JP6851877B2 - Membrane filtration device - Google Patents

Description

The present invention relates to a membrane filtration device 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 having RO membranes or NF membranes, in many cases, from the viewpoint of effective use of water (water saving), a part of 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 water is returned 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 wastewater 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 keep the flow rate of permeated water constant by adjusting the supply pressure of the raw water.

In the flow rate control of permeated water, when the supply pressure of raw water is adjusted so that the flow rate of permeated water becomes constant, the flow rate of concentrated water separated by the RO membrane or the NF membrane also changes accordingly. Such a change in the flow rate of concentrated water leads to clogging of the membrane due to fouling and scaling, and damage to the membrane due to an increase in pressure loss. Control is required. However, in the membrane filtration device having the above-described configuration, the ratio of the concentrated water to the flow rate of the permeated water is set to a predetermined ratio by controlling the flow rate of the concentrated recirculated water or the concentrated drainage with respect to the change in the flow rate of the concentrated water due to the flow rate control of the permeated water. If you try to maintain it, the flow control of each other may interfere and hunting may occur.

Therefore, Patent Document 1 proposes, as a method of avoiding hunting, a method of always keeping the flow rate of concentrated water constant by providing a constant flow valve in the concentrated water line through which concentrated water is circulated. According to this method, the flow rate control of the permeated water does not affect the flow rate of the concentrated water, so that whatever the flow rate control is performed on the concentrated water side, it interferes with the flow rate control of the permeated water. Hunting can be avoided.

Japanese Unexamined Patent Publication No. 2014-21260

By the way, the constant flow valve 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 normally, but in some cases. It has been confirmed by the present inventors that the supply pressure of raw water may increase remarkably and the pressure difference between the primary side and the secondary side of the constant flow valve may exceed the operating differential pressure range of the constant flow valve. There is. For example, when multiple membranes are connected in series, when a membrane for medium and high pressure is used, or when the water temperature drops extremely, the above-mentioned pressure difference corresponds to the operating differential pressure range of the constant flow valve. If it exceeds, the flow rate of concentrated water will not be kept constant. As a result, the flow rate control of the permeated water affects the flow rate of the concentrated water, and when the flow rate control of the concentrated reflux water or the concentrated wastewater is attempted, the flow rate control of each other may interfere with each other and cause hunting.

In addition, if the flow rate of concentrated water is not kept constant and increases, if the flow rate of concentrated reflux water or concentrated wastewater is controlled to maintain the recovery rate, the increased amount of concentrated water will be used as concentrated reflux water as raw water. Reflux to. As a result, the flow rate of the circulating concentrated water increases and the discharge flow rate of the pressurizing pump increases, but the lift of the pressurizing pump decreases accordingly, so that the required flow rate of permeated water cannot be obtained. There is a risk. In this case, the required flow rate of permeated water can be obtained by increasing the rotation speed (output) of the pressurizing pump, but this is not preferable from the viewpoint of energy saving.

Therefore, an object of the present invention is to provide a membrane filtration device that realizes stable flow rate control and is excellent in energy saving.

In order to achieve the above-mentioned object, the membrane filtering device according to one aspect of the present invention is connected to a filtering means having a back-penetrating membrane or a nano-filtering membrane that separates the water to be treated into permeated water and concentrated water, and the filtering means. A supply line that supplies the water to be treated to the filtering means, a permeated water line that is connected to the filtering means and distributes the permeated water from the filtering means, and a permeated water line that is connected to the filtering means and distributes the concentrated water from the filtering means. Concentrated water line, 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, and a concentrated water line that branches off from the concentrated water line and is connected to the supply line and flows through the concentrated water line. A recirculation water line that returns the rest of the water to the supply line, a first flow control means that adjusts the flow rate of the permeated water flowing through the permeated water line to a set flow rate, and a concentration provided in the concentrated water line and flowing through the concentrated water line. It has a constant flow valve that keeps the flow rate of water constant, and a pressure reducing valve that is provided in the concentrated water line on the upstream side of the constant flow valve and reduces the pressure of the concentrated water flowing through the concentrated water line.

In order to achieve the above-mentioned object, the membrane filtering device according to one aspect of the present invention is connected to a filtering means having a back-penetrating membrane or a nano-filtering membrane that separates the water to be treated into permeated water and concentrated water, and the filtering means. A supply line that supplies the water to be treated to the filtering means, a permeated water line that is connected to the filtering means and distributes the permeated water from the filtering means, and a permeated water line that is connected to the filtering means and distributes the concentrated water from the filtering means. A concentrated water line , a constant flow valve provided in the concentrated water line that keeps the flow rate of concentrated water flowing through the concentrated water line constant, and a branch from the concentrated water line on the downstream side of the constant flow valve, and flow through the concentrated water line. A drainage line that discharges a part of the concentrated water to the outside, and a return that branches off from the concentrated water line on the downstream side of the constant flow valve and is connected to the supply line, and the rest of the concentrated water flowing through the concentrated water line is returned to the supply line. The first flow control means for adjusting the flow rate of the permeated water flowing through the flowing water line and the permeated water line to the set flow rate, and the second flow control means for adjusting the flow rate of the concentrated water flowing through the drainage line to the set flow rate. , The opening degree of the flow control valve is adjusted based on the flow rate adjusting valve provided in the drainage line, 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. It has a second flow control means having a control unit for adjusting, and a pressure reducing valve provided in the concentrated water line on the upstream side of the constant flow valve to reduce the pressure of the concentrated water flowing through the concentrated water line. There is.

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. A supply line that is connected to the most upstream filtration means among the plurality of filtering means and supplies water to be treated to the most upstream filtering means, and the most downstream side of the plurality of filtering means. A permeated water line that is connected to the filtering means and circulates permeated water from the most downstream filtering means, and a concentrated water line that is connected to the most upstream filtering means and circulates concentrated water from the most upstream filtering means. A constant flow valve installed in the concentrated water line that keeps the flow rate of concentrated water flowing through the concentrated water line constant, and a concentrated water branching from the concentrated water line on the downstream side of the constant flow valve and flowing through the concentrated water line. A drainage line that discharges a part to the outside, and a recirculation water line that branches off from the concentrated water line on the downstream side of the constant flow valve and is connected to the supply line to return the rest of the concentrated water flowing through the concentrated water line to the supply line. The first flow control means for adjusting the flow rate of the permeated water flowing through the permeated water line to the set flow rate, and the second flow control means for adjusting the flow rate of the concentrated water flowing through the drain line to the 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. It has a second flow control means having a portion, and a pressure reducing valve provided in the concentrated water line on the upstream side of the constant flow valve to reduce the pressure of the concentrated water flowing through the concentrated water line.

As described above, according to the present invention, it is possible to provide a membrane filtration device that can realize stable flow rate control and is excellent in energy saving.

It is the schematic which shows the structure of the membrane filtration apparatus which concerns on 1st Embodiment of this invention. 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. 1 is a schematic view showing the configuration of a membrane filtration apparatus according to the first embodiment of the present invention.

The membrane filtration device 10 of the present embodiment is an apparatus for generating treated water by removing impurities contained in raw water (water to be treated), and permeates the raw water with concentrated water containing impurities and from which impurities have been removed. It has a filtration 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 pressurizing pump 21, 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 has a permeated water flow rate control mechanism (first flow rate control means) 20 that adjusts the flow rate of the permeated water flowing through the permeated water line 2 to a set flow rate.

The permeated water flow rate control mechanism 20 is provided in the supply line 1, and includes a pressurizing pump (pressure adjusting means) 21 for adjusting the pressure of the raw water flowing through the supply line 1 (the pressure of supplying the raw water to the filtering means 11) and the permeated water. Pressurized based on the permeated water flow meter (flow rate detecting means) 22 provided on the line 2 and detecting the flow rate of the permeated water flowing through the permeated water line 2 and the flow rate of the permeated water detected by the permeated water flow meter 22. It has a permeated water flow rate control unit 23 that controls the pump 21.

The permeated water flow rate control unit 23 includes an inverter (not shown) that controls the rotation speed of the pressurizing pump 21 so that the permeated water flow rate detected by the permeated water flow meter 22 becomes constant. It controls the number of rotations of 21. 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 rotation speed of the pressurizing pump 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 increases the supply pressure of raw water by increasing the rotation speed of the pressurizing pump 21 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 separated by the RO membrane or the NF membrane increases. Therefore, the permeated water flow rate control unit 23 lowers the supply pressure of raw water by lowering the rotation speed of the pressurizing pump 21 so as to cancel this increase.

As described above, in the present embodiment, the flow rate of the permeated water is maintained constant (preset target flow rate) by adjusting the rotation speed of the pressurizing pump 21, that is, the supply pressure of the raw water, but the raw water is maintained. The flow rate of the concentrated water separated by the RO membrane or the NF membrane also changes according to the change in the supply pressure of. In order to suppress such a change in the flow rate of the concentrated water itself, the concentrated water line 3 is provided with a constant flow valve 12 that keeps the flow rate of the concentrated water flowing through the concentrated water line 3 constant. As a result, the flow rate of the concentrated water can be kept constant even when the rotation speed of the pressurizing pump 21 is changed by the permeated water flow rate control unit 23 and the supply pressure of the raw water to the filtration means 11 is changed. ..

By the way, the constant flow valve 12 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 12 normally. Therefore, depending on the conditions, such as 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 12 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, in the present embodiment, 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 12 (that is, the pressure on the secondary side is lower than the pressure on the primary side). A pressure reducing valve 13 is 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 12 is kept within the operating differential pressure range to keep the constant flow rate valve 12 in place. It can be operated normally, and the flow rate of the concentrated water flowing through the concentrated water line 3 can be kept constant.

In this way, by providing the pressure reducing valve 13 and the constant flow rate valve 12 in the concentrated water line 3, the flow rate of the concentrated water separated by the filtering means 11 is always kept constant, and the flow rate control of the permeated water is controlled by the drainage line 4. And does not affect the flow rate of concentrated water flowing through the reflux water line 5. As a result, no matter what flow rate control is performed in the drainage line 4 or the recirculated 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 constant flow valve 12 operates normally and the flow rate of the concentrated water is kept constant, the discharge flow rate of the pressurizing pump 21 does not increase, which is the rotation speed (output) of the pressurizing pump. There is no need to raise it. Further, providing the pressure reducing valve 13 is not only advantageous in terms of safety because the peripheral members (piping, etc.) on the downstream side of the pressure reducing valve 13 are not required to have so much pressure resistance, but also the pressure resistance is not so high and inexpensive. The availability of general-purpose products is also advantageous in terms of cost.

The specified flow rate of the constant flow valve 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, if the specified flow rate of the constant flow valve 12 is increased more than necessary, the flow rate required for the pressurizing pump 21 becomes larger than necessary, and as a result, the size of the pressurizing pump 21 becomes larger, which consumes energy. It is not preferable in that respect. Therefore, the specified flow rate of the constant flow valve 12 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.} The type of the pressure reducing valve 13 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 12, but the specified flow rate of the constant flow rate valve 12 It is necessary to select one in which the above flow rate flows or one in which 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.

As described above, by installing the constant flow rate valve 12 and the pressure reducing valve 13, the flow rate control of the permeated water does not affect the flow rate of the concentrated water, and as a result, the concentrated water flowing through the drainage line 4 or the recirculated water line 5. Flow rate control becomes easily feasible. 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 wastewater 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 value detected 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 constant flow valve 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. 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, in the present embodiment, although not shown, 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)

From the viewpoint of surely suppressing the occurrence of scaling, a flow rate exceeding the target flow rate calculated by the above formula (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 target flow rate as the set flow rate of the 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 solubility of silica in the detected water temperature (mgSiO ₂ / L) and _{C S,} when the pre-measured silica concentration of the raw water (mgSiO ₂ / L) was _{F S,} It is calculated from the following formula (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 set 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. 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 detected by the permeated water flow meter 22 for calculating the set flow rate of the concentrated wastewater.

When controlling the recovery rate as described above, it is preferable to use an electric proportional control valve as the flow rate adjusting valve 31. As a result, the opening degree can be adjusted steplessly within the resolution range of the electric proportional control valve, and the recovery rate can be adjusted more smoothly than the opening degree adjustment in multiple stages by combining solenoid valves. Can be done. For example, in the multi-step method 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 be adjusted only to 60%, and wasteful concentrated wastewater is generated. Therefore, using an 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 such waste of concentrated wastewater.

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 valve 12 can be reduced, and as a result, energy saving can be realized by using the pressurizing pump 21 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; Phosphate-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. / Nonionic 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 Industries, 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.

As described above, in the present embodiment, since the flow rate of the concentrated water is kept constant by the constant flow rate valve 12 and the pressure reducing valve 13, the flow rate of the concentrated water flowing through one of the drainage line 4 and the recirculating water line 5 is defined. Only by itself, the flow rate of concentrated water flowing through the other can be specified. Therefore, in the illustrated embodiment, the drainage line 4 is provided with the flow rate control means (flow rate adjusting valve 31 and the drainage flow meter 32), and the recirculation water line 5 is the concentrated water flowing through the drainage line 4 and the recirculation water line 5. A manual valve (pressure adjusting valve) 14 for adjusting the pressure balance is provided, but the reverse may be performed. That is, the recirculation 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 one flow rate control unit adjusts the flow rate of the permeated water and the flow rate of the concentrated wastewater. It may be like this.

(Second embodiment)
FIG. 2 is a schematic view showing the configuration of the membrane filtration apparatus according to the second embodiment of the present invention. 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) 15 is provided on the downstream side thereof. The second filtration means 15 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 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 15, and the second filtering means 15 is connected 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 15 is connected to the second filtering means 15. In the second filtration means 15, 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 15 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 pressurizing pump 21 in order to return all the concentrated water separated by the second filtering means 15 to the supply line 1. It is connected to 1. 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 15 is discharged to the outside when the RO membrane or the NF membrane of the second filtering means 15 is washed. A drainage line may be connected.

The second concentrated water line 6 is provided with a manual valve 16 and a concentrated water flow meter 17 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 15 with respect to the recovery rate of the second filtration means 15 (the sum of the flow rate of the permeated water from the second filtration means 15 and the flow rate of the concentrated water from the second filtration means 15). Permeated water flow rate ratio) can be adjusted arbitrarily. In addition, in order to eliminate the complexity of manually adjusting the recovery rate, instead of the manual valve 16, 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 17 is provided. 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 16 and the concentrated water flow meter 17. In this case, as in the first embodiment, the pressure difference between the primary side and the secondary side of the constant flow valve may exceed the operating differential pressure range depending on the conditions. A pressure reducing valve may be provided on the upstream side of the constant flow 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 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 15) and a measured value by the concentrated water flow meter 17 (from the second filtering means 15). 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 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 17. , 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 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 15 by one pressurizing pump 21, the supply pressure of the raw water to the first filtration means 11 by the pressurizing pump 21 is set. It is larger than that of the first embodiment. Therefore, the specified flow rate of the first constant flow valve 12 needs to be set in consideration of this point, and the type of the pressure reducing valve 13 also needs to consider the specified flow rate of the first constant flow valve 12. For example, when RO membranes having a diameter of about 20.32 cm (8 inches) are used as the two filtration means 11 and 15, the applicable temperature range of the first filtration means 11 is 5 to 35 ° C., and the silica concentration of the raw water and the like. When the control range of the recovery rate is assumed to be 50 to 85% from the calcium concentration, for example, the first constant flow valve 12 is manufactured by Keihin Co., Ltd. (product number: NSPW-25, set flow rate: 55 L / min). A constant flow valve can be used, and as the pressure reducing valve 13, a pressure reducing valve manufactured by Yoshitake Co., Ltd. (product number: GD-200H) can be used.

Further, in the present embodiment, the installation of the pressure reducing valve 13 is more effective because the supply pressure of the raw water to the first filtration means 11 increases as described above. Regarding this point, when the present inventors conducted a water flow test using the membrane filtration device shown in FIG. 2, the output of the pressurizing pump 21 was 2 to 2 as compared with a similar device not provided with a pressure reducing valve. It has been confirmed that it is 5% lower. This is because if the pressure reducing valve is not provided, the pressure difference between the primary side and the secondary side of the constant flow valve exceeds the operating differential pressure range of the constant flow valve, and the constant flow valve functions as an orifice. It is probable that this is because the discharge flow rate of the pressurizing pump increased, the lift became lower, and the output of the pressurizing pump increased.

In the above-described embodiment, the two filtration means are connected in series, but the number of the filtration means is not limited to this, and even if three or more filtration means are connected in series and provided. Good. Even in that case, the constant flow valve and the pressure reducing valve are provided in the concentrated water line connected to the most upstream filtration means among the three or more filtration means, and the permeated water separated by the most downstream filtration means. Will be adjusted to the set flow rate (preset target flow rate). 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 Supply line 2 Permeated water line 2a First permeated water line 2b Second permeated water line 3 Concentrated water line (first concentrated water line)
4 Drainage line 5 Reflux water line 6 Second concentrated water line 10 Membrane filtration device 11 Filtration means (first filtration means)
12 Constant flow valve (first constant flow valve)
13 Pressure reducing valve 14, 16 Manual valve 15 Second filtration means 17 Concentrated water flow meter 20 Permeated water flow control mechanism 21 Pressurized pump 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 (8)

A filtration means 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 filtration means and supplying water to be treated to the filtration means,
A permeated water line connected to the filtering means and flowing permeated water from the filtering means, and a permeated water line.
A concentrated water line connected to the filtering means and circulating concentrated water from the filtering means,
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.
A drainage line that branches off from the concentrated water line on the downstream side of the constant flow valve and discharges a part of the concentrated water flowing through the concentrated water line to the outside.
A reflux water line that branches off from the concentrated water line on the downstream side of the constant flow valve, 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 first flow rate control means for adjusting the flow rate of permeated water flowing through the permeated water line to a set flow rate, and
A second flow rate control means for adjusting the flow rate of concentrated water flowing through the drainage line to a set flow rate, the flow rate adjusting valve provided in the drainage line and the flow rate for detecting the flow rate of concentrated water flowing through the drainage line. 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.
A pressure reducing valve provided in the concentrated water line on the upstream side of the constant flow valve to reduce the pressure of the concentrated water flowing through the concentrated water line.
Membrane filtration device with. 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 permeated water line that is connected to the most downstream filtration means among the plurality of filtration means and circulates permeated water from the most downstream filtration 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 constant flow valve provided in the concentrated water line to keep the flow rate of concentrated water flowing through the concentrated water line constant.
A drainage line that branches off from the concentrated water line on the downstream side of the constant flow valve and discharges a part of the concentrated water flowing through the concentrated water line to the outside.
A reflux water line that branches off from the concentrated water line on the downstream side of the constant flow valve, 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 first flow rate control means for adjusting the flow rate of permeated water flowing through the permeated water line to a set flow rate, and
A second flow rate control means for adjusting the flow rate of concentrated water flowing through the drainage line to a set flow rate, the flow rate adjusting valve provided in the drainage line and the flow rate for detecting the flow rate of concentrated water flowing through the drainage line. 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.
A pressure reducing valve provided in the concentrated water line on the upstream side of the constant flow valve to reduce the pressure of the concentrated water flowing through the concentrated water line.
Membrane filtration device with. The control unit of the second flow rate control means 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 membrane filtration device according to claim 1 , wherein the set flow rate of concentrated water flowing through the drainage line is determined so that a certain recovery rate becomes a predetermined value. It has a water temperature detecting means for detecting the water temperature of any one of the water to be treated supplied to the filtering means, the permeated water from the filtering means, and the concentrated water from the filtering means.
Based on the water temperature detected by the water temperature detecting means, the control unit of the second flow control means has a recovery rate of silica or silica on the membrane surface of the reverse osmosis membrane or the nanofiltration membrane of the filtration means. The membrane filtration apparatus according to claim 3 , wherein the set flow rate of the concentrated water flowing through the drainage line is determined so that the maximum recovery rate at which calcium does not precipitate is obtained. It has an intermediate permeated water line that is connected to the most upstream filtration means and circulates permeated water from the most upstream filtration means.
The control unit of the second flow rate control means determines the flow rate of the permeated water flowing through the intermediate permeated water line with respect to the sum of the flow rate of the permeated water flowing through the intermediate permeated water line and the flow rate of the concentrated water flowing through the drainage line. The membrane filtration device according to claim 2 , wherein the set flow rate of concentrated water flowing through the drainage line is determined so that the recovery rate, which is a ratio, becomes a predetermined value. A water temperature detecting means for detecting the 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 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 5 , 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 membrane filtration according to any one of claims 1 to 6 , which is provided in the reflux water line and has a pressure adjusting valve for adjusting the pressure of the concentrated water flowing through the drainage line and the concentrated water flowing through the reflux water line. apparatus. The first flow rate control means is provided in the supply line, and a pressure adjusting means for adjusting the pressure of the water to be treated flowing through the supply line and a flow rate detecting means for detecting the flow rate of the permeated water flowing through the permeated water line. The membrane filtration device according to any one of claims 1 to 7 , further comprising a control unit that controls the pressure adjusting means based on the flow rate of the permeated water detected by the flow rate detecting means.

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