WO2014133101A1

WO2014133101A1 - Method for producing desalinated water

Info

Publication number: WO2014133101A1
Application number: PCT/JP2014/054941
Authority: WO
Inventors: 谷口　雅英; 智宏前田
Original assignee: 東レ株式会社
Priority date: 2013-02-28
Filing date: 2014-02-27
Publication date: 2014-09-04
Also published as: JPWO2014133101A1; JP6269486B2

Abstract

　Desalinated water is stably produced with minimal membrane degradation and fouling during operation of a water treatment apparatus based on a reverse osmosis membrane using natural energy as primary power. A method for pressurizing water to be treated, feeding the water to a semipermeable membrane unit (7), treating the water, and obtaining desalinated water by using as the primary power source electric power obtained from a natural energy generator unit (15), wherein a minimum feed water pressure (Pfmin) is determined on the basis of an osmotic pressure calculated from the quality of the water to be treated that is fed to the semipermeable membrane unit (7), and if the pressure cannot be raised to Pfmin when a preset minimum water flow volume (Qfmin) of feed water has been supplied, either an operation is carried out in which the recovery ratio (R), which is the value of the ratio of the passed water flow volume (Qp) to the fed water flow volume (Qf), is set to zero, or the operation of the semipermeable membrane unit (7) is stopped and the recovery ratio (R) is controlled so that the concentrated water flow volume does not exceed Qfmin when the pressure can be raised to Pfmin.

Description

Demineralized water production method

The present invention relates to a method for producing demineralized water that obtains demineralized water using a water treatment process that removes impurities from the water to be treated using natural energy.

With the worsening of the water environment that has become increasingly serious in recent years, water treatment technology has become more important than ever, and separation membrane utilization technology has been applied very widely. Separation membrane utilization technology has been mainly applied to purification of river water, lake water, etc. in order to obtain drinking water, industrial water, agricultural water, and the like. On the other hand, seawater desalination has been promoted mainly by the evaporation method in the Middle East region where water resources are extremely small and heat resources from oil are very abundant. However, there is a growing need for seawater desalination even in areas where heat sources other than the Middle East are abundant, especially since 1990, the desalination process using semipermeable membranes (especially reverse osmosis membranes) with low power requirements has been adopted, and the Caribbean Islands Many plants have been built and put into practical use in the Mediterranean and Mediterranean areas. In reverse osmosis membrane equipment, concentrated seawater having pressure energy is discharged, so that pressure recovery is generally performed by an energy recovery unit, which further reduces the required power. Recently, in addition to the improvement in reliability and cost reduction due to technological advancement of reverse osmosis, a significant improvement in energy recovery technology has led to the establishment of many reverse osmosis seawater desalination plants in the Middle East.

However, seawater desalination by reverse osmosis membranes is not universal, and high-concentration seawater, such as in the Middle East, and when the temperature is high, the desalination capacity decreases and the salt concentration of treated water (freshwater) tends to increase (Non-patent Document 1), in order to obtain high-quality treated water, there are many methods called the permeated water two-stage method in which desalted water is treated again with a low-pressure reverse osmosis membrane. There is a need to further reduce energy requirements by improving osmotic membrane performance and improving process systems. For this purpose, a method of combining a plurality of types of reverse osmosis membranes (Patent Document 1), a method of treating concentrated water of a reverse osmosis membrane again with a reverse osmosis membrane (Patent Document 2), a pretreatment with a nanofiltration membrane, and a hardness component That improves the recovery rate of reverse osmosis membranes (Patent Document 3), and a method of treating nanofiltration membranes with nanofiltration membranes again (Non-Patent Document 2) has been proposed and has been put to practical use. Not a few.

Furthermore, even though energy consumption has been reduced, power is required for water treatment by separation membranes, and the source is energy that is not necessarily environmentally friendly, such as oil and coal thermal power and nuclear power. . For this reason, attempts have been made to utilize electric power generated by natural energy such as solar energy, wind power, and wave power (Non-Patent Document 3 and Patent Document 4). Stable supply. That is, almost no solar energy can be obtained at night, and no wind power can be obtained for the kite. Therefore, as described in Non-Patent Document 3, it is necessary to provide a large storage battery and absorb fluctuations in the amount of power generation. However, a high-cost storage battery has a significant impact on desalination costs and is a major obstacle to commercialization and dissemination. It has become. Currently, technologies that are combined with electric power from conventional power generation technologies such as hydropower, thermal power, and nuclear power have been put into practical use. However, for stable power supply, it is necessary to focus on hydropower and thermal power that make it easy to control power generation. However, the water treatment process using the power obtained by the power generation method that varies depending on the situation such as natural energy as the main power source has not been put into practical use and popularized.

In particular, when applying reverse osmosis membranes to seawater desalination, fresh water cannot be obtained unless pressure higher than the osmotic pressure is applied. Only fresh water can be produced. In addition, even if the operation is started, the power generation capacity by natural energy changes every moment, so if you have a large-capacity storage battery or if you do not use conventional power in combination, it is not possible to operate the reverse osmosis membrane stably under certain conditions. I can't. On the other hand, in the operation of the reverse osmosis membrane, it is required to keep the supply water flow rate, the concentrated water flow rate, and the permeation flux (permeate flow rate per membrane area) suitable for the reverse osmosis membrane element in an appropriate range. That is, for example, if the supply water flow rate exceeds the appropriate range, an excessive load is applied to the reverse osmosis membrane element, causing deformation of the membrane element, if the concentrated water flow rate is too small, or if the permeation flux is too large, It will promote the accumulation (fouling) of dirt on the film surface. Therefore, if the amount of power generated using natural energy fluctuates, and the pump output fluctuates, operating in the normal operating condition range with the operating conditions set at the start cannot be performed. As a result, the lifetime of the reverse osmosis membrane was shortened.

Japanese Patent No. 3551127 Japanese Laid-Open Patent Publication No. 8-108048 Japanese Laid-Open Patent Publication No. 8-206460 Japanese Unexamined Patent Publication No. 2000-202441

An object of the present invention is to stably produce demineralized water while suppressing membrane deterioration and fouling during operation of a water treatment apparatus using a reverse osmosis membrane mainly using natural energy.

In order to solve the above problems, the present invention relates to the following embodiments (1) to (7).

(1) Using the electric power obtained from the power generation unit using natural energy as the main power source, the water to be treated is pressurized and supplied to the semipermeable membrane unit, separated into permeated water and concentrated water, and the permeated water is used as desalted water. In the obtaining method, the minimum supply water pressure Pfmin is determined based on the osmotic pressure calculated based on the quality of the water to be treated supplied to the semipermeable membrane unit, and a preset minimum supply water flow rate Qfmin is flowed. When the supply water pressure Pf cannot be increased to the minimum supply water pressure Pfmin, the recovery rate R obtained as the value of the ratio of the permeate flow rate Qp to the supply water flow rate Qf is set to 0, or When the supply water pressure Pf can be increased to the minimum supply water pressure Pfmin when the supply water minimum flow rate Qfmin is controlled by controlling the operation of the permeable membrane unit to stop, Method for producing demineralized water flow rate Qb to control the recovery rate R to be larger than the feed water minimum flow Qfmin.

(2) The method for producing desalted water according to (1), wherein when the semipermeable membrane unit is operated with the recovery rate R set to 0, (1) the supply water flow rate Qf to the semipermeable membrane unit (2) Make the supply water pressure Pf smaller than the minimum supply water pressure Pfmin, (3) Concentrated water discharged from the semipermeable membrane unit to the semipermeable membrane unit A method for producing demineralized water, wherein at least one of refluxing as treated water to be supplied is performed.

(3) The method for producing desalted water according to (1) or (2), wherein a maximum recovery rate Rmax is calculated as an upper limit value of the recovery rate R based on the quality of the water to be treated, and the recovery A method for producing demineralized water, wherein the feed water pressure Pf is controlled so that the rate R does not exceed the maximum recovery rate Rmax.

(4) The method for producing demineralized water according to any one of (1) to (3), wherein once the recovery rate R is set to 0, the semi-permeable membrane unit for water to be treated is operated. The desalinated water is set to be switched between the inlet of the treated water and the outlet of the concentrated water in the semipermeable membrane unit, and then the supply of the treated water to the semipermeable membrane unit is resumed. Production method.

(5) The method for producing desalted water according to any one of (1) to (4), wherein the pressure energy of the concentrated water discharged from the semipermeable membrane unit is converted into a pressure exchange type energy recovery unit. A method for producing demineralized water for energy recovery.

(6) The method for producing desalted water according to any one of (1) to (5), wherein the natural energy includes either sunlight or wind power.

(7) The method for producing desalted water according to any one of (1) to (6), wherein at least one selected from a capacitor, a capacitor, a lead storage battery, and a lithium ion battery is stored together with the power generation unit. A method for producing demineralized water, which is used as a means to suppress fluctuations in power supplied during operation of the semipermeable membrane unit.

According to the method for producing desalted water of the present invention, the semipermeable membrane unit is stably operated while suppressing membrane deterioration and fouling of the separation membrane while using unstable electric power obtained from natural energy as a power source. Demineralized water can be produced.

It is a flowchart which shows an example of the water treatment apparatus used with the manufacturing method of the desalted water of this invention. It is a flowchart which shows an example of the water treatment apparatus which added the post-processing unit to the water treatment apparatus of FIG. It is a water treatment apparatus of other embodiment used with the manufacturing method of the desalted water of this invention, Comprising: It is a flowchart which shows an example of the water treatment apparatus provided with the pressure exchange type energy recovery unit.

Hereinafter, embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited to the embodiments shown in the drawings.

FIG. 1 is a flowchart showing an example of an embodiment of a water treatment apparatus applicable to the method for producing desalted water of the present invention.

1, raw water 1 is supplied to a raw water tank 2, supplied to a pretreatment unit 4 by a pretreatment pump 3, processed, and stored in a pretreatment water tank 5. The pretreated water discharged from the pretreated water tank 5 is pressurized by the high-pressure pump 6, supplied and processed to the semipermeable membrane unit 7, and separated into permeated water and concentrated water. The permeated water (demineralized water) is stored in the permeated water tank 8. The concentrated water discharged from the semipermeable membrane unit 7 is taken out from the concentrated water valve 13a through the concentrated water line 12a.

1 is supplied with power by a natural energy power generation unit 15 as a power source using natural energy. A small power storage unit 14 can be provided to absorb fluctuations in the amount of power supply for a short time. Further, the power stabilized by the power stable supply control unit 16 is supplied to each unit, for example, the pretreatment pump 3 and the high pressure pump 6 in FIG.

Here, examples of the natural energy used by the natural energy power generation unit 15 include sunlight, wind power, wave power, and hydropower. The present invention can be applied to sunlight and wind power, which are greatly affected by climate, and has a great effect.

The stable power supply control unit 16 is adjusted so that sudden power fluctuations from the power generation unit 15 can be absorbed to some extent by supplementing the power obtained from the natural energy power generation unit 15 mainly with the power storage unit 14. Accordingly, the power storage unit 14 is not particularly limited, but is preferably a capacitor, a capacitor, a secondary battery, or the like suitable for high output. In particular, a capacitor that is most suitable for a large output and less deteriorated due to charge / discharge is most preferable. In addition, in the case of secondary batteries, the usage status of the power storage unit repeats charging and discharging shallower than the repetition of full charge and complete discharge, so a nickel-cadmium battery or nickel metal hydride battery with a memory effect is not very suitable. Lithium ion batteries are preferred.

In the water treatment apparatus to which the present invention is applied, a semipermeable membrane unit flow rate control unit 21 may be installed to determine a threshold value for controlling the operation and to control the operation conditions. In the illustrated example, the semipermeable membrane unit flow control unit 21 determines the minimum supply water pressure Pfmin based on the osmotic pressure π calculated based on the quality of the water to be treated measured by the concentration sensor 20, and the measured supply While detecting the water pressure Pf, the operating conditions of the high-pressure pump 6, the concentrated water valve 13a, and the permeated water valve 17 are controlled. That is, when the water to be treated is supplied to the semipermeable membrane unit 7 at the minimum supply water flow rate Qfmin, and the supply water pressure Pf of the semipermeable membrane unit 7 cannot be increased to the minimum supply water pressure Pfmin, the supply water flow rate Qf The recovery rate R = Qp / Qf obtained as the value of the ratio of the permeated water flow rate Qp to is operated with 0, or the operation of the semipermeable membrane unit is stopped. On the other hand, when the supply water pressure Pf of the semipermeable membrane unit 7 can be increased to the minimum supply water pressure Pfmin, the permeate water is controlled while controlling the recovery rate R so that the concentrated water flow rate Qb is larger than the minimum supply water flow rate Qfmin. Operate to obtain stable (demineralized water).

At this time, it is often based on the guidelines and technical data of the semipermeable membrane manufacturer, but the supply water flow rate Qf does not exceed the maximum supply water flow rate Qfmax, and the supply water flow rate Qf does not fall below the minimum concentrated water flow rate Qbmin. That is, care must be taken so that Qfmin = Qbmin. As a result, the supply water flow rate Qf needs to be set so that Qf ≧ Qfmin + Qp. That is, the recovery rate R is obtained by R = Qp / Qf, and the recovery rate R is controlled so that R ≦ 1-Qfmin / Qf.

In addition, when supplying the treated water to the semipermeable membrane unit 7, the recovery rate R is controlled so that the concentrated water flow rate Qb does not fall below the supply water minimum flow rate Qfmin. Here, in determining the minimum supply water flow rate Qfmin, it is most common and safe to follow the instructions for the minimum concentrated water flow rate Qbmin based on the guidelines and technical data of the semipermeable membrane manufacturer. That is, when the permeate flow rate Qp is 0, the supply water minimum flow rate Qfmin is equal to the minimum concentrated water flow rate Qbmin, which is the smallest value.

However, in the instruction of the concentrated water minimum flow rate Qbmin, the premise is that the permeated water maximum flow rate Qpmax or the permeated water maximum flux (maximum permeate flow rate per membrane area) Fpmax is included in the guideline. . That is, when the actual design permeate flow rate is smaller than the permeate maximum flux Qpmax of the instruction, the concentrated water minimum flow rate Qbmin can be set to a value smaller than the instruction. Non-patent literature (M. Taniguchi et al., “Behavior of a reverse osmosis plant adopting a brine conversion two-stage process and its computer simulation,” Journal of Membrane Science 183, p249-257, 2001) It can also be obtained by performing a simulation calculation based on the concentration polarization model shown in FIG. Experimentally, a component having relatively low solubility under the conditions of the permeate maximum flow rate Qpmax and the permeate minimum flow rate Qpmin, that is, a component that easily precipitates (for example, soluble silica) is supplied water (treated water). The concentration of the solute is increased and the solute begins to precipitate in the semipermeable membrane unit, that is, the solute concentration when the pressure loss starts to increase due to the precipitation is obtained. Using the supply water (treated water) of this solute concentration, when the permeate flow rate Qp is set to the design value, the concentrated water flow rate Qb is lowered, and the pressure loss in the semipermeable membrane unit is a pressure loss corresponding to the concentrated water flow rate. The concentrated water flow rate Qb when starting to become larger than this can be obtained, and this can be used as the concentrated water minimum flow rate Qbmin. That is, in the present invention, the concentrated water minimum flow rate Qbmin at this time is preset as the supply water minimum flow rate Qfmin. The supply water flow rate Qf to the semipermeable membrane unit 7 can be adjusted according to the operating conditions of the high-pressure pump 6.

In the present invention, the minimum supply water pressure Pfmin in the semipermeable membrane unit 7 is determined based on the osmotic pressure π calculated based on the quality of the water to be treated supplied to the semipermeable membrane unit 7 measured by the concentration sensor 20. To do. Specifically, Pfmin = π + Pp + α. Here, π is the osmotic pressure [atm] of the water to be treated, Pp is the permeated water pressure [atm], and α is a pressure [atm] greater than zero. The permeated water pressure Pp is a pressure when a slight pressure loss or the like on the permeated water side occurs, and is otherwise almost zero. α may be any number exceeding 0, but when α is close to 0, the quality of the permeate decreases when the supply water pressure Pf of the semipermeable membrane unit 7 is close to the minimum supply water pressure Pfmin, If α is too large, the operable pressure range in which the permeated water can be obtained becomes narrow, so care must be taken. Specifically, α is preferably 2 to 5 atm.

Here, based on the concentration CM [mg / l] of the water to be treated supplied to the semipermeable membrane unit 7 measured by the concentration sensor 20, the osmotic pressure π [atm] of the water to be treated is calculated. As a calculation method, it is typical to use the following Phanto-Hoff equation.

π = CM × R × (T + 273.15)
In the formula, π: osmotic pressure [atm]
CM: Molar concentration [mol / l]
R: Gas constant = 0.082 [l · atm / (K · mol)]
T: Temperature [℃]

When applying the above Phantohoff equation to a mixture such as seawater, it can be obtained by calculating and summing the osmotic pressure based on the concentration of each component based on a typical composition. The calculation of osmotic pressure π is also cited in other non-patent literatures such as Masahide Taniguchi, “Estimation of Transport Parameters of RO Membranes for Seawater Desalination,” AIChE Journal Vol. 46, p1967-1973 (2000) ”. An approximate expression based on actual measurement values can also be used.

Even when the water to be treated is other than seawater, the osmotic pressure π can be obtained based on the approximate expression by measuring the component of the water to be treated and if the approximate expression based on the actual measurement value can be obtained. I can do it.

There are no particular restrictions on the operating conditions other than the recovery rate R during the operation period when the recovery rate R of the semipermeable membrane unit 7 is 0. The simplest method for setting the recovery rate R = 0 is to reduce the supply water pressure Pf to near the osmotic pressure π by making the supply water flow rate Qf smaller than the minimum supply water flow rate Qfmin. 17 is fully closed. Of course, it is certain that these methods are carried out at the same time, but when the permeate valve 17 is fully closed, the permeate pressure is basically the same as the supply water pressure Pf. It is necessary to set the supply water pressure Pf so as not to exceed. Usually, in the case of seawater desalination, the pressure resistance on the supply water side is often about 70 to 80 atm and the pressure resistance on the permeate side is often about 10 atm, so the pressure on the permeate side of the device exceeds the pressure limit. It is preferable to provide safety measures such as providing a limiter for the supply water pressure Pf or installing a relief valve or pressure release plate on the permeate side.

Moreover, since the recovery rate R = 0 means that there is no permeation of the membrane, there is no suction of dirt (fouling) substances to the membrane surface. For this reason, there is no problem even if the supply water flow rate Qf to the normally recommended semipermeable membrane unit is smaller than the preset minimum supply water flow rate Qfmin. As an operating condition for obtaining the recovery rate R = 0, it is possible to make the supply water pressure Pf smaller than the minimum supply water pressure Pfmin because permeate is not obtained. However, if the supply water pressure Pf is made smaller than the aforementioned osmotic pressure π, a reverse flow of the permeate from the permeate side to the supply side occurs, which may cause damage to the membrane. For this reason, it is required to set the supply water pressure Pf in consideration of the strength of the membrane. In order to suppress the flow rate of the permeated water flowing backward, it is important to appropriately implement the supply water pressure Pf on the supply side and the method of throttling the permeated water valve 17.

Further, when the recovery rate R = 0, the water to be treated supplied to the semipermeable membrane unit is directly discharged from the concentrated water discharge line. Therefore, in order to suppress the loss that the water to be treated flows out of the apparatus, it is also preferable to recirculate the water to be treated discharged from the concentrated water discharge line 12a to the pretreatment water tank 5 as it is.

When the semipermeable membrane unit 7 is operated with the recovery rate R set to 0, or when the semipermeable membrane unit 7 is stopped, the power consumption of the semipermeable membrane unit 7 is reduced. It is also a preferred embodiment to use the electric power obtained from the power source) by turning it to other units such as pretreatment, for example, increasing the pretreatment flow rate. As another example, as shown in FIG. 2, it is possible to equip the downstream side of the semipermeable membrane unit 7 with a post-processing unit 10, and in this case, the power saved by stopping the semipermeable membrane unit 7. Can be distributed to post-processing in addition to pre-processing. In FIG. 2, the desalinated water stored in the permeate tank 8 is processed by the low pressure semipermeable membrane unit which is the post-treatment unit 10 by the booster pump 9, and the permeate is used as product water (demineralized water). Sent to. Moreover, the concentrated water discharged | emitted from the post-processing unit 10 is taken out through the concentrated water line 12b from the concentrated water valve | bulb 13b. Since this concentrated water is water obtained by concentrating the permeated water of the semipermeable membrane unit 7, it is very clear, and it is also a very preferable embodiment to recirculate to the raw water tank 2, the pretreatment water tank 5, and the like. When the concentrated water discharged from the post-processing unit 10 is refluxed, the reflux amount can be appropriately determined. In particular, when it is desired to reduce the osmotic pressure of the semipermeable membrane unit 7, the amount of reflux can be increased. For this operation, in addition to the concentration sensor 20a, it is also a preferred embodiment to include a concentration sensor 20b for the supply water to the semipermeable membrane unit 7 after the reflux water is mixed. When the concentration sensor 20b is disposed, the osmotic pressure of the water to be treated can be calculated based on the water quality detected by the concentration sensor 20b. In this case, it is preferable to control the reflux amount to reduce the concentration of water supplied to the semipermeable membrane unit 7 (the quality of the water to be treated), that is, the fluctuation of the osmotic pressure.

As a point to be noted in carrying out the present invention, there is a maximum recovery rate Rmax that is an upper limit value of the recovery rate R in the semipermeable membrane unit 7. The maximum recovery rate Rmax can be determined based on the measured value of the quality of the supplied treated water or the concentration limit based on the component ratio of the supplied treated water that has been actually measured. Specifically, the concentration limit concentration based on the solubility product can be obtained by calculation, or the concentration at which the feed water is concentrated and precipitation starts is measured, so that the concentration does not exceed the maximum concentration at which precipitation does not occur. It is advisable to determine the maximum recovery rate Rmax.

In an environment where the quality of the water to be treated supplied to the semipermeable membrane unit 7 is greatly fluctuated, such as when affected by tides, or when mixing two or more raw waters having different osmotic pressures to obtain the treated water, The recovery rate R may exceed the concentration limit of the water to be treated simply by controlling the concentrated water flow rate Qb to be larger than the minimum supply water flow rate Qfmin. In this case, it becomes a problem that a component that cannot be completely dissolved becomes a scale. For this reason, it is necessary to determine the maximum recovery rate Rmax so as not to exceed this value. As a method for adjusting the recovery rate R, for example, when it is desired to reduce the recovery rate, the supply water flow rate Qf is increased, the concentrated water flow rate Qb is increased, that is, the permeate flow rate Qp is decreased, and the like. The supply water pressure Pf can be controlled.

However, since the maximum recovery rate Rmax can be increased by adding a scale inhibitor to the feed water, it is also a preferred embodiment that Rmax is a function of the scale inhibitor addition concentration.

By the way, in carrying out the present invention, during the operation period in which the recovery rate R is set to 0, the supply of the water to be treated to the semipermeable membrane unit is temporarily stopped and the water to be treated supplied in the semipermeable membrane unit is temporarily stopped. When the flow direction is set to the opposite direction and the supply of the water to be processed to the semipermeable membrane unit is resumed, the fouling substance adhered and deposited in the semipermeable membrane element or on the membrane surface can be removed. Therefore, it is preferable. That is, before and after stopping the supply of treated water to the semipermeable membrane unit, the inlet of treated water to the semipermeable membrane unit and the outlet for concentrated water from the semipermeable membrane unit are switched. Thus, it is preferable to operate the semipermeable membrane unit.

In the present invention, the concentrated water taken out from the semipermeable membrane unit 7 is drained, but this concentrated water causes a pressure loss at the concentrated water valve 13a in FIGS. Yes. In order to recover the pressure energy of the concentrated water, it is preferable to provide an energy recovery unit instead of the concentrated water valve 13a. Examples of the energy recovery unit include a reverse pump, a Pelton turbine, a turbocharger, and a pressure exchange. In the present invention, the supply water pressure Pf is varied in order to control the concentrated water flow rate Qb. It is preferable to use a pressure exchange type energy recovery unit suitable for such conditions. That is, the energy recovery efficiency of the pressure exchange type energy recovery unit is greatly influenced by the flow rate, but is not greatly affected by the pressure, so in the present invention where the flow rate range is narrow, by using the pressure exchange type energy recovery unit, High energy recovery efficiency can be achieved under any operating conditions. Other energy recovery is not very suitable for the present invention because the efficiency is affected by pressure fluctuation and flow rate fluctuation and it is difficult to maintain high energy recovery efficiency. An example of the apparatus provided with the pressure exchange type energy recovery unit 18 is shown in FIG.

In FIG. 3, at least a part of the pretreated water stored in the pretreated water tank 5 is passed through the pressure exchange type energy recovery unit 18 by the two booster pumps 19 and concentrated from the semipermeable membrane unit 7. The pressure is exchanged with water and supplied to the semipermeable membrane unit 7.

In the method for producing demineralized water of the present invention, examples of the pretreatment unit 4 include sand filtration and a separation membrane. In the case of a separation membrane, various separation membrane units can be used. Depending on the quality of raw water and water, a wound filter, non-woven filter, microfiltration membrane, ultrafiltration membrane, etc. capable of high-precision solid-liquid separation of micrometer or less can be used. Can be used.

In addition, since these pretreatment units, semipermeable membrane units and the like are contaminated by dirt components contained in the raw water, it is common to perform on-line or off-line cleaning as appropriate in order to restore performance. . In the case of online, the cleaning chemical is injected into the water to be treated. Examples include hypochlorous acid, chloramine, chlorine dioxide, potassium permanganate, sodium hyposulfite, 2,2-dibromo-3-nitrilopropionamide (which is continuously or intermittently injected into water intake and supply water to the unit, etc. And bactericides such as DBNPA), general acids such as sulfuric acid, hydrochloric acid and citric acid, and alkalis such as sodium hydroxide. In the case of off-line, the treated water or treated water is used as it is, or it is generally heated or added with the above-mentioned cleaning chemicals to increase the cleaning effect, supply to the contaminated part, flush, or dip Is. The contaminated part here may be on either the treated water side or the treated water side, but it is preferably applied to the treated water side where contamination easily occurs.

The treated water (raw water) to which the present invention is applicable is not particularly limited, and various treated water such as river water, seawater, sewage treated water, rain water, industrial water, industrial waste water, or mixed water thereof. Although water can be mentioned, application to seawater or brackish water having osmotic pressure is particularly suitable.

Note that the present invention is not limited to the above-described embodiment, and modifications, improvements, and the like can be made as appropriate. In addition, the material, shape, dimension, numerical value, form, number, arrangement location, and the like of each component in the above-described embodiment are arbitrary and are not limited as long as the present invention can be achieved.

This application is based on Japanese Patent Application No. 2013-038199 filed on Feb. 28, 2013, the contents of which are incorporated herein by reference.

The present invention prevents the contamination of the separation membrane unit and reduces the environmental load by operating the semipermeable membrane unit and other units efficiently while using electric power obtained from unstable natural energy as a power source. It is possible to provide a method for stably operating the semipermeable membrane unit.

1: Raw water 2: Raw water tank 3: Pretreatment pump 4: Pretreatment unit 5: Pretreatment water tank 6: High pressure pump 7: Semipermeable membrane unit 8: Permeate water tank 9: Booster pump 10: Posttreatment unit 11:

Production Water tanks

12a, 12b:

Concentrated water lines

13a, 13b: Concentrated water valve 14: Electric power storage unit 15: Natural energy power generation unit (power source)
16: Power stable supply control unit 17: Permeated water valve 18: Pressure exchange type energy recovery unit 19: Booster pumps 20, 20a, 20b: Concentration sensor 21: Semipermeable membrane unit flow control unit

Claims

In a method of boosting the water to be treated using the electric power obtained from the power generation unit using natural energy as the main power source, supplying it to the semipermeable membrane unit, separating it into permeated water and concentrated water, and obtaining permeated water as desalted water The minimum supply water pressure Pfmin is determined based on the osmotic pressure calculated based on the quality of the water to be treated supplied to the semipermeable membrane unit, and when a preset supply water minimum flow rate Qfmin is flowed, When the supply water pressure Pf cannot be increased to the minimum supply water pressure Pfmin, the recovery rate R obtained as the value of the ratio of the permeate flow rate Qp to the supply water flow rate Qf is operated as 0, or the semipermeable membrane unit When the supply water pressure Pf can be increased to the minimum supply water pressure Pfmin when the supply water minimum flow rate Qfmin is flowed, Method for producing demineralized water Qb controls the recovery rate R to be larger than the feed water minimum flow Qfmin.
A method for producing demineralized water according to claim 1,
When operating the semipermeable membrane unit with the recovery rate R set to 0, (1) the supply water flow rate Qf to the semipermeable membrane unit is made smaller than the supply water minimum flow rate Qfmin, (2) the supply water pressure Desalinated water that performs at least one of reducing Pf to be lower than the minimum supply water pressure Pfmin, and (3) returning the concentrated water discharged from the semipermeable membrane unit as treated water to be supplied to the semipermeable membrane unit Manufacturing method.
A method for producing demineralized water according to claim 1 or 2,
As an upper limit value of the recovery rate R, a maximum recovery rate Rmax is calculated based on the quality of the water to be treated, and the supply water pressure Pf is controlled so that the recovery rate R does not exceed the maximum recovery rate Rmax. A method for producing salt water.
A method for producing demineralized water according to any one of claims 1 to 3,
During the period when the recovery rate R is set to 0, the supply of the water to be treated to the semipermeable membrane unit is temporarily stopped, and the inlet of the water to be treated and the outlet of the concentrated water are exchanged in the semipermeable membrane unit. After setting so, the manufacturing method of the desalinated water which restarts supply to the semipermeable membrane unit of to-be-processed water.
A method for producing demineralized water according to any one of claims 1 to 4,
A method for producing demineralized water, wherein the pressure energy of the concentrated water discharged from the semipermeable membrane unit is recovered by a pressure exchange type energy recovery unit.
A method for producing demineralized water according to any one of claims 1 to 5,
The manufacturing method of the desalinated water in which the said natural energy contains either sunlight or a wind power.
A method for producing demineralized water according to any one of claims 1 to 6,
A method for producing desalted water that suppresses fluctuations in power supplied during operation of the semipermeable membrane unit by using at least one selected from a capacitor, a capacitor, a lead storage battery, and a lithium ion battery as a power storage unit together with the power generation unit.