JP7106395B2 - 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 (the ratio of the permeate flow rate to the sum of the permeate flow rate and the concentrated wastewater 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 permeate by adjusting the supply pressure of the raw water.

In permeate flow rate control, when the feed pressure of raw water is adjusted so that the flow rate of permeate water is constant, the flow rate of concentrated water separated by the RO membrane or NF membrane also changes accordingly. Such changes in the flow rate of the concentrate lead to clogging of the membrane due to fouling and scaling, and damage to the membrane due to increased pressure loss. Control is required. However, in the membrane filtration device with the above-described configuration, the flow rate of the concentrated water is controlled to a predetermined ratio to the flow rate of the permeated water by controlling the flow rate of the concentrated reflux water or the concentrated waste water. If you try to maintain it, the flow control may interfere with each other and hunting may occur.

Therefore, Patent Document 1 proposes, as a method of avoiding hunting, a method of always maintaining a constant flow rate of concentrated water by providing a constant flow valve in a concentrated water line through which the concentrated water flows. According to this method, the permeate flow rate control does not affect the concentrate flow rate, so whatever flow control is performed on the concentrate side interferes with the permeate flow rate control. Therefore, hunting can be avoided. On top of that, in Patent Document 1, as a flow rate control of concentrated wastewater, a flow rate of concentrated wastewater can be adjusted to a set flow rate by providing a flow meter and a flow rate adjustment valve in a wastewater line that discharges concentrated wastewater to the outside. Have been described.

However, in the flow rate control of concentrated wastewater described in Patent Document 1, when the pressure in the supply line that supplies raw water to the membrane filtration device becomes low, the concentrated refluxed water is sent to the wastewater line through the refluxed water line that returns the concentrated refluxed water to the supply line. The pressure on the primary side of the provided flow control valve becomes lower than the pressure on the secondary side, and there is a possibility that the concentrated water cannot be discharged to the outside from the drain line. In such a situation, for example, in addition to the target membrane filtration device, there are multiple points of use that receive raw water from the same raw water supply source, and raw water is used simultaneously at these multiple points of use. can occur in some cases.

On the other hand, in Patent Document 2, by providing a pressure regulating valve in the recirculated water line, the pressure on the primary side of the flow rate regulating valve provided in the drainage line is set to a predetermined pressure (higher than the pressure on the secondary side) ) has been proposed. According to this method, even if the pressure of the raw water flowing through the supply line becomes low under the above-described conditions, it is possible to avoid the situation where the concentrated water cannot be discharged to the outside from the drain line.

Japanese Patent No. 6161384 JP 2016-203084 A

However, in the method described in Patent Document 2, in addition to flow rate control of permeated water and concentrated water (concentrated wastewater), pressure control of concentrated water is also performed, so more measuring equipment is required. For example, the device configuration becomes complicated. In addition, more complicated control is required, and as a result, it may not be possible to suppress the occurrence of hunting.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a membrane filtration apparatus that achieves stable flow rate control with a simpler configuration even if the pressure of the water to be treated fluctuates.

In order to achieve the above object, a membrane filtration device according to one aspect of the present invention includes filtration means having a reverse osmosis membrane or nanofiltration membrane that separates water to be treated into permeated water and concentrated water, and is connected to the filtration means. A supply line for supplying water to be treated to the filtering means, a permeated water line connected to the filtering means for circulating permeated water from the filtering means, and a permeated water line connected to the filtering means for circulating concentrated water from the filtering means A concentrated water line, a drain line that branches from the concentrated water line and discharges part of the concentrated water flowing through the concentrated water line to the outside, and a concentrated water line that branches from the concentrated water line and is connected to the supply line and flows through the concentrated water line. A reflux water line for returning the remaining water to the supply line, a first flow rate control means for adjusting the flow rate of the permeated water flowing through the permeated water line to a set flow rate, and a concentrated water line provided in the concentrated water line to concentrate the concentrated water flowing through the concentrated water line. a constant flow rate valve for keeping the flow rate of water constant; a second flow control means for adjusting the flow rate of the concentrated water flowing through the drainage line to a set flow rate; A flow rate detection means provided in the line for detecting the flow rate of the concentrated water flowing through the drainage line , and a control section for adjusting the opening degree of the flow rate adjustment valve based on the flow rate of the concentrated water detected by the flow rate detection means. and a manual valve provided in the drain line for adjusting the pressure of the concentrated water flowing through the drain line .

In addition, a membrane filtration device according to another aspect of the present invention is a plurality of filtration means connected in series, each of which comprises a reverse osmosis membrane or a nanofiltration membrane for separating the water to be treated into permeated water and concentrated water. a plurality of filtering means, a supply line connected to the most upstream filtering means among the plurality of filtering means and supplying the water to be treated to the most upstream filtering means, and the most downstream of the plurality of filtering means A permeated water line that is connected to the filtering means and circulates the permeated water from the most downstream filtering means, and a concentrated water line that is connected to the most upstream filtering means and circulates the concentrated water from the most upstream 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 first flow control means for adjusting the flow rate of the permeated water flowing through the permeated water line to a set flow rate, and the concentrated water flow rate provided in the concentrated water line and flowing through the concentrated water line. and 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, the flow rate adjustment valve provided in the reflux water line and the flow rate adjustment valve provided in the drainage line. a flow rate detection means for detecting the flow rate of concentrated water flowing through the drainage line ; and a control section for adjusting the opening degree of the flow rate adjustment valve based on the flow rate of the concentrated water detected by the flow rate detection means. and a manual valve provided in the drain line for adjusting the pressure of the concentrated water flowing through the drain line .

According to such a membrane filtration device, the flow rate control valve provided in the reflux line for adjusting the flow rate of the concentrated water (concentrated wastewater) flowing through the drainage line adjusts the pressure of the concentrated water flowing through the drainage line and the reflux water line. It also functions as a pressure regulating valve that adjusts the balance. Therefore, for example, even if a deviation occurs in the above-mentioned pressure balance due to a pressure drop of the water to be treated flowing through the supply line, the deviation is compensated for and the flow rate of the concentrated wastewater is increased without separately providing a special pressure adjustment mechanism. Can be adjusted to the set flow rate.

As described above, according to the present invention, it is possible to provide a membrane filtration device that realizes stable flow rate control with a simpler configuration even if the pressure of the water to be treated fluctuates.

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.

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 the pressure pump 21, 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 has a permeate flow rate control mechanism (first flow rate control means) 20 that adjusts the flow rate of permeate flowing through the permeate line 2 to a set flow rate.

The permeate flow rate control mechanism 20 is provided in the supply line 1 and includes a pressure pump (pressure adjustment means) 21 for adjusting the pressure of the raw water flowing through the supply line 1 (supply pressure of the raw water to the filtration means 11), and the permeate A permeate flow meter (flow rate detection means) 22 provided in the line 2 for detecting the flow rate of the permeate flowing through the permeate line 2, and based on the flow rate of the permeate detected by the permeate flow meter 22, pressurization and a permeate water flow control unit 23 for controlling the pump 21 .

The permeate flow rate control unit 23 includes an inverter (not shown) that controls the rotation speed of the pressure pump 21, and controls the pressure pump so that the permeate flow rate detected by the permeate flow meter 22 is constant. 21 rotation speed is controlled. 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 rotation speed of the pressure pump 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, the permeate water flow control unit 23 increases the supply pressure of the raw water by increasing the rotational speed of the pressure pump 21 so as to compensate for this decrease. 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 reduces the supply pressure of the raw water by reducing the rotational speed of the pressure pump 21 so as to cancel out this increase.

Thus, 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. The flow rate of the concentrated water separated by the RO membrane or NF membrane also changes according to the change in the supply pressure. 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, 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 filtering means 11 is changed, the flow rate of the concentrated water can be kept constant. .

Here, the specified flow rate of the constant flow valve 12 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 12 is increased more than necessary, the flow rate required of the pressure pump 21 will be increased more than necessary, and as a result the size of the pressure pump 21 will increase, resulting in energy consumption. It is not preferable in terms of Therefore, the specified flow rate of the constant flow valve 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 20.32 cm. (8 inch) RO membrane, it ranges from 1 to 15 m ³ /h. The minimum flow rate of the concentrated water required for the filtering means 11 means the minimum flow rate of the concentrated water to be flowed through the concentrated water line 3 so as not to cause clogging of the membrane due to fouling or scaling.

By the way, the constant flow valve 12 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 12 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 extremely, 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 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, the pressure of the concentrated water flowing through the concentrated water line 3 on the upstream side of the constant flow valve 12 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 if 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 12 is kept within the differential pressure range of the constant flow valve 12. 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 12. 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 .

As described above, the installation of the constant flow valve 12 prevents the flow rate control of the permeated water from affecting the flow rate of the concentrated water. easily feasible. Therefore, the membrane filtration device 10 of the present embodiment includes a waste water flow rate control mechanism (second flow rate control means) 30 for adjusting the flow rate of concentrated water (hereinafter referred to as "concentrated waste water") flowing through the waste water line 4 to a set flow rate. have. 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 wastewater flow rate control mechanism 30 includes a flow rate adjustment valve 31 provided in the recirculated water line 5, a wastewater flowmeter 32 provided in the wastewater line 4 for detecting the flow rate of the concentrated wastewater, and the concentrated wastewater detected by the wastewater flowmeter 32. and a drainage flow control unit 33 that adjusts the opening degree of the flow control valve 31 based on the flow rate.

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 constant flow valve 12, when the flow rate of the concentrated waste water decreases, naturally, the flow rate of the concentrated water flowing back from the reflux water line 5 to the supply line 1 increases. do. 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 this 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 deposition 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 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).
(Target flow rate of concentrated wastewater) =
(Detected flow rate of permeated water/Target recovery rate) - (Detected flow rate of permeated water) (1)

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 target flow rate as the set flow rate of the concentrated waste water. As the recovery rate (target recovery rate), a value expressed in percent is usually used, but in the above formula (1), it goes without saying that a value expressed in decimals is used.

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 the 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.

[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)

The recovery rate, which is the ratio of the permeate flow rate to the sum of the permeate flow rate and the concentrated wastewater flow rate, is the ratio of the concentrated water flow rate to the sum of the permeate flow rate and the concentrated wastewater flow rate. It can be expressed as a magnification. That is, the recovery rate Y can be expressed by the following formula (4), where N is the allowable concentration factor.
Y=(N−1)/N (4)

Therefore, the above formulas (1) to (3) can be expressed as follows using the above formula (4).
(Target flow rate of concentrated wastewater) = (Detected flow rate of permeated water) / (Allowable concentration ratio - 1) (1')
N _S =C _S /F _S (2′)
N _C =C _C /F _C (3′)
Here, N _S is the permissible concentration ratio corresponding to the precipitation recovery rate of calcium, and N _C is the permissible concentration ratio corresponding to the precipitation recovery rate of silica.

The method for calculating the precipitation recovery rate of silica and calcium and the method for calculating the set flow rate of concentrated wastewater may be used when there are restrictions on the recovery rate and flow rate in advance due to restrictions on device design such as the capacity of the pressurizing pump and the flow rate of raw water. is not limited to the above. In addition, a preset target flow rate of permeate can be used to calculate the set flow rate of concentrated wastewater. This is not preferable because the recovery rate of the product may deviate from the target recovery rate. That is, if the actual permeate flow rate is greater than the target flow rate, scaling occurs due to the actual recovery exceeding the target recovery rate, or if the actual permeate flow rate is less than the target flow rate. If the actual recovery rate falls below the target recovery rate, it becomes impossible to save water.

Therefore, as described above, it is preferable to use the detected flow rate of the permeated water by the permeated water flow meter 12 for calculating the set flow rate of the concentrated waste water. As a result, even if the flow rate control of the permeated water is not appropriately performed, it is possible to prevent the actual recovery rate from deviating from the target recovery rate. In actual calculation, it is preferable to use an average flow rate for a predetermined detection time or a predetermined number of times of detection in order to minimize the influence of variations in the detected flow rate of permeated water.

However, if the flow rate of the permeate is not stable and the variation in the detected flow rate is very large, such as when starting up the device or restarting operation, the permeate Using the target flow rate of, the set flow rate of the concentrated waste water may be calculated. Further, the flow rate of the permeated water used for calculating the set flow rate of the concentrated waste water may be switched according to the difference between the target flow rate and the actual flow rate of the permeated water. That is, if the difference is within a predetermined range, the target flow rate may be used for calculation, and if the difference is outside the predetermined range, the actual flow rate may be used for calculation.

When performing recovery rate control as described above, it is preferable to use an electric proportional control valve as the flow control valve 31 . 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.

However, when an electric proportional control valve is used as the flow control valve 31, it is necessary to pay attention to the relationship between the opening/closing speed and the calculation speed (computation speed) of the set flow rate of the concentrated waste water by the waste water flow control unit 33. For example, if the two speeds are significantly different, hunting may occur if the set flow rate of the concentrated waste water is changed before the electric proportional control valve is completely opened and closed and the flow rate of the concentrated waste water is stabilized. . In addition, since the set flow rate of the concentrated waste water is determined based on the flow rate of the permeated water detected by the permeated water flow meter 22, the flow rate control of the concentrated waste water also depends on the response speed of the inverter that controls the rotation speed of the pressure pump 21. may be affected. Therefore, it is preferable to consider the opening/closing speed of the electric proportional control valve and the response speed of the inverter when determining the calculation speed of the set flow rate of the concentrated waste water by the waste water flow control unit 33 . That is, it is preferable to slow the response speed of the inverter when the opening/closing speed of the electric proportional control valve is slow, and to increase the response speed of the inverter when the opening/closing speed of the electric proportional control valve is fast. In this embodiment, as described above, the flow rate control of the permeated water and the flow rate control of the concentrated water are performed independently by installing the constant flow valve 12, so that the mutual flow control is prevented from interfering. be able to. As a result, the occurrence of hunting as described above can be suppressed as much as possible, and deviation of the actual recovery rate from the target recovery rate can be suppressed. Also from this point, it is preferable that the concentrated water line 3 is provided with the constant flow valve 12 .

In the present embodiment, a scale inhibitor is added to the raw water for the purpose of increasing the above-mentioned deposition recovery rate in order to set the target value of the recovery rate higher and achieve further water saving. can be In this case, the specified flow rate of the constant flow rate valve 12 can be reduced, and as a result, energy saving can be realized by using the pressure pump 21 with a smaller capacity. 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, (meth)acrylic acid/acrylamide-arylsulfonic acid/substituted (meth)acrylamide terpolymer, and the like. 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.

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 adjustment valve 31 for adjusting the flow rate of the concentrated waste water is provided in the recirculated water line 5. It will also function as a pressure regulating valve to adjust the pressure balance of the flowing concentrated water. That is, by adjusting the opening degree of the flow rate adjustment valve 31 while monitoring the detected flow rate of the concentrated wastewater by the wastewater flow meter 32, the flow rate of the concentrated wastewater is adjusted to the set flow rate, and at the same time, the wastewater line 4 and the return The pressure balance of the concentrated water flowing through the running water line 5 is adjusted to an appropriate state. Therefore, even if the above-mentioned pressure balance is deviated due to the pressure drop of the raw water flowing through the supply line 1, the deviation is compensated for and the flow rate of the concentrated wastewater is adjusted to the set flow rate without providing a separate special pressure adjustment mechanism. can be adjusted. In addition to the membrane filtration device 1 of the present embodiment, the pressure drop of the raw water flowing through the supply line 1 has a plurality of use points where raw water is supplied from the same raw water supply pipe (water supply means to be treated). This may occur when raw water is used simultaneously at those multiple points of use.

By the way, in order to adjust the flow rate of a fluid flowing through a target pipe, it is common technical knowledge to install a set of a flow rate adjusting valve and a flow rate detection means (flow meter) in the pipe. Therefore, in the present embodiment, the drainage line 4 is provided with a flow rate detection means (drainage flow meter 32). It is also conceivable to adjust the opening degree of the flow control valve 31 based on the detected flow rate of the flowing concentrated water (hereinafter referred to as "concentrated reflux water"). That is, the flow rate adjustment valve 31 is adjusted so that the detected flow rate of the concentrated reflux water by the reflux water flow meter is the difference between the specified flow rate of the constant flow rate valve 12 and the set flow rate of the concentrated waste water determined in consideration of the recovery rate. It is also conceivable to adjust the opening of

However, since the specified flow rate of the constant flow valve 12 generally has an error of about ±10%, the opening degree of the flow rate adjustment valve 31 is , there is a risk that the flow rate of concentrated wastewater cannot be adjusted to the set flow rate. For example, when the specified flow rate of the constant flow valve 12 is 3300 L / h, the set flow rate of the permeated water is 1000 L / h, and the target recovery rate is 75%, the set flow rate of the concentrated waste water is 400 L / h. The set flow rate of running water (the difference between the specified flow rate of the constant flow valve 12 and the set flow rate of the concentrated waste water) is 2900 L/h. Here, if the specified flow rate of the constant flow valve 12 has an error of +10%, the actual flow rate of the concentrated water flowing through the concentrated water line 3 is 3630 L/h. Therefore, when the flow rate of concentrated reflux water is adjusted to 2900 L/h as described above, the flow rate of concentrated waste water is adjusted to 730 L/h, and the actual recovery rate is 57.8%, which is lower than the target recovery rate and wasteful. wastewater will occur. On the other hand, if the specified flow rate of the constant flow valve 12 has an error of -10%, the actual recovery rate is 93.5%, which greatly exceeds the target recovery rate, and the risk of scale generation becomes very high. put away. For this reason, in order to control the flow rate of the concentrated waste water with higher accuracy, a flow rate adjusting means (a waste water flow meter 32) is installed in the waste water line 4 as in the present embodiment, and the recirculated water line 5 Installation of the flow control valve 31 is essential.

In the above-described embodiment, when the pressure of the raw water flowing through the supply line 1 increases and the pressure on the secondary side of the flow control valve 31 becomes higher than the pressure on the primary side through the connection with the recirculated water line 5, the recirculated water There is a possibility that the concentrated water will stop flowing in line 5. In addition, when the pressure of the raw water flowing through the supply line 1 increases and the flow rate control valve 31 is fully opened, the pressure on the primary side of the flow rate control valve 31 (that is, the pressure on the secondary side of the constant flow rate valve 12) becomes constant. If the differential pressure is so high that it is outside the operating differential pressure range of the flow valve 12, the flow rate of concentrate flowing through the concentrate line may not be kept constant. Therefore, a pressure reducing valve for reducing the pressure of the raw water flowing through the supply line 1 may be provided in the supply line 1 on the upstream side of the connecting portion with the recirculated water line 5 . As a result, even if the pressure of the raw water flowing through the supply line 1 increases, the pressure on the secondary side of the flow control valve 31 can be maintained lower than the pressure on the primary side, and the pressure on the primary side and the secondary side of the constant flow valve 12 can be maintained. can be kept within the operating differential pressure range. Further, when the pressure of the raw water flowing through the supply line 1 fluctuates greatly, or when the pressure of the concentrated water flowing through the drainage line 4 fluctuates greatly, the drainage line 4 is provided with a manual valve for pressure adjustment. good too. In this case, when the pressure of the raw water in the supply line 1 is maximum, or when the pressure of the concentrated water flowing through the drain line 4 is minimum, the flow control valve 31 is fully opened, and the flow rate of the concentrated water flowing through the drain line 4 is reduced to If the manual valve is adjusted so as to achieve the set flow rate at the maximum recovery rate described above, there is no need to adjust the manual valve thereafter, and complicated control is not required. Moreover, since there is no need to monitor the pressure of the concentrated water at this time, there is no need to install an additional pressure gauge, and the simplicity of the device configuration is not impaired.

Further, in the above-described embodiment, the permeate flow control unit and the waste water flow 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.

In this embodiment, in addition to the filtering means (first filtering means) 11 of the first embodiment, another filtering means (second filtering means) 13 is provided downstream thereof. The second filtering means 13 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, a first permeate line (intermediate permeate line) 6 for circulating the permeated water from the first filter means 11 is connected to the upstream side of the second filtration means 13, and a second A second permeated water line 2 for passing the permeated water from the filtering means 13 of No. 2 is connected. Thereby, the membrane filtration device 10 of the present embodiment can generate treated water of better quality than the first embodiment.

A second concentrated water line 7 for circulating the concentrated water from the second filtering means 13 is connected to the second filtering means 13 . In the second filtering means 13, 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 7 is arranged upstream of the pressurizing pump 21 to return all of the concentrated water separated by the second filtering means 13 to the supply line 1. 1. Alternatively, the second concentrated water line 7 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 7, part or all of the concentrated water from the second filtering means 13 is discharged to the outside when cleaning the RO membrane or NF membrane of the second filtering means 13. A drain line may be connected.

The second concentrated water line 7 is provided with a manual valve 14 and a concentrated water flow meter 15 for adjusting the flow rate of the concentrated water flowing through the second concentrated water line 7 . As a result, the recovery rate of the second filtering means 13 (the sum of the flow rate of the permeated water from the second filtering means 13 and the flow rate of the concentrated water from the second filtering means 13, from the second filtering means 13 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 14, 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 15 is provided. may have been Alternatively, a constant flow valve may be provided in place of the manual valve 14 and the concentrate flow meter 15 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 (the allowable range of the pressure difference for normal operation of the constant flow valve). However, in order to avoid this, 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 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 2 . For this reason, the wastewater flow rate control unit 33 needs to separately know the flow rate of the permeate flowing through the first permeate line 6 in calculating the set flow rate of the concentrated wastewater 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 13) and the measured value by the concentrated water flow meter 15 (the flow rate of the permeated water from the second filtering means 13). The flow rate of the permeate flowing through the first permeate line 6 can be calculated from the sum of the flow rate of the concentrated water). Also, as described above, when a constant flow valve is provided instead of the manual valve 14 and the concentrated water flow meter 15, the specified flow rate of the constant flow valve is used instead of the measured value by the concentrated water flow meter 15. , the permeate flow rate through the first permeate line 6 can be calculated. Alternatively, a flow meter (not shown) may be provided in the first permeated water line 6 to directly detect the flow rate of the permeated water from the first filtering means 11 .

In this embodiment, since it is necessary to supply raw water to the two filtering means 11 and 13 with one pressurizing pump 21, the supply pressure of the raw water to the first filtering means 11 by the pressurizing pump 21 is It becomes larger than in the first embodiment. Therefore, the prescribed flow rate of the constant flow rate valve 12 must be set in consideration of this point as well. For example, when RO membranes having a diameter of about 20.32 cm (8 inches) are used as the two filtration means 11 and 13, respectively, the applicable temperature range of the first filtration means 11 is 5 to 35 ° C., and the silica concentration and When the control range of the recovery rate is assumed to be 50 to 85% from the calcium concentration, for example, the constant flow valve 12 is a constant flow valve manufactured by Keihin Corporation (product number: NSPW-25, set flow rate: 55 L / min). can be used.

In the above-described embodiment, two filtering means are connected in series, but the number of filtering means is not limited to this, and even if three or more filtering means are connected in series, good. Even in that case, the pressure reducing valve is provided in the concentrated water line connected to the most upstream filtering means among the three or more filtering means, and the permeated water separated by the most downstream filtering means is the set flow rate ( preset target flow rate). However, it is needless to say that the flow rate distribution between the permeated water and the concentrated water needs to be appropriately set and adjusted by any flow rate adjusting means in all the filtering means except for the most upstream filtering means. Furthermore, in calculating the set flow rate of concentrated wastewater from the most upstream filtration means, the flow rate of the permeated water separated by the most upstream filtration means is used instead of the permeate separated by the most downstream filtration means. Note that used 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 (distribution side of raw water and concentrated water) and finally connected to the concentrated water line, and the secondary side (distribution side of permeated water) is It will be connected in parallel and finally connected to the permeate line.

1 feed line 2 permeate line (second permeate line)
3 Concentrated water line (first concentrated water line)
4 drainage line 5 reflux water line 6 first permeated water line 7 second concentrated water line 10 membrane filtration device 11 filtration means (first filtration means)
12 Constant Flow Valve 13 Second Filtration Means 14 Manual Valve 15 Concentrated Water Flow Meter 20 Permeated Water Flow Control Mechanism 21 Pressure Pump 22 Permeated Water Flow Meter 23 Permeated Water Flow Control Part 30 Drainage Flow Control Mechanism 31 Flow Control Valve 32 Drainage Flow meter 33 Wastewater flow control unit

Claims (8)

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 first flow rate control means for adjusting the flow rate of the permeate flowing through the permeate line to a set flow rate;
a constant flow valve provided in the concentrated water line for maintaining a constant flow rate of the concentrated water flowing through the concentrated water 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 adjustment valve provided in the reflux water line ; A second flow rate control comprising flow rate detection means for detecting a flow rate of concentrated water, and a control section for adjusting an opening degree of the flow rate adjustment valve based on the flow rate of the concentrated water detected by the flow rate detection means. means and
A manual valve provided in the drainage line for adjusting the pressure of the concentrated water flowing through the drainage line;
A membrane filtration device having a plurality of filtering means connected in series, each filtering means having a reverse osmosis membrane or a nanofiltration membrane for separating the water to be treated into permeated water and concentrated water;
a supply line connected to the most upstream filtering means among the plurality of filtering means and supplying water to be treated to the most upstream filtering means;
a permeated water line connected to the most downstream filtering means among the plurality of filtering means and for circulating the permeated water from the most downstream filtering means;
a concentrated water line connected to the most upstream filtering means and for circulating the concentrated water from the most upstream 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 first flow rate control means for adjusting the flow rate of the permeate flowing through the permeate line to a set flow rate;
a constant flow valve provided in the concentrated water line for maintaining a constant flow rate of the concentrated water flowing through the concentrated water 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 adjustment valve provided in the reflux water line ; A second flow rate control comprising flow rate detection means for detecting a flow rate of concentrated water, and a control section for adjusting an opening degree of the flow rate adjustment valve based on the flow rate of the concentrated water detected by the flow rate detection means. means and
A manual valve provided in the drainage line for adjusting the pressure of the concentrated water flowing through the drainage line;
A membrane filtration device having 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. 2. The membrane filtration device according to claim 1, wherein said set flow rate of concentrated water flowing through said drainage line is determined such that a certain recovery rate becomes a predetermined value. 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 rate control means detects the recovery rate based on the water temperature detected by the water temperature detection means, silica or silica on the membrane surface of the reverse osmosis membrane or nanofiltration membrane of the filtration means. 4. The membrane filtration device according to claim 3, wherein said set flow rate of concentrated water flowing through said drainage line is determined so as to achieve a maximum recovery rate at which calcium is not precipitated. Having an intermediate permeate line connected to the most upstream filtering means and through which the permeated water from the most upstream filtering means flows;
The control unit of the second flow control means controls the flow rate of the permeate flowing through the intermediate permeate line with respect to the sum of the flow rate of the permeate flowing through the intermediate permeate line and the flow rate of the concentrated water flowing through the drain line. 3. The membrane filtration device according to claim 2, wherein said set flow rate of concentrated water flowing through said drainage line is determined so that a recovery rate, which is a ratio, becomes a predetermined value. Water temperature detection means for detecting the water temperature of any one of the water to be treated supplied to the most upstream filtering means, the permeated water from the most upstream filtering means, and the concentrated water from the most upstream filtering means. has
The control unit of the second flow rate control means determines that the recovery rate is the reverse osmosis membrane or nanofiltration membrane of the most upstream filtration means based on the water temperature detected by the water temperature detection means. 6. The membrane filtration device according to claim 5, wherein said set flow rate of concentrated water flowing through said drainage line is determined so as to achieve a maximum recovery rate at which silica or calcium is not precipitated on the surface. The membrane filtration device according to any one of claims 1 to 6, wherein the supply line is connected to a water supply means for supplying water to be treated to a plurality of points of use. The first flow rate control means is provided in the supply line, pressure adjustment means for adjusting the pressure of the water flowing through the supply line, and flow rate detection means for detecting the flow rate of the permeated water flowing through the permeate line. 8. The membrane filtration device according to any one of claims 1 to 7, further comprising: a controller for controlling said pressure adjusting means based on the flow rate of said permeated water detected by said flow rate detecting means.

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