JP2014034005A - Salt water desalination apparatus and fresh water production method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a salt water desalination apparatus in which fresh water is obtained from salt water such as sea water and brine by using a reverse osmosis membrane module and to provide a fresh water production method.SOLUTION: The salt water desalination apparatus includes: a supply pump 1 for pressurizing salt water; a first-stage reverse osmosis membrane module 2 for separating the pressurized salt water; a second-stage reverse osmosis membrane module 3 for separating first fresh water; a first salt water supply line 13; a second salt water supply line 14; a first fresh water discharge line 15 having a water quality meter 11 capable of measuring salinity or physical quantity, which can be converted to the salinity, of the first fresh water; a first concentrated water discharge line 16; a treated water discharge line 17; a second concentrated water discharge line 18 having a bypass line-branched part 19 and a bypass line changeover unit; a bypass line 20; and a bypass line control unit 12 for controlling the bypass line changeover unit on the basis of the water quality data obtained from the water quality meter 11.

Description

  The present invention relates to a salt water desalination apparatus and a fresh water generation method for obtaining fresh water from salt water using a reverse osmosis membrane module. Specifically, the present invention relates to salt water from fresh water by switching to an optimal water supply line according to the quality of treated water. The present invention relates to a salt water desalination apparatus and a method for producing fresh water.

  Seawater desalination and brine desalination using the reverse osmosis membrane method can separate and remove salinity and harmful substances without phase change, and are easy to manage and energy efficient. It is used in the field. To prevent reverse osmosis membrane permeability and separability from decreasing, sand filtration, coagulation sedimentation, pressurized flotation, microfiltration membrane and ultrafiltration membrane filtration are usually performed before supplying seawater or brine to the reverse osmosis membrane. Pre-processing is performed using a method such as

  Based on the permeation principle of reverse osmosis membranes, it is necessary to make the supply water pressure higher than the osmotic pressure using a high-pressure pump or the like so that the supply water containing a certain amount of salt, such as seawater or brine, can permeate the reverse osmosis membrane. . The osmotic pressure is related to the salinity concentration. For example, when seawater is separated by a reverse osmosis membrane, a pressure of at least about 3 MPa or at least about 5 MPa is required in consideration of practicality. Even in the case of irrigation, a pressure of at least about 1 MPa is required.

  If the required quality of treated water cannot be obtained with only the first-stage reverse osmosis membrane module for the target water quality of the production water, the treated water from the first-stage reverse osmosis membrane module is supplied to the second-stage reverse osmosis membrane module. In some cases, two-stage processing is performed. By performing the two-stage treatment, it is possible to obtain a good treated water quality that cannot be obtained only by the one-stage reverse osmosis membrane module. On the other hand, as a demerit in performing the two-stage process, there is a decrease in the total recovery rate. The recovery rate indicates the ratio of treated water amount / feed water amount, and the closer to 1, the greater the amount of treated water obtained from the same amount of feed water. The total recovery rate indicates a ratio of the second-stage treated water amount / first-stage supplied water amount in a salt water desalination apparatus equipped with a two-stage reverse osmosis membrane module. When processing seawater with a general TDS (total dissolved salt concentration) of 35,000 mg / L, the recovery rate of the first-stage reverse osmosis membrane module is about 30% to 60%, and the second-stage reverse osmosis membrane module The recovery rate is often about 70% to 90%. That is, in one-stage treatment, what can produce treated water at a recovery rate of about 30% to 60%, but the total recovery rate is reduced to 21% to 54% by performing two-stage treatment.

  If the supply water is a water whose salinity has been clarified in advance, the necessary quality and quantity of treated water can be obtained by designing the device according to the supply water salinity. In equipment that requires the use of various raw water as feed water, the supply water salinity is not clear from the time of design, and low-salt water that can be treated in one stage is treated in two stages. If this happens, the amount of treated water will be reduced.

  Various proposals have been made to solve this problem. Patent Document 1 proposes a fresh water generation method using a line that bypasses the second-stage reverse osmosis membrane module so that two-stage treatment is performed when raw water is seawater, and one-stage treatment is performed when brine is used.

JP 2006-263542 A

  However, the quality of the treated water of the first-stage reverse osmosis membrane module has various fluctuation factors other than whether the raw water is seawater or brine, that is, the salt concentration of the raw water. For example, a reverse osmosis membrane usually deteriorates with time due to continuous or intermittent operation, and thus its desalting capacity gradually decreases. As a result, there is a problem of producing treated water that deviates from the production water standard during the first stage treatment.

  The treatment capacity of the reverse osmosis membrane is greatly influenced by the temperature of the feed water. For example, when the supply water has a high salinity concentration such as seawater, the desalination ability of the first-stage reverse osmosis membrane module is improved by increasing the viscosity of the supply water if the temperature is low. Nevertheless, the conventional fresh water generation method has a problem that the production water is unnecessarily reduced by performing the two-stage treatment.

  In addition, in the conventional fresh water generation method, when the fresh water operation is performed by using brine as supply water and bypassing the second-stage reverse osmosis membrane module, the water staying in the container of the second-stage reverse osmosis membrane module or the second-stage reverse osmosis membrane In the water adhering to the osmosis membrane, a biofilm or the like caused by microorganisms is easily generated, which causes the reverse osmosis membrane surface to be clogged, and has a problem that the desalination performance is deteriorated at an early stage.

  An object of the present invention is to provide a salt water desalination apparatus that obtains fresh water from salt water such as seawater and brine using a reverse osmosis membrane module, and provides salt concentration, raw water temperature, demineralization performance of the first-stage reverse osmosis membrane module, etc. Regardless of this, it is necessary to ensure a constant amount of treated water and treated water quality and to suppress a decrease in the desalting performance of the second-stage reverse osmosis membrane even during the first-stage reverse osmosis membrane treatment.

  The present invention for solving the above-described problems has the following characteristics.

  (1) A supply pump that boosts salt water, a first-stage reverse osmosis membrane module that separates the boosted salt water into first fresh water and first concentrated water by a reverse osmosis membrane, and a reverse osmosis membrane for the first fresh water A second-stage reverse osmosis membrane module that separates into second fresh water and second concentrated water, a first salt water supply line having one end coupled to the salt water supply unit and the other end coupled to the supply pump, and one end A second salt water supply line coupled to the supply pump and having the other end coupled to the supply port of the first-stage reverse osmosis membrane module, and one end coupled to the first fresh water discharge port of the first-stage reverse osmosis membrane module A first fresh water discharge line having a water quality meter, the other end of which is coupled to the supply port of the second-stage reverse osmosis membrane module and capable of measuring the salt concentration of the first fresh water or a physical quantity that can be converted into the salt concentration; Is the first stage reverse osmosis membrane module A first concentrated water discharge line coupled to the first concentrated water discharge port and the other end coupled to the concentrated water recovery unit, and one end coupled to the second fresh water discharge port of the second-stage reverse osmosis membrane module, A treated water discharge line having the other end coupled to the treated water recovery unit, one end coupled to the second concentrated water discharge port of the second-stage reverse osmosis membrane module, and the other end coupled to the first concentrated water discharge line A second concentrated water discharge line having a bypass line branch part and a bypass line switching unit, a bypass line having one end coupled to the bypass line branch part and the other end coupled to the treated water discharge line, and the water quality A salt water desalination apparatus comprising: a bypass line control unit that controls the bypass line switching unit based on water quality data obtained from a meter.

  (2) A supply pump for boosting salt water, a first-stage reverse osmosis membrane module for separating the boosted salt water into first fresh water and first concentrated water by a reverse osmosis membrane, and the first fresh water by a reverse osmosis membrane A second-stage reverse osmosis membrane module that separates into second fresh water and second concentrated water, a first salt water supply line having one end coupled to the salt water supply unit and the other end coupled to the supply pump, and one end A second salt water supply line coupled to the supply pump and having the other end coupled to the supply port of the first-stage reverse osmosis membrane module, and one end coupled to the first fresh water discharge port of the first-stage reverse osmosis membrane module A first fresh water discharge line having the other end coupled to the supply port of the second-stage reverse osmosis membrane module, and one end coupled to the first concentrated water discharge port of the first-stage reverse osmosis membrane module. The first concentrated water discharge is coupled to the concentrated water recovery unit A treated water discharge line having one end coupled to the second fresh water discharge port of the second-stage reverse osmosis membrane module and the other end coupled to the treated water recovery unit, and one end coupled to the second-stage reverse osmosis membrane module The second concentrated water discharge line is connected to the second concentrated water discharge port, the other end is connected to the first concentrated water discharge line, and has a bypass line branching unit and a bypass line switching unit, and one end is the bypass line branch. A fresh water producing method for obtaining treated water by desalinating salt water using a salt water desalination apparatus comprising a bypass line coupled to the treated water discharge line and the other end coupled to the treated water discharge line. A fresh water production method comprising controlling the bypass line switching unit based on a salinity of fresh water or a physical quantity that can be converted into a salinity.

  According to the present invention, in a salt water desalination apparatus that obtains fresh water from salt water such as seawater and brine using a reverse osmosis membrane module, the salt concentration of raw water, the raw water temperature, the desalination performance of the first-stage reverse osmosis membrane module, etc. Regardless, the treated water quality of the first-stage reverse osmosis membrane module is compared with the water quality reference value, and a certain amount of treated water and treated water quality are secured by switching the concentrated water bypass line of the second-stage reverse osmosis membrane module. Even during the reverse osmosis membrane treatment of the stage, it is possible to suppress a decrease in the desalting performance of the second-stage reverse osmosis membrane module.

It is a flowchart which shows the salt water desalination apparatus which can measure the quality of the treated water of the 1st-stage reverse osmosis membrane module based on this invention, and has the bypass line of the 2nd-stage reverse osmosis membrane module concentrated water. It is a flowchart which shows the conventional salt water desalination apparatus which has a 1st step | paragraph reverse osmosis membrane module and a 2nd step | paragraph reverse osmosis membrane module.

  In order to describe an embodiment of the present invention, first, a conventional salt water desalination apparatus having a first-stage reverse osmosis membrane module and a second-stage reverse osmosis membrane module will be described as a comparative example.

  As shown in FIG. 2, the conventional salt water desalination apparatus mainly comprises a supply pump 1 for boosting salt water, a first-stage reverse osmosis membrane module 2 comprising a reverse osmosis membrane (RO membrane), and a reverse osmosis membrane. Second-stage reverse osmosis membrane module 3, second-stage reverse osmosis for switching whether the first fresh water separated by the first-stage reverse osmosis membrane module is passed through the second-stage reverse osmosis membrane module 3 or bypassed Membrane module supply valve 5, second-stage reverse osmosis membrane module bypass valve 6, check valve 4 for preventing backflow to the second-stage reverse osmosis membrane module 3, and first-stage separated by the first-stage reverse osmosis membrane module 2 The first-stage concentrated water flow rate adjustment valve 7 for adjusting the flow rate of the concentrated water, and the second-stage concentrated water flow rate adjustment valve 8 for adjusting the flow rate of the second concentrated water separated by the second-stage reverse osmosis membrane module 3.

  The flow of salt water desalination of a conventional salt water desalination apparatus is typically as described below. The salt water introduced from the pretreatment device is pressurized by the supply pump 1 and supplied to the first-stage reverse osmosis membrane module 2. The water supplied to the first-stage reverse osmosis membrane module 2 is separated into first fresh water and first concentrated water by a reverse osmosis membrane method, and the first fresh water is supplied to the second-stage reverse osmosis membrane module 3. . The supply water to the second-stage reverse osmosis membrane module 3, that is, the first fresh water is separated into the second fresh water and the second concentrated water by the second-stage reverse osmosis membrane module 3 by the reverse osmosis membrane method. Fresh water is discharged to the treated water recovery unit as treated water. The first concentrated water discharged from the first-stage reverse osmosis membrane module 2 and the second concentrated water discharged from the second-stage reverse osmosis membrane module 3 are respectively the first-stage concentrated water flow rate control valve 7 and the second-stage concentrated water. The flow rate is adjusted by the concentrated water control valve 8 and discharged to the concentrated water recovery unit.

  A water production method using a conventional salt water desalination apparatus is typically as follows. When the salt water introduced into the pretreatment device is seawater, the first fresh water of the first-stage reverse osmosis membrane module 2 is supplied to the second-stage reverse osmosis membrane module 3 and separated into second fresh water and second concentrated water, The second fresh water is discharged as treated water to the treated water recovery unit. That is, the second-stage reverse osmosis membrane module supply valve 5 is opened, the second-stage reverse osmosis membrane module bypass valve 6 is closed, and the total amount of the first fresh water obtained by the first-stage reverse osmosis membrane module 2 is 2 It is supplied to and separated from the stage reverse osmosis membrane module 3 to obtain second fresh water as treated water. On the other hand, when the brine supplied to the pretreatment is brine, the first fresh water of the first-stage reverse osmosis membrane module 2 bypasses the second-stage reverse osmosis membrane module 3, and the entire amount is treated as treated water to the treated water recovery unit. Discharged. That is, by closing the second-stage reverse osmosis membrane module supply valve 5 and opening the second-stage reverse osmosis membrane module bypass valve 6, the first fresh water obtained by the first-stage reverse osmosis membrane module 2 remains as it is. It is discharged as treated water to a treated water recovery unit.

  Here, the reverse osmosis membrane used in the first-stage reverse osmosis membrane module 2 and the second-stage reverse osmosis membrane module 3 according to the present invention allows some components of the supply liquid, such as salt, to pass through, It is a semipermeable membrane that does not allow components to permeate. The material can be a polymer material such as cellulose acetate polymer, polyamide, polyester, polyimide, vinyl polymer. Examples of membrane forms include hollow fiber membranes and flat membranes. In this invention, it can utilize regardless of the raw material and membrane form of a reverse osmosis membrane. Regardless of which membrane material and membrane form are used, the desalting ability decreases with time by intermittent or continuous desalting. For this reason, in the conventional desalination method using the salt water desalination apparatus, the quality of the produced water deteriorates with time in the one-stage treatment using brine as the supply water, and as a result, there is a problem of deviating from the production water standard. .

  Here, the desalting ability of the reverse osmosis membrane used in the first-stage reverse osmosis membrane module 2 and the second-stage reverse osmosis membrane module 3 according to the present invention greatly depends on the viscosity of the salt water which is the raw water. That is, when the viscosity is high, the desalting ability is improved, and when the viscosity is low, the desalting ability is lowered. In addition, in saltwater desalination equipment for disaster countermeasures, saltwater that is raw water includes seawater that is close to 0 ° C. in the Arctic Circle and seawater that exceeds 40 ° C. in the Middle East. In general, the viscosity of salt water increases as the temperature decreases, and the viscosity of salt water decreases as the temperature increases. That is, when salt water having a low temperature is desalted, the desalting ability is improved, and when salt water having a high temperature is desalted, the desalting ability is lowered. For example, when the salt water salt concentration (TDS) is 25,000 mg / L and the water temperature is 30 ° C. or higher, the treated water salinity concentration (TDS) after the first-stage reverse osmosis membrane module treatment is 200 mg / L or more, and the water temperature is 30 If it is less than ° C., the treated water salt concentration (TDS) after the first-stage reverse osmosis membrane module treatment is less than 200 mg / L. In other words, in the conventional salt water desalination apparatus fresh water generation method, seawater is always treated in two stages. For example, when the water temperature is low, undesired desalination causes a reduction in the recovery rate. As a result, there is a problem that the production water volume is reduced unnecessarily.

  Further, salt water treated by a salt water desalination apparatus for disaster countermeasures is a general term for water containing salt, and a relatively low concentration generally referred to as brine having a chloride ion concentration of about 300 to 15,000 mg / L. Salt water and relatively high concentration salt water generally called seawater with a chloride ion concentration of about 15,000 to 40,000 mg / L, but there is no clear distinction between seawater and brine. Low concentration seawater may be treated as brine. Depending on where salt water is taken, for example, in rivers close to the sea, the salinity concentration changes over time due to tides. That is, the conventional salt water desalination apparatus that performs bypass determination of the second-stage reverse osmosis membrane module 3 depending on the raw water type cannot cope with salt water whose salinity concentration changes with time as described above.

  Further, in a saltwater desalination apparatus for disaster countermeasures, the water intake location is uncertain, and it is necessary to always provide a reverse osmosis membrane in the second-stage reverse osmosis membrane module 3. On the other hand, in the desalination method using the conventional salt water desalination apparatus, when the brine is taken and desalted, that is, when the second-stage reverse osmosis membrane module 3 is bypassed, the second-stage reverse is performed. The accumulated water in the osmotic membrane module container or the piping is blocked by a switching means such as a valve. In the blocked environment, the accumulated water in the container or the piping easily generates biofilms due to microorganisms, etc., causing the second-stage reverse osmosis membrane surface to be clogged, resulting in a decrease in the amount of produced water and the quality of the produced water. I have a problem of salt performance degradation.

  In order to solve the various problems as described above, in the present invention, it is possible to obtain a constant treated water quality and treated water amount irrespective of the raw water quality, temperature, desalting performance of the reverse osmosis membrane, etc. Also proposes a fresh water generating apparatus and a fresh water generating method capable of suppressing a decrease in desalting performance of the second-stage reverse osmosis membrane module 3. An embodiment according to the present invention is as shown in FIG.

  As shown in FIG. 1, a supply pump 1 that mainly boosts salt water, and a first-stage reverse osmosis membrane module 2 that separates the pressurized salt water into first fresh water and first concentrated water by a reverse osmosis membrane; , A second-stage reverse osmosis membrane module 3 that separates the first fresh water into a second fresh water and a second concentrated water by a reverse osmosis membrane, one end coupled to the salt water supply unit, and the other end coupled to the supply pump 1 The first salt water supply line 13, one end is coupled to the supply pump 1, the other end is coupled to the supply port of the first-stage reverse osmosis membrane module 2, and one end is reversed to the first stage. It is coupled to the first fresh water discharge port of the osmosis membrane module 2 and the other end is coupled to the supply port of the second-stage reverse osmosis membrane module 3 to measure the physical concentration that can be converted into the salt concentration or the salt concentration of the first fresh water. A first fresh water discharge line 15 having a water quality meter 11; Is connected to the first concentrated water discharge port of the first stage reverse osmosis membrane module 2 and the other end is connected to the concentrated water recovery unit, and one end is connected to the second stage reverse osmosis membrane module 3. The treated water discharge line 17 is connected to the second fresh water discharge port, the other end is connected to the treated water recovery unit, and the other end is connected to the second concentrated water discharge port of the second-stage reverse osmosis membrane module 3. One end is coupled to the first concentrated water discharge line 16, the second concentrated water discharge line 18 having a bypass line branch portion 19 and a bypass line switching unit, one end is coupled to the bypass line branch portion 19, and the other end is treated water. A bypass line 20 coupled to the discharge line 17; and a bypass line control unit 12 for controlling the bypass line switching unit based on water quality data obtained from the water quality meter 11. .

  Here, the water quality meter 11 for measuring the treated water quality of the first-stage reverse osmosis membrane module 2 can measure the salinity concentration, or the electric conductivity, chloride ion amount, sodium ion amount, total electrolytic mass that can be converted into the salinity concentration. There is no limitation as long as it has a function of measuring physical quantities such as refractive index and spectrophotometer and converting the physical quantities into salinity concentration using the correlation, for example, an electric conductivity meter, a salinity meter, a TDS meter, A refractometer, a spectroscopic densitometer, or the like can be used.

  The second-stage concentrated water bypass valve 10 and the second-stage concentrated water on-off valve 9 that are switching means to the second-stage concentrated water bypass line are not particularly limited as long as they switch the water supply line, and the form thereof is Ball valves, butterfly valves, globe valves, etc. can be used. The drive system is preferably a drive system that can be automatically switched from a control device or the like, and an electric valve driven by an electric motor, an air driven valve driven by compressed air, an electromagnetic valve using an electromagnetic coil as a drive source, or the like can be used. The bypass line control unit 12 is not particularly limited as long as it can compare water quality data with a water quality reference value and output a switching instruction to the valve as the switching means. For example, a programmable logic controller (PLC) or a distributed control can be used. A system (DCS), a digital indicator, a microcomputer, etc. can be used.

  Further, considering that the saltwater desalination apparatus of the present invention is mainly used for disaster countermeasures and the like, a compact apparatus configuration that can be installed in a small space is required from the viewpoint of portability to a water intake place. Therefore, the first-stage reverse osmosis membrane module 2 and the second-stage reverse osmosis membrane module 3 are connected via the first fresh water drainage line 15, and the second-stage reverse osmosis membrane from the intermediate tank for storing the first fresh water or the intermediate tank. A supply pump for supplying the module 3 is not installed, and the first-stage reverse osmosis membrane module 2 and the second-stage reverse osmosis membrane module 3 are preferably arranged in series.

  Specifically, the fresh water generation method of the present invention is carried out as follows.

  Regardless of whether the raw water is seawater or brine, regardless of water quality and temperature, and regardless of the performance deterioration of the first-stage reverse osmosis membrane module, supply salt water as supply water to the first-stage reverse osmosis membrane module 2 And separated into first fresh water and first concentrated water. At the same time, the salinity concentration of the first fresh water obtained from the first-stage reverse osmosis membrane module 2 is measured by the water quality meter 11, and the measured water quality data is compared with the water quality reference value by the bypass line control unit 12. At this time, if the measured water quality data is less than the water quality reference value, the second-stage concentrated water on-off valve 9 is closed and the second-stage concentrated water bypass valve 10 is opened by a switching instruction from the bypass line control unit 12. To do. That is, the first fresh water obtained by the first-stage reverse osmosis membrane module 2 is not boosted to the required osmotic pressure by the second-stage reverse osmosis membrane module 3, and the entire amount passes through the second-stage reverse osmosis membrane module 3. Water is passed, discharged from the second concentrated water discharge port, and further discharged directly to the treated water recovery unit via the bypass line 20 as treated water.

  If the measured water quality data is equal to or higher than the water quality reference value, the second-stage concentrated water on-off valve 9 is opened and the second-stage concentrated water bypass valve 10 is closed by a switching instruction from the bypass line control unit 12. That is, the first fresh water obtained by the first-stage reverse osmosis membrane module 2 is supplied to the second-stage reverse osmosis membrane module 3, and the second-stage concentrated water flow rate control valve 8 adjusts the flow rate of the second concentrated water. Thus, the pressure is increased to the osmotic pressure and separated into the second fresh water and the second concentrated water, and the second fresh water is discharged to the treated water recovery unit as treated water.

  Here, the water quality reference value to be compared by the bypass line control unit 12 is not particularly limited, and is a threshold value determined by the use of the production water. For example, if used as drinking water, it is desirable to use the water quality standard value (TDS 500 mg / L) of the World Health Organization (WHO) or the standard value (200 mg / L) defined by the Japan Water Quality Standard. In addition, if it is ultrapure water used as industrial water such as semiconductors, high-purity water quality is required for use, and a reference value far lower than the drinking water standard is used. For example, the TDS value is about 0.05 mg / L. It is desirable to do.

  Specific examples are as follows.

  The first fresh water quality of the first-stage reverse osmosis membrane module 2 when using a reverse osmosis membrane with a TDS value of 25,000 mg / L of salt water supplied to the pretreatment device, a water temperature of 25 ° C., and a polyamide membrane material The data resulted in a TDS value of 150 mg / L. At this time, as a result of setting the Japanese drinking water reference value of 200 mg / L as the first fresh water quality reference value, the second-stage concentrated water on-off valve 9 is closed and the second-stage concentration is performed according to an instruction from the bypass line control unit 12. The water bypass valve 10 is opened and switched to the bypass line, and the entire amount of the first fresh water passes through the second-stage reverse osmosis membrane module 3 and is treated as treated water via the second concentrated water discharge port and the bypass line 20. It was discharged to the water recovery unit.

  On the other hand, the TDS value of the salt water supplied to the pretreatment device is 25,000 mg / L, the water temperature is 36 ° C., and the first fresh water of the first-stage reverse osmosis membrane module when using a reverse osmosis membrane made of polyamide as a membrane material. The treated water quality was TDS value 350 mg / L. At this time, as described above, the Japanese drinking water reference value 200 mg / L was set as the first freshwater quality reference value. As a result, the second-stage concentrated water on-off valve 9 was opened by the instruction from the bypass line control unit 12, and the second-stage concentrated water on-off valve 9 was opened. The first concentrated water bypass valve 10 is closed, the first fresh water is pressurized by the second-stage concentrated water flow rate control valve 8, and the second fresh water discharged from the second-stage reverse osmosis membrane module is treated as treated water to the treated water recovery unit. It was discharged.

  Thus, based on the fresh water generation method of the present invention, the quality of the treated water of the first-stage reverse osmosis membrane module 2 regardless of the salinity concentration of raw water, the raw water temperature, the desalting performance of the first-stage reverse osmosis membrane module 2, etc. By comparing the data with the water quality reference value and switching the bypass line 20 provided in the second concentrated water discharge line 18 of the second-stage reverse osmosis membrane module 3, a certain amount of treated water and treated water quality can be secured. It is possible to suppress the occurrence of a biofilm or the like that causes a decrease in desalting performance by circulating salt water or fresh water through the reverse osmosis membrane module 3.

1: Supply pump 2: First stage reverse osmosis membrane module 3: Second stage reverse osmosis membrane module 4: Second stage reverse osmosis membrane module Fresh water outlet check valve 5: Second stage reverse osmosis membrane module supply valve 6: 2 Stage reverse osmosis membrane module bypass valve 7: Stage 1 concentrated water flow control valve 8: Stage 2 concentrated water flow control valve 9: Stage 2 concentrated water on-off valve 10: Stage 2 concentrated water bypass valve 11: Water quality meter 12: Bypass line control unit 13: First salt water supply line 14: Second salt water supply line 15: First fresh water discharge line 16: First concentrated water discharge line 17: Treated water discharge line 18: Second concentrated water discharge line 19 : Bypass line branch 20: Bypass line

Claims (2)

A supply pump for boosting salt water;
A first-stage reverse osmosis membrane module that separates the pressurized salt water into first fresh water and first concentrated water by a reverse osmosis membrane;
A second-stage reverse osmosis membrane module that separates the first fresh water into a second fresh water and a second concentrated water by a reverse osmosis membrane;
A first salt water supply line having one end coupled to the salt water supply unit and the other end coupled to the supply pump;
A second salt water supply line having one end coupled to the supply pump and the other end coupled to the supply port of the first-stage reverse osmosis membrane module;
One end is coupled to the first freshwater discharge port of the first-stage reverse osmosis membrane module, and the other end is coupled to the supply port of the second-stage reverse osmosis membrane module, and converted to the salinity or salt concentration of the first freshwater A first fresh water discharge line having a water quality meter capable of measuring possible physical quantities;
A first concentrated water discharge line having one end coupled to the first concentrated water discharge port of the first-stage reverse osmosis membrane module and the other end coupled to the concentrated water recovery unit;
A treated water discharge line having one end coupled to the second fresh water discharge port of the second-stage reverse osmosis membrane module and the other end coupled to the treated water recovery unit;
The second concentrated water having one end coupled to the second concentrated water discharge port of the second-stage reverse osmosis membrane module and the other end coupled to the first concentrated water discharge line and having a bypass line branching unit and a bypass line switching unit A discharge line;
A bypass line having one end coupled to the bypass line branch and the other end coupled to the treated water discharge line;
Based on the water quality data obtained from the water quality meter, a bypass line control unit that controls the bypass line switching unit;
A saltwater desalination apparatus. A supply pump for boosting salt water;
A first-stage reverse osmosis membrane module that separates the pressurized salt water into first fresh water and first concentrated water by a reverse osmosis membrane;
A second-stage reverse osmosis membrane module that separates the first fresh water into a second fresh water and a second concentrated water by a reverse osmosis membrane;
A first salt water supply line having one end coupled to the salt water supply unit and the other end coupled to the supply pump;
A second salt water supply line having one end coupled to the supply pump and the other end coupled to the supply port of the first-stage reverse osmosis membrane module;
A first fresh water discharge line having one end coupled to the first fresh water discharge port of the first-stage reverse osmosis membrane module and the other end coupled to the supply port of the second-stage reverse osmosis membrane module;
A first concentrated water discharge line having one end coupled to the first concentrated water discharge port of the first-stage reverse osmosis membrane module and the other end coupled to the concentrated water recovery unit;
A treated water discharge line having one end coupled to the second fresh water discharge port of the second-stage reverse osmosis membrane module and the other end coupled to the treated water recovery unit;
The second concentrated water having one end coupled to the second concentrated water discharge port of the second-stage reverse osmosis membrane module and the other end coupled to the first concentrated water discharge line and having a bypass line branching unit and a bypass line switching unit A discharge line;
A bypass line having one end coupled to the bypass line branch and the other end coupled to the treated water discharge line;
A desalination method for obtaining treated water by desalinating salt water using a salt water desalination apparatus comprising:
The fresh water generation method characterized in that the bypass line switching unit is controlled based on a salinity concentration of the first fresh water or a physical quantity that can be converted into a salinity concentration.

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