JP6907745B2 - Membrane separation device - Google Patents

Description

The present invention relates to a membrane separation device.

High-purity pure water containing no impurities is used in the semiconductor manufacturing process, cleaning of electronic parts, cleaning of medical equipment, and the like. This type of pure water is generally produced by treating raw water such as groundwater or tap water with a reverse osmosis membrane (hereinafter, also referred to as “RO membrane”).

When pure water is produced from an RO membrane, a phenomenon occurs in which the hardness component contained in the raw water is deposited as scale on the surface of the RO membrane. In addition, a phenomenon called fouling occurs in which suspended solids (for example, insoluble colloidal iron) contained in raw water are deposited on the surface of the RO membrane or in the pores. When scale precipitation or fouling occurs on the RO membrane, the water permeability (water permeability coefficient) of the RO membrane decreases. As a result, the flow rate of permeated water decreases.

Therefore, in order to suppress the precipitation of calcium carbonate-based scale, a system for supplying soft water to the RO membrane has been proposed. In this system, raw water (hard water) is softened by a hard water softening device using a cation exchange resin as a pretreatment of the RO device (see Patent Document 1).

On the other hand, in the RO membrane in a state where scale precipitation and fouling do not occur, the water permeability coefficient changes depending on the temperature of the supplied water (hereinafter, also referred to as “supplied water”). The water permeability coefficient of the RO membrane increases as the temperature of the supply water increases. Therefore, even if the supply water is supplied to the RO membrane at a constant pressure, the flow rate of the permeated water increases as the temperature rises. As the flow rate of the permeated water increases, the concentration of solute components progresses on the primary side of the RO membrane.

In general, a hard water softener cannot remove silica components and suspended solids contained in raw water. Therefore, as the concentration of solute components progresses on the primary side of the RO film, silica-based scale precipitation and fouling are likely to occur. That is, when soft water is supplied to the RO membrane, the precipitation of calcium carbonate-based scale can be suppressed, but the precipitation of silica-based scale and the occurrence of fouling cannot be suppressed depending on the temperature.

Therefore, in order to keep the flow rate of the permeated water in the RO membrane constant regardless of the temperature of the supply water, a system for performing flow rate feedback control has been proposed. In this flow rate feedback control, the operating frequency of the pressurizing pump that sends the supply water to the RO membrane is controlled by the inverter so that the flow rate of the permeated water produced by the RO membrane becomes the target value (see Patent Document 2). ..

Japanese Unexamined Patent Publication No. 2010-82610 Japanese Unexamined Patent Publication No. 2005-296945

However, when the water temperature or pH of the supply water fluctuates, the hardness scale may precipitate.

An object of the present invention is to provide a membrane separation device capable of suppressing the precipitation of hardness scale and the occurrence of fouling in an RO membrane.

The present invention is a reverse permeable membrane module that separates the supply water into permeated water and concentrated water, and is driven at a rotation rate according to the input drive frequency, sucks the supply water, and directs it toward the reverse permeable membrane module. A pressurizing pump that discharges, an inverter that outputs the drive frequency corresponding to the input calculated value signal to the pressurizing pump, and a physical amount in the system so that the flow rate of permeated water becomes a preset target flow rate value. A control unit that calculates the drive frequency of the pressurizing pump and outputs a calculated value signal corresponding to the calculated value of the drive frequency to the inverter, and a temperature that detects the temperature of supply water, permeated water, or concentrated water. A detection means, a drainage flow rate adjusting means capable of adjusting the drainage flow rate of concentrated water discharged to the outside of the device, a first flow rate detection unit that detects the flow rate of the permeated water as a first detection flow rate value, and discharge to the outside of the device. a second flow rate detection unit for detecting the flow rate of the concentrated water to the second detected flow value, a membrane separation apparatus Ru wherein the drainage flow rate control means is composed of the drain valve, wherein the control unit, (i ) From the pH, hardness, M alkalinity of the supply water, and the detection temperature value of the temperature detecting means obtained in advance, the allowable concentration ratio of calcium carbonate in the concentrated water is calculated based on the calcium carbonate solubility, and (ii) calculated value of the allowable concentration rate, and calculates the waste water flow from the target flow rate value of the permeate, (iii) as the second detected flow value is the computed value of the waste water flow rate, controls the drain valve The membrane separation device further includes a target recovery rate setting unit that sets a target recovery rate, which is an operation target within a predetermined deviation from the allowable recovery rate calculated based on the allowable concentration ratio, and the control unit is the control unit. The opening degree of the drain valve is changed so that the actually measured recovery rate calculated from the first detected flow rate value and the second detected flow rate value becomes the target recovery rate, and the actually measured recovery rate is the permissible. When the recovery rate is within a predetermined deviation, the control unit fixes the opening degree of the drain valve, and when the actually measured recovery rate is outside the predetermined deviation from the allowable recovery rate, the control unit The present invention relates to a membrane separating device for changing the opening degree of the drain valve.

Further, it is preferable that the control unit calculates the permissible concentration ratio so that the water quality of the permeated water satisfies the required water quality.

Further, the required water quality is preferably determined according to the standard relating to the electric conductivity and / or the silica concentration of the permeated water.

Further, it is preferable that the control unit calculates the allowable concentration ratio based on the concentration of carbonate ion and bicarbonate ion of the concentrated water obtained by multiplying the concentration ratio as a coefficient.

Further, a pH detecting means for detecting the pH of the supply water and / or the concentrated water is further provided, and the control unit has the permissible concentration ratio based on the detected pH value detected by the pH detecting means as the pH of the supply water. It is preferable to calculate.

Further, it is preferable that the target recovery rate setting unit discontinuously changes the target recovery rate every time the allowable recovery rate changes by a predetermined amount in accordance with the change in the allowable recovery rate.

Further, it is preferable that the target recovery rate setting unit discontinuously changes the target recovery rate every time the detected temperature value changes by a predetermined amount in response to the change in the detected temperature value.

According to the present invention, it is possible to provide a membrane separation device capable of suppressing the precipitation of hardness scale and the occurrence of fouling in an RO membrane.

It is an overall block diagram of the water treatment system 1 which concerns on 1st Embodiment. It is a flowchart which shows the processing procedure when the control unit 10 of 1st Embodiment executes the flow rate feedback water amount control. It is a flowchart which shows the processing procedure when the control unit 10 of 1st Embodiment executes drain valve control. It is a figure which shows the relationship between the permissible recovery rate and the target recovery rate. It is an overall block diagram of the water treatment system 1A which concerns on 2nd Embodiment.

[First Embodiment]
The water treatment system 1 according to the first embodiment of the present invention will be described with reference to the drawings. The water treatment system 1 is applied to, for example, a pure water production system that produces pure water from fresh water. FIG. 1 is an overall configuration diagram of the water treatment system 1 according to the first embodiment.

As shown in FIG. 1, the water treatment system 1 according to the first embodiment includes a raw water pump 2, a hard water softening device 3, a salt water tank 4 as a regenerating liquid supply means, and a temperature sensor as a temperature detecting means (hereinafter,). (Also also referred to as “temperature detecting means”) 5. Further, the water treatment system 1 includes a pressurizing pump 6, an inverter 7, an RO membrane module 8 as a reverse osmosis membrane module, a flow rate sensor 9 as a flow rate detecting means, a control unit 10, a drain valve 11, and the like. To be equipped. Of these, the pressurizing pump 6, the RO membrane module 8, the flow rate sensor 9, and the control unit 10 constitute the membrane separation device according to the present embodiment. Further, in FIG. 1, the electrical connection path is shown by a broken line.

Further, the water treatment system 1 includes a raw water line L1, a soft water line L2, a salt water line L3, and a drainage line L4. Further, the water treatment system 1 includes a permeated water line L5 and a concentrated water line L6. As used herein, the term "line" is a general term for lines capable of flowing fluids such as flow paths, routes, and pipelines.

The upstream end of the raw water line L1 is connected to a source of raw water W1 (not shown). On the other hand, the downstream end of the raw water line L1 is connected to a process control valve (not shown) of the hard water softening device 3.

The raw water pump 2 is provided on the raw water line L1. The raw water pump 2 pumps the raw water W1 such as tap water and groundwater supplied from the supply source toward the hard water softening device 3. The raw water pump 2 is electrically connected to the control unit 10. The operation (drive and stop) of the raw water pump 2 is controlled by the control unit 10.

In the softening process, the raw water line L1 and the raw water pump 2 supply the raw water W1 having an electric conductivity of 150 mS / m or less and a total hardness of 500 mgCaCO ₃ / L or less to the hard water softening device 3.

The hard water softening device 3 is a facility for producing soft water W2 by substituting the hardness components (calcium ion and magnesium ion) contained in the raw water W1 with sodium ions (or potassium ions) in a cation exchange resin bed.

The salt water tank 4 stores the salt water W3 that regenerates the cation exchange resin bed of the hard water softening device 3. An upstream end of the salt water line L3 is connected to the salt water tank 4. The downstream end of the salt water line L3 communicates with the process control valve and is connected to each of the various lines constituting the process control valve.

The salt water line L3 is provided with a salt water valve (not shown). The salt water valve opens and closes the salt water line L3. The salt water valve is incorporated in the process control valve of the hard water softening device 3. In the salt water valve, the driving unit of the valve body is electrically connected to the control unit 10 via a signal line (not shown). The opening and closing of the valve in the salt water valve is controlled by the control unit 10. In the regeneration process, the salt water tank 4 sends the salt water W3 that regenerates the cation exchange resin bed to the pressure tank of the hard water softening device 3.

The temperature sensor 5 is a device that detects the temperature of the soft water W2 flowing through the soft water line L2. Further, the temperature sensor 5 is electrically connected to the control unit 10. The temperature of the soft water W2 detected by the temperature sensor 5 (hereinafter, also referred to as “detected temperature value”) is transmitted to the control unit 10 as a detection signal.

The pressurizing pump 6 is a device that sucks in the soft water W2 sent out from the hard water softening device 3 and discharges it toward the RO membrane module 8. The pressurizing pump 6 is electrically connected to the inverter 7 (described later). The pressurizing pump 6 is supplied with driving power whose frequency has been converted from the inverter 7. The pressurizing pump 6 is driven at a rotation speed according to the input drive frequency.

The inverter 7 is an electric circuit that supplies driving power whose frequency is converted to the pressurizing pump 6. The inverter 7 is electrically connected to the control unit 10. A current value signal is input to the inverter 7 from the control unit 10. The inverter 7 outputs a drive frequency corresponding to the input current value signal to the pressurizing pump 6.

The RO membrane module 8 is a facility that separates the soft water W2 produced by the hard water softening device 3 into permeated water W5 from which dissolved salts have been removed and concentrated water W6 from which dissolved salts have been concentrated. The RO membrane module 8 includes a single or multiple RO membrane elements (not shown). The RO membrane module 8 separates the soft water W2 by these RO membrane elements to produce permeated water W5 and concentrated water W6. The primary side inlet port of the RO membrane module 8 is connected to the downstream side of the hard water softening device 3 (process control valve) via the soft water line L2.

The upstream end of the permeated water line L5 is connected to the secondary port of the RO membrane module 8. The permeated water W5 obtained by the RO membrane module 8 is sent to a demand location or the like via the permeated water line L5. Further, the upstream end of the concentrated water line L6 is connected to the primary outlet port of the RO membrane module 8. The concentrated water W6 obtained in the RO membrane module 8 is discharged to the outside of the RO membrane module 8 via the concentrated water line L6. A drain valve 11 (described later) is connected to the downstream side of the concentrated water line L6.

A part of the concentrated water W6 discharged from the concentrated water line L6 may be returned to the soft water line L2 on the upstream side of the pressurizing pump 6. By refluxing a part of the concentrated water W6 to the soft water line L2, the water flow velocity on the surface of the RO membrane module 8 can be kept within a predetermined range.

The RO membrane module 8 in the present embodiment has a reverse osmosis membrane (not shown) in which a load-electric skin layer made of crosslinked total aromatic polyamide is formed on the membrane surface. ^{This reverse osmosis membrane has a water permeability coefficient of 1.5 × 10 −} when an aqueous solution of sodium chloride having a concentration of 500 mg / L, a pH of 7.0, and a temperature of 25 ° C. is supplied at an operating pressure of 0.7 MPa and a recovery rate of 15%. ^{It has a performance of 11} m ³ · m ^-2 · s ^-1 · Pa ^-1 or more and a salt removal rate of 99% or more.

In the desalination treatment of fresh water, the lower the hardness of the feed water, the more the reverse osmosis membrane set to such performance has the salt removal rate when evaluated by the electrical conductivity (EC) (that is, (supply water EC-). Permeated water EC) / supplied water EC × 100) becomes higher. _{Therefore, by constantly supplying high-purity soft water W2 (actual value of 0.8 mgCaCO 3} or less) produced by the hard water softening device 3 that performs split flow regeneration, a high salt removal rate (usually 98. 5% or more) can be maintained.

The operating pressure is an average operating pressure as defined in JIS K3802-1995 “Membrane Term”. The operating pressure refers to the average value of the inlet pressure on the primary side and the outlet pressure on the primary side of the RO membrane module 8. The recovery rate refers to the ratio of the flow rate Qp of the permeated water to the flow rate Qf of the water supplied to the RO membrane module 8 (here, the sodium chloride aqueous solution) (that is, Qp / Qf × 100).

The water permeability coefficient is ^{a value obtained by dividing the flow rate [m 3} / s] of permeated water by the membrane area [m ² ] and the effective pressure [Pa]. The water permeability coefficient is an index showing the water permeation performance of the reverse osmosis membrane. That is, the water permeability coefficient means the amount of water that permeates the unit area of the membrane in a unit time when a unit effective pressure is applied. Effective pressure is defined in JIS K3802-1995 "Membrane Term". The effective pressure is the pressure obtained by subtracting the osmotic pressure difference and the secondary side pressure (back pressure) from the operating pressure (average operating pressure).

The salt removal rate is a value calculated from the concentration of a specific salt before and after permeating the membrane (here, the concentration of sodium chloride). The salt removal rate is an index showing the ability of the reverse osmosis membrane to prevent solutes. The salt removal rate is determined by (1-Cp / Cf) × 100 from the concentration Cf of the supply water and the concentration Cp of the permeated water.

A reverse osmosis membrane that satisfies the conditions of the water permeability coefficient and the salt removal rate of the present embodiment is commercially available as a reverse osmosis membrane element. As the reverse osmosis membrane element, for example, Toray Industries, Inc .: model name "TMG20-400", Unjin Chemical Co., Ltd .: model name "RE8040-BLF", Nitto Denko Corporation: model name "ESPA1", etc. may be used. can.

The flow rate sensor 9 is a device that detects the flow rate of the permeated water W5 flowing through the permeated water line L5. The flow rate sensor 9 is electrically connected to the control unit 10. The flow rate of the permeated water W5 detected by the flow rate sensor 9 (hereinafter, also referred to as “detected flow rate value”) is transmitted to the control unit 10 as a detection signal.

The drain valve 11 is a valve that regulates the drainage flow rate of the drainage W4 discharged from the concentrated water line L6. The drainage flow rate of the drainage W4 discharged from the concentrated water line L6 can be adjusted by opening and closing the drainage valve 11. The drain valve 11 is electrically connected to the control unit 10. The opening and closing of the valve body in the drain valve 11 is controlled by a drive signal from the control unit 10.

The control unit 10 is composed of a microprocessor (not shown) including a CPU and a memory. The control unit 10 controls the operation of the process control valve of the hard water softening device 3 based on a soft water flow rate sensor (not shown), a detection signal input from a salt water flow rate sensor, and the like. In the memory of the control unit 10, a control program for executing the operation of the hard water softening device 3 according to the first embodiment is stored in advance. The CPU of the control unit 10 controls the process control valve so as to sequentially switch the softening process ST1 to the refilling process ST6 described above according to the control program stored in the memory.

Further, the control unit 10 calculates the drive frequency of the pressurizing pump 6 by using the detected flow rate value of the permeated water W5 as a feedback value so that the flow rate of the permeated water W5 becomes a preset target flow rate value. Then, the control unit 10 outputs a current value signal corresponding to the calculated value of the calculated drive frequency to the inverter 7 (hereinafter, also referred to as “flow rate feedback water amount control”). This flow rate feedback control is a control mode executed when the flow rate of the permeated water W5 is normally detected by the flow rate sensor 9.

Here, the flow rate feedback water amount control by the control unit 10 will be described. FIG. 2 is a flowchart showing a processing procedure when the control unit 10 executes the flow rate feedback water amount control. The processing of the flowchart shown in FIG. 2 is repeatedly executed during the operation of the water treatment system 1.

In step ST11 shown in FIG. 2, the control unit 10 acquires the target flow rate value Qp'of the permeated water W5. This target flow rate value Qp'is, for example, a set value input to the memory by the system administrator via a user interface (not shown).

In step ST12, the control unit 10 determines whether or not the time counting t by the internal timer (not shown) has reached the control cycle of 100 ms. In step ST12, when the control unit 10 determines (YES) that the timer has reached 100 ms, the process proceeds to step ST13. Further, in step ST12, when the control unit 10 determines that the time counting by the timer has not reached 100 ms (NO), the process returns to step ST12.

In step ST13 (step ST12: YES determination), the control unit 10 acquires the detected flow rate value Qp of the permeated water W5 detected by the flow rate sensor 9.

In step ST14, the control unit 10 operates by the velocity type digital PID algorithm so that the deviation between the detected flow rate value (feedback value) Qp acquired in step ST13 and the target flow rate value Qp'acquired in step ST11 becomes zero. Calculate the quantity U. In the speed type digital PID algorithm, the change amount of the operation amount is calculated for each control cycle (100 ms), and this is added to the previous operation amount to determine the current operation amount.

In step ST15, the control unit 10 calculates the drive frequency F of the pressurizing pump 6 based on the operation amount U, the target flow rate value Qp', and the maximum drive frequency (set value of 50 Hz or 60 Hz) of the pressurizing pump 6. ..

In step ST16, the control unit 10 converts the calculated value of the drive frequency F into the corresponding current value signal (4 to 20 mA).
In step ST17, the control unit 10 outputs the converted current value signal to the inverter 7. As a result, the processing of this flowchart ends (returns to step ST11).

Further, the control unit 10 controls the drainage flow rate of the concentrated water W6 based on the calcium carbonate solubility based on the pH, hardness, M alkalinity of the supply water acquired in advance, and the detection temperature value of the temperature detecting means (the control unit 10). Hereinafter, it is also referred to as "drainage flow rate control"). This drainage flow rate control is executed in parallel with the flow rate feedback water amount control described above.

More specifically, the calcium carbonate solubility is influenced and changed by the water temperature, hardness, pH, and M alkalinity of the feed water. Therefore, when the supplied water is concentrated, the allowable concentration ratio, which is the maximum concentration ratio at which the carbonic acid concentration does not exceed the solubility of calcium carbonate, is obtained in consideration of the temperature and water quality of the supply water, and is based on this allowable concentration ratio. The control unit 10 controls the drainage flow rate of the concentrated water W6.

Next, the drainage flow rate control by the control unit 10 will be described. FIG. 3 is a flowchart showing a processing procedure when the control unit 10 executes wastewater flow rate control. The processing of the flowchart shown in FIG. 3 is repeatedly executed during the operation of the water treatment system 1.

In step ST21, the control unit 10 is based on a theoretical formula from the water quality of the soft water W2, which is the RO supply water supplied to the RO membrane, specifically, the pH value of the soft water W2 obtained in advance, and the M alkalinity. , HCO ₃ in the soft water W2 ^- calculating a (bicarbonate ions), _CO ^{3 2-(carbonate} ions), CO ₂ each concentration (this hereinafter, also referred to as "the carbonate concentration") (free carbonate) ..

In step ST22, the control unit 10 said, "Of the above-mentioned carbonate concentrations in the soft water W2 calculated based on the theoretical formula, free carbonate is not concentrated because it passes through the RO membrane, and bicarbonate ion and carbonate ion are not concentrated. By multiplying the bicarbonate ion concentration and the carbonate ion concentration by the concentration ratio as a coefficient on the assumption that "concentration is performed", each carbonate concentration in the concentrated water W6 is calculated for each concentration ratio. Further, the control unit 10 calculates the permissible concentration ratio based on the calculated carbonic acid concentration in the concentrated water W6 and the calcium carbonate solubility at the detected temperature value. Here, as a method of calculating the allowable concentration ratio, for example,
(1) Based on the calculated carbonic acid concentration in the concentrated water W6, the pH value and M alkalinity of the concentrated water W6 are calculated from the same theoretical formula used in step S21, and detected. The Langeria index is calculated from the temperature value and the hardness, and the concentration ratio allowed by the Langeria index is obtained. Specifically, the maximum concentration ratio among the concentration ratios so that the Langeria index does not become positive is defined as the allowable concentration ratio;
(2) Obtain the allowable concentration ratio at which the solubility product of calcium carbonate calculated from the carbonic acid concentration in the concentrated water W6 is less than the solubility product of calcium carbonate determined based on the detected temperature value;
It is possible to use such a method.

In step ST23, the control unit 10 determines the target drainage flow rate of the concentrated water W6 from the calculated permissible concentration ratio and the amount of the permeated water W5, and controls the drain valve 11 so as to reach the target drainage flow rate. do. As a result, the processing of this flowchart ends (returns to step ST21).

The permissible recovery rate can be calculated by using the permissible concentration ratio calculated in step S22. Specifically, when the concentration ratio is N and the permissible recovery rate is X, the permissible recovery from the concentration ratio is performed using the mathematical formula "allowable recovery rate X [%] = 100 × (N-1) / N". The rate can be calculated. FIG. 4 shows the relationship between the allowable recovery rate and the target recovery rate. As described above, the parameters for determining the permissible recovery rate include the carbonic acid concentration, hardness, pH, water temperature, etc. in the soft water W2, but in FIG. 4, only the water temperature changed among these parameters. An example of the change between the permissible recovery rate and the target recovery rate is shown below.

As can be seen in FIG. 4, as the water temperature rises in 5 ° C increments of 10 ° C → 15 ° C → 20 ° C → 25 ° C → 30 ° C → 35 ° C → 40 ° C, the permissible recovery rate is 73% → 73%. → 71% → 69% → 67% → 64% → 62%. In the graph of FIG. 4, the permissible recovery rate changes sequentially in a straight line, but is not limited to this, and may change in a curved line, for example.

At this time, for example, as the water temperature rises from 15 ° C. to 20 ° C., the permissible recovery rate decreases from 73% to 71%, but the control unit 10 as the target recovery rate setting unit allows the target recovery rate. Rather than linearly decreasing from 73% to 71% to match changes in recovery, the target recovery rate was reduced from 73% to 71% by 2% when the permissible recovery rate began to decline. , Lower in steps.
After that, when the permissible recovery rate reaches 71% and begins to decrease further, the control unit 10 as the target recovery rate setting unit lowers the target recovery rate from 71% to 70% in a stepwise manner by 1%. Let me.
Hereinafter, the control unit 10 as the target recovery rate setting unit lowers the target recovery rate in 1% increments in accordance with the decrease in the allowable recovery rate.

As described above, in the example shown in FIG. 4, in the region where the allowable recovery rate is 70% or more, the control unit 10 as the target recovery rate setting unit lowers the target recovery rate in 2% increments. In the region where the allowable recovery rate is less than 70%, the control unit 10 as the target recovery rate setting unit lowers the target recovery rate in 1% increments. In the low recovery rate region where the water saving effect is large, the target recovery rate is changed in small spans such as in 1% increments, and in the high recovery rate region where the influence on the enrichment is large, the target recovery rate is set, for example. Change in large spans, such as in 2% increments. As a result, even if an inexpensive and not highly accurate flow rate sensor is used as the flow rate sensor, it is possible to realize recovery rate control in which the risk of film clogging and the water saving effect are balanced.

In the example shown in FIG. 4, the target recovery rate changes stepwise every time the change in the allowable recovery rate changes in 1% increments or 2% increments, but this is just an example. And it is not limited to this. For example, the target recovery rate may change stepwise each time the change in water temperature changes by a predetermined range.

As shown in FIG. 4, when the control unit 10 controls the drain valve 11 according to the target recovery rate that changes stepwise, if the measured recovery rate is within a predetermined deviation from the allowable recovery rate. , The control unit 10 fixes the opening degree of the drain valve 11, and when the measured recovery rate is outside the predetermined deviation from the allowable recovery rate, the control unit 10 may change the opening degree of the drain valve 11. It is possible.

Further, as described above, the control unit 10 executes the two controls of the flow rate feedback water amount control and the drainage flow rate control in parallel. For example, by using the technique described in Japanese Patent No. 5787040, these controls are used. In addition to the control, the control unit 10 may detect the water quality of the permeated water W5 and calculate the permissible concentration ratio so that the water quality satisfies the required water quality.
More specifically, in Japanese Patent No. 5787040, the control unit has the target electrical conductivity, which is an index of the purity required for the permeated water, and the measured electricity measured by the electrical conductivity sensor, which is input by the user. The drainage valve is controlled so that the deviation between the measured electrical conductivity and the target electrical conductivity becomes zero by acquiring the conductivity. Similarly to this in the present embodiment, the control unit 10 calculates the permissible concentration ratio based on the target electric conductivity of the permeated water W5 and the actually detected measured electric conductivity, and the permissible concentration ratio is calculated. The opening degree of the drain valve 11 may be changed so as to satisfy the above conditions.
Further, the control unit 10 calculates the permissible concentration ratio so as to satisfy the required water quality based on the silica concentration instead of the electric conductivity or in addition to the electric conductivity, and so as to satisfy the permissible concentration ratio. The opening degree of the drain valve 11 may be changed.

According to the water treatment system 1 according to the first embodiment described above, for example, the following effects can be obtained.

In the water treatment system 1 according to the first embodiment, the control unit 10 calculates the drive frequency of the pressurizing pump 6 using the physical quantity in the system so that the flow rate of the permeated water becomes a preset target flow rate value. Then, the calculated value signal corresponding to the calculated value of the drive frequency is output to the inverter 7 of the pressurizing pump 6, and calcium carbonate is obtained from the pH, hardness, M alkalinity, and detected temperature value of the supply water acquired in advance. Based on the solubility, the permissible concentration ratio of calcium carbonate in the concentrated water is calculated, the drainage flow rate is calculated from the calculated value of the permissible concentration ratio and the target flow rate value of the permeated water, and the actual drainage flow rate of the concentrated water is the drainage flow rate. The drain valve 11 is controlled so as to have the calculated value of.
As a result, even when the water temperature or pH of the supplied water fluctuates, the precipitation of the calcium carbonate-based scale in the RO membrane module 8 can be more reliably suppressed while maximizing the recovery rate of the permeated water.
Further, in the first embodiment, the permissible concentration ratio can be obtained by adding each carbonate ion concentration calculated according to the concentration ratio, and the detected pH value is further used to obtain the respective carbonate ion concentration. Can be calculated more accurately.

Further, in the water treatment system 1 according to the first embodiment, the control unit 10 calculates the permissible concentration ratio so that the water quality of the permeated water satisfies the required water quality, and the required water quality is the electrical conductivity of the permeated water. , And / or according to the criteria for silica concentration.
This makes it possible to maximize the recovery rate of permeated water while maintaining the quality of permeated water.

Further, in the water treatment system 1 according to the first embodiment, the control unit 10 calculates the allowable concentration ratio based on the concentrations of carbonate ion and bicarbonate ion of the concentrated water obtained by multiplying the concentration ratio as a coefficient.
Therefore, when trying to obtain the permissible concentration ratio using the Langeria index, it is necessary to calculate the M alkali of the concentrated water in advance from each carbonate ion concentration, but when obtaining the permissible concentration ratio from the solubility product. The control unit 10 can calculate the allowable concentration ratio as long as each carbonate ion concentration of the concentrated water is present, without necessarily interposing the M alkali of the concentrated water.

Further, in the water treatment system 1 according to the first embodiment, the control unit 10 changes the opening degree of the drain valve 11 so that the actual measurement recovery rate becomes the target recovery rate, and the actual measurement recovery rate is calculated from the allowable recovery rate. If it is within the predetermined deviation, the control unit 10 fixes the opening degree of the drain valve 11, and if the measured recovery rate is outside the predetermined deviation from the allowable recovery rate, the control unit 10 controls the drain valve 11. Change the opening of.
As a result, when the measured recovery rate is within a predetermined deviation from the permissible recovery rate, the control unit 10 reduces the control frequency of the drain valve 11 by fixing the opening degree of the drain valve 11, and the drain valve 11 is controlled. 11 is extended.

Further, in the water treatment system 1 according to the first embodiment, the control unit 10 as the target recovery rate setting unit sets the target recovery rate every time the allowable recovery rate changes by a predetermined amount according to the change in the allowable recovery rate. It may be changed discontinuously, or the target recovery rate may be changed discontinuously every time the detected temperature value changes by a predetermined amount according to the change of the detected temperature value.
By controlling the target recovery rate step by step, the control frequency of the drain valve 11 is further reduced, and the life of the drain valve 11 is extended.

[Second Embodiment]
Next, the water treatment system 1A according to the second embodiment of the present invention will be described with reference to FIG. FIG. 5 is an overall configuration diagram of the water treatment system 1A according to the second embodiment. In the second embodiment, the differences from the first embodiment will be mainly described. In the second embodiment, the same or equivalent configurations as those in the first embodiment will be described with the same reference numerals. Further, in the second embodiment, the description overlapping with the first embodiment will be omitted as appropriate.

As shown in FIG. 5, the water treatment system 1A according to the second embodiment includes a raw water pump 2, a hard water softening device 3, a salt water tank 4, a temperature sensor 5, a pressurizing pump 6, an inverter 7, and the like. RO membrane module 8, control unit 10A, drain valve 11, first pH sensor 12 and second pH sensor 13 as pH measuring means, hardness sensor 14 as hardness measuring means, and first flow rate as flow measuring means. A sensor 15, a second flow rate sensor 16, and a permeation water valve 17 are provided.

The first pH sensor 12 is an apparatus for measuring the pH of soft water W2 flowing through the soft water line L2. The first pH sensor 12 is electrically connected to the control unit 10A. The pH value of the soft water W2 measured by the first pH sensor 12 (hereinafter, also referred to as “measured pH value”) is transmitted to the control unit 10A as a detection signal.

The second pH sensor 13 is an apparatus for measuring the pH of the concentrated water W6 flowing through the concentrated water line L6. The second pH sensor 13 is electrically connected to the control unit 10A. The pH value of the concentrated water W6 measured by the second pH sensor 13 (hereinafter, also referred to as “measured pH value”) is transmitted to the control unit 10A as a detection signal.

The hardness sensor 14 is a device for measuring the calcium hardness (hardness leak amount: calcium carbonate conversion value) of the soft water W2 flowing through the soft water line L2. The hardness sensor 14 is electrically connected to the control unit 10A. The calcium hardness of the soft water W2 measured by the hardness sensor 14 (hereinafter, also referred to as “measured hardness value”) is transmitted to the control unit 10A as a detection signal.

The first flow rate sensor 15 is a device that detects the flow rate of the permeated water W5 flowing through the permeated water line L5. The first flow rate sensor 15 is electrically connected to the control unit 10A. The flow rate of the permeated water W5 detected by the first flow rate sensor 15 (hereinafter, also referred to as “first detected flow rate value”) is transmitted to the control unit 10A as a detection signal.

The second flow rate sensor 16 is a device that detects the flow rate of the concentrated water W6 flowing through the concentrated water line L6. The second flow rate sensor 16 is electrically connected to the control unit 10A. The flow rate of the concentrated water W6 detected by the second flow rate sensor 16 (hereinafter, also referred to as “second detected flow rate value”) is transmitted to the control unit 10A as a detection signal.

The permeated water valve 17 is a valve that regulates the flow rate of the permeated water W5 flowing through the permeated water line L5. The flow rate of the permeated water W5 flowing through the permeated water line L5 can be adjusted by opening and closing the permeated water valve 17. The permeated water valve 17 is electrically connected to the control unit 10A. The opening and closing of the valve body in the permeated water valve 17 is controlled by a drive signal from the control unit 10A.

In the water treatment system 1 according to the first embodiment described above, in step ST21, the control unit 10 determines the HCO ₃ ^{− in the soft water W2 based on the theoretical formula from the pH and M alkalinity of the soft water W2 acquired in advance.} Calculate the concentrations of (bicarbonate ion), CO ₃ ^2- (carbonate ion), and CO ₂ (free carbon dioxide). Further, in step ST22, the control unit 10 calculates the permissible concentration ratio based on the calculated carbonic acid concentration in the concentrated water W6 and the calcium carbonate solubility at the detected temperature value.

On the other hand, in the water treatment system 1A according to the second embodiment, the control unit 10A calculates the permissible concentration ratio according to the same flowchart as in FIG. 3 and controls the drain valve 11, but it was acquired in advance in step ST22. The permissible concentration ratio is calculated based on the calcium carbonate solubility in the concentrated water W6 and the detected temperature value obtained in consideration of the hardness, pH value, and water temperature of the soft water W2 obtained in real time instead of the data. .. Further, the control unit 10A calculates the permissible concentration ratio based not only on the pH value of the soft water W2 but also on the pH value of the concentrated water W6. Specifically, instead of using the calculated pH value of the concentrated water calculated by the theoretical formula from the carbonated water concentration in the concentrated water W6 obtained by calculation in the water treatment system 1 according to the first embodiment, in real time. The detected pH value of the concentrated water W6 obtained in the above is used.

According to the water treatment system 1A according to the second embodiment described above, for example, the following effects can be obtained.

To repeat the above, in the water treatment system 1A according to the second embodiment, the control unit 10A considers the hardness, pH value, and water temperature of the soft water W2 obtained in real time, not the data acquired in advance. The maximum concentration ratio at which the calcium carbonate concentration does not exceed the calcium carbonate solubility as compared with the calcium carbonate solubility obtained in the above is calculated as the allowable concentration ratio. Further, the control unit 10A calculates the permissible concentration ratio based not only on the pH value of the soft water W2 but also on the pH value of the concentrated water W6.
This makes it possible to accurately calculate the permissible concentration ratio even when the water quality fluctuates not only with the water temperature but also with the passage of time, and the control unit 10A can use not only the pH value of the soft water W2 but also the concentrated water W6. Since it is also based on the pH value, the permissible concentration ratio can be calculated more accurately.

Although the preferred embodiment of the present invention has been described above, the present invention is not limited to the above-described embodiment, and can be implemented in various forms.

An example of adjusting the drainage flow rate of the concentrated water W6 by controlling the valve opening degree of the drain valve 11 has been described. Not limited to this, a plurality of drainage valves may be provided in parallel, and the drainage flow rate of the concentrated water W6 may be controlled to be adjusted stepwise by increasing or decreasing the number of open drainage valves. According to this, the drainage flow rate of the concentrated water W6 can be adjusted.

Further, the water treatment systems 1 and 1A according to the above embodiment include a hard water softening device 3, but this is not essential. Further, the temperature detection position by the temperature sensor 5 and the number of the temperature sensors 5 themselves may be changed or expanded as appropriate in consideration of the lengths of the raw water line L1 and the soft water line L2 and the temperature difference between the outside air and the water temperature.

1,1A Water treatment system 3 Hard water softener 5 Temperature sensor (Temperature detection means)
6 Pressurizing pump 7 Inverter 8 RO membrane module 9 Flow sensor (flow detection means)
10,10A Control unit 11 Drain valve 12 1st pH sensor 13 2nd pH sensor 14 Hardness sensor (hardness measuring means)
15 First flow rate sensor (flow rate detecting means)
16 Second flow rate sensor (flow rate detecting means)
L1 Raw water line L2 Soft water line L3 Salt water line L4 Drainage line L5 Permeated water line L6 Concentrated water line W1 Raw water W2 Soft water W3 Salt water W4 Drainage W5 Permeated water W6 Concentrated water

Claims (7)

A reverse osmosis membrane module that separates the supply water into permeated water and concentrated water,
A pressure pump that is driven at a rotation speed according to the input drive frequency, sucks in supply water, and discharges it toward the reverse osmosis membrane module.
An inverter that outputs the drive frequency corresponding to the input calculated value signal to the pressurizing pump, and
The drive frequency of the pressurizing pump is calculated using the physical quantity in the system so that the flow rate of the permeated water becomes a preset target flow rate value, and the calculated value signal corresponding to the calculated value of the drive frequency is generated by the inverter. The control unit that outputs to
A temperature detecting means for detecting the temperature of supply water, permeated water or concentrated water,
A drainage flow rate adjusting means that can adjust the drainage flow rate of concentrated water discharged to the outside of the device,
A first flow rate detection unit that detects the flow rate of the permeated water as a first detection flow rate value,
A second flow rate detection unit for detecting the flow rate of the concentrated water is discharged to the outside of the apparatus as the second detected flow value, a membrane separation apparatus Ru provided with,
The drainage flow rate adjusting means is composed of a drainage valve.
The control unit (i) allows the permissible concentration ratio of calcium carbonate in the concentrated water based on the calcium carbonate solubility based on the pH, hardness, M alkalinity of the supply water acquired in advance, and the detection temperature value of the temperature detecting means. (Ii) Calculate the drainage flow rate from the calculated value of the permissible concentration ratio and the target flow rate value of the permeated water, and (iii) so that the second detected flow rate value becomes the calculated value of the drainage flow rate. , Control the drain valve ,
The membrane separation device further includes a target recovery rate setting unit for setting a target recovery rate, which is an operation target within a predetermined deviation from the allowable recovery rate calculated based on the allowable concentration ratio.
The control unit changes the opening degree of the drain valve so that the actual measurement recovery rate calculated from the first detected flow rate value and the second detected flow rate value becomes the target recovery rate, and the actual measurement When the recovery rate is within a predetermined deviation from the permissible recovery rate, the control unit fixes the opening degree of the drain valve, and the actually measured recovery rate is outside the predetermined deviation from the permissible recovery rate. The control unit changes the opening degree of the drain valve .
Membrane separation device. The membrane separation device according to claim 1, wherein the control unit calculates the permissible concentration ratio so that the water quality of the permeated water satisfies the required water quality. The membrane separation device according to claim 2, wherein the required water quality is determined according to a standard relating to the electrical conductivity and / or silica concentration of the permeated water. The membrane according to any one of claims 1 to 3, wherein the control unit calculates the permissible concentration ratio based on the concentration of carbonate ion and bicarbonate ion of the concentrated water obtained by multiplying the concentration ratio as a coefficient. Separator. Further provided with a pH detecting means for detecting the pH of the feed water and / or the concentrated water,
The membrane separation device according to claim 4, wherein the control unit calculates the permissible concentration ratio based on the detected pH value detected by the pH detecting means as the pH of the supply water. In response to said allowable recovery index change, every time the allowable recovery varies a predetermined amount, the target recovery ratio setting unit changes the target recovery rate discontinuously, reverse osmosis according to claim 1 Membrane separation device. In accordance with a change in the detected temperature value, for each of the detected temperature value is changed a predetermined amount, the target recovery ratio setting unit changes the target recovery rate discontinuously, reverse osmosis according to claim 1 Membrane separation device.

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