JP7303861B2 - Membrane filtration device - Google Patents

Description

The present invention relates to membrane filtration devices having reverse osmosis membranes or nanofiltration membranes.

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

In many cases, in a membrane filtration device having an RO membrane or an NF membrane, from the viewpoint of effective use of water (water saving), part of the concentrated water containing impurities is discharged to the outside as concentrated waste water, and the rest is discharged as concentrated reflux water. A configuration is adopted in which the gas is returned to the upstream side of the RO membrane or the NF membrane. As a result, the recovery rate (ratio of the permeate flow rate to the sum of the permeate flow rate and the concentrated waste water flow rate) can be improved compared to the case where all the concentrated water is discharged as concentrated waste water, resulting in water savings. can be realized.

At the same time, in the membrane filtration device, in order to respond to changes in the flow rate of permeate due to changes in water temperature (i.e., changes in water viscosity), the rotation speed of the pressure pump is controlled to allow the RO or NF membrane to Flow rate control is also performed to maintain a constant flow rate of permeated water by adjusting the supply pressure of raw water (see, for example, Patent Document 1).

JP 2005-296945 A

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 on a three-phase 200V AC power supply. is feasible. However, for example, when using a pressurization pump that operates on a single-phase 100V AC power supply, it is difficult to obtain a corresponding general-purpose inverter, so it is difficult to even control the rotation speed of the pressurization pump. . Therefore, the above-described method is substantially limited to an environment where a three-phase 200V AC power supply is available, and cannot be said to have high versatility as a method for controlling the flow rate of permeate.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a highly versatile membrane filtration device that achieves stable flow rate control.

In order to achieve the object described above, the membrane filtration device of the present invention is connected to filtration means having a reverse osmosis membrane or nanofiltration membrane that separates water to be treated into permeated water and concentrated water, and filtration means. A supply line that supplies water to be treated to the means, a permeated water line that is connected to the filtering means and circulates the permeated water from the filtering means, and a concentrated water line that is connected to the filtering means and circulates the concentrated water from the filtering means. , a drain line that branches off from the concentrated water line and discharges part of the concentrated water flowing through the concentrated water line to the outside, and a drain line that branches off from the concentrated water line and is connected to the supply line, and the rest of the concentrated water flowing through the concentrated water line. to the supply line, a vane pump provided in the supply line for supplying a constant flow rate of the water to be treated to the filtration means, and adjusting the flow rate of the permeated water flowing through the permeated water line to a preset target flow rate A first flow rate control means, which is a flow rate control valve provided in the concentrated water line, a flow rate detection means for detecting the flow rate of the permeate flowing through the permeate line, and the permeate detected by the flow rate detection means. a first flow rate control means having a control unit that adjusts the opening degree of the flow rate adjustment valve based on the flow rate and adjusts the flow rate of the permeated water flowing through the permeated water line to a target flow rate; , a pressure regulating valve with an adjustable opening that adjusts the pressure balance between the concentrated water flowing through the drainage line and the concentrated water flowing through the reflux line , and the second flow rate control that adjusts the flow rate of the concentrated water flowing through the drainage line to a set flow rate. means, comprising: a flow rate adjusting valve provided in a drainage line; a flow rate detection means for detecting a flow rate of concentrated water flowing through the drainage line; and a second flow rate control means having a control unit that adjusts the opening degree of 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 and a water temperature detecting means for detecting the temperature of the permeate flowing through the permeate line with respect to the sum of the flow rate of the permeate flowing through the permeate line and the flow rate of the concentrated water flowing through the drain line. Based on the water temperature detected by the water temperature detection means, so that the recovery rate, which is the ratio of the water flow rate, is the maximum recovery rate that does not precipitate silica or calcium on the membrane surface of the reverse osmosis membrane or nanofiltration membrane of the filtration means. to determine the set flow rate of concentrate flowing through the drain line .

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

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

BRIEF DESCRIPTION OF THE DRAWINGS It is the schematic which shows the structure of the membrane filtration apparatus which concerns on the 1st Embodiment of this invention. It is a schematic diagram showing the configuration of a membrane filtration device according to a second embodiment of the present invention. It is a schematic diagram showing the configuration of a membrane filtration device according to a third embodiment of the present invention. It is a schematic diagram showing the configuration of a membrane filtration device according to a fourth embodiment of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(First embodiment)
FIG. 1 is a schematic diagram showing the configuration of a membrane filtration device according to a 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. It has filtering means 11 for separating from water. The filtering means 11 has a reverse osmosis membrane (RO membrane) or a nanofiltration membrane (NF membrane).

In addition, the membrane filtration device 10 includes a plurality of lines respectively connected to the filtration means 11, that is, a supply line 1 that supplies raw water to the filtration means 11, and a permeated water line 2 that distributes the permeated water from the filtration means 11. , and a concentrated water line 3 for circulating the concentrated water from the filtering means 11 . In addition, the membrane filtration device 10 has two lines branched from the concentrated water line 3, that is, a drain 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 the rest of the concentrated water. It has a reflux water line 5 for refluxing to 1. After being branched from the concentrated water line 3, the reflux water line 5 is connected to the supply line 1 on the upstream side of a metering pump 12, which will be described later. Note that the return water line 5 may be connected to a raw water tank (not shown) provided on the supply line 1 instead of being directly connected to the supply line 1 .

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

The permeate flow control unit 23 controls the opening degree of the flow control valve 21 so that the permeate flow rate detected by the permeate water flow meter 22 is constant (preset target flow rate). For example, when the water temperature changes, the flow rate of the permeate separated by the RO or NF membrane also changes due to the change in the viscosity of the water. The permeate water flow control unit 23 controls the opening degree of the flow control valve 21 according to this change. That is, the lower the water temperature, the higher the viscosity of the water, resulting in a decrease in the flow rate of the permeate separated by the RO or NF membrane. Therefore, in order to compensate for this decrease, the permeate water flow rate control unit 23 controls the flow rate adjustment valve 21 to close, and the pressure of the raw water applied to the RO membrane or the NF membrane (the pressure of the raw water supplied to the filtration means 11 ). Also, as the water temperature increases, the viscosity of the water decreases, resulting in an increase in the flow rate of the permeate separated by the RO or NF membrane. Therefore, the permeate water flow rate control unit 23 controls to open the flow rate adjustment valve 21 to reduce the supply pressure of the raw water in order to cancel this increase. In this way, the permeate flow rate control unit 23 adjusts the opening degree of the flow rate adjustment valve 21 to adjust the pressure of the raw water applied to the RO membrane or the NF membrane, thereby maintaining a constant flow rate of the permeate water. can.

Further, in the present embodiment, as described above, the supply line 1 is provided with the metering pump 12, so that the flow rate of the concentrated water flowing through the concentrated water line 3 can be adjusted even against such a pressure change of the raw water. can be held 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 above a certain level. Therefore, even if the opening degree of the flow rate adjustment 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 kept constant. , so that the concentrate flow rate can also be kept constant.

In this way, since the flow rate of the concentrated water separated by the filtering means 11 is always kept constant, the control of the flow rate of the permeated water does not affect the flow rate of the concentrated water flowing through the drainage line 4 and the reflux water line 5. . As a result, no matter what kind of flow rate control is performed in the drainage line 4 or the return water line 5, it will not interfere with the flow rate control of the permeated water, so hunting can be avoided. In addition, since the method of controlling the flow rate of permeated water described above does not need to control the rotation speed of the pump, it can be implemented, for example, when using a pressure pump that operates with a single-phase 100V AC power supply. Therefore, high versatility can be achieved as a method of controlling the flow rate of permeate.

The type of metering pump 12 used in this embodiment is not particularly limited as long as the discharge flow rate can be kept constant when the pressure of the raw water is above a certain level. Here, "constant" means that the discharge flow rate is not only strictly constant, but may fluctuate (pulsate) within a predetermined error range. Accordingly, examples of the metering pump 12 include vane pumps, diaphragm pumps, plunger pumps, piston pumps, and screw pumps. Among them, it is preferable to use a vane pump or 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 clogging of the membrane due to fouling or scaling does not occur, and that the membrane is not damaged due to an increase in pressure loss. However, increasing the prescribed 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 undesirable 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 concentrated water required for the filtration means 11. For example, the diameter of the filtration means 11 is about 10.16 cm. (4 inches), the range is 300 to 1800 L/h depending on 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 control 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 drain line 4 or the return water line 5 . In this embodiment, a drainage flow rate control mechanism (second flow rate control means) 30 is provided for adjusting the flow rate of concentrated water (hereinafter referred to as "concentrated drainage") flowing through the drainage line 4 to a set flow rate. The flow rate control of the concentrated waste water by the waste water 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 adjustment valve (flow rate adjustment means) 31 provided in the drainage line 4, a drainage flow meter (flow rate detection means) 32 for detecting the flow rate of concentrated waste water, and a drainage flow rate meter 32. and a waste water flow control unit 33 that adjusts the opening degree of the flow control valve 31 based on the flow rate of the concentrated waste water.

The wastewater flow rate control unit 33 determines the set flow rate of the concentrated wastewater 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 wastewater, and the value detected by the wastewater flow meter 32 is the set flow rate, the opening degree of the flow control valve 31 is adjusted. 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 the 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 wastewater decreases, the flow rate of the concentrated water that flows back 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 (especially silica or calcium) are deposited on the membrane surface of the RO membrane or NF membrane of the filtering means 11, tends to occur. Therefore, the flow rate of the concentrated wastewater is set so that the recovery rate is maximized in a range in which the concentration of impurities in the concentrated water does not exceed the solubility, that is, the recovery rate is maximized in a range in which the impurities silica or calcium do not precipitate. is set to

However, the solubility of impurities varies depending on the water temperature. For example, for silica, its solubility increases proportionally with temperature, and for calcium (calcium carbonate), its solubility decreases with increasing temperature. Therefore, when the water temperature is low, the solubility of silica is relatively low, and silica tends to precipitate (silica scale is likely to occur). is likely to precipitate (calcium scale is likely to occur). Therefore, in the present embodiment, although not shown, a temperature sensor (water temperature detection means) is provided for detecting the water temperature of any one of the raw water, the permeated water, and the concentrated water. Based on, the optimum set flow rate of the concentrated waste water 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 The recovery rate of (hereinafter referred to as "calcium precipitation recovery rate") is calculated. Methods for calculating the silica precipitation recovery rate and the calcium precipitation recovery rate will be described later. Next, the silica deposition recovery rate and the calcium deposition recovery rate are compared, and the smaller deposition 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 waste water is calculated and set by the following equation (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 method of calculating the set flow rate of the concentrated wastewater described above may be subject to limitations in device design, such as upper limits on the capacity of the metering pump and the flow rate of the raw water. In addition, a preset target flow rate of permeate can be used to calculate the set flow rate of concentrated wastewater, but this method causes scaling if the target flow rate of permeate does not match the actual flow rate. It is not desirable because it can occur. Therefore, as described above, it is preferable to use the flow rate of permeate detected by the permeate flow meter 22 (average flow rate over a predetermined period of time) for calculating the set flow rate of the concentrated waste water.

From the viewpoint of reliably 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. It is preferable to set the determined target flow rate as the set flow rate of the concentrated waste water.

Here, the methods for calculating the silica deposition recovery rate and the calcium deposition recovery rate will be described respectively.

(Method for calculating precipitation recovery rate of silica)
The silica precipitation recovery rate Y _S is expressed as follows, where _CS is the solubility of silica (mg/L) at the detected water temperature and _FS is the silica concentration (mg/L) of the raw water measured in advance. It is calculated from Equation (2).
Y _S =(C _S −F _S )/C _S (2)

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

(Method for calculating precipitation recovery rate of calcium)
The precipitation recovery rate of calcium is calculated using a method for calculating the Langerier index of concentrated water. Here, the Langerier index (saturation index) is an index indicating the possibility of precipitation of calcium (calcium carbonate), and the actual pH of water and the theoretical pH (pHs: calcium carbonate in water neither dissolves nor precipitates It means the difference (pH - pHs) from the pH at equilibrium. That is, the larger the absolute value of the positive value of the Langerier index, the easier it is for calcium carbonate to precipitate, while the negative value does not precipitate calcium carbonate. Therefore, the precipitation recovery rate of calcium is calculated as the recovery rate when the Langelier index of the concentrated water becomes zero. In order to set a safer value, the recovery rate of calcium precipitation may be the recovery rate when the Langelier index of the concentrated water becomes a negative value.

The Langerier index of the concentrate is calculated from the pH of the concentrate, the concentration of impurities in the concentrate (calcium concentration, total alkalinity, and evaporation residue concentration), and the detected water temperature. As a method for calculating the Langelier index, for example, the method described in Japanese Patent Application Laid-Open No. 11-267687 (paragraphs [0025] to [0027]) can be used. In addition, the concentration of impurities in the concentrated water (calcium concentration, total alkalinity, and concentration of evaporation residue) is calculated from the previously measured impurity concentration of raw water (calcium concentration, total alkalinity, and concentration of evaporation residue) and the recovery rate. calculated from Therefore, the calcium deposition recovery rate Y _C is _the impurity concentration (mg / L) of the concentrated water when the Langerier index of the concentrated water becomes zero, and the impurity concentration (mg / L) of the raw water measured in advance. is represented by the relationship of the following _formula (3).
Y _C =(C _C −F _C )/C _C (3)

As the flow control valve 31, for example, a combination of a plurality of solenoid valves or constant flow valves (a plurality of which are connected in parallel) can be used. Preferably, a control valve is used. As a result, the degree of opening can be finely adjusted according to the resolution of the electric proportional control valve, and the recovery rate can be adjusted more smoothly than when adjusting the degree of opening in a stepwise manner using a combination of solenoid valves. For example, in a staged formula that can only control the recovery rate in the range of 50 to 70% in 5 stages (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 useless concentrated waste water. Therefore, the use of the electric proportional control valve as the flow control valve 31 is advantageous from the viewpoint of saving water because it is possible to reduce waste of such concentrated waste water.

In order to achieve further water saving, it is necessary to set a higher target value for the recovery rate. It may be designed to 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 scale inhibitor can be done by a dosing pump.

The scale inhibitor is not particularly limited as long as it is a substance capable of suppressing 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, nitrilotrimethylphosphonic acid, and salts thereof. Phosphonic acid-based compounds; phosphoric acid-based compounds such as orthophosphates and polymerized phosphates; maleic acid-based compounds such as polymaleic acid and maleic acid copolymers; are copolymers such as poly(meth)acrylic acid, maleic acid/(meth)acrylic acid, (meth)acrylic acid/sulfonic acid, (meth)acrylic acid/nonionic group-containing monomers, and (meth)acrylic acid/sulfonic acid /nonionic group-containing monomer, (meth)acrylic acid/acrylamide-alkylsulfonic acid/substituted (meth)acrylamide, and (meth)acrylic acid/acrylamide-arylsulfonic acid/substituted (meth)acrylamide terpolymer. Examples of the (meth)acrylic acid constituting the terpolymer include methacrylic acid, acrylic acid, and (meth)acrylic acid salts such as sodium salts thereof. Examples of acrylamide-alkylsulfonic acids constituting the terpolymer include 2-acrylamido-2-methylpropanesulfonic acid and salts thereof. Examples of substituted (meth)acrylamides constituting the terpolymer include t-butylacrylamide, t-octylacrylamide and dimethylacrylamide.

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 order to simultaneously suppress scale derived from calcium and silica, 2-phosphonobutane-1,2,4-tricarboxylic acid, acrylic acid and (meth)acrylic acid/2-acrylamido-2-methylpropanesulfonic acid It is particularly preferred to use a scale inhibitor consisting of a mixture of /substituted (meth)acrylamide with a terpolymer.

In addition, commercially available scale inhibitors for RO membranes include the "Orpersion" series manufactured by Organo Corporation, the "Flocon (registered trademark)" series manufactured by BWA Water Additives, and the "PermaTreat (registered trademark)" manufactured by Nalco. series, General Electric Company's "Hypersperse (registered trademark)" series, and Kurita Water Industries Ltd.'s "Kuriverter (registered trademark)" series.

As described above, in this embodiment, the flow rate of the concentrated water is maintained constant by the metering pump 12. Therefore, only by specifying the flow rate of the concentrated water flowing through one of the drainage line 4 and the recirculated water line 5, the other can be changed. The flow rate of the flowing concentrate can also be defined. Therefore, in the illustrated embodiment, the drainage line 4 is provided with a flow rate control means (a flow rate adjustment valve 31 and a drainage flow meter 32), and the return water line 5 is provided with concentrated water flowing through the drainage line 4 and the return water line 5. A manual valve (pressure regulating valve) 13 is provided for regulating the pressure balance, but the reverse is also possible. That is, the return water line 5 may be provided with a flow rate control valve (proportional control valve) and a flow meter as flow control means, and the drainage line 4 may be provided with a manual valve for pressure balance adjustment. Alternatively, both the drain line 4 and the return water line 5 may be provided with a flow control valve (proportional control valve) and a flow meter as flow control means. Further, in the above-described embodiment, the permeate flow rate control unit and the waste water flow rate control unit are provided separately, but one flow control unit adjusts the flow rate of the permeated water and the concentrated waste water. It can be like this.

(Second embodiment)
FIG. 2 is a schematic diagram showing the configuration of a membrane filtration device according to a second embodiment of the present invention. In the following, configurations similar to those of the first embodiment are denoted by the same reference numerals in the drawings, description thereof is omitted, and only configurations different from those of the first embodiment are described.

This embodiment is a modification of the first embodiment, and differs from the first embodiment in the configuration of the permeate flow rate control mechanism 20 . Specifically, it differs from the first embodiment in that the flow control valve 21 is provided in the supply line 1 instead of the concentrated water line 3 . 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 equipped with the metering pump 12 of the first embodiment. Instead, a pressurizing pump 15 is provided whose discharge flow rate changes according to pressure fluctuations of the raw water. A flow control valve 21 is arranged between the pressure pump 15 and the filtering means 11 .

In this embodiment, the permeate flow rate control by the permeate water flow rate control mechanism 20 is performed as follows. For example, when the water temperature decreases, the viscosity of the water increases, and as a result, the flow rate of the permeate separated by the RO membrane or the NF membrane decreases. It is controlled to increase the supply pressure of raw water to the filtering means 11 . In addition, when the water temperature rises, the viscosity of the water decreases, and as a result, the flow rate of the permeate separated by the RO membrane or NF membrane increases. controlled to reduce the raw water supply pressure. Thus, the degree of opening of the flow control 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 in this embodiment as well.

Although the flow rate of concentrated water separated by the RO membrane or NF membrane of the filtering means 11 also changes according to changes in the supply pressure of the raw water to the filtering means 11, in the present embodiment, the concentrated water line L3 A constant flow valve 14 is provided as described above. Therefore, even when the opening degree of the flow control 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 permeate flow control by the permeate flow control mechanism 20 .

Here, the specified flow rate of the constant flow valve 14 should be such that clogging of the membrane due to fouling or scaling does not occur on the one hand, and that the membrane 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 pressure pump 15 will be increased more than necessary, and as a result the size of the pressure pump 15 will increase, resulting in energy consumption. It is not preferable in terms of Therefore, the specified flow rate of the constant flow valve 14 is set in consideration of the permeation flux of the filtration means 11 and the minimum flow rate of concentrated water required for the filtration means 11. For example, the diameter of the filtration means 11 is about 10.16 cm. (4 inch) RO membrane is in the range of 200 to 1500 L/h.

By the way, the constant flow valve 14 has an operating differential pressure range (permissible range of pressure difference between the primary side and the secondary side of the constant flow valve) for operating the constant flow valve 14 normally. Therefore, depending on the conditions, for example, when a medium- and high-pressure RO membrane is used as the filtration means 11, or when the water temperature drops significantly, the supply pressure of the raw water rises significantly 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 on the upstream side of the constant flow valve 14 is reduced (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 the raw water to the filtering means 11 rises significantly, the pressure difference between the primary side and the secondary side of the constant flow valve 14 is kept within the differential pressure range of the constant flow valve 14. 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 addition, by providing the pressure reducing valve, peripheral members (such as pipes) downstream of the pressure reducing valve are not required to have such a high pressure resistance performance. Therefore, installation of a pressure reducing valve is not only advantageous in terms of safety, but is also advantageous in terms of cost, since inexpensive general-purpose products with not so high pressure resistance can be used. The type of pressure reducing valve is not particularly limited as long as it can reduce the pressure of the concentrated water to within the operating differential pressure range of the constant flow valve 14. or the pressure on the secondary side is greater than the water flow differential pressure of the drainage line 4 and the recirculated water line 5 .

(Third embodiment)
FIG. 3 is a schematic diagram showing the configuration of a membrane filtration device according to a third embodiment of the present invention. In the following, configurations similar to those of the above-described embodiment are denoted by the same reference numerals in the drawings, description thereof is omitted, and only configurations different from the above-described embodiment are described.

This embodiment is a modification of the first embodiment in that another filter means (second filter means) 16 is provided downstream of the filter means (first filter means) 11. , differs from the first embodiment. The second filtering means 16 is connected in series with the first filtering means 11 and treats permeated water separated by the first filtering means 11 as water to be treated. That is, the upstream side of the second filtering means 16 is connected to the first permeated water line 2a for circulating the permeated water from the first filtering means 11, and the downstream side from the second filtering means 16 A second permeated water line 2b is connected for circulating the permeated water. Thereby, the membrane filtration device 10 of this embodiment can generate treated water of better quality than 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 permeated water and concentrated water. does not need to be discharged to Therefore, from the viewpoint of saving water, the second concentrated water line 6 is arranged upstream of the metering pump 12 to return all of the concentrated water separated by the second filtering 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 on 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 cleaning the RO membrane or NF membrane of the second filtering means 16. A drain 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, the recovery rate of the second filtering means 16 (the sum of the flow rate of the permeated water from the second filtering means 16 and the flow rate of the concentrated water from the second filtering means 16, from the second filtering means 16 permeate flow rate) can be arbitrarily adjusted. In addition, in order to eliminate the complexity of manual adjustment of the recovery rate, instead of the manual valve 17, a proportional control valve whose opening can be adjusted based on the flow rate of the concentrated water detected by the concentrated water flow meter 18 is provided. may have been Alternatively, a constant flow valve may be provided instead of the manual valve 17 and the concentrate flow meter 18 in order to keep the recovery rate within a certain range. In this case, depending on the conditions, the pressure difference between the primary side and the secondary side of the constant flow valve may exceed the operating differential pressure range. As in the case of 14, a pressure reducing valve may be provided upstream of the constant flow valve.

In this embodiment, the permeate flow meter 22 of the permeate flow rate control mechanism 20 is used to supply a constant flow rate of treated water to, for example, an electrodeionization water production device connected downstream of the membrane filtration device 10. is provided in the second permeate line 2b. For this reason, the waste water flow rate control unit 33 needs to separately know the flow rate of the permeate flowing through the first permeate line 2a in calculating the set flow rate of the concentrated waste water based on the target value of the recovery rate. In embodiments, the flow rate can be detected indirectly. That is, the waste water flow rate control unit 33 controls the measured value by the permeated water flow meter 22 (the flow rate of the permeated water from the second filtering means 16) and the measured value by the concentrated water flow meter 18 (the flow rate of the permeated water from the second filtering means 16). The flow rate of the concentrated water) can be used to calculate the flow rate of the permeate flowing through the first permeate line 2a. Also, as described above, when a constant flow 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 measured value by the concentrated water flow meter 18. , the flow rate of the permeate flowing through the first permeate line 2a can be calculated. Alternatively, a flow meter (not shown) may be provided in the first permeated water line 2a to directly detect the flow rate of the permeated water from the first filtering means 11 .

In this 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. may Even in that case, the flow rate adjustment valve for controlling the flow rate of the permeated water is provided in the concentrated water line connected to the most upstream filtering means among the three or more filtering means, and the most downstream filtering means The separated permeate is adjusted to the set flow rate (preset target flow rate). Here, "connected in series" means that the water to be treated is sequentially treated by a plurality of filtration means, and in two adjacent filtration means, separated by the upstream filtration means It means that the permeated water is supplied to the filtering means on the downstream side as the water to be treated. Moreover, each filtering means may be composed of a plurality of RO membranes or NF membranes. In this case, a plurality of RO membranes or NF membranes are connected in series on the primary side (the distribution side of raw water and concentrated water) and finally connected to the concentrated water line, and the secondary side (the distribution side of permeated water) is connected in series. It will be connected in parallel and finally connected to the permeate line.

(Fourth embodiment)
FIG. 4 is a schematic diagram showing the configuration of a membrane filtration device according to a fourth embodiment of the present invention. In the following, configurations similar to those of the above-described embodiment are denoted by the same reference numerals in the drawings, description thereof is omitted, and only configurations different from the above-described embodiment are described.

This embodiment is a modification of the second embodiment and also a modification of the third embodiment. The configuration is different from that of the third embodiment. That is, the flow control valve 21 is provided in the supply line 1 instead of the first concentrated water line 3, and along with this, the first concentrated water line 3 is provided with a constant flow valve 14, and the supply line 1 is provided with a constant flow valve 14. A pressure pump 15 is provided. Other configurations are the same as those of the second embodiment or the third embodiment.

In this embodiment, since it is necessary to supply raw water to the two filtering means 11 and 16 with one pressurizing pump 15, the supply pressure of the raw water to the first filtering means 11 by the pressurizing pump 15 is It becomes larger than the second embodiment. Therefore, in this embodiment, the pressure difference between the primary side and the secondary side of the constant flow valve 14 is likely to exceed the operating differential pressure range. preferably.

Also in this embodiment, the number of filtering means is not limited to two, and it goes without saying that the number may be three or more.

1 feed line 2 permeate line 2a first permeate line (intermediate permeate line)
2b second permeate line 3 concentrate line (first concentrate line)
4 drainage line 5 reflux water line 6 second concentrated water line 10 membrane filtration device 11 filtration means (first filtration means)
12 metering pump 13, 17 manual valve 14 constant flow valve 15 pressure 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 section 30 drainage Flow Control Mechanism 31 Flow Control Valve 32 Drainage Flow Meter 33 Drainage Flow Controller

Claims (1)

Filtration means having a reverse osmosis membrane or nanofiltration membrane for separating the water to be treated into permeated water and concentrated water;
a supply line connected to the filtering means for supplying water to be treated to the filtering means;
a permeated water line connected to the filtering means for circulating the permeated water from the filtering means;
a concentrated water line connected to the filtering means and for circulating the concentrated water from the filtering means;
a drainage line branching from the concentrated water line and discharging a part of the concentrated water flowing through the concentrated water line to the outside;
a reflux water line that is branched from the concentrated water line and connected to the supply line to return the rest of the concentrated water flowing through the concentrated water line to the supply line;
a vane pump provided in the supply line for supplying a constant flow rate of water to be treated to the filtering means;
A first flow control means for adjusting the flow rate of the permeate flowing through the permeate line to a preset target flow rate, comprising: a flow control valve provided in the concentrated water line; and a permeate flowing through the permeate line. Flow rate detecting means for detecting the flow rate of water; and based on the flow rate of the permeated water detected by the flow rate detecting means, the opening degree of the flow rate adjusting valve is adjusted to control the flow rate of the permeated water flowing through the permeated water line. a first flow rate control means having a control unit that adjusts to the target flow rate;
a pressure regulating valve provided in the reflux water line and having an adjustable opening for adjusting the pressure balance of the concentrated water flowing through the drain line and the concentrated water flowing through the reflux line;
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, comprising: a flow rate adjusting valve provided in the drainage line; and a flow rate for detecting the flow rate of the concentrated water flowing through the drainage line. second flow rate control means having detection means and a control section that adjusts the degree of opening of the flow rate adjustment valve based on the flow rate of the concentrated water detected by the flow rate detection means;
water temperature detection 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 ,
The control unit of the second flow control means controls the ratio of the flow rate of the permeate flowing through the permeate line to the sum of the flow rate of the permeate flowing through the permeate line and the flow rate of the concentrated water flowing through the drain line. Based on the water temperature detected by the water temperature detection means, such that a certain recovery rate is the maximum recovery rate at which silica or calcium does not precipitate on the membrane surface of the reverse osmosis membrane or nanofiltration membrane of the filtration means, A membrane filtration device that determines the set flow rate of concentrated water flowing through the drainage line .

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