Patent ID: 12194414

DESCRIPTION OF SPECIFIC EMBODIMENTS OF THE INVENTION

Hereinafter, a desalination apparatus24of a first embodiment and an ultrapure water production system12including the desalination apparatus24will be described with reference to the drawings. The desalination apparatus24is an example of a water treatment apparatus according to the technology of the present disclosure.

Hereinafter, the term “flow direction” refers to a flow direction of treated water. The terms “upstream” and “downstream” mean “upstream” and “downstream” in the flow direction of the treated water, respectively.

As shown inFIG.1, the ultrapure water production system12includes a pretreatment device14, a primary pure water apparatus16, a pure water tank18, and a secondary pure water apparatus20.

The pretreatment device14pretreats raw water used for producing ultrapure water. As the pretreatment device14, for example, a flocculation precipitation treatment device, a turbidity removal device such as a microfilter or an ultrafiltration device, and an activated carbon adsorption device are installed. As the raw water, for example, fresh water such as city water, well water, or industrial water is used. However, depending on the concentration of impurities in the raw water, it is also possible to send the raw water to the primary pure water apparatus16without performing the pretreatment by the pretreatment device14as indicated by a one-dot chain line inFIG.1. In the technology of the present disclosure, the pretreated raw water is also described as “raw water”.

The treated water pretreated by the pretreatment device14is subjected to each treatment such as adsorption, filtration, and ion exchange in the primary pure water apparatus16, so that impurities that cannot be removed by the pretreatment device14are removed, and primary pure water is generated. In the present embodiment, the desalination apparatus24is included in the primary pure water apparatus16. The desalination apparatus24is an apparatus that removes impurities from treated water by passing the treated water through a reverse osmosis membrane56(details will be described later) to obtain permeated water that has permeated through the reverse osmosis membrane56and concentrated water other than the permeated water. A normal-pressure type degassing apparatus may be installed at a stage prior to the desalination apparatus24. In general, an ultraviolet irradiation device, a mixed bed ion exchange device, an electric regeneration type ion exchange device, a degassing membrane device, and the like are installed at a subsequent stage of the desalination apparatus24. The primary pure water generated by the primary pure water apparatus16is temporarily stored in the pure water tank18, and then sent to the secondary pure water apparatus20.

The primary pure water is subjected to each treatment such as adsorption, filtration, and ion exchange in the secondary pure water apparatus20, and impurities that cannot be removed by the primary pure water apparatus16are further removed to generate secondary pure water. The secondary pure water is sent to a use point22and used. The water may be sent to the use point22at the stage of temporary pure water.

As shown inFIG.2, the desalination apparatus24includes a first water treatment unit26and a water recovery unit28. The treated water is supplied from the upstream side to the first water treatment unit26by a raw water pipe30. The treated water may be raw water supplied to the pretreatment device14or water obtained by subjecting the raw water to a predetermined treatment. Hereinafter, a case where raw water is used as treated water will be described as an example.

The raw water pipe30is provided with a raw water pump32and a raw water valve34from the upstream side.

The raw water pump32is a pump that increases the pressure of the raw water supplied to the first water treatment unit26and supplies the raw water to the first water treatment unit26. An output range is set such that a high pressure is applied to the raw water as compared with a raw water pump120of a first comparative example and a second comparative example to be described later, and the water recovery unit28can be continuously operated.

As shown inFIG.3, the first water treatment unit26has one or a plurality of banks50. In the example shown inFIG.3, there are three banks including a first bank50A, a second bank50B, and a third bank50C. In the case of the configuration having a plurality of banks, the plurality of banks50are arranged in series along the flow direction.

Each of the banks50has one or more vessels52. In the example shown inFIG.3, the first bank50A has four vessels52, the second bank50B has two vessels52, and the third bank50C has one vessel52. When the bank50has the plurality of vessels52, the plurality of vessels52are arranged in parallel with the flow direction.

The vessel52includes a plurality of modules54. In the example shown inFIG.3, four modules54A to54D are arranged in series along the flow direction in one vessel52.

Each of the modules54includes the reverse osmosis membrane56therein. The treated water that has flowed into the module54is separated into permeated water that permeates through the reverse osmosis membrane56and concentrated water other than the permeated water. For example, as shown inFIG.2, the permeated water generated by the module54A on the most upstream side in the one vessel52is sent from the first water treatment unit26to the primary pure water apparatus16through the treatment water pipe38. On the other hand, the concentrated water generated in the module54flows into the second module54B from the upstream side, and is separated again into the permeated water that permeates the reverse osmosis membrane56and the concentrated water other than the permeated water. In this manner, in one vessel52, the operation of separating the treated water into the permeated water and the concentrated water is repeatedly performed.

The concentrated water generated in the plurality of vessels52of the first bank50A is once merged and then flows as treated water into any of the plurality of vessels52of the second bank50B. Similarly, in the vessel52of the second bank50B, the treated water is separated into the permeated water and the concentrated water by the module54, and the permeated water is sent to the primary pure water apparatus16through the treatment water pipe38. After the concentrated water is merged, in the vessel52of the third bank50C, the treated water is separated into the permeated water and the concentrated water by the plurality of modules54, and the permeated water is sent from the first water treatment unit26to the primary pure water apparatus16through the treatment water pipe38. On the other hand, as shown inFIG.2, the concentrated water generated by the module54is sent to the water recovery unit28through a concentrated water pipe36.

As described above, in one vessel52, the treated water that has not passed through the reverse osmosis membrane56becomes the concentrated water in all of the four modules54arranged in series along the flow direction of the treated water. On the other hand, the treated water that has permeated through the reverse osmosis membrane56in any one of the modules54becomes the permeated water.

In the first water treatment unit26, since the plurality of modules54are arranged in series along the flow direction of the treated water, a recovery rate of the first water treatment unit26can be increased as compared with a configuration in which one module54is disposed in series. For example, when the recovery rate of the module54alone is 10 to 20%, the recovery rate of the first water treatment unit26as a whole is 75 to 90%. That is, the water recovery rate is increased to satisfy a condition close to a condition where scale occurs. Specifically, for example, a Langelier index is preferably 0 or less, more preferably −1 to 0, still more preferably −0.5 to 0, and it is preferable to concentrate such that a silica concentration is concentrated to about 80 to 120 ppm.

In the first bank50A of the first water treatment unit26, since the plurality of vessels52, that is, the modules54are arranged in parallel in the flow direction of the treated water, a larger amount of treated water can be treated as compared with a configuration in which one module54is disposed in parallel. The number of the modules54arranged in a parallel direction decreases toward the downstream side. That is, the number of the modules54arranged in the parallel direction is four (four columns) in the first bank50A, two (two columns) in the second bank50B, and one (one column) in the third bank50C. Since the amount of the treated water treated by the module54decreases toward the downstream side, the treatment of the treated water is not affected even if the number of the modules54arranged in the parallel direction decreases toward the downstream side as described above. That is, it is possible to reliably treat the treated water while simplifying the configuration. A plurality of the first water treatment units26may be arranged in parallel with each other in the flow direction.

As shown inFIG.4, the water recovery unit28has one or a plurality of banks50. In the example shown inFIG.4, the water recovery unit28has two banks50, which are a first bank50D and a second bank50E. In the case of the configuration having the plurality of banks50, the plurality of banks50are arranged in series along the flow direction of the treated water.

Each of the banks50in the water recovery unit28has one or a plurality of vessels52. In the bank (the first bank50D in the example shown inFIG.4) having the plurality of vessels52, the vessels52are arranged in parallel in the flow direction of the treated water. The vessel52has the plurality of modules54, and in one vessel52, the four modules54A to54D are arranged in series along the flow direction of the treated water.

Also in the water recovery unit28, similarly to the first water treatment unit26, in one vessel52, the treated water that has not passed through the reverse osmosis membrane56in all of the four modules54arranged in series along the flow direction of the treated water is concentrated and becomes the waste water. On the other hand, the treated water that has permeated through the reverse osmosis membrane56in any one of the modules54becomes recovered water. Since the treated water supplied to the water recovery unit28is the concentrated water generated in the first water treatment unit26, the flow rate thereof is smaller than that of the raw water which is the treated water in the first water treatment unit26. Therefore, the water recovery unit28can be made smaller than the first water treatment unit26. A plurality of the water recovery units28may also be arranged in parallel with each other in the flow direction.

The first water treatment unit26and the water recovery unit28are directly connected by the concentrated water pipe36. The concentrated water generated by the first water treatment unit26is supplied as treated water directly to the water recovery unit28. Then, in the water recovery unit28, the concentrated water is separated into recovered water that has passed through the reverse osmosis membrane56and waste water other than the recovered water. Although the recovered water may be recovered from the desalination apparatus24and sent to another apparatus, in the present embodiment, the recovered water is recycled water. That is, the recovered water passes through a recovered water pipe46, is returned to the raw water pipe30on the upstream side of the raw water pump32, and is reused in the desalination apparatus24.

As shown inFIG.2, the desalination apparatus24has a treatment water valve40. The treatment water valve40is provided in the treatment water pipe38through which the permeated water flows out as treated water from the first water treatment unit26. By adjusting the treatment water valve40, pressure loss of the treatment water pipe38can be adjusted, and the flow rate of the treated water can be increased or decreased.

In the present embodiment, as described above, the output of the raw water pump32is higher than the output of the raw water pump120of the first comparative example and the second comparative example. The raw water pump32, the concentrated water pipe36, and the treatment water valve40form an example of pressure increasing means.

In addition, the desalination apparatus24includes a drain valve44. The drain valve44is provided in a drain pipe42through which the concentrated water flows out as waste water from the water recovery unit28. The pressure loss of the drain pipe42can be adjusted by adjusting the drain valve44.

The raw water pipe30is provided with a raw water pressure sensor60between the raw water valve34and the first water treatment unit26. The raw water pressure sensor60can detect the pressure of water flowing through the raw water pipe30.

In the treatment water pipe38, a treatment water pressure sensor62and a treatment water flow rate sensor64are provided between the first water treatment unit26and the treatment water valve40. The treatment water pressure sensor62can detect the water pressure of the treated water flowing through the treatment water pipe38. The treatment water flow rate sensor64can detect the flow rate of the treated water flowing through the treatment water pipe38.

A concentrated water pressure sensor66and a concentrated water flow rate sensor68are provided at the concentrated water pipe36. The concentrated water pressure sensor66can detect the water pressure of the concentrated water flowing through the concentrated water pipe36. The concentrated water flow rate sensor68can detect the flow rate of the concentrated water flowing through the concentrated water pipe36.

A recovered water pressure sensor70is provided at the recovered water pipe46. The recovered water pressure sensor70can detect the water pressure of the recovered water flowing through the recovered water pipe46.

A waste water pressure sensor72and a waste water flow rate sensor74are provided at the drain pipe42. The waste water pressure sensor72is provided between the water recovery unit28and the drain valve44, and can detect the water pressure of the waste water flowing through the drain pipe42. The waste water flow rate sensor74is provided downstream of the drain valve44, and can detect the flow rate of the waste water flowing through the drain pipe42.

In the present embodiment, the first water treatment unit26, the water recovery unit28, the treatment water valve40, the drain valve44, the raw water pressure sensor60, the treatment water pressure sensor62, the treatment water flow rate sensor64, the concentrated water pressure sensor66, the concentrated water flow rate sensor68, the waste water pressure sensor72, and the waste water flow rate sensor74are collectively installed in a single skit76.

Next, the operation of the desalination apparatus24of the first embodiment and a liquid treatment method will be described while being compared with the desalination apparatus and the liquid treatment method of Comparative Example. In the first comparative example and the second comparative example described below, elements and the like similar to those in the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

In the desalination apparatus24of the first embodiment, the raw water as the treated water is supplied to the first water treatment unit26. In the first water treatment unit26, the raw water is separated into the permeated water that has permeated through the reverse osmosis membrane56(seeFIG.3) and the concentrated water other than the permeated water. The concentrated water is water in which impurities in the treated water are concentrated, and is supplied to the water recovery unit28through the concentrated water pipe36.

In the water recovery unit28, the supplied concentrated water is separated into recovered water that has passed through the reverse osmosis membrane56(seeFIG.4) and waste water other than the recovered water. The recovered water is water obtained by removing impurities from the concentrated water. The recovered water can be supplied again to the first water treatment unit26to be reused as treated water (recycled water), and the treated water can be efficiently generated. The recovered water may be used for purposes other than the treated water in the desalination apparatus24.

The raw water used in the water treatment apparatus of the technology of the present disclosure contains a scale component, and the concentration of the scale component increases in the concentrated water after desalination. In addition to the scale component, the raw water also contains various impurities that cause fouling and scaling in the water recovery unit28, that is, a fouling component and the scale component. Since the raw water is separated into the permeated water and the concentrated water by the first water treatment unit26, the concentration of the fouling component and the scale component in the concentrated water is higher than the concentration of the raw water.

As in the present embodiment, when the liquid treatment apparatus is the desalination apparatus24, for example, when a flux of the raw water is 0.6 m/d, operating pressure at an inlet portion (the pressure is hereinafter referred to as “inlet operating pressure”) of the first water treatment unit26is set to 1.0 MPa or more and 1.5 MPa or less. On the other hand, in the water recovery unit28, since the concentration of the fouling component of the concentrated water is high, the operation is performed at a recovery rate different from that of the first water treatment unit26, for example, 30% or more and 65% or less. In this case, since the concentration of the fouling component is high in the concentrated water, the inlet operating pressure is set to a higher pressure in the water recovery unit28as compared with the first water treatment unit26. For example, when the flux of the concentrated water is 0.6 m/d, the operating pressure at the inlet portion of the water recovery unit28is set to 1.0 MPa or more and 1.8 MPa or less. In other words, as the ability of the raw water pump32, the ability to the extent that the inlet operating pressure can be achieved is required.

FIG.5shows a change over time of a necessary supply pressure applied for operating each of the first water treatment unit26and the water recovery unit28. The numerical range of the necessary supply pressure of the first water treatment unit26is 1.0 MPa or more and 1.5 MPa or less as described above. In the first water treatment unit26, fouling gradually progresses with elapse of operation time, and therefore, in accordance therewith the necessary supply pressure gradually increases. Similarly, the numerical range of the necessary supply pressure of the water recovery unit28is 1.0 MPa or more and 1.8 MPa or less, and as with the necessary supply pressure of the first water treatment unit26, the necessary supply pressure gradually increases due to the progress of fouling with elapse of the operation time.

At the start of the operation, the values of the necessary supply pressures of the first water treatment unit26and the water recovery unit28are the same (1 MPa in the example ofFIG.5). Since both the raw water and the concentrated water contain the fouling component, the necessary supply pressure increases with elapse of the operation time; however, in particular, since the concentration of the fouling component in the concentrated water is higher than that in the raw water, a rate of increase in the necessary supply pressure of the water recovery unit28is large.

The fouling component can be removed by cleaning each of the first water treatment unit26and the water recovery unit28at predetermined time intervals (1 to 3 M in the example ofFIG.5). As a result, the necessary supply pressure is reduced in both the first water treatment unit26and the water recovery unit28; however, even immediately after cleaning, the necessary supply pressure is slightly higher than that at the start of operation or immediately after cleaning performed one stage before the start of operation. Therefore, even if such periodic cleaning is repeatedly performed to recover the first water treatment unit26and the water recovery unit28, the necessary supply pressure substantially gradually increases with the operation. As indicated by 1 to 3Y inFIG.5, when the necessary supply pressure reaches a predetermined value (1.5 MPa in the first water treatment unit26and 1.8 MPa in the water recovery unit28), the module54is replaced. A replacement time of the reverse osmosis membrane56can be set, for example, such that operation costs of the first water treatment unit26and the water recovery unit28are further reduced.

As can be seen from the above description, although the inlet operating pressures of the first water treatment unit26and the water recovery unit28are the same at the start of operation, the inlet operating pressure of the water recovery unit28is larger than that of the first water treatment unit26thereafter.

Here, a desalination apparatus104of the first comparative example shown inFIG.6will be described.

In the desalination apparatus104of the first comparative example, a concentrated water pipe106is divided into two pipes in the middle, that is, into an upstream portion106A and a downstream portion106B. A concentrated water tank108is provided between the upstream portion106A and the downstream portion106B, and the concentrated water generated in the first water treatment unit26is temporarily stored in the concentrated water tank108. The amount of the concentrated water stored in the concentrated water tank108can be calculated from a water level detected by a water level sensor116.

A concentrated water valve110is provided at the upstream portion106A of the concentrated water pipe106, so that the amount of the concentrated water flowing from the first water treatment unit26to the concentrated water tank108can be adjusted.

A concentrated water pump112, a concentrated water valve114, and a concentrated water pressure sensor78are provided at the downstream portion106B of the concentrated water pipe106, that is, between the concentrated water tank108and the water recovery unit28. By operating the concentrated water pump112, the concentrated water stored in the concentrated water tank108can be pressurized and supplied to the water recovery unit28. By adjusting an opening degree of the concentrated water valve114, the concentrated water can be supplied to the water recovery unit28at a desired pressure and a desired flow rate. As described above, although the necessary supply pressure of the water recovery unit28is larger than the necessary supply pressure of the first water treatment unit26, the necessary supply pressure can be secured as the supply pressure of the concentrated water to the water recovery unit28by increasing the pressure of the concentrated water by the concentrated water pump112. Therefore, the raw water pump120of the desalination apparatus104of the first comparative example can have a lower output than the raw water pump32of the desalination apparatus24of the first embodiment.

In the desalination apparatus104of the first comparative example, the concentrated water tank108is provided in the middle of the concentrated water pipe106as described above, and the concentrated water tank108and the water level sensor116are installed in a skit118B. The first water treatment unit26, the concentrated water valve110, the raw water pressure sensor60, the treatment water pressure sensor62, the concentrated water pressure sensor66, the treatment water flow rate sensor64, and the concentrated water flow rate sensor68are installed in a skit118A, and the water recovery unit28, the drain valve44, and the waste water pressure sensor72are installed in a skit118C.

When the concentrated water has a high-concentration scale component, it is desirable to suppress precipitation of the scale component in the water recovery unit28. For example, by injecting a scale inhibitor into the concentrated water to improve a concentration rate of the scale component, the amount of the recovered water can be increased, so that the recovery rate can be increased. A pH adjusting agent may be injected into the concentrated water to adjust the pH. Since the desalination apparatus104of the first comparative example includes the concentrated water tank108, it is easy to inject these agents.

In the desalination apparatus104of the first comparative example, the concentrated water is temporarily stored in the concentrated water tank108. Thus, pressurization management of the concentrated water by the concentrated water pump112for suppressing fouling in the water recovery unit28and flow rate management of the concentrated water by control of the concentrated water valve114are separately performed. In addition, since the first water treatment unit26and the water recovery unit28have different degrees of increase in supply pressure required for operation (amounts of increase per hour), the operation of the water recovery unit28is controlled under operation conditions (supply pressure, supply amount, etc., of treated water) different from those of the first water treatment unit26.

However, in the desalination apparatus104of the first comparative example, a flow of the concentrated water from the first water treatment unit26to the water recovery unit28is divided by the concentrated water tank108. Thus, the first water treatment unit26and the water recovery unit28need to be placed under different operation controls.

In addition, when a concentrate is stored in the concentrated water tank108as in the first comparative example, impurities contained in the concentrated water are concentrated to near the limit where scale occurs, and therefore, the impurities may be retained in the concentrated water tank108. For example, an impurity concentration of the concentrate may temporarily and locally exceed a saturation concentration due to influences of evaporation of moisture, dissolution of carbonic acid, and the like. In addition, a concentrated turbid content may serve as a nucleus to promote the precipitation of the scale. Therefore, scaled fine particles gradually increase in the concentrated water in the tank as the operation is continued. For example, a coagulant added to the raw water may be concentrated in the concentrated water tank108. In the concentrated water tank108, a mineral component contained in the raw water is concentrated in the concentrated water tank108, and the concentrated water tank108may be in a state of being rich in nutrients for microorganisms such as viable bacteria, and in this case, propagation of microorganisms is likely to occur. When the concentrated water in this state is supplied to the water recovery unit28, scaling and fouling in the module54of the water recovery unit28may be promoted by insoluble components such as scale, a concentrated coagulant, and microorganisms.

FIG.7shows a change over time of the necessary supply pressure necessary for operating each of the first water treatment unit26and the water recovery unit28in the desalination apparatus104of the first comparative example. In the desalination apparatus104of the first comparative example, the pressure of the concentrated water is increased by the concentrated water pump112so as to obtain a pressure at which the water recovery unit28can be operated.

Also in the desalination apparatus104of the first comparative example, the necessary supply pressure at the start of operation is the same (1 MPa) as the example shown inFIG.5. However, the degree of increase (rate of increase per unit time) in the necessary supply pressure in the water recovery unit28is larger than the example shown inFIG.5. For this reason, a time for reaching the upper limit of the pressure (1.8 MPa) set as a reference for membrane replacement (actually, replacement of the module54(seeFIGS.3and4)) is short. For example, when viewed at a time interval of 1 to 3Y, it is necessary to frequently perform cleaning in order to continue the operation of the water recovery unit28in this state.

In order to eliminate the inconvenience caused by providing the concentrated water tank108as described above, for example, it is conceivable to use a desalination apparatus124of the second comparative example shown inFIG.8. Although the desalination apparatus124includes the raw water pump120similarly to the desalination apparatus104of the first comparative example, the output of the raw water pump120is lower than the output of the raw water pump32of the first embodiment. However, the raw water pump120has such an output that water pressure necessary for separating raw water (treated water) into treated water and concentrated water in the first water treatment unit26is applied to the raw water.

In the desalination apparatus124of the second comparative example, the first water treatment unit26and the water recovery unit28are directly connected by the concentrated water pipe36, and the concentrated water is not retained between the first water treatment unit26and the water recovery unit28. Therefore, it is also possible to suppress a situation in which fouling is likely to occur in the water recovery unit28due to an insoluble component retained in the concentrated water tank108(seeFIG.6).

However, in the desalination apparatus124of the second comparative example, the concentrated water pump112(seeFIG.6) provided in the desalination apparatus104of the first comparative example is not provided. Therefore, as a result, the raw water pump32is responsible for the supply pressure of the concentrated water to the water recovery unit28. However, in the desalination apparatus124of the second comparative example, a supply ability of the raw water pump32is set to such an extent that the first water treatment unit26can be operated (raw water can be separated into permeated water and concentrated water), specifically, 1.0 MPa or more and 1.5 MPa or less. Since there is the pressure loss in the first water treatment unit26, an actual pressure of the concentrated water flowing out of the water recovery unit28further decreases. Since the necessary supply pressure of the water recovery unit28is 1.0 MPa or more and 1.8 MPa or less, the pressure may be insufficient to separate the concentrated water into the recovered water and the waste water in the water recovery unit28.

On the other hand, in the desalination apparatus24of the first embodiment, the first water treatment unit26and the water recovery unit28are directly connected by the concentrated water pipe36, and there is no site where the concentrated water is retained in a path through which the concentrated water flows from the first water treatment unit26to the water recovery unit28. Since the concentrated water is not retained, aggregation of an aggregated component in the concentrated water can be suppressed. As a result, fouling in the water recovery unit28can be suppressed. As a result, an increase in pressure necessary for the operation of the water recovery unit28can also be suppressed, and a large flow rate of the treated water (concentrated water) flowing through the water recovery unit28can be secured. It is possible to reliably return the recovered water to the first water treatment unit26and to perform efficient liquid treatment for a long period of time by reducing a frequency of cleaning and membrane replacement of the water recovery unit28.

FIG.9shows a change over time of the necessary supply pressure in the first water treatment unit26and the water recovery unit28in the desalination apparatus24of the first embodiment.

Table 1 shows various states at the start of the operation and at three years after the start of the operation in the first comparative example, the second comparative example, the first embodiment, and the second embodiment to be described later.

TABLE 1First comparativeSecond comparativeexampleexampleFirst embodimentSecond embodimentAfter 3After 3After 3After 3yearsyearsyearsyearsAt start ofhaveAt start ofhaveAt start ofhaveAt start ofhaveoperationpassedoperationpassedoperationpassedoperationpassedFirst waterNecessary1.0 MPa1.5 MPa1.0 MPa1.5 MPa1.2 MPa2.0 MPa1.0 MPa1.5 MPatreatmentsupplyunitpressurePermeatedNoNoNoNo0.2 MPa0.0 MPaNoNowater pressurepressurepressurepressurepressurepressurepressureConcentratedNoNo0.8 MPa1.3 MPa1.0 MPa1.8 MPa0.8 MPa1.3 MPawater pressurepressurepressureConcentratedCapacity5 m3NoneNoneNonewater tankConcentratedSupply1.8 MPaNoneNoneDirect supply + 0.5water pumppressureMPaWaterNecessary1.0 MPaPressure has1.0 MPa1.8 MPa1.0 MPa1.8 MPa1.0 MPa1.8 MParecoverypressurereached 1.8(Insufficient(InsufficientunitMPa for 1.5pressure)pressure)yearsCleaningfrequencyhas increasedOperation stateFlow rate decreases afterTreatment amount shortageFlow rate is stableFlow rate is stable1.5 years and module usagePoor water quality due tofor 3 yearsfor 3 yearsperiod is shorteninsufficient pressure

In the desalination apparatus24of the first embodiment, the output of the raw water pump32is set higher than that of the desalination apparatus104of the first comparative example. By adjusting the opening degree of the treatment water valve40, the inlet operating pressure in the first water treatment unit26can be set to a desired pressure. Specifically, the supply pressure to the first water treatment unit26is set to be 1.2 MPa or more and 2.0 MPa or less. In the first water treatment unit26, since there is predetermined pressure loss (for example, about 0.2 MPa) when the treated water flows in and flows out as the concentrated water, the supply pressure of the concentrated water supplied to the water recovery unit28is also lowered accordingly. However, a pressure range of 1.0 MPa or more and 1.8 MPa or less, which is the pressure range required for the separation of the concentrated water in the water recovery unit28, is maintained.

As described above, in the desalination apparatus24of the first embodiment, the output of the raw water pump32is set higher than the output of the raw water pump120of the first comparative example and the second comparative example, thereby ensuring the supply pressure of the treated water (concentrated water) to the water recovery unit28. By configuring the pressure increasing means with a simple configuration without newly adding a pump, it is possible to secure the pressure of the treated water required for the operation of the water recovery unit28and to achieve a reliable operation in the water recovery unit28.

Moreover, in the water recovery unit28, fouling progresses with the lapse of time, and the pressure loss increases; however, the pressure of the concentrated water, that is, the supply pressure to the water recovery unit28is increased by gradually increasing the output of the raw water pump32. Thus, fouling in the water recovery unit28can be suppressed even after the operation time has elapsed, and a decrease in efficiency of separating the concentrated liquid into the recovered liquid and the waste liquid can be suppressed. In the liquid recovery unit28, it is possible to reduce the influence of the increase in the pressure loss with the lapse of time and to achieve a stable operation of the liquid recovery unit28.

In addition, the desalination apparatus24of the first embodiment includes the treatment water valve40, and can adjust the pressure of the permeated water (treatment water) flowing through the treatment water pipe38. As a result, it is possible to adjust the water pressure of the concentrated water flowing through the concentrated water pipe36and to supply the concentrated water to the water recovery unit28at a suitable water pressure. For example, when the supply pressure of the raw water to the first water treatment unit26is increased with the progress of fouling of the water recovery unit28, the opening degree of the treatment water valve40is reduced, so that it is possible to secure the water pressure of the concentrated water and to suppress an excessive increase in pressure of the treated water.

By suitably setting the output of the raw water pump32and the opening degree of the treatment water valve40, it is easy to adjust the recovery rate in the first water treatment unit26and the water recovery unit28to a desired value.

In addition, since the concentrated water tank108is not provided in the concentrated water pipe36, the structure can be simplified, and the desalination apparatus24can be operated at low cost. Since the concentrated water tank108is not provided, the concentrated water continuously flows from the first water treatment unit26to the water recovery unit28, so that it is not necessary to place the water recovery unit28under operation control different from that of the first water treatment unit26.

Since the desalination apparatus104of the first comparative example includes the three skits118A,118B, and118C as shown inFIG.6, the desalination apparatus is likely to be subject to restrictions on the installation location, and there is a possibility that the installation cost will increase. On the other hand, in the desalination apparatus24of the first embodiment, the concentrated water tank108is not provided, and the desalination apparatus can be configured as one skit76; therefore, a degree of freedom of the installation place increases, and the installation cost can be reduced. In addition, as the number of pumps, only the single raw water pumps32is needed in the desalination apparatus24of the first embodiment, and therefore, the installation space is small as compared with the configuration using two pumps including the raw water pump120and the concentrated water pump112as in the desalination apparatus104of the first comparative example.

The raw water contains the scale component as described above. By adjusting the concentration of the scale component and an optimal flow rate of a treated liquid in the first water treatment unit26, it is possible to achieve the recovery rate in the first water treatment unit26in a range of 75% or more and 90% or less. Considering only efficiency of water recovery, the recovery rate is preferably higher. However, when the recovery rate is set to be too high, scale is highly likely to occur, and therefore, the upper limit of the recovery rate is set to about 90%, preferably about 80% from the viewpoint of suppressing the scale.

Next, a modification of the first embodiment will be described. In the modification of the first embodiment, elements similar to those in the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

FIG.10shows a desalination apparatus84of the modification of the first embodiment. In the desalination apparatus84of the modification of the first embodiment, a second water treatment unit86is disposed instead of the treatment water valve40(seeFIG.2) in the desalination apparatus24of the first embodiment.

Similarly to the first water treatment unit26, the second water treatment unit86includes one or a plurality of banks50(seeFIG.3) therein, and the bank50includes one or a plurality of vessels52. Permeated water of the first water treatment unit26is supplied as treated water to the second water treatment unit86. Then, the permeated water is separated into second permeated water that has permeated through the reverse osmosis membranes56provided in the plurality of modules54of the vessel52and concentrated water other than the second permeated water.

The concentrated water pipe36is provided with a concentrated water valve88. By adjusting the opening degree of the concentrated water valve88, the water pressure and the flow rate of the concentrated water flowing through the concentrated water pipe36can be adjusted. In the modification of the first embodiment, the pressure increasing means includes the raw water pump32, the second water treatment unit86, and the concentrated water valve88.

Although a pressure gauge and a flow meter provided in each pipe are not illustrated inFIG.10, for example, similarly to the desalination apparatus24of the first embodiment, the pressure gauge and the flow meter are provided at appropriate positions of each pipe.

Also in the desalination apparatus84of the modification of the first embodiment having the configuration as described above, the first water treatment unit26and the water recovery unit28are directly connected by the concentrated water pipe36, and there is no site where the concentrated water is retained. Since the concentrated water is not retained, aggregation of an aggregated component in the concentrated water can be suppressed. Fouling in the water recovery unit28can be suppressed, and an increase in pressure loss of the water recovery unit28can also be suppressed. Thus, the increase in pressure necessary for the operation of the water recovery unit28can also be suppressed, and a large flow rate of the treated water (concentrated water) flowing through the water recovery unit28can be secured.

Moreover, the desalination apparatus84of the modification of the first embodiment includes the second water treatment unit86. The second water treatment unit86is located on the downstream side of the first water treatment unit26, and the treated water of the first water treatment unit26is further separated into second treatment water and the concentrated water by the second water treatment unit86. Therefore, as the second treatment water obtained by the desalination apparatus84of the modification of the first embodiment, water having less impurities than the treated water obtained by the desalination apparatus24of the first embodiment is obtained.

In the desalination apparatus84of the modification of the first embodiment, the concentrated water valve88is provided in the concentrated water pipe36. In the raw water pump32of the desalination apparatus84, a higher pressure than the raw water pump120of the first comparative example and the second comparative example is applied to the treated water; however, the pressure and the flow rate of the concentrated water supplied from the first water treatment unit26to the water recovery unit28can be adjusted to suitable ranges by adjusting the opening degree of the concentrated water valve88.

In the desalination apparatus84of the modification of the first embodiment, with a simple configuration in which the raw water pump32, the second water treatment unit86, and the concentrated water valve88are provided, it is possible to secure the pressure of the treated water required for the operation of the water recovery unit28and to achieve reliable operation in the water recovery unit28.

Next, the second embodiment will be described. In the second embodiment, elements similar to those in the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

As shown inFIG.11, in a desalination apparatus204of the second embodiment, the treatment water valve40(seeFIG.2) and the second water treatment unit86(seeFIG.10) are not provided in a treatment water pipe38.

A concentrated water pipe36is provided with a concentrated water pump206and a concentrated water valve208in order from a first water treatment unit26side. The concentrated water pump206can increase the pressure of concentrated water flowing through the concentrated water pipe36and supply the concentrated water to the water treatment unit. The concentrated water valve208can adjust the pressure and the flow rate of the concentrated water increased in pressure by the concentrated water pump206. In the second embodiment, the pressure increasing means includes the concentrated water pump206and the concentrated water valve208.

Although a pressure gauge and a flow meter provided in each pipe are not illustrated inFIG.11, for example, similarly to the desalination apparatus24of the first embodiment, the pressure gauge and the flow meter are provided at appropriate positions of each pipe.

Also in the desalination apparatus204of the second embodiment having the configuration as described above, the first water treatment unit26and the water recovery unit28are directly connected by the concentrated water pipe36, and there is no site where the concentrated water is retained. Since the concentrated water is not retained, aggregation of an aggregated component in the concentrated water can be suppressed. Since it is possible to suppress fouling in the water recovery unit28can be suppressed and the increase in pressure loss of the water recovery unit28, the increase in pressure necessary for the operation of the water recovery unit28can also be suppressed, and a large flow rate of the treated water (concentrated water) flowing through the water recovery unit28can be secured.

In the desalination apparatus204of the second embodiment, the concentrated water pump206is provided in the concentrated water pipe36. Although a portion of the pressure of the raw water pump32is applied to the concentrated water, it is possible to increase the pressure of the concentrated water by the concentrated water pump206and supply the concentrated water to the water recovery unit28while using this pressure. That is, a shortage of the pressure of the raw water pump32can be suitably compensated using the concentrated water pump206, and a state in which the compressed water has a predetermined pressure can be achieved. As a result, in the raw water pump32, it is not necessary to increase the pressure of the concentrated water in consideration of the water treatment in the water recovery unit28. That is, since pressurization to such an extent that water treatment can be performed in the first water treatment unit26is sufficient, the size of the raw water pump32can be reduced. Since the concentrated water is directly pressurized, the pressure can be efficiently increased to a desired pressure.

FIG.12shows the necessary supply pressure in the first water treatment unit26and the water recovery unit28in the desalination apparatus84of the second embodiment and concentrated water pressure discharged from the first water treatment unit26.

In the desalination apparatus204of the second embodiment, the output of the raw water pump32is set such that an inlet supply pressure of the first water treatment unit26is 1.0 MPa or more and 1.8 MPa or less. Thus, the pressure of the concentrated water at an outlet of the first water treatment unit26decreases by the pressure loss of the first water treatment unit26. In the example shown inFIG.12, the concentrated water pressure at the outlet of the first water treatment unit26decreases to lower than the necessary supply pressure to the first water treatment unit26. However, since the concentrated water is pressurized by the concentrated water pump206provided in the concentrated water pipe36, the pressure of the concentrated water can be increased to the necessary supply pressure of the water recovery unit28.

In the desalination apparatus204of the second embodiment, with a simple configuration in which the concentrated water pump206and the concentrated water valve208are provided, it is possible to secure the pressure of the treated water required for the operation of the water recovery unit28and to achieve reliable operation in the water recovery unit28.

In the above description, an example is described in which the liquid treatment apparatus of the technology of the present disclosure is a desalination apparatus; however, the liquid treatment apparatus can be widely applied to an apparatus that removes impurities from raw water using the reverse osmosis membrane.

The treated liquid as a treatment target in the liquid treatment apparatus is not limited to the above-described fresh water such as city water, well water, and industrial water, and may be, for example, sea water. In addition, a solvent of the treated liquid is not limited to water.

The ultrapure water production system12described above is an example of a pure water production system in the technology of the present disclosure. Depending on the impurity concentration of the generated water, for example, the secondary pure water apparatus20may be omitted to configure the pure water production system.

The disclosure of Japanese Patent Application No. 2020-173516, filed on Oct. 14, 2020, is incorporated herein by reference in its entirety.

All publications, patent applications, and technical standards mentioned in this description are incorporated herein by reference to the same extent as if each individual publication, patent application, or technical standard was specifically and individually indicated to be incorporated by reference.