JP7045814B2 - Membrane filtration device - Google Patents

Description

The present invention relates to a membrane filtration apparatus having a reverse osmosis membrane or a nanofiltration membrane.

As a water treatment device for removing impurities contained in water to be treated, a membrane filtration device having a reverse osmosis membrane (RO membrane) or a nanofiltration membrane (NF membrane) is known. In this device, the water to be treated (raw water) supplied to the RO membrane or the NF membrane at a predetermined supply pressure is separated into permeated water and concentrated water by the RO membrane or the NF membrane. As a result, treated water (permeated water) from which impurities have been removed is obtained.

In membrane filtration devices with RO membranes or NF membranes, in many cases, from the viewpoint of effective use of water (water saving), part of the concentrated water containing impurities is discharged to the outside as concentrated wastewater, and the rest is used as concentrated reflux water. A configuration is adopted in which the water is refluxed to the upstream side of the RO membrane or the NF membrane. As a result, the recovery rate (the ratio of the permeated water flow rate to the sum of the permeated water flow rate and the concentrated drainage flow rate) can be improved as compared with the case where all the concentrated water is discharged as concentrated wastewater, and water saving can be achieved. It can be realized.

At the same time, in the membrane filtration device, in order to respond to the change in the flow rate of the permeated water due to the change in the water temperature (that is, the change in the viscosity of the water), the rotation speed of the pressurizing pump is controlled to change to the RO membrane or the NF membrane. The flow rate is also controlled to maintain a constant flow rate of the permeated water by adjusting the supply pressure of the raw water (see, for example, Patent Document 1).

Japanese Unexamined Patent Publication No. 2005-296945

By the way, the method of adjusting the supply pressure of raw water by controlling the rotation speed of the pressurizing pump is relatively easy by using a general-purpose inverter when using a pressurizing pump that operates with a three-phase 200V AC power supply. Is feasible. However, for example, when using a pressurizing pump that operates with a single-phase 100V AC power supply, it is difficult to obtain a corresponding general-purpose inverter, and therefore it is difficult to even control the rotation speed of the pressurizing pump. .. Therefore, the above method is substantially limited to an environment where a three-phase 200V AC power supply can be used, and cannot be said to be highly versatile as a method for controlling the flow rate of permeated water.

Therefore, an object of the present invention is to provide a highly versatile and highly versatile membrane filtration device that realizes stable flow rate control.

In order to achieve the above-mentioned object, the membrane filtration device according to one aspect of the present invention is a plurality of filtering means connected in series, each of which is back-permeated to separate the water to be treated into permeated water and concentrated water. A supply line connected to a plurality of filtering means having a membrane or a nano-filtering membrane, the most upstream filtering means among the plurality of filtering means, and supplying water to be treated to the most upstream filtering means, and the most upstream side. From the first permeated water line connected to the filtering means and flowing the permeated water from the most upstream filtering means, and from the most downstream filtering means connected to the most downstream filtering means among the plurality of filtering means . A second permeated water line that circulates the permeated water, a concentrated water line that is connected to the most upstream filtering means and that circulates concentrated water from the most upstream filtering means, and a concentrated water line that branches off from the concentrated water line and concentrates. A drainage line that discharges a part of the concentrated water flowing through the water line to the outside, and a recirculation water line that branches off from the concentrated water line and is connected to the supply line and returns the rest of the concentrated water flowing through the concentrated water line to the supply line. , A vane pump provided in the supply line that supplies a constant flow of water to be treated to the most upstream filtering means, and a first flow control means that adjusts the flow rate of the permeated water flowing through the second permeated water line to a set flow rate. Based on the flow rate adjusting valve provided in the concentrated water line, the flow rate detecting means for detecting the flow rate of the permeated water flowing through the second permeated water line, and the flow rate of the permeated water detected by the flow rate detecting means. A first flow control means having a control unit for adjusting the opening degree of the flow control valve, and a second flow control means for adjusting the flow rate of concentrated water flowing through the drain line to a set flow rate. Control to adjust the opening degree of the flow control valve based on the flow rate adjusting valve provided in, the flow rate detecting means for detecting the flow rate of the concentrated water flowing through the drainage line, and the flow rate of the concentrated water detected by the flow rate detecting means. A second flow control means having a unit, and a control unit of the second flow control means includes a flow rate of permeated water flowing through the first permeated water line and a flow rate of concentrated water flowing through the drainage line. The set flow rate of the concentrated water flowing through the drainage line is determined so that the recovery rate, which is the ratio of the flow rate of the permeated water flowing through the first permeated water line to the sum of the above, becomes a predetermined value .

Further, the membrane filtering device according to another aspect of the present invention is a plurality of filtering means connected in series, each of which has a back-penetrating membrane or a nano-filtering membrane that separates the water to be treated into permeated water and concentrated water. It is connected to a plurality of filtering means having, a supply line connected to the most upstream filtering means among the plurality of filtering means, and supplying water to be treated to the most upstream filtering means, and connected to the most upstream filtering means. The first permeated water line that circulates the permeated water from the most upstream filtering means is connected to the most downstream filtering means among the plurality of filtering means, and the permeated water from the most downstream filtering means is circulated. The second permeated water line, the concentrated water line connected to the most upstream filtering means and circulating the concentrated water from the most upstream filtering means, and the concentrated water branching from the concentrated water line and flowing through the concentrated water line. A drainage line that discharges a part of the water to the outside, a recirculation water line that branches from the concentrated water line and is connected to the supply line, and returns the rest of the concentrated water flowing through the concentrated water line to the supply line, and a recirculation water line provided in the supply line. A pressurizing pump that operates with a single-phase 100V AC power supply, a constant flow valve that is installed in the concentrated water line and keeps the flow of concentrated water flowing through the concentrated water line constant, and a permeation flowing through the second permeated water line. A first flow control means for adjusting the flow rate of water to a set flow rate, a flow rate adjusting valve provided on the supply line, a flow rate detecting means for detecting the flow rate of the permeated water flowing through the second permeated water line, and a flow rate detecting means. A first flow control means having a control unit for adjusting the opening degree of the flow control valve based on the flow rate of the permeated water detected by the flow rate detecting means, and the flow rate of the concentrated water flowing through the drainage line as the set flow rate. The second flow control means for adjusting, the flow control valve provided in the drain line, the flow detection means for detecting the flow rate of the concentrated water flowing through the drain line, and the flow rate of the concentrated water detected by the flow detection means. The control unit of the second flow control means has a second flow control means having a control unit for adjusting the opening degree of the flow control valve based on the above, and the control unit of the second flow control means has a first permeated water line. Concentration flowing through the drainage line so that the recovery rate, which is the ratio of the flow rate of the permeated water flowing through the first permeated water line to the sum of the flow rate of the permeated water flowing through the drainage line and the flow rate of the concentrated water flowing through the drainage line, becomes a predetermined value. Determine the set flow of water .

According to such a membrane filtration device, as a method of controlling the flow rate of permeated water, it is not necessary to control the rotation speed of the pump, so that it can be used in various environments and high versatility can be realized. ..

As described above, according to the present invention, it is possible to provide a highly versatile membrane filtration device that realizes stable flow rate control.

It is a schematic diagram which shows the structure of the membrane filtration apparatus which concerns on 1st Embodiment of this invention. It is a schematic diagram which shows the structure of the membrane filtration apparatus which concerns on 2nd Embodiment of this invention. It is a schematic diagram which shows the structure of the membrane filtration apparatus which concerns on 3rd Embodiment of this invention. It is a schematic diagram which shows the structure of the membrane filtration apparatus which concerns on 4th Embodiment of this invention.

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

(First Embodiment)
FIG. 1 is a schematic view showing the configuration of the membrane filtration device according to the first embodiment of the present invention.

The membrane filtration device 10 of the present embodiment is a device that removes impurities contained in raw water (water to be treated) to generate treated water, and the raw water is permeated with concentrated water containing impurities and permeation from which impurities have been removed. It has a filtering means 11 that separates from water. 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 plurality of lines connected to the filtration means 11, that is, a supply line 1 for supplying raw water to the filtration means 11, and a permeation water line 2 for circulating the permeated water from the filtration means 11. It also has a concentrated water line 3 for circulating concentrated water from the filtration means 11. In addition, the membrane filtration device 10 has two lines branched from the concentrated water line 3, that is, a drainage line 4 for discharging a part of the concentrated water flowing through the concentrated water line 3 to the outside, and a supply line for supplying the rest of the concentrated water. It has a reflux water line 5 for refluxing to 1. The recirculated water line 5 is connected to the supply line 1 on the upstream side of the metering pump 12, which will be described later, after branching from the concentrated water line 3. The recirculated water line 5 may be connected to a raw water tank (not shown) provided in the supply line 1 instead of being directly connected to the supply line 1.

Further, the membrane filtration device 10 is provided in the supply line 1 and has a metering pump 12 that supplies a constant flow rate of raw water to the filtration means 11 and a permeated water flow rate that adjusts the flow rate of the permeated water flowing through the permeated water line 2 to a set flow rate. It has a control mechanism (first flow rate control means) 20. The permeated water flow rate control mechanism 20 includes a flow rate adjusting valve 21 provided in the concentrated water line 3, a permeated water flow meter (flow rate detecting means) 22 for detecting the flow rate of the permeated water flowing through the permeated water line 2, and a permeated water flow rate. It has a permeated water flow rate control unit 23 that adjusts the opening degree of the flow rate adjusting valve 21 based on the flow rate of the permeated water detected by the total 22.

The permeated water flow rate control unit 23 controls the opening degree of the flow rate adjusting valve 21 so that the flow rate of the permeated water detected by the permeated water flow meter 22 becomes constant (a preset target flow rate). For example, when the water temperature changes, the viscosity of the water changes, so that the flow rate of the permeated water separated by the RO membrane or the NF membrane also changes. In response to this change, the permeated water flow rate control unit 23 controls the opening degree of the flow rate adjusting valve 21. That is, as the water temperature decreases, the viscosity of the water increases, and as a result, the flow rate of the permeated water separated by the RO membrane or the NF membrane decreases. Therefore, the permeated water flow rate control unit 23 controls to close the flow rate adjusting valve 21 in order to compensate for this decrease, and the pressure of the raw water applied to the RO membrane or the NF membrane (the pressure of supplying the raw water to the filtration means 11). ) Is increased. Further, as the water temperature increases, the viscosity of the water decreases, and as a result, the flow rate of the permeated water separated by the RO membrane or the NF membrane increases. Therefore, the permeated water flow rate control unit 23 controls to open the flow rate adjusting valve 21 in order to cancel this increase, and reduces the supply pressure of the raw water. In this way, the permeated water flow rate control unit 23 can maintain the permeated water flow rate constant by adjusting the opening degree of the flow rate adjusting valve 21 to adjust the pressure of the raw water applied to the RO membrane or the NF membrane. can.

Further, in the present embodiment, even with respect to such a pressure change of raw water, as described above, since the metering pump 12 is provided in the supply line 1, the flow rate of the concentrated water flowing through the concentrated water line 3 can be increased. Can be kept constant. That is, the metering pump 12 has a function of keeping the discharge flow rate constant when the pressure of the raw water flowing through the supply line 1 is constant or higher. Therefore, even when the opening degree of the flow rate adjusting valve 21 is changed by the permeated water flow rate control unit 23 and the pressure of the raw water applied to the RO membrane or the NF membrane is changed, the flow rate of the raw water supplied to the filtration means 11 is constant. It can be kept constant, so that the flow rate of the concentrated water can also be kept constant.

In this way, the flow rate of the concentrated water separated by the filtering means 11 is always kept constant, so that the flow rate control of the permeated water does not affect the flow rate of the concentrated water flowing through the drainage line 4 and the recirculated water line 5. .. As a result, no matter what flow rate control is performed in the drainage line 4 or the recirculation water line 5, it does not interfere with the flow rate control of the permeated water, so that hunting can be avoided. Further, since the above-mentioned method of controlling the flow rate of permeated water does not need to control the rotation speed of the pump, it can be carried out, for example, when a pressurizing pump operating with a single-phase 100V AC power supply is used. Therefore, high versatility can be realized as a method of controlling the flow rate of permeated water.

The type of the metering pump 12 used in the present embodiment is not particularly limited as long as the discharge flow rate can be kept constant when the pressure of the raw water is constant or higher. Here, "constant" means that the discharge flow rate is not only strictly constant but also may fluctuate (pulsate) within a predetermined error range. Therefore, examples of the metering pump 12 include a vane pump, a diaphragm pump, a plunger pump, a piston pump, a screw pump, and the like. Among them, it is preferable to use a vane pump and a diaphragm pump in terms of low noise and compactness, and it is more preferable to use a vane pump in terms of less pulsation than other pumps.

The specified discharge flow rate of the metering pump 12 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, increasing the specified discharge flow rate of the metering pump 12 more than necessary leads to an increase in the size of the metering pump 12, which is not preferable in terms of energy consumption. Therefore, the specified discharge flow rate of the metering pump 12 is set in consideration of the permeation flux of the filtration means 11 and the minimum flow rate of the concentrated water required for the filtration means 11, for example, the diameter of the filtration means 11 is about 10.16 cm. When a (4 inch) RO membrane is used, the range is 300 to 1800 L / h according to the properties of the raw water.

As described above, the flow rate of the concentrated water is always kept constant by adjusting the opening degree of the metering pump 12 and the flow rate adjusting valve 21, so that the flow rate control of the permeated water does not affect the flow rate of the concentrated water. As a result, it becomes possible to easily control the flow rate of the concentrated water flowing through the drainage line 4 or the recirculation water line 5. In the present embodiment, a drainage flow rate control mechanism (second flow rate control means) 30 for adjusting the flow rate of the concentrated water flowing through the drainage line 4 (hereinafter referred to as “concentrated drainage”) to a set flow rate is provided. The flow rate control of the concentrated drainage by the drainage flow rate control mechanism 30 is performed independently of the flow rate control of the permeated water by the permeated water flow rate control mechanism 20.

The drainage flow rate control mechanism 30 is detected by a flow rate adjusting valve (flow rate adjusting means) 31 provided in the drainage line 4, a drainage flow meter (flow rate detecting means) 32 for detecting the flow rate of concentrated drainage, and a drainage flow meter 32. It has a drainage flow rate control unit 33 that adjusts the opening degree of the flow rate adjusting valve 31 based on the flow rate of the concentrated drainage.

The drainage flow rate control unit 33 determines the set flow rate of the concentrated drainage in consideration of the recovery rate, which is the 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, and the detection value by the drainage flow meter 32. Is adjusted so that the opening degree of the flow rate adjusting valve 31 becomes the set 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 metering pump 12, when the flow rate of the concentrated drainage decreases, the flow rate of the concentrated water returning from the reflux water line 5 to the supply line 1 naturally increases. .. As a result, when the concentration of impurities in the raw water increases, scaling in which impurities (particularly silica or calcium) are deposited 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 is such that the recovery rate is maximized 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 to.

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 precipitate (silica scale is likely to occur), 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 occur). Therefore, although not shown in the present embodiment, a temperature sensor (water temperature detecting means) for detecting the water temperature of any of raw water, permeated water, and concentrated water is provided, and the water temperature detected by this temperature sensor is provided. Based on, the optimum set flow rate of concentrated wastewater is calculated.

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 22, 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)

It should be noted that the above-mentioned method for calculating the set flow rate of concentrated wastewater may be subject to equipment design restrictions such as an upper limit on the capacity of the metering pump and the flow rate of raw water. In addition, a preset target flow rate of permeated water can be used to calculate the set flow rate of concentrated wastewater, but this method scales when the target flow rate of permeated water and the actual flow rate do not match. It is not preferable because it may occur. Therefore, as described above, it is preferable to use the flow rate of the permeated water (average flow rate in a predetermined time) detected by the permeated water flow meter 22 for calculating the set flow rate of the concentrated wastewater.

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

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

(Calculation method of silica precipitation recovery rate)
The silica precipitation recovery rate YS is as follows, where the solubility (mg / _L ) of silica at the detected water temperature is CS and the silica concentration (mg / _L ) of the raw water measured in advance is _FS . Calculated from equation (2).
Y _S = ( _CS - _FS ) / _CS (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 calcium precipitation recovery rate is calculated using a method for calculating the Langeria index of concentrated water. Here, the Langeria index (saturation index) is an index showing the possibility of calcium (calcium carbonate) precipitation, 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 deposited, and when the value is negative, calcium carbonate is not deposited. Therefore, the calcium precipitation recovery rate is calculated as the recovery rate when the Langeria index of the 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 No. 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. Therefore, for the calcium precipitation recovery rate YC, the impurity concentration (mg / L) of the concentrated water when the _Langeria index of the concentrated water becomes zero is defined as CC, and the impurity concentration (mg / _L ) of the raw water measured in advance is used. When is _FC , it is expressed by the relation of the following equation (3).
Y _C = ( _CC - _FC ) / _CC (3)

As the flow rate adjusting valve 31, for example, a combination of a plurality of solenoid valves and constant flow rate valves (several connected in parallel) can be used, but when the recovery rate is controlled as described above, the electric proportionality is proportional. It is preferable to use a control valve. 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 stepped system where 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 31 is advantageous from the viewpoint of water saving because it is possible to reduce the waste of such concentrated wastewater.

In order to further save water, it is necessary to set a higher target value for the recovery rate, but in the present embodiment, an antiscale agent 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 discharge flow rate of the metering pump 12 can be reduced within a range not lower than the minimum flow rate of the concentrated water, and energy saving can be realized. The addition of the anti-scale agent can be done by a medicated pump.

The anti-scale agent 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. Phosphoric 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; 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) acrylic acid salts such as sodium salts thereof. Examples of the acrylamide-alkylsulfonic acid constituting the terpolymer include 2-acrylamide-2-methylpropanesulfonic 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 anti-scale agents 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, "Hypersperse (registered trademark)" series manufactured by General Electric Co., Ltd., "Cliberter (registered trademark)" series manufactured by Kurita Water Industries, Ltd., and the like.

As described above, in the present embodiment, since the flow rate of the concentrated water is kept constant by the metering pump 12, it is only necessary to specify the flow rate of the concentrated water flowing through one of the drainage line 4 and the recirculated water line 5, and the other is used. The flow rate of concentrated water to flow can also be specified. Therefore, in the illustrated embodiment, the drainage line 4 is provided with a flow rate control means (flow rate adjusting valve 31 and a drainage flow meter 32), and the recirculation water line 5 is a concentrated water flowing through the drainage line 4 and the recirculation water line 5. A manual valve (pressure adjusting valve) 13 for adjusting the pressure balance is provided, but vice versa. That is, the return water line 5 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 4 may be provided with a manual valve for adjusting the pressure balance. Alternatively, both the drainage line 4 and the recirculation water line 5 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 permeated water flow rate control unit and the drainage flow rate control unit are separately provided, but the flow rate adjustment of the permeated water and the flow rate adjustment of the concentrated drainage are performed by one flow rate control unit. It may be like this.

(Second embodiment)
FIG. 2 is a schematic view showing the configuration of the membrane filtration device according to the second embodiment of the present invention. Hereinafter, the same configurations as those of the first embodiment are designated by the same reference numerals to the drawings, and the description thereof will be omitted, and only the configurations different from those of the first embodiment will be described.

This embodiment is a modification of the first embodiment, and the configuration of the permeated water flow rate control mechanism 20 is different from that of the first embodiment. Specifically, it differs from the first embodiment in that the flow rate adjusting valve 21 is provided not in the concentrated water line 3 but in the supply line 1. Along with this, the concentrated water line 3 is provided with a constant flow valve 14 that keeps the flow rate of the concentrated water flowing through the concentrated water line 3 constant, and the supply line 1 is the metering pump 12 of the first embodiment. Instead, a pressurizing pump 15 is provided in which the discharge flow rate changes according to the pressure fluctuation of the raw water. The flow rate adjusting valve 21 is arranged between the pressurizing pump 15 and the filtering means 11.

In the present embodiment, the flow rate control of the permeated water by the permeated water flow rate control mechanism 20 is performed as follows. For example, when the water temperature becomes low, the viscosity of the water becomes high, and as a result, the flow rate of the permeated water separated by the RO membrane or the NF membrane decreases, but the flow rate adjusting valve 21 opens to compensate for this decrease. It is controlled and increases the supply pressure of raw water to the filtration means 11. Further, as the water temperature increases, the viscosity of the water decreases, and as a result, the flow rate of the permeated water separated by the RO membrane or the NF membrane increases, but the flow rate adjusting valve 21 closes so as to cancel this increase. It is controlled and reduces the supply pressure of raw water. In this way, the opening degree of the flow rate adjusting valve 21, that is, the supply pressure of the raw water is adjusted, and the flow rate of the permeated water can be kept constant even in the present embodiment.

The flow rate of the concentrated water separated by the RO membrane or the NF membrane of the filtering means 11 also changes according to the change in the supply pressure of the raw water to the filtering means 11, but in the present embodiment, the concentrated water line L3 is used. As described above, the constant flow valve 14 is provided. Therefore, even when the opening degree of the flow rate adjusting valve 21 changes and the supply pressure of the raw water changes, the flow rate of the concentrated water flowing through the concentrated water line 3 can be kept constant. As a result, as in the first embodiment, the flow rate control of the permeated water does not affect the flow rate of the concentrated water flowing through the drainage line 4 and the recirculated water line 5, and the flow rate of the concentrated drainage by the drainage flow rate control mechanism 30 The control can be performed independently of the flow rate control of the permeated water by the permeated water flow rate control mechanism 20.

Here, the specified flow rate of the constant flow rate valve 14 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 14 is increased more than necessary, the flow rate required for the pressurizing pump 15 becomes larger than necessary, and as a result, the size of the pressurizing pump 15 becomes large, so that energy consumption is consumed. It is not preferable in terms of. Therefore, the specified flow rate of the constant flow rate valve 14 is set in consideration of the permeation flux of the filtration means 11 and the minimum flow rate of the concentrated water required for the filtration means 11, for example, the diameter of the filtration means 11 is about 10.16 cm. When a (4 inch) RO membrane is used, it is in the range of 200 to 1500 L / h.

By the way, the constant flow rate valve 14 defines an operating differential pressure range (allowable range of pressure difference between the primary side and the secondary side of the constant flow rate valve) for operating the constant flow rate valve 14 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 is extremely lowered, the supply pressure of the raw water rises remarkably and the pressure of the concentrated water rises. The pressure difference between the primary side and the secondary side of the constant flow valve 14 may exceed the operating differential pressure range. In that case, the flow rate of the concentrated water flowing through the concentrated water line 3 may not be kept constant.

Therefore, the pressure of the concentrated water flowing through the concentrated water line 3 is reduced to the concentrated water line 3 on the upstream side of the constant flow valve 14 (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 14 is kept within the operating differential pressure range, and the constant flow rate valve 14 is provided. It can be operated normally, and the flow rate of the concentrated water flowing through the concentrated water line 3 can be kept constant. Further, by providing the pressure reducing valve, the peripheral members (pipes, etc.) on the downstream side of the valve are not required to have such pressure resistance. Therefore, the installation of the pressure reducing valve is not only advantageous in terms of safety, but also advantageous in terms of cost because an inexpensive general-purpose product whose pressure resistance performance is not so high can be used. The type of pressure reducing valve is not particularly limited as long as it can reduce the pressure of concentrated water within the operating differential pressure range of the constant flow rate valve 14, but it is equal to or higher than the specified flow rate of the constant flow rate valve 14. It is necessary to select one in which the flow rate of the water flows and the pressure on the secondary side is larger than the water flow differential pressure of the drainage line 4 and the recirculation water line 5.

(Third embodiment)
FIG. 3 is a schematic view showing the configuration of the membrane filtration device according to the third embodiment of the present invention. Hereinafter, the same configurations as those of the above-described embodiment will be described with reference to the same reference numerals, and the description thereof will be omitted, and only the configurations different from the above-described embodiments will be described.

This embodiment is a modification of the first embodiment, in that a further filtering means (second filtering means) 16 is provided on the downstream side of the filtering means (first filtering means) 11. , Different from the first embodiment. The second filtration means 16 is connected in series with the first filtration means 11 and treats the permeated water separated by the first filtration means 11 as the water to be treated. That is, the first permeated water line 2a for flowing the permeated water from the first filtering means 11 is connected to the upstream side of the second filtering means 16, and the second filtering means 16 connects to the downstream side. A second permeated water line 2b for circulating the permeated water is connected. As a result, the membrane filtration device 10 of the present embodiment can generate treated water having better water quality than that of the first embodiment.

A second concentrated water line 6 for circulating the concentrated water from the second filtering means 16 is connected to the second filtering means 16. In the second filtering means 16, the permeated water from the first filtering means 11 is further separated into the permeated water and the concentrated water. Therefore, from the viewpoint of water quality, the concentrated water from the second filtering means 16 is not necessarily external. There is no need to discharge to. Therefore, from the viewpoint of water saving, the second concentrated water line 6 is supplied on the upstream side of the metering pump 12 in order to return all the concentrated water separated by the second filtration means 16 to the supply line 1. It is connected to the. Alternatively, the second concentrated water line 6 may be connected to a raw water tank (not shown) provided in the supply line 1 instead of being directly connected to the supply line 1. In the second concentrated water line 6, part or all of the concentrated water from the second filtering means 16 is discharged to the outside when the RO membrane or the NF membrane of the second filtering means 16 is washed. A drainage line may be connected.

The second concentrated water line 6 is provided with a manual valve 17 and a concentrated water flow meter 18 for adjusting the flow rate of the concentrated water flowing through the second concentrated water line 6. As a result, from the second filtration means 16 with respect to the recovery rate of the second filtration means 16 (the sum of the flow rate of the permeated water from the second filtration means 16 and the flow rate of the concentrated water from the second filtration means 16). Permeable 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 18 is provided instead of the manual valve 17. 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 17 and the concentrated water flow meter 18. In this case, depending on the conditions, the pressure difference between the primary side and the secondary side of the constant flow rate valve may exceed the operating differential pressure range. In order to avoid this, the constant flow rate valve of the second embodiment is used. As in the case of 14, a pressure reducing valve may be provided on the upstream side of the constant flow rate valve.

In the present embodiment, in order to supply a constant flow rate of treated water to, for example, an electric deionized water production device connected to the downstream side of the membrane filtration device 10, the permeated water flow meter 22 of the permeated water flow rate control mechanism 20 is used. Is provided on the second permeated water line 2b. Therefore, in calculating the set flow rate of the concentrated wastewater based on the target value of the recovery rate, the wastewater flow rate control unit 33 needs to separately know the flow rate of the permeated water flowing through the first permeated water line 2a. In the embodiment, the flow rate can be indirectly detected. That is, the drainage flow rate control unit 33 has a measured value by the permeated water flow meter 22 (flow rate of permeated water from the second filtering means 16) and a measured value by the concentrated water flow meter 18 (from the second filtering means 16). The flow rate of the permeated water flowing through the first permeated water line 2a can be calculated from the sum with the flow rate of the concentrated water). Further, as described above, when a constant flow rate valve is provided instead of the manual valve 17 and the concentrated water flow meter 18, the specified flow rate of the constant flow valve is used instead of the value measured by the concentrated water flow meter 18. , The flow rate of the permeated water flowing through the first permeated water line 2a can be calculated. Alternatively, a flow meter (not shown) may be provided on the first permeated water line 2a so as to directly detect the flow rate of the permeated water from the first filtering means 11.

In the present embodiment, two filtering means 11 and 16 are connected in series, but the number of filtering means is not limited to this, and three or more filtering means are connected in series and provided. You may. Even in that case, the flow rate adjusting valve for controlling the flow rate of the permeated water is provided in the concentrated water line connected to the most upstream filtration means among the three or more filtration means, and is provided in the most downstream filtration means. The separated permeated water will be adjusted to the set flow rate (preset target flow rate). In addition, "connected in series" here means that the water to be treated is sequentially treated by a plurality of filtering means, and is separated by the filtering means on the upstream side in the two adjacent filtering means. It means that the permeated water is supplied to the filtration means on the downstream side as water to be treated. Further, each filtration means may be composed of a plurality of RO membranes or NF membranes. In this case, in the plurality of RO membranes or NF membranes, the primary side (raw water and concentrated water distribution side) is connected in series and finally connected to the concentrated water line, and the secondary side (permeated water distribution side) is connected. It will be connected in parallel and eventually connected to the permeated water line.

(Fourth Embodiment)
FIG. 4 is a schematic view showing the configuration of the membrane filtration device according to the fourth embodiment of the present invention. Hereinafter, the same configurations as those of the above-described embodiment will be described with reference to the same reference numerals, and the description thereof will be omitted, and only the configurations different from the above-described embodiments will be described.

This embodiment is a modification of the second embodiment as well as a modification of the third embodiment. Similar to the second embodiment for the first embodiment, the permeated water flow rate control mechanism 20 The configuration is different from the third embodiment. That is, the flow rate adjusting valve 21 is provided not in the first concentrated water line 3 but in the supply line 1, and accordingly, the constant flow rate valve 14 is provided in the first concentrated water line 3 and the supply line 1 is provided with the constant flow rate valve 14. A pressurizing pump 15 is provided. Other configurations are the same as those of the second embodiment or the third embodiment.

In the present embodiment, since it is necessary to supply the raw water to the two filtration means 11 and 16 by one pressurizing pump 15, the supply pressure of the raw water to the first filtering means 11 by the pressurizing pump 15 is set. It will be larger than the second embodiment. Therefore, in the present embodiment, there is a high possibility that the pressure difference between the primary side and the secondary side of the constant flow rate valve 14 exceeds the operating differential pressure range, and therefore, a pressure reducing valve is provided on the upstream side of the constant flow rate valve 14. It is preferable to have.

Needless to say, also in this embodiment, the number of filtration means is not limited to two, and may be three or more.

1 Supply line 2 Permeated water line 2a First permeated water line (intermediate permeated water line)
2b 2nd permeated water line 3 Concentrated water line (1st concentrated water line)
4 Drainage line 5 Reflux water line 6 Second concentrated water line 10 Film filtration device 11 Filtration means (first filtration means)
12 Metering pump 13, 17 Manual valve 14 Constant flow rate valve 15 Pressurizing pump 16 Second filtration means 18 Concentrated water flow meter 20 Permeated water flow control mechanism 21 Flow control valve 22 Permeated water flow meter 23 Permeated water flow control unit 30 Drainage Flow control mechanism 31 Flow control valve 32 Drainage flow meter 33 Drainage flow control unit

Claims (4)

A plurality of filtration means connected in series, each having a reverse osmosis membrane or a nanofiltration membrane that separates the water to be treated into permeated water and concentrated water.
A supply line connected to the most upstream filtration means among the plurality of filtration means and supplying water to be treated to the most upstream filtration means.
A first permeated water line that is connected to the most upstream filtration means and circulates permeated water from the most upstream filtration means.
A second permeated water line that is connected to the most downstream filtering means among the plurality of filtering means and circulates permeated water from the most downstream filtering means.
A concentrated water line that is connected to the most upstream filtration means and circulates concentrated water from the most upstream filtration means.
A 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.
A reflux water line that branches from the concentrated water line, is connected to the supply line, and returns the rest of the concentrated water flowing through the concentrated water line to the supply line.
A vane pump provided in the supply line and supplying a constant flow rate of water to be treated to the most upstream filtration means,
A first flow rate control means for adjusting the flow rate of the permeated water flowing through the second permeated water line to a set flow rate, the flow rate adjusting valve provided in the concentrated water line and the second permeated water line. A first flow rate having a flow rate detecting means for detecting the flow rate of the flowing permeated water and a control unit for adjusting the opening degree of the flow rate adjusting valve based on the flow rate of the permeated water detected by the flow rate detecting means. Control means and
It is a second flow rate control means for adjusting the flow rate of the concentrated water flowing through the drainage line to a set flow rate, and is a flow rate for detecting the flow rate of the flow rate adjusting valve provided in the drainage line and the concentrated water flowing through the drainage line. It has a second flow rate control means having a detection means and a control unit for adjusting the opening degree of the flow rate adjusting valve based on the flow rate of the concentrated water detected by the flow rate detection means .
The control unit of the second flow rate control means permeates the permeated water line flowing through the first permeated water line with respect to the sum of the flow rate of the permeated water flowing through the first permeated water line and the flow rate of the concentrated water flowing through the drainage line. A membrane filtration device that determines the set flow rate of concentrated water flowing through the drainage line so that the recovery rate, which is the ratio of the flow rate of water, becomes a predetermined value . A plurality of filtration means connected in series, each having a reverse osmosis membrane or a nanofiltration membrane that separates the water to be treated into permeated water and concentrated water.
A supply line connected to the most upstream filtration means among the plurality of filtration means and supplying water to be treated to the most upstream filtration means.
A first permeated water line that is connected to the most upstream filtration means and circulates permeated water from the most upstream filtration means.
A second permeated water line that is connected to the most downstream filtering means among the plurality of filtering means and circulates permeated water from the most downstream filtering means.
A concentrated water line that is connected to the most upstream filtration means and circulates concentrated water from the most upstream filtration means.
A 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.
A reflux water line that branches from the concentrated water line, is connected to the supply line, and returns the rest of the concentrated water flowing through the concentrated water line to the supply line.
A pressurizing pump provided in the supply line and operating with a single-phase 100V AC power supply,
A constant flow valve provided in the concentrated water line to keep the flow rate of concentrated water flowing through the concentrated water line constant.
It is a first flow rate control means for adjusting the flow rate of the permeated water flowing through the second permeated water line to a set flow rate, and flows through the flow rate adjusting valve provided in the supply line and the second permeated water line. A first flow rate control having a flow rate detecting means for detecting the flow rate of the permeated water and a control unit for adjusting the opening degree of the flow rate adjusting valve based on the flow rate of the permeated water detected by the flow rate detecting means. Means and
It is a second flow rate control means for adjusting the flow rate of the concentrated water flowing through the drainage line to a set flow rate, and is a flow rate for detecting the flow rate of the flow rate adjusting valve provided in the drainage line and the concentrated water flowing through the drainage line. It has a second flow rate control means having a detection means and a control unit for adjusting the opening degree of the flow rate adjusting valve based on the flow rate of the concentrated water detected by the flow rate detection means .
The control unit of the second flow rate control means permeates the permeated water line flowing through the first permeated water line with respect to the sum of the flow rate of the permeated water flowing through the first permeated water line and the flow rate of the concentrated water flowing through the drainage line. A membrane filtration device that determines the set flow rate of concentrated water flowing through the drainage line so that the recovery rate, which is the ratio of the flow rate of water, becomes a predetermined value . A water temperature detecting means for detecting the water temperature of either the water to be treated supplied to the most upstream filtration means, the permeated water from the most upstream filtration means, or the concentrated water from the most upstream filtration means. Have,
The control unit of the second flow control means has a recovery rate based on the water temperature detected by the water temperature detecting means, and the recovery rate is the membrane of the reverse osmosis membrane or the nanofiltration membrane of the filtration means on the most upstream side. The membrane filtration apparatus according to claim 1 or 2 , wherein the set flow rate of the concentrated water flowing through the drainage line is determined so that the maximum recovery rate at which silica or calcium does not precipitate on the surface is obtained. The film according to any one of claims 1 to 3 , which is provided in the recirculation water line and has a pressure adjusting valve for adjusting the pressure balance between the concentrated water flowing through the drainage line and the concentrated water flowing through the recirculation water line. Filtration device.

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