
Transmittance was individually measured and corrected for operating conditions
Obtained from conductivity. Using such a film degradation rate coefficient
By understanding the performance of the membrane,
A decision can be made. In addition,useData collection with short time t
At the stage where the product is low, the number given by the reverse osmosis membrane
You may use a value.

In this embodiment, the membrane exchange rate calculating means assumes that the membrane exchange is performed once a year and is exchanged at a constant membrane exchange rate every year. The membrane exchange rate is determined under the condition that the water quality after membrane exchange predicted in each of the first and second stages does not always exceed a predetermined design value. However, the present means may be configured to be able to calculate the relationship between the membrane exchange rate and the membrane exchange time at which a predetermined water quality is maintained. In this way, the optimum membrane exchange time and membrane exchange rate can be obtained.

FIG. 3 shows an operation and a processing flow for setting a membrane exchange rate using such a reverse osmosis membrane exchange rate setting device. The conductivity of each reverse osmosis membrane (“RO membrane” in the table) is measured once a month and input to the personal computer controller 107 (S
1). The record of the operating conditions detected by the sensors is also input to the same device (S2). At this time, a correction coefficient for correcting the conductivity is automatically calculated and input for each operation condition (S
3). From these, the water quality correction value for each reverse osmosis membrane is calculated to create a water quality correction value table (S4). Table 1 shows a part of the raw conductivity data input table and the water quality correction value record table.
And Table 2. This water quality correction includes a correction between the water supply side and the brine side that have different supply water qualities even in the same stage.

Next, in this embodiment, since the membrane is exchanged once a year, the record is also input to the personal computer control unit 107 (S5). Then, a period in which each unit reverse osmosis membrane has been used after the membrane exchange is calculated (S6). From the corrected water quality and the use period of each reverse osmosis membrane, a corrected water quality transition table for the use period of each system is created (S7). In the actual table, monthly data is created for all the films, and a part thereof is shown in Table 3.

[Table 1]

[Table 2]

[Table 3]

On the basis of the corrected water quality transition table, total data is compiled for each of the first and second stages, statistical data for each month passed after the start of use of the plant is compiled, and a consolidation coefficient and a membrane deterioration rate coefficient are calculated. From these, assuming that the membrane exchange is performed once a year at a constant membrane exchange rate, the membrane exchange rate is calculated so that the water quality that changes over time does not exceed the design performance. These are put together in a table and displayed as a water quality table for the period of use (S
8). Table 4 exemplifies a part of such a first-stage demineralized water concentration transition totaling table, and FIG. 4 shows this in a graph.

[Table 4]

In Table 4, the number of elapsed months indicates the number of months after the exchange of the reverse osmosis membrane, and data of a group of membranes having the same number of elapsed months is entered every month. Only shows. The membrane degradation rate coefficient is calculated monthly based on the water quality obtained by adding three times the standard deviation to the average value of the measured and corrected group of data. Then, in the calculation of the expected performance of water quality calculated every December with the membrane exchange rate kept constant, an average value of the membrane deterioration rate coefficients calculated every month for December is used.
However, due to little data accumulation, the calculation in Table 4 uses the film deterioration rate coefficient given by the manufacturer for the time being. The consolidation coefficient also uses the value recommended by the film manufacturer. In the table, the design performance and new expected performance columns are
The graph shows the transition in the case where the membrane was not replaced, based on the original design and the corrected actual measurement (ppm).
In this case, the guaranteed water quality as the design performance is 400 ppm, and if the performance of the device is as designed, the water quality is 36 ppm.
After the month, the guaranteed value will be exceeded. As the new expected performance when the membrane is not exchanged and the expected performance when the membrane is exchanged, a safe value that takes into account the standard deviation three times the average value of the corrected measured values is used as described above. Based on this, the performance change when the membrane is replaced at a constant rate every year is calculated. The expected transition (ppm) at the time of membrane exchange in the right column shows the expected water quality with respect to the number of elapsed months when the membrane is exchanged at a constant membrane exchange rate of 7%, 9% or 18%, respectively. Although the actual calculation is performed up to 15 years, Table 4 exemplifies up to 72 months (6 years). The first 7% exchange rate in the right column indicates the maximum membrane exchange rate that exceeds the guaranteed value of 400 ppm when the membrane exchange rate is calculated at a 2% pitch, and is not found in the table. The expected performance exceeds 400 ppm after 9 years (108 months). The next 9% exchange rate was calculated in the same way to find the lowest value that did not exceed the guaranteed value of 400 ppm. With this membrane exchange rate, the water quality approached 400 ppm most after 12 years (144 April). I have. The exchange rate of 18% at the right end is a numerical value that can be freely selected, and may be equal to the center column (in this case, 9%) if the degree of data accumulation is sufficient. The values in the exchange rate column of the table indicate values calculated when the membrane was replaced every 12 months after the start of operation, including the effect of subsequent membrane replacement. FIG. 4 is a graph showing the result. Replacement rate is 7% as replacement performance
(At the time of replacement 1) and 18% (at the time of replacement 2).

Table 5 shows an example of a tabulation table of operating conditions input from the operation record. The actual measurement value is corrected based on these operation parameters. FIGS. 5 and 6 show graphs of the demineralized water concentration distribution of the unit reverse osmosis membrane in the designated elapsed month and the demineralized water concentration transition summarized for each stage and each series. Table 6 is an example of a reverse osmosis membrane exchange record table for calculating the use period of the reverse osmosis membrane.

[Table 5]

[Table 6] The various calculations and processes described above can be efficiently performed by, for example, commercially available spreadsheet software and an analysis program of BASIC.

With such a reverse osmosis membrane exchange rate setting device, the recommended value of the membrane exchange rate of the conventionally used manufacturer is 25%.
In contrast to １５30%, a membrane exchange rate of 15% or less can be adopted, and the economics of the plant has been greatly improved. Then, by gradually adding the collected data, the reliability of the performance prediction is increased, and the membrane exchange rate can be further reduced. Further, it is possible to simultaneously grasp the overall performance of the plant and record the membrane replacement.

Depending on the type of the reverse osmosis membrane, the membrane exchange may be carried out mainly on the amount of water rather than the quality of water.
In such a case, the amount of water in each unit reverse osmosis membrane can be detected, and based on this, the membrane exchange rate can be determined by similar processing. In the above, when the membrane is actually replaced, the difference in the degree of deterioration of the membrane due to, for example, a difference in the influence of microorganisms and other use conditions and a difference in the characteristics of the individual membranes is taken into consideration before the replacement. In the water quality correction value record table described above, it is desirable to replace a predetermined number of films in order from the film having the largest water quality decrease.

[0027]

As described above, according to the present invention, it is possible to set an appropriate membrane exchange rate, and to reduce the maintenance cost of the seawater desalination apparatus.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a configuration of a reverse osmosis membrane exchange rate setting device of an example.

FIG. 2 is an explanatory view showing an arrangement of unit reverse osmosis membrane devices of a seawater desalination apparatus to which the above-mentioned apparatus is applied.

FIG. 3 is a flowchart when the membrane exchange rate is determined by the above apparatus.

FIG. 4 is a graph showing a change in expected concentration of desalinated water.

FIG. 5 is a graph showing a concentration distribution of desalinated water.

FIG. 6 is a graph showing changes in the concentration of desalinated water.

[Explanation of symbols]

1F to 65F, 1Br to 65Br First stage unit reverse osmosis membrane 1F 'to 30F', 1Br 'to 30Br' Second stage unit reverse osmosis membrane 101, 102 Sampling rack (conductivity measuring means) 103, 104 Instrument rack (conductive) Rate measuring means) 105, 106 Operation panel (input means) 107 Controller (processing means, membrane exchange rate calculating means) 107a CRT (input means) 107b Keyboard (input means)

Claims (2)

(57) [Claims] 1. A reverse osmosis membrane exchange rate setting method for use in a freshwater production apparatus in which a large number of unit reverse osmosis membranes are provided in parallel or in series to constitute an aggregate, wherein the conductivity of permeated water is determined for each unit reverse osmosis membrane. Measuring, inputting the electrical conductivity and the use period of the unit reverse osmosis membrane at the time when the electrical conductivity was measured , to the processing means, and using the input data and a consolidation coefficient for consolidating the reverse osmosis membrane, By determining the degradation rate coefficient of, the consolidation coefficient and the degradation rate coefficient, so that the quality of the permeated water predicted as the freshwater production apparatus does not always exceed a predetermined value, to configure the freshwater production apparatus Determining a membrane exchange rate per unit period, which is a ratio of the number of unit reverse osmosis membranes exchanged in a unit period to the total number of reverse osmosis membranes. 2. A reverse osmosis membrane exchange rate setting device for use in a freshwater production apparatus in which a large number of unit reverse osmosis membranes are provided in parallel or in series to constitute an aggregate, wherein the conductivity of permeated water is determined for each unit reverse osmosis membrane. Conductivity measuring means for measuring , input means for inputting the measured conductivity and the use period of the unit reverse osmosis membrane at the time when the conductivity was measured to the processing means, and the input data The processing means for determining a degradation rate coefficient of the reverse osmosis membrane based on a consolidation coefficient for consolidating the reverse osmosis membrane; and a permeation expected as the freshwater production apparatus calculated by the consolidation coefficient and the degradation rate coefficient. Membrane per unit period, which is the ratio of the number of unit reverse osmosis membranes replaced in a unit period with respect to the total number of reverse osmosis membranes constituting the freshwater production apparatus so that the water quality of the water does not always exceed a predetermined value. Membrane exchange rate meter to determine exchange rate A reverse osmosis membrane exchange rate setting device, comprising: