JP6842976B2 - Pure water production equipment - Google Patents

Description

The present invention relates to a pure water production apparatus.

As a method of producing pure water from raw water such as industrial water, well water, and city water, raw water is separated into permeated water and concentrated water by a reverse osmosis membrane (RO membrane) or nanofiltration membrane (NF membrane), and then permeated. A method of producing deionized water (pure water) by further passing water through an ion exchanger is known. That is, as an apparatus for producing pure water from raw water, a pure water production apparatus that combines a membrane filtration apparatus having an RO membrane or an NF membrane and an electric deionized water production apparatus is known.

In such a pure water production apparatus, when the water temperature fluctuates, the flow rate of the permeated water separated by the RO membrane or the NF membrane of the membrane filtration apparatus fluctuates and is supplied from the membrane filtration apparatus to the electric deionized water production apparatus. The flow rate of permeated water fluctuates. As a result, the flow rate (treatment flow rate) of the permeated water flowing into the desalination chamber filled with the ion exchanger may fluctuate, causing problems such as unstable flow rate of the pure water produced. is there. In particular, when the treatment flow rate increases, the water flow differential pressure rises, causing water leakage or damage, and when the treatment flow rate further increases and a load exceeding the treatment capacity is applied, the treatment water quality may deteriorate. is there. On the other hand, the permeated water supplied from the membrane filtration device flows into not only the desalting chamber but also the concentrating chambers arranged on both sides thereof via ion exchangers and the electrode chamber in which the electrodes are housed. Therefore, if the amount of inflow into these fluctuates, scale is likely to be generated in the concentration chamber, or the gas generated in the electrode chamber may be difficult to be discharged.

Patent Document 1 describes fluctuations in the flow rate of permeated water supplied from a membrane filtration device to an electric deionized water production device and fluctuations in the flow rate of deionized water (pure water) produced by the electric deionized water production device. A method of suppressing the above is described. In the method described in Patent Document 1, fluctuations in the flow rate of permeated water from the membrane filtration apparatus can be suppressed by controlling the supply pressure of raw water to the membrane filtration apparatus according to the water temperature. In addition to this, a line that discharges a part of the concentrated water from the membrane filtration device to the outside, a line that returns the rest to the upstream side of the membrane filtration device, and a concentration chamber of the electric deionized water production device. Pure water at a specified flow rate can be produced by providing orifices in the line for returning the wastewater to the upstream side of the membrane filtration device and the line for discharging the wastewater from the electrode chamber to the outside.

Japanese Unexamined Patent Publication No. 2006-255652

By the way, from the viewpoint of effective use of water (water saving), it is preferable that the flow rate of concentrated water (concentrated wastewater) discharged to the outside from the membrane filtration device is as small as possible. That is, it is preferable that the recovery rate of the membrane filtration device (the ratio of the flow rate of permeated water to the sum of the flow rate of permeated water and the flow rate of concentrated wastewater) is as high as possible. On the other hand, when the recovery rate is high, scaling in which impurities are precipitated on the film surface of the RO film or the NF film is likely to occur. Therefore, it is necessary to consider the risk of scaling when setting the recovery rate, but since the solubility of impurities changes according to the water temperature, this risk also changes according to the water temperature. Therefore, it is preferable that the recovery rate can be adjusted according to the water temperature, and thus it is preferable that the recovery rate can be set to an optimum value in consideration of the risk of water saving and scaling.

However, in the pure water production apparatus described in Patent Document 1, since the flow rate ratio of the concentrated waste water to the concentrated water is determined by the orifice, the recovery rate cannot be changed when the water temperature fluctuates. Therefore, depending on the water temperature, concentrated wastewater may be wasted or the risk of scaling may increase.

Therefore, an object of the present invention is to provide a pure water production apparatus capable of saving water by simultaneously suppressing fluctuations in the flow rate of the pure water produced and adjusting the recovery rate of the membrane filtration apparatus. ..

In order to achieve the above-mentioned object, the pure water production apparatus of the present invention is a pure water production apparatus that sequentially treats water to be treated to produce pure water, and is a membrane filtration apparatus and a downstream side of the membrane filtration apparatus. It has an electric deionized water production device connected to the membrane filtration device and supplied with permeated water from the membrane filtration device, and a control unit for controlling the operation of the membrane filtration device and the electric deionized water production device. The device distributes a filtration means having a back-penetration membrane or a nanofiltration membrane that separates the water to be treated into permeated water and concentrated water, a supply line that supplies the water to be treated to the filtering means, and permeated water from the filtering means. From the permeated water line, the concentrated water line that circulates the concentrated water from the filtration means, the drainage line that branches off from the concentrated water line and discharges a part of the concentrated water flowing through the concentrated water line to the outside, and the concentrated water line. A reflux water line that branches and returns the rest of the concentrated water flowing through the concentrated water line to the supply line, a pressure adjusting means provided in the supply line that adjusts the supply pressure of the water to be treated to the filtration means, and a concentrated water line. It has a constant flow valve provided in the infiltration water line to keep the flow rate of the concentrated water flowing through the infiltration line constant, and a flow rate adjusting means provided in the drainage line to adjust the flow rate of the concentrated water flowing through the drainage line. The microdeionized water production apparatus is located between the anode and the cathode, is partitioned by an anion exchange membrane on the anode side and a cation exchange membrane on the cathode side, and is filled with at least one of the cation exchange and the anion exchange. It has a desalting chamber and a treated water line for passing the treated water obtained by passing the permeated water from the membrane filtration device through the desalting chamber, and the control unit is the treated water flowing through the treated water line. The target flow rate of the concentrated water flowing through the drainage line is calculated from the first flow rate control that controls the pressure adjusting means so that the flow rate of the water flow reaches the set flow rate, and the flow rate of the permeated water flowing through the permeation water line, and the concentration flowing through the drainage line. The second flow control, which controls the flow adjustment means so that the water flow reaches the target flow rate, is executed independently and in parallel.

According to such a pure water production apparatus, the flow rate of the treated water from the electric deionized water production apparatus can be kept constant, and at the same time, the flow rate of the concentrated water discharged to the outside from the membrane filtration apparatus can be maintained. It can be changed arbitrarily. As a result, it is possible to simultaneously suppress fluctuations in the flow rate of pure water produced by the pure water production apparatus and adjust the recovery rate of the membrane filtration apparatus to save water.

As described above, according to the present invention, it is possible to provide a pure water production apparatus capable of saving water by simultaneously suppressing fluctuations in the flow rate of the pure water produced and adjusting the recovery rate of the membrane filtration apparatus. ..

It is the schematic which shows the structure of the pure water production apparatus which concerns on 1st Embodiment of this invention. It is the schematic which shows two configuration examples for changing the set flow rate of treated water in the 1st flow rate control. It is the schematic which shows the structure of the membrane filtration apparatus which concerns on 2nd Embodiment of this invention.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(First Embodiment)

FIG. 1A is a schematic configuration diagram of a pure water production apparatus according to the first embodiment of the present invention. FIG. 1B is a schematic configuration diagram of an electric deionized water production apparatus constituting the pure water production apparatus of FIG. 1A.

The pure water production device 1 has a raw water tank 2, a membrane filtration device 10, and an electric deionized water production device 20, and sequentially treats the water to be treated (raw water) to produce pure water, and the pure water is produced. It supplies water to use point 3. Further, the pure water production device 1 has a control unit 30 that controls the operation of the membrane filtration device 10 and the electric deionized water production device 20.

The membrane filtration device 10 is a device that removes impurities in the raw water supplied from the raw water tank 2 to generate permeated water, and divides the raw water into concentrated water containing impurities and permeated water from which impurities have been removed. It has a filtration means 11 for separation. The filtration means 11 has a reverse osmosis membrane (RO membrane) or a nanofiltration membrane (NF membrane).

Further, the membrane filtration device 10 includes a supply line L1 for supplying raw water to the filtration means 11, a permeated water line L2 for circulating the permeated water from the filtering means 11, and a concentrated water line for circulating the concentrated water from the filtering means 11. Branching from L3 and concentrated water line L3 and discharging a part of concentrated water flowing through concentrated water line L3 to the outside, branching from concentrated water line L3 and returning the rest of concentrated water to raw water tank 2. It has a reflux water line L5 to be allowed to flow. The supply line L1 is connected to the raw water tank 2, and the permeated water line L2 is connected to the electric deionized water production apparatus 20. Further, the permeated water return line L6 connected to the raw water tank 2 via the three-way valve 12 is connected to the permeated water line L2. A raw water supply line L7 is connected to the raw water tank 2, and raw water is supplied as needed. The raw water tank 2 does not necessarily have to be provided, and the recirculation water line L5 and the permeated water return line L6 may be directly connected to the supply line L1.

Further, the membrane filtration device 10 includes a pressurizing pump 13 provided in the supply line L1, a permeated water flow meter 14 provided in the permeated water line L2, and a constant flow valve 15 provided in the concentrated water line L3. It has a flow rate adjusting valve 16 and a drainage flow meter 17 provided in the drainage line L4, and a manual valve 18 provided in the return water line L5.

The rotation speed of the pressurizing pump 13 is controlled by an inverter (not shown), and the pressure adjusting means for adjusting the pressure of the raw water flowing through the supply line L1 (the pressure of supplying the raw water to the filtration means 11). Functions as. The permeated water flow meter 14 has a function of detecting the flow rate of permeated water flowing through the permeated water line L2. The constant flow rate valve 15 has a function of keeping the flow rate of the concentrated water flowing through the concentrated water line L3 constant, suppressing interference between two flow rate controls described later, and avoiding hunting. The flow rate adjusting valve 16 functions as a flow rate adjusting means for adjusting the flow rate of the concentrated water (hereinafter referred to as "concentrated drainage") flowing through the drainage line L4, and the drainage flow meter 17 has a function of detecting the flow rate of the concentrated drainage. doing. The manual valve 18 functions as a pressure adjusting valve for adjusting the pressure balance between the concentrated water flowing through the drainage line L4 and the concentrated water flowing through the recirculating water line L5.

The electric deionized water production apparatus 20 is an apparatus that combines electrophoresis and electrodialysis, and simultaneously performs deionization (demineralization) treatment of the water to be treated by an ion exchanger and regeneration treatment of the ion exchanger. It is a device. The electric deionized water production device 20 is connected to the downstream side of the membrane filtration device 10, and the permeated water from the membrane filtration device 10 is supplied as the water to be treated via the permeation water line L2. Further, the electric deionized water production apparatus 20 has a treated water line L8 that circulates the produced treated water (deionized water) and supplies it to the use point 3. The treated water return line L9 connected to the raw water tank 2 via the three-way valve 4 is connected to the treated water line L8. As a result, the treated water produced by the electric deionized water production apparatus 20 is returned to the raw water tank 2 at the time of starting the apparatus, restarting the operation, or when there is no demand for the treated water (pure water) at the use point 3. It is also possible to perform circular operation. When the raw water tank 2 is not provided, the treated water return line L9 is directly connected to the supply line L1.

The electric deionized water producing apparatus 20 includes an anode chamber E1 provided with an anode 21, a cathode chamber E2 provided with a cathode 22, a desalting chamber D provided between the anode chamber E1 and the cathode chamber E2, and a desalting chamber D. A pair of concentrating chambers C1 and C2 arranged on both sides of the desalting chamber D, on the anode 21 side of the desalting chamber D, the anode side concentrating chamber C1 adjacent to the desalting chamber D via the anion exchange film a1. And, on the cathode 22 side of the desalting chamber D, it has a pair of concentrating chambers C1 and C2 including the desalting chamber D and the cathode side concentrating chamber C2 adjacent to the desalting chamber D via the cation exchange film c1. The anode-side concentration chamber C1 is adjacent to the anode chamber E1 via the cation exchange membrane c2, and the cathode-side concentration chamber C2 is adjacent to the cathode chamber E2 via the anion exchange membrane a2.

The desalting chamber D is filled with at least one of the cation exchanger and the anion exchanger, preferably a mixture of the cation exchanger and the anion exchanger. That is, it is preferable that the cation exchanger and the anion exchanger are filled in a so-called mixed bed form. Examples of the cation exchanger include a cation exchange resin, a cation exchange fiber, a monolithic porous cation exchanger, and the like, and the most general-purpose cation exchange resin is preferably used. Examples of the type of the cation exchanger include a weakly acidic cation exchanger and a strongly acidic cation exchanger. Examples of the anion exchange body include an anion exchange resin, anion exchange fiber, and a monolithic porous anion exchange body, and the most general-purpose anion exchange resin is preferably used. Examples of the type of anion exchanger include a weakly basic anion exchanger and a strongly basic anion exchanger.

The anode-side concentration chamber C1 and the cathode-side concentration chamber C2 are provided to take in the anion component and the cation component discharged from the desalting chamber D, respectively, and discharge them to the outside by the concentrated water. In order to suppress the electric resistance of the electric deionized water production apparatus 10, it is preferable that the concentration chambers C1 and C2 are filled with an ion exchanger.

The anode chamber E1 houses an anode 21 made of a metal mesh or plate. The cathode chamber E2 houses a cathode 22 made of a metal mesh or plate. In order to suppress the electric resistance of the electric deionized water production apparatus 1, it is preferable that the anode chamber E1 and the cathode chamber E2 are filled with a conductive substance such as an ion exchanger.

The permeated water line L2 from the membrane filtration device 10 is branched into three and connected to the desalting chamber D, the anode side concentration chamber C1 and the cathode chamber E2, respectively, and the permeated water from the membrane filtration device 10 is treated with the water to be treated. , Concentrated water, and electrode water. That is, the first branch line L21 is connected to the desalting chamber D, the second branch line L22 is connected to the anode side concentration chamber C1, and the third branch line L23 is connected to the cathode chamber E2. It is connected. The anode-side concentrating chamber C1 forms a series flow path with the cathode-side concentrating chamber C2, and the concentrated water flowing out of the anode-side concentrating chamber C1 flows into the cathode-side concentrating chamber C2. A concentrated water discharge line L24 for discharging concentrated water to the outside is connected to the cathode side concentration chamber C2. The cathode chamber E2 forms a series flow path with the anode chamber E1, and the electrode water flowing out of the cathode chamber E2 flows into the anode chamber E1. An electrode water discharge line L25 for discharging the electrode water to the outside is connected to the anode chamber E1. Further, the desalting chamber D is connected to the treated water line L8.

The operation of the electric deionized water production apparatus 20 is performed as follows. First, a DC voltage is applied between the anode 21 and the cathode 22 so that the current value flowing between the two poles 21 and 22 becomes a predetermined value, and the permeated water (permeated water from the membrane filtration device 10) is applied to the desalting chamber D. Water to be treated) is supplied. At this time, a part of the water to be treated is supplied to the anode side concentration chamber C1 and the cathode side concentration chamber C2 as concentrated water, and similarly, a part of the water to be treated is supplied to the anode chamber E1 and the cathode chamber E2. It is supplied as electrode water. When the water to be treated passes through the desalting chamber D, the cation component and the anion component in the water to be treated are adsorbed and removed by the cation exchanger and the anion exchanger filled in the desalting chamber D, respectively. In this way, the water to be treated from which the cation component and the anion component have been removed is supplied as treated water (deionized water) from the treatment chamber D to the use point 3 through the treated water line L8.

On the other hand, in the desalting chamber D, the water dissociation reaction in which water dissociates ^{into hydrogen ions (H +} ) and hydroxide ions (OH ^{−) is continuously proceeding.} H ⁺ is exchanged for the cation component adsorbed on the cation exchanger, and OH ⁻ is exchanged for the anion component adsorbed on the anion exchanger. In this way, the cation exchanger and the anion exchanger filled in the desalting chamber D are regenerated, respectively.

The cation component released from the cation exchanger in the desalting chamber D is attracted to the cathode 22 side by the potential difference between the anode 21 and the cathode 22, passes through the cation exchange membrane c1 and moves to the cathode side concentration chamber C2. The anion component released from the anion exchanger of the desalting chamber D is attracted to the anode 21 side by the potential difference between the anode 21 and the cathode 22, passes through the anion exchange membrane a1 and moves to the anode side concentration chamber C1. The cation component transferred to the cathode side concentration chamber C2 is taken into the concentrated water supplied to the cathode side concentration chamber C2, and the anion component transferred to the anode side concentration chamber C1 is the concentrated water supplied to the anode side concentration chamber C1. And both are discharged to the outside through the concentrated water discharge line L24. However, depending on the quality of the concentrated water, a part or all of the concentrated water may be returned to the raw water tank 2.

The first branch line L21 is provided with a manual valve 23a and a pressure gauge (not shown) for detecting the pressure of the permeated water flowing into the desalting chamber D. The second branch line L22 is provided with a manual valve 23b and a flow meter and a pressure gauge (both not shown) for detecting the flow rate and pressure of the concentrated water flowing through the second branch line L22, respectively. The third branch line L23 is provided with a manual valve 23c and a flow meter and a pressure gauge (both not shown) for detecting the flow rate and pressure of the electrode water flowing through the third branch line L23, respectively. Further, the treated water line L8 is provided with a treated water flow meter 24, a manual valve 25a, and a pressure gauge (not shown) for detecting the pressure of the treated water flowing through the treated water line L8. The concentrated water discharge line L24 is provided with a manual valve 25b and a pressure gauge (not shown) for detecting the pressure of the concentrated water flowing through the concentrated water discharge line L24. A manual valve 25c is provided on the electrode water discharge line L25.

With such a configuration, in the present embodiment, the flow rate balance (flow rate ratio) and pressure balance of the treated water, the concentrated water, and the electrode water flowing in the electric deionized water production apparatus 20 can be adjusted. That is, the three manual valves 23a to 23c provided on the supply side function as flow rate adjusting means, respectively, to adjust the flow rates of the treated water, the concentrated water, and the electrode water, and balance their flow rates (flow rate). Ratio) can be adjusted. In addition, the three manual valves 25a to 25c provided on the discharge side function as pressure adjusting means, respectively, to adjust the pressures of the treated water, the concentrated water, and the electrode water to adjust their pressure balance. can do.

As will be described later, in the present embodiment, since the flow rate of the treated water flowing through the treated water line L8 is kept constant, the flow rate of the permeated water supplied from the membrane filtration device 10 is also kept constant. Therefore, the flow rate balance can be adjusted if there are two of the three manual valves 23a to 23c provided on the supply side, and for example, the manual valve 23a of the first branch line L21 can be omitted. Further, in this case, in order to eliminate the complexity of manual adjustment of the flow rate balance, a constant flow rate valve is provided instead of the manual valve 23b of the second branch line L22 and the flow meter (not shown), and a third A constant flow rate valve may be provided in place of the manual valve 23c of the branch line L23 and the flow meter (not shown). Such a design change is similarly possible when a part of the treated water is used as the electrode water, as will be described later. That is, the permeated water line L2 branches into two, the first branch line L21 and the second branch line L22, and the third branch line L23 is connected to the treated water line L8 on the upstream side of the treated water flow meter 24. Even in this case, the manual valve 23a can be omitted, or the manual valves 23b and 23c can be replaced with constant flow rate valves, respectively.

The above-mentioned configuration of the electric deionized water production apparatus 20 is merely an example, and the configuration (number, arrangement, etc.) and flow path configuration of each room may be changed, valves, measuring instruments, etc. may be added. Needless to say, it can be changed as appropriate according to the purpose of use, application, and required performance of the device. For example, two or more desalting chambers may be provided. In this case, the desalination chamber and the concentration chamber are alternately provided via a cation exchange membrane or an anion exchange membrane, and the concentration chamber located on the most anode side is adjacent to the anode chamber and the concentration chamber is located on the most cathode side. Will be adjacent to the cathode chamber. At that time, by omitting the ion exchange membrane between the concentration chamber and the electrode chamber (anode chamber or cathode chamber) or omitting the concentration chamber adjacent to the electrode chamber, the electrode chamber can also serve as the concentration chamber. It can also be. If the concentration chamber adjacent to the electrode chamber is omitted, the desalination chamber adjacent to the electrode chamber may have a different structure from the desalination chamber arranged between the pair of concentration chambers. The ion exchange membrane arranged between the two may be changed as appropriate.

Further, regarding the flow path configuration, the concentrated water may flow into the cathode side concentration chamber first, or the electrode water may flow into the anode chamber first. Alternatively, the pair of concentration chambers may form a parallel flow path, and the electrode chamber may also form a parallel flow path. Further, as described above, a part of the treated water may be used as the electrode water. Further, when the desalination chamber is partitioned into two small desalination chambers forming a series flow path by an intermediate ion exchange membrane arranged between the anion exchange membrane and the cation exchanger, the water to be treated is treated. A part of the intermediate treated water obtained by passing water through one of the small desalination chambers may be used as electrode water. When a part of the intermediate treated water is used as the electrode water, the intermediate treated water becomes acidic when the small desalting chamber through which the water to be treated is passed is filled with the cation exchanger, so that the surface of the cathode surface. It is advantageous in that the generation of calcium carbonate scale can be suppressed.

The control unit 30 controls two flow rates during the normal operation (pure water production) of the pure water production device 1, that is, the flow control of the treated water (pure water) produced by the electric deionized water production device 20. The flow control for adjusting the recovery rate of the membrane filtration device 10 is performed in parallel. Specifically, the control unit 30 controls the first flow rate that controls the pressurizing pump 13 so that the flow rate of the treated water flowing through the treated water line L8 becomes a set flow rate, and the permeated water flowing through the permeated water line L2. The target flow rate of the concentrated water (concentrated drainage) flowing through the drainage line L4 is calculated from the flow rate, and the second flow rate control for controlling the flow rate adjusting valve 16 so that the flow rate of the concentrated drainage becomes the target flow rate is executed in parallel. To do. The details of these two flow rate controls will be described below.

In the first flow rate control, the membrane filtration device 10 is pressurized so that the flow rate of the treated water detected by the treated water flow meter 24 of the electric deionized water production device 20 becomes constant (preset flow rate). The pump 13 is controlled. For example, when the water temperature changes, the flow rate of the permeated water separated by the filtration means 11 changes due to the change in the viscosity of the water, and as a result, the flow rate of the treated water produced by the electric deionized water production apparatus 20 also changes. To do. In response to this change, the control unit 30 controls the rotation speed of the pressurizing pump 13. That is, when the water temperature is lowered, the viscosity of the water is increased, and as a result, the flow rate of the permeated water from the filtration means 11 is reduced, and the flow rate of the treated water produced by the electric deionized water manufacturing apparatus 20 is also reduced. .. Therefore, the control unit 30 increases the supply pressure of the raw water by increasing the rotation speed of the pressurizing pump 13 so as to compensate for this decrease. Further, as the water temperature increases, the viscosity of the water decreases, and as a result, the flow rate of the permeated water from the filtration means 11 increases, and the flow rate of the treated water produced by the electric deionized water production apparatus 20 also increases. .. Therefore, the control unit 30 lowers the supply pressure of the raw water by lowering the rotation speed of the pressurizing pump 13 so as to cancel this increase.

In this way, the first flow rate control adjusts the rotation speed of the pressurizing pump 13, that is, the supply pressure of the raw water, and the flow rate of the treated water flowing through the treated water line L8 is kept constant to produce pure water. Fluctuations in the flow rate of pure water produced by the apparatus 1 can be suppressed.

The flow rate of concentrated water separated by the RO membrane or NF membrane of the filtration means 11 also changes according to the change in the supply pressure of the raw water to the filtration means 11 (change in the rotation speed of the pressurizing pump 13). The concentrated water line L3 is provided with a constant flow valve 15 as described above. Therefore, by the first flow rate control, the flow rate of the concentrated water flowing through the concentrated water line L3 can be kept constant even when the rotation speed of the pressurizing pump 13 changes and the supply pressure of the raw water changes. As a result, the first flow rate control does not affect the flow rate of the concentrated water flowing through the drainage line L4 and the recirculated water line L5, and the second flow rate control described later does not interfere with the first flow rate control. It will be done independently.

Here, the specified flow rate of the constant flow valve 15 may be such that, on the one hand, the film is not clogged due to fouling or scaling, and on the other hand, the film is not damaged due to an increase in pressure loss. However, if the specified flow rate of the constant flow valve 15 is increased more than necessary, the flow rate required for the pressurizing pump 13 becomes larger than necessary, and as a result, the size of the pressurizing pump 13 becomes larger, which consumes energy. It is not preferable in that respect. Therefore, the specified flow rate of the constant flow valve 15 is set in consideration of the permeated flux of the filtering means 11 and the minimum flow rate of the concentrated water required for the filtering means 11, for example, the diameter of the filtering means 11 is about 20.32 cm. When using a (8 inch) RO membrane, the range is 1 to ^{15 m 3 / h.}

By the way, the constant flow valve 15 defines an operating differential pressure range (allowable range of pressure difference between the primary side and the secondary side of the constant flow valve) for operating the constant flow valve 15 normally. Therefore, depending on the conditions, for example, when an RO membrane for medium and high pressure is used as the filtration means 11 or when the water temperature drops extremely, the supply pressure of raw water rises remarkably and the pressure of concentrated water rises. The pressure difference between the primary side and the secondary side of the constant flow valve 15 may exceed the operating differential pressure range. In that case, the flow rate of the concentrated water flowing through the concentrated water line L3 may not be kept constant.

Therefore, the pressure of the concentrated water flowing through the concentrated water line L3 is reduced to the concentrated water line L3 on the upstream side of the constant flow valve 15 (that is, the pressure on the secondary side can be made lower than the pressure on the primary side). A pressure reducing valve may be provided. As a result, even when the supply pressure of raw water to the filtration means 11 rises remarkably, the pressure difference between the primary side and the secondary side of the constant flow rate valve 15 is kept within the operating differential pressure range to keep the constant flow rate valve 15 in place. It can be operated normally, and the flow rate of the concentrated water flowing through the concentrated water line L3 can be kept constant. Further, if the pressure reducing valve is provided, the constant flow rate valve 15 does not operate normally and the flow rate of the concentrated water does not increase. Therefore, the flow rate of the concentrated drainage is adjusted to the target flow rate by the second flow rate control described later. The flow rate of the concentrated water flowing through the recirculation water line L5 does not increase, and the discharge flow rate of the pressurizing pump 13 does not increase. Therefore, there is no possibility that the required flow rate of the permeated water cannot be obtained because the lift of the pressurizing pump 13 is lowered. Further, providing a pressure reducing valve is not only advantageous in terms of safety because the peripheral members (piping, etc.) on the downstream side are not required to have so much pressure resistance, but it is also inexpensive because the pressure resistance is not so high. The availability of general-purpose products is also advantageous in terms of cost. The type of the pressure reducing valve is not particularly limited as long as the pressure of the concentrated water can be reduced within the operating differential pressure range of the constant flow rate valve 15, but the flow rate is equal to or higher than the specified flow rate of the constant flow rate valve 15. It is necessary to select one in which the flow rate of the water flows or the pressure on the secondary side is larger than the sum of the water flow differential pressure of the drainage line L4 and the recirculation water line L5 and the back pressure on the drainage side.

The set flow rate of the treated water in the first flow rate control is not only fixed to be constant, but may be appropriately changed according to the amount of the treated water used at the use point 3. By changing the set flow rate of the treated water according to the amount used at the use point 3 in this way, the power consumption of the pressurizing pump 13 can be suppressed when the amount used is small. Hereinafter, with reference to FIGS. 2 (a) and 2 (b), two configuration examples for changing the set flow rate of the treated water according to the amount used at the use point 3 will be described. 2 (a) and 2 (b) are schematic views showing two such configuration examples, respectively.

In any of the configuration examples shown in FIGS. 2A and 2B, the treated water tank 5 and the treated water tank 5 connected to the electric deionized water production apparatus 20 via the treated water line L8. A water supply pump 6 is provided on the water supply line L10 connecting the use point 3 and feeds the treated water in the treated water tank 5 to the use point 3. In addition, in the configuration example shown in FIG. 2 (a), the treated water tank 5 is provided with a float type water level sensor 7 for measuring the water level in the tank, and in the configuration example shown in FIG. 2 (b), water is sent. The line L10 is provided with a water supply flow meter 8 for measuring the flow rate of the treated water supplied from the treated water tank 5 to the use point 3.

In the configuration example shown in FIG. 2A, the control unit 30 determines the set flow rate of the treated water based on the amount of change in the water level in the treated water tank 5. That is, the control unit 30 calculates the usage amount of the treated water at the use point 3 per unit time from the water level change amount in the treated water tank 5 measured by the water level sensor 7, and newly uses the calculated usage amount. Set as the set flow rate. There is no particular limitation on the method of measuring (calculating) the amount of water level change (change in water level per unit time) in the treated water tank 5, but for example, as the water level sensor 7, there are three water levels of high, medium, and low. When a three-point float switch capable of detecting the above is used, the following calculation method can be used. As an example, if the water level changes from the medium water level to the low water level, the water level change amount V at that time corresponds to the low water level after the operation time interval of the float switch (the float switch corresponding to the medium water level is turned off). It is calculated from V = L / t, where t is the time until the float switch is turned off and L is the amount of water held corresponding to the difference in water level between the medium water level and the low water level. However, if the amount of water level change cannot be calculated, such as when the water level of the treated water tank 5 is between two float switches when the device is started or when the operation is restarted, the set flow rate of the treated water is set until it can be calculated. Needless to say, a predetermined value is used as. The water level sensor 7 is not limited to the float type described above, and may be a continuous type such as an ultrasonic type, a capacitance type, a differential pressure type, and a laser type, in which case the water level sensor 7 is detected. By dividing the amount of water held into small pieces, it is possible to shorten or eliminate the period during which the amount of change in water level cannot be calculated.

On the other hand, in the configuration example shown in FIG. 2B, the control unit 30 determines the set flow rate of the treated water based on the flow rate of the treated water sent from the treated water tank 5 to the use point 3. That is, the control unit 30 calculates the usage amount of the treated water at the use point 3 per unit time from the flow rate of the treated water measured by the water supply flow meter 8, and sets the calculated usage amount as a new set flow rate. To do.

In the second flow rate control, concentrated drainage (concentrated water flowing through the drainage line L4) in consideration of the recovery rate of the membrane filtration device 10 (ratio of the flow rate of the permeated water to the sum of the flow rate of the permeated water and the flow rate of the concentrated drainage). The opening degree of the flow rate adjusting valve 16 is adjusted so that the target flow rate of the above is calculated and the flow rate of the concentrated drainage detected by the drainage flow meter 17 becomes the target flow rate. The recovery rate at this time is preferably as high as possible from the viewpoint of effective use of water (water saving). That is, it is preferable that the flow rate of concentrated waste water is as small as possible. However, since the flow rate of the concentrated water is kept constant by the constant flow valve 15, when the flow rate of the concentrated drainage decreases, the flow rate of the concentrated water returning from the reflux water line L5 to the supply line L1 naturally increases. To do. As a result, when the concentration of impurities in the raw water increases, scaling in which impurities (particularly silica or calcium) are precipitated on the film surface of the RO film or NF film of the filtration means 11 tends to occur. Therefore, the flow rate of the concentrated waste water maximizes the recovery rate in the range where the impurity concentration of the concentrated water does not exceed the solubility, that is, the recovery rate is maximized in the range where the impurities silica or calcium do not precipitate. Is set.

However, the solubility of impurities changes depending on the water temperature. For example, in the case of silica, its solubility increases in proportion to temperature, and in the case of calcium (calcium carbonate), its solubility decreases as the temperature rises. Therefore, when the water temperature is low, the solubility of silica is relatively low and silica is likely to be precipitated (silica scale is likely to be generated), but when the water temperature is high, the solubility of calcium is relatively low and therefore calcium. Is likely to precipitate (calcium scale is likely to be generated). Therefore, although not shown, the membrane filtration device 10 is provided with a temperature sensor (water temperature detecting means) for detecting the temperature of any one of raw water, permeated water, and concentrated water, and the temperature sensor detects the temperature. The optimum target flow rate of concentrated wastewater is calculated based on the water temperature.

Specifically, first, the theoretical recovery rate at which silica precipitates at the detected water temperature (hereinafter referred to as "silica precipitation recovery rate") and the theoretical recovery rate at which calcium (calcium carbonate) precipitates at the detected water temperature. Recovery rate (hereinafter referred to as "calcium precipitation recovery rate") is calculated. The methods for calculating the silica precipitation recovery rate and the calcium precipitation recovery rate will be described later. Next, the precipitation recovery rate of silica and the precipitation recovery rate of calcium are compared, and the smaller precipitation recovery rate is set as the target recovery rate. Then, based on this target recovery rate and the flow rate of the permeated water detected by the permeated water flow meter 14, the target flow rate of the concentrated wastewater is calculated and set by the following formula (1).
(Flow rate of concentrated wastewater) = (Flow rate of permeated water / Target recovery rate)-(Flow rate of permeated water) (1)

From the viewpoint of surely suppressing the occurrence of scaling, a flow rate exceeding the flow rate calculated by the above formula (1) can be set as the target flow rate of the concentrated wastewater, but it is calculated from the viewpoint of water saving. It is preferable to set the flow rate as the target flow rate of concentrated wastewater.

Here, a method for calculating the precipitation recovery rate of silica and the precipitation recovery rate of calcium will be described respectively.

(Calculation method of silica precipitation recovery rate)
Precipitation recovery rate Y _S of the silica, when the solubility of silica in the detected water temperature (mg / L) and C _S, premeasured silica concentration of the raw water (mg / L) was F _S, the following Calculated from equation (2).
_{Y S = (C S -F S} ) / C S (2)

As a method for calculating the solubility of silica, a method specified in ASTM (American Society for Testing and Materials) D4993-89 or the like can be used.

(Calcium precipitation recovery rate calculation method)
The precipitation recovery rate of calcium is calculated by using a method of calculating the Langeria index of concentrated water. Here, the Langeria index (saturation index) is an index showing the possibility of precipitation of calcium (calcium carbonate), and the actual pH of water and the theoretical pH (pHs: calcium carbonate in water do not dissolve or precipitate). It means the difference (pH-pHs) from pH) in an equilibrium state. That is, when the Langeria index is a positive value and the absolute value is large, calcium carbonate is more likely to be precipitated, and when the value is negative, calcium carbonate is not precipitated. Therefore, the calcium precipitation recovery rate is calculated as the recovery rate when the Langeria index of concentrated water becomes zero. In order to set the value on the safer side, the calcium precipitation recovery rate may be the recovery rate when the Langeria index of the concentrated water becomes a negative value.

The Langeria index of concentrated water is calculated from the pH of the concentrated water, the impurity concentration (calcium concentration, total alkalinity, and evaporation residue concentration) of the concentrated water, and the detected water temperature. As a method for calculating the Langeria index, for example, the method described in JP-A-11-267687 (paragraphs [0025] to [0027]) can be used. In addition, the impurity concentration (calcium concentration, total alkalinity, and evaporation residue concentration) of the concentrated water is the impurity concentration (calcium concentration, total alkalinity, and evaporation residue concentration) of the raw water measured in advance, and the recovery rate. It is calculated from. Accordingly, precipitation recovery rate Y _C of calcium, the impurity concentration of the impurity concentration of the concentrated water when Langelier index of concentrated water becomes zero (mg / L) and C _C, the raw water that is measured in advance (mg / L) the when the F _C, will be represented by the relationship of equation (3) below.
_{Y C = (C C -F C} ) / C C (3)

The method of calculating the precipitation recovery rate of silica and calcium and the method of calculating the target flow rate of concentrated wastewater are limited in advance due to device design restrictions such as the capacity of the pressurizing pump and the flow rate of raw water. In some cases, this is not the case as described above.

When the recovery rate is controlled as described above, it is preferable to use an electric proportional control valve as the flow rate adjusting valve 16 for adjusting the flow rate of the concentrated waste water. As a result, the opening degree can be finely adjusted according to the resolution of the electric proportional control valve, and the recovery rate can be smoothly adjusted as compared with the stepwise opening degree adjustment by a combination of solenoid valves or the like. For example, in a step system in which the recovery rate in the range of 50 to 70% can be controlled only in 5 steps (50%, 55%, 60%, 65%, 70%), when the target recovery rate is set to 64%, The recovery rate can only be adjusted to 60%, resulting in wasteful concentrated wastewater. Therefore, using the electric proportional control valve as the flow rate adjusting valve 16 is advantageous from the viewpoint of water saving because it is possible to reduce the waste of such concentrated wastewater. Further, as described above in relation to FIG. 2, when the set flow rate of the treated water is changed according to the amount used at the use point 3 in the first flow rate control, the set flow rate is frequently changed. , The flow rate of the permeated water from the membrane filtration device 10 also fluctuates frequently. Therefore, in the stepwise formula as described above, the recoverable recovery rate that can be set changes irregularly, and the actual recovery rate becomes unstable. Therefore, using the electric proportional control valve as the flow rate adjusting valve 16 is also advantageous in that the recovery rate can be stably maintained even in such a configuration in which the flow rate of the permeated water can fluctuate.

In order to realize further water saving, it is necessary to set a higher target value of the recovery rate, but in the present embodiment, a scale inhibitor is added to the raw water for the purpose of increasing the above-mentioned precipitation recovery rate. You may be able to do it. In this case, the specified flow rate of the constant flow rate valve 15 can be reduced within a range not lower than the minimum flow rate of the concentrated water, and as a result, energy saving can be realized by using the pressurizing pump 13 having a smaller capacity. .. The addition of the anti-scale agent can be done by a chemical injection pump.

The scale inhibitor is not limited to a specific substance as long as it is a substance capable of suppressing the precipitation of scale components such as silica and calcium. Examples thereof include phosphonic acids such as 1-hydroxyethylidene-1,1-diphosphonic acid, 2-phosphonobutane-1,2,4-tricarboxylic acid, ethylenediaminetetramethylenephosphonic acid, and nitrilotrimethylphosphonic acid and salts thereof. Phosphonic acid-based compounds; phosphoric acid-based compounds such as orthophosphates and polymerized phosphates; maleic acid-based compounds such as polymaleic acid and maleic acid copolymers; acrylic acid-based polymers, and the like. Is a copolymer of poly (meth) acrylic acid, maleic acid / (meth) acrylic acid, (meth) acrylic acid / sulfonic acid, (meth) acrylic acid / nonionic group-containing monomer, and (meth) acrylic acid / sulfonic acid. / Nonion group-containing monomer, (meth) acrylic acid / acrylamide-alkylsulfonic acid / substituted (meth) acrylamide, (meth) acrylic acid / acrylamide-arylsulfonic acid / substituted (meth) acrylamide tarpolymer and the like can be mentioned. Examples of the (meth) acrylic acid constituting the terpolymer include methacrylic acid and acrylic acid, and (meth) acrylates such as sodium salts thereof. Examples of the acrylamide-alkyl sulfonic acid constituting the terpolymer include 2-acrylamide-2-methylpropane sulfonic acid and a salt thereof. Examples of the substituted (meth) acrylamide constituting the terpolymer include t-butyl acrylamide, t-octyl acrylamide, and dimethyl acrylamide.

Among these, it is preferable to use one containing at least one of a phosphonic acid-based compound and an acrylic acid-based polymer. In addition, in order to suppress the scale derived from calcium and silica at the same time, 2-phosphonobutane-1,2,4-tricarboxylic acid, acrylic acid and (meth) acrylic acid / 2-acrylamide-2-methylpropanesulfonic acid It is particularly preferred to use an anti-scale agent consisting of a mixture of / substituted (meth) acrylamide with a terpolymer.

Commercially available scale inhibitors for RO membranes include the "Olpage" series manufactured by Organo Corporation, the "Flocon (registered trademark)" series manufactured by BWA Water Adaptives, and the "PermaTreat (registered trademark)" manufactured by Nalco. Series, "Hyperspace (registered trademark)" series manufactured by General Electric Co., Ltd., "Cliberter (registered trademark)" series manufactured by Kurita Water Industries, Ltd., and the like.

For example, when the device is started or the operation is restarted, the water permeated from the membrane filtration device 10 to the electric deionized water production device 20 until the water quality of the permeated water from the membrane filtration device 10 reaches a certain level or higher. The supply can be stopped and the permeated water can be circulated in the membrane filtration device 10. That is, by switching the three-way valve 12, the permeated water separated by the filtration means 11 can be returned to the raw water tank 2 through the permeated water return line L6 and returned to the supply line L1. During such a circulation operation, the treated water does not flow through the treated water line L8, so that the control unit 30 cannot execute the first flow rate control that controls the pressurizing pump 13 according to the flow rate of the treated water. Therefore, instead of the first flow rate control, the control unit 30 pressurizes the flow rate of the circulating permeated water, specifically, the flow rate of the permeated water detected by the permeated water flow meter 14 to a set flow rate. A third flow rate control that controls the pump 13 can be performed. Alternatively, the control unit 30 can keep the rotation speed of the pressurizing pump 13 constant when the membrane filtration device 10 is circulated.

As described above, in the present embodiment, since the flow rate of the concentrated water is kept constant by the constant flow valve 15, it is only necessary to specify the flow rate of the concentrated water flowing through one of the drainage line L4 and the recirculation water line L5, and the other. The flow rate of concentrated water flowing through the water can also be specified. Therefore, in the illustrated embodiment, the drainage line L4 is provided with the flow rate adjusting valve 16 and the drainage flowmeter 17 as the flow rate control means, and the recirculation water line L5 is provided with the manual valve 18 for adjusting the pressure balance. The reverse may be true. That is, the recirculation water line L5 may be provided with a flow rate adjusting valve (proportional control valve) and a flow meter as the flow rate control means, and the drainage line L4 may be provided with a manual valve for adjusting the pressure balance. Alternatively, both the drainage line L4 and the recirculation water line L5 may be provided with a flow rate adjusting valve (proportional control valve) and a flow meter as flow rate control means. Further, in the above-described embodiment, the first flow rate control and the second flow rate control are performed by one control unit, but the control unit for the first flow rate control and the second flow rate control unit. It may be provided separately.
(Second embodiment)
FIG. 3 is a schematic view showing the configuration of the membrane filtration apparatus according to the second embodiment of the present invention. This embodiment is a modification of the first embodiment, and is a modification in which the configuration of the membrane filtration apparatus is changed. Therefore, the pure water production apparatus of the present embodiment has the same configuration as that of the first embodiment except for the configuration of the membrane filtration apparatus. Hereinafter, the same configurations as those of the first embodiment will be described by adding the same reference numerals to the drawings and omitting the description thereof, and only the configurations different from those of the first embodiment will be described.

In the present embodiment, in addition to the filtration means (first filtration means) 11 of the first embodiment, another filtration means (second filtration means) 41 is provided on the downstream side thereof. The second filtration means 41 is connected in series with the first filtration means 11, and the permeated water separated by the first filtration means 11 is treated as the water to be treated. That is, the second filtration means 41 is connected to the first filtration means 11 via the first permeated water line L2, and is connected to the electric deionized water production apparatus 20 via the second permeated water line L11. Has been done. As a result, the membrane filtration device 10 of the present embodiment can generate permeated water having better water quality than that of the first embodiment. In this embodiment, the permeated water flow meter 14 and the three-way valve 12 are provided on the second permeated water line L11.

A second concentrated water line L12 for circulating concentrated water from the second filtering means 41 is connected to the second filtering means 41. In the second filtration means 41, the permeated water from the first filtration means 11 is further separated into permeated water and concentrated water. Therefore, from the viewpoint of water quality, the concentrated water from the second filtration means 41 is not necessarily external. There is no need to discharge to. Therefore, the second concentrated water line L12 is connected to the raw water tank 2 from the viewpoint of saving water, and all the concentrated water separated by the second filtration means 41 is returned to the raw water tank 2. In the second concentrated water line L12, a part or all of the concentrated water from the second filtering means 41 is discharged to the outside when the RO membrane or the NF membrane of the second filtering means 41 is washed. A drainage line may be connected.

The second concentrated water line L12 is provided with a manual valve 42 and a concentrated water flow meter 43 for adjusting the flow rate of the concentrated water flowing through the second concentrated water line L12. Further, in the present embodiment, as described above, the permeated water flow meter 14 is provided on the second permeated water line L11. As a result, the recovery rate of the second filtration means 41 (from the second filtration means 41 with respect to the sum of the flow rate of the permeated water from the second filtration means 41 and the flow rate of the concentrated water from the second filtration means 41). Permeated water flow rate ratio) can be adjusted arbitrarily. In addition, in order to eliminate the complexity of manually adjusting the recovery rate, a proportional control valve capable of adjusting the opening degree based on the flow rate of the concentrated water detected by the concentrated water flow meter 43 is provided instead of the manual valve 42. It may have been. Alternatively, in order to keep the recovery rate within a certain range, a constant flow rate valve may be provided instead of the manual valve 42 and the concentrated water flow meter 43. As a constant flow rate valve at this time, the flow rate of concentrated water from the second filtration means 41 (that is, the specified flow rate of the constant flow rate valve) is 1/20 of the flow rate of the permeated water from the second filtration means 41. It is preferable to select one that is ~ 1/2 times larger. This is because the permeated water from the first filtration means 11 having a low impurity concentration is supplied to the second filtration means 41, so that the recovery rate of the second filtration means 41 is set high from the viewpoint of water saving. This is because it is preferable. Further, when the constant flow rate valve is provided in the second concentrated water line L12, as in the case of the constant flow rate valve 15 of the first filtration means 11, depending on the conditions, the primary side and the secondary side of the constant flow rate valve The pressure difference on the side may exceed the operating differential pressure range, but in order to avoid this, a pressure reducing valve may be provided on the upstream side of the constant flow rate valve.

In the present embodiment, the flow meter is not provided in the first permeated water line L2, but the control unit 30 indirectly detects the flow rate of the permeated water flowing through the first permeated water line L2. The flow rate control of 2 can be executed. That is, the control unit 30 has a measured value by the permeated water flow meter 14 (flow rate of permeated water from the second filtering means 41) and a measured value by the concentrated water flow meter 43 (concentrated water from the second filtering means 41). The flow rate of the permeated water flowing through the first permeated water line L2 can be calculated from the sum of the flow rate and the flow rate of the permeated water. Further, as described above, when a constant flow valve is provided instead of the manual valve 16 and the concentrated water flow meter 17, the specified flow rate of the constant flow valve is used instead of the value measured by the concentrated water flow meter 43. , The flow rate of the permeated water flowing through the first permeated water line L2 can be calculated. Alternatively, a flow meter (not shown) may be provided on the first permeated water line L2 to directly detect the flow rate of the permeated water from the first filtration means 11.

In the present embodiment, since it is necessary to supply the raw water to the two filtration means 11 and 41 by one pressurizing pump 13, the supply pressure of the raw water to the first filtration means 11 by the pressurizing pump 13 is determined. It is larger than that of the first embodiment. Therefore, the specified flow rate of the constant flow rate valve 15 needs to be set in consideration of this point as well. For example, when RO membranes having a diameter of about 20.32 cm (8 inches) are used as the two filtration means 11 and 41, when the applicable temperature range of the first filtration means 11 is 5 to 35 ° C., for example, a constant flow rate. As the valve 15, a constant flow valve manufactured by Keihin Co., Ltd. (product number: NSPW-25, set flow rate: 55 L / min) can be used.

In the present embodiment, two filtration means are connected in series, but the number of filtration means is not limited to this, and three or more filtration means may be provided in series. .. Even in that case, a constant flow valve is provided in the concentrated water line connected to the most upstream filtration means among the three or more filtration means, and the flow rate of the permeated water flowing through the permeated water line connected to the filtration means. The second flow rate control is executed based on. The term "connected in series" here means that the water to be treated is sequentially treated by a plurality of filtration means, and is separated by the upstream filtration means in the two adjacent filtration means. This means that the permeated water is supplied to the filtration means on the downstream side as water to be treated.

1 Pure water production equipment 2 Raw water tank 3 Use points 4,12 Three-way valve 5 Treated water tank 6 Water supply pump 7 Water level sensor 8 Water supply flow meter 10 Membrane filtration device 11 Filtration means (first filtration means)
13 Pressurized pump 14 Permeate water flow meter 15 Constant flow valve 16 Flow control valve 17 Drainage flow meter 18, 23a to 23c, 25a to 25c Manual valve 20 Electric deionized water production equipment 21 Anode 22 Cathode 24 Treated water flow meter 30 Control unit D Desalting chamber C1 Anode side concentrating chamber C2 Cathode side concentrating chamber E1 Anode chamber E2 Cathode chamber a1, a2 Anion exchange membrane c1, c2 Cation exchange membrane L1 Supply line L2 Permeated water line (first permeated water line)
L3 concentrated water line (first concentrated water line)
L4 Drainage line L5 Reflux water line L6 Second concentrated water line L7 Raw water supply line L8 Treated water line L9 Treated water return line L10 Water supply line L11 Second permeated water line L12 Second concentrated water line L21 First branch line L22 2nd branch line L23 3rd branch line L24 Concentrated water discharge line L25 Electrode water discharge line

Claims (10)

A pure water production device that sequentially treats water to be treated to produce pure water.
A membrane filtration device, an electric deionized water production device connected to the downstream side of the membrane filtration device and supplied with permeated water from the membrane filtration device, the membrane filtration device and the electric deionized water production device. Has a control unit that controls the operation of
The membrane filtration device has a filtration means having a back-penetration membrane or a nanofiltration membrane that separates the water to be treated into permeated water and concentrated water, a supply line for supplying the water to be treated to the filtration means, and the filtration means. A permeated water line that circulates the permeated water, a concentrated water line that circulates the concentrated water from the filtration means, and a part of the concentrated water that branches from the concentrated water line and flows through the concentrated water line is discharged to the outside. A drainage line, a recirculation water line that branches from the concentrated water line and returns the rest of the concentrated water flowing through the concentrated water line to the supply line, and a recirculated water line provided in the supply line and treated with water to the filtration means. A pressure adjusting means for adjusting the supply pressure, a constant flow valve provided in the concentrated water line to keep the flow rate of the concentrated water flowing through the concentrated water line constant, and a constant flow valve provided in the drain line and flowing through the drain line. It has a flow rate adjusting means for adjusting the flow rate of concentrated water, and has.
The electric deionized water production apparatus is located between the anode and the cathode, is partitioned by the anion exchange membrane on the anode side and the cation exchange membrane on the cathode side, and at least the cation exchanger and the anion exchanger. It has a desalting chamber filled with one of them, and a treated water line for circulating the treated water obtained by passing the permeated water from the membrane filtration device through the desalting chamber.
The control unit controls the pressure adjusting means so that the flow rate of the treated water flowing through the treated water line becomes a set flow rate, and the drainage line is based on the flow rate of the permeated water flowing through the permeated water line. The target flow rate of the concentrated water flowing through the drainage line is calculated, and the second flow rate control for controlling the flow rate adjusting means so that the flow rate of the concentrated water flowing through the drainage line becomes the target flow rate is executed independently and in parallel. Pure water production equipment. In the second flow rate control, the control unit is the ratio of the flow rate of the permeated water flowing through the permeated water line to the sum of the flow rate of the permeated water flowing through the permeated water line and the flow rate of the concentrated water flowing through the drainage line. The pure water production apparatus according to claim 1, wherein the target flow rate is calculated so that a certain recovery rate becomes a predetermined value. The control unit determines the recovery rate of the filtration means based on the water temperature of any one of the water to be treated, the permeated water from the filtration means, and the concentrated water from the filtration means. The pure water production apparatus according to claim 2, wherein the target flow rate is calculated so that the maximum recovery rate at which silica or calcium does not precipitate on the membrane surface of the reverse osmosis membrane or the nanofiltration membrane is calculated. It has a treated water tank connected to the electric deionized water production apparatus via the treated water line.
The pure water production apparatus according to any one of claims 1 to 3, wherein the control unit determines the set flow rate based on the amount of change in the water level in the treated water tank in the first flow rate control. .. It has a treated water tank connected to the electric deionized water production apparatus via the treated water line.
The control unit determines the set flow rate based on the flow rate of the treated water sent from the treated water tank to the use point in the first flow rate control, according to any one of claims 1 to 3. The pure water production apparatus described. The electric deionized water production apparatus was arranged on both sides of the desalting chamber via the anode chamber provided with the anode, the cathode chamber provided with the cathode, and the anion exchange membrane and the cation exchange membrane. It has a pair of concentrating chambers and
The permeated water line includes a line that supplies permeated water to the desalting chamber, a line that supplies permeated water to the anode chamber and the cathode chamber, and a line that supplies permeated water to the pair of concentrating chambers. The item according to any one of claims 1 to 5, which is branched into one line, and at least two of the three lines are provided with a flow rate adjusting means for adjusting the flow rate of the permeated water flowing through the line. The pure water production apparatus described. The pure water production apparatus according to claim 6, wherein the flow rate adjusting means is a constant flow valve. When the control unit stops the supply of permeated water from the membrane filtration device to the electric deionized water production device, instead of the first flow control, the permeated water separated by the filtration means is used. Any one of claims 1 to 7, wherein the third flow control is executed by circulating the water back to the supply line and controlling the pressure adjusting means so that the flow rate of the circulated permeated water becomes a set flow rate. The pure water production apparatus according to. Any one of claims 1 to 8, wherein the membrane filtration device is provided in the concentrated water line on the upstream side of the constant flow valve and has a pressure reducing valve for reducing the pressure of the concentrated water flowing through the concentrated water line. The pure water production apparatus according to. The pure water according to any one of claims 1 to 9, wherein the membrane filtration device has at least one other filtration means connected in series via the permeated water line on the downstream side of the filtration means. Manufacturing equipment.

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