JPH08132038A - Fresh water generator - Google Patents

Abstract

PURPOSE: To enhance a water recovering rate of a fresh water generator using a reverse osmosis membrane device. CONSTITUTION: A concentrated water take-out line 31, deposition preventive agent feed line 32, washing chemicals feed line 34 and respective valves 30, 36, 38 and 40 are provided on a feed pipe 20 for feeding concentrated water on a precedent RO device 12 to a rear RO device 24, and while the precedent RO device is operated, the rear RO device can be washed.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention uses pure water by the reverse osmosis membrane method,
The present invention relates to a desalination apparatus and a desalination method for obtaining demineralized water and the like.

[0002]

2. Description of the Related Art A reverse osmosis membrane device (hereinafter referred to as RO device) can separate water to be treated into permeated water having a reduced impurity content and concentrated water having an increased impurity content. When the ratio becomes high, these deposit on the reverse osmosis membrane and reduce the filtration rate. Conventionally, in the RO device, in order to prevent these precipitations, the recovery rate (= permeated water /
It is common practice to operate with the water to be treated) lowered. For example, in the case of water to be treated containing silica,
Normally, the concentration of silica in concentrated water is its saturation concentration of 100
The operation is performed with the upper limit of about ppm (however, when the water temperature is about 25 ° C.). Since the treated water such as city water and industrial water usually contains 15 to 25 ppm of silica, in this case, by setting the recovery rate to 75 to 80% and operating, the silica concentration in the concentrated water is increased. Is kept below its saturation concentration. As a result, 20 of the water supplied
~ 25% is not used and is discarded as wastewater. In order to improve this problem, the pH of the water to be treated is adjusted, or a dispersant is added to the water to be treated to prevent the precipitation of silica, and it is considered to improve the recovery rate. Not necessarily successful.

Several problems need to be considered in improving recovery. As described above, it is possible to some extent to improve the recovery rate by adding pH adjusting agents or chemicals such as dispersants. However, in the case of improving the recovery rate of the water to be treated by performing reverse osmosis treatment of the concentrated water of the previous stage with the RO apparatus of the next stage using a plurality of RO apparatuses, the recovery rate is Even if the value is increased, the amount of permeated water in the portion operating at a high concentration, that is, the RO membrane located downstream may decrease in a few months. In this case, the operation of the RO device is stopped, the entire device is washed with a chemical such as acid or alkali, and then the operation is restarted.

During this period, the reverse osmosis treatment of water cannot be performed, so that the cleaning time of the apparatus is actually shortened as much as possible.
In some cases, there is a problem that sufficient cleaning cannot be performed.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object thereof is to provide a fresh water producing apparatus and a high fresh water producing method.

[0006]

In order to achieve the above object, the present invention provides a pre-stage reverse osmosis membrane device for treating water to be treated with a reverse osmosis membrane to separate the pre-stage permeated water and the pre-stage concentrated water, and the pre-stage. A supply pipe for supplying concentrated water to the latter-stage reverse osmosis membrane device, and a desalination apparatus for separating the former-stage concentrated water supplied via the supply pipe into a latter-stage permeated water and a latter-stage condensed water by reverse osmosis membrane treatment, The supply pipe is provided with a concentrated water extraction line, a deposition inhibitor injection line, a cleaning chemical supply line, and a flow path switching means for these lines, and in normal operation, the concentrated water extraction line and the cleaning chemical supply line are provided. The deposition inhibitor is supplied from the deposition inhibitor injection line to the supply pipe at the same time, and the deposition inhibitor injection line is closed during cleaning to stop the deposition of the deposition inhibitor and stop the concentrated water extraction line from the concentrated water extraction line. This is to propose a desalination apparatus that is characterized by cleaning the rear reverse osmosis membrane device while operating the front stage reverse osmosis membrane device by supplying the cleaning chemicals from the cleaning chemical supply line and removing the latter stage reverse osmosis membrane device. The reverse osmosis membrane is a looser reverse osmosis membrane than the reverse osmosis membrane of the former stage reverse osmosis membrane device, and the former stage concentrated water outlet is directly connected to the feed water inlet of the latter stage reverse osmosis membrane device without passing through a pump, and the latter stage reverse osmosis It includes that the membrane device is operated by the residual pressure of the concentrated water of the preceding stage reverse osmosis membrane device.

In the present invention, the water to be treated is subjected to reverse osmosis membrane treatment in a front-stage reverse osmosis membrane device to separate front-stage permeated water and front-stage concentrated water to obtain front-stage permeated water. In the water production method in which the reverse osmosis membrane treatment is performed with the osmosis membrane device to separate the latter-stage permeate water and the latter-stage concentrated water, when the reverse osmosis membrane of the latter-stage reverse osmosis membrane device is washed, the former-stage reverse osmosis membrane device is operated to perform the former-stage permeation. It is a water production method characterized in that the operation of the latter-stage reverse osmosis membrane device is stopped while water is taken out to wash the reverse-osmosis membrane of the latter-stage reverse osmosis membrane device.

The present invention will be described in detail below.

In the present invention, the plurality of RO devices are divided into the front stage and the rear stage, and the rear stage RO device is operated while the rear stage RO device is operating.
The apparatus is configured to be washable, for example, acid wash or alkali wash.

FIG. 1 shows an embodiment of the water producing apparatus of the present invention. In the figure, 2 is water to be treated. Examples of the water to be treated 2 include industrial water, tap water, well water, river water, and recovered water. The water to be treated 2 is subjected to pretreatment such as turbidity by the pretreatment device 4 depending on the quality of the water.

Examples of the pretreatment device include a sand filtration device and a membrane filtration device.

Reference numeral 6 is an acid supply line, in which an acid such as hydrochloric acid is added to the outlet water of the pretreatment apparatus in order to efficiently remove carbonic acid components in the water to be treated, and the pH thereof is adjusted to about 6;
It is sent to the deaerator 8 to remove carbon dioxide, oxygen, nitrogen and the like. As the deaerator 8, a decarbonation tower, a vacuum deaerator, a membrane deaerator or the like is selected according to the purpose. The outlet water of the pretreatment device adjusted to about pH 6 is decarbonated by the deaerator 8 so that its pH rises to about 6.5. The deaerator outlet water is then pressurized by the pump 10 and sent to the pre-stage RO device 12, where it is separated into the pre-stage permeated water 14 and the pre-stage concentrated water 16. The front-stage permeated water 14 is taken out from the front-stage permeated water extraction line 18 in a state where the impurity concentration is reduced, and is used as demineralized water or further as an electric desalination device, an ion exchange device, a reverse osmosis membrane device, an ultrafiltration membrane device. It is used for various purposes after increasing the purity.

Reference numeral 20 is a supply pipe, which allows the front RO
The concentrated water outlet 22 of the device 12 and the feed water inlet 26 of the post-stage RO device 24 are connected.

Reference numeral 28 is a first pressure adjusting valve provided in the supply pipe 20, and a valve 30 is provided downstream of the first pressure adjusting valve.

Reference numeral 31 denotes a concentrated water extraction line, which is branched from the supply pipe 20 between the first pressure adjusting valve 28 and the valve 30. Further, the valve 30 and the post-stage RO device 24
An anti-sedimentation agent injection line 32 and a cleaning chemicals supply line 34 are connected to the supply pipe 20 between the supply water inlet 26 and the supply water inlet 26. In addition, 36, 38, and 40 are valves, 42 is an injection pump installed in the injection line 32, 43 is a pump installed in the cleaning chemical supply line 34, and 45 is cleaning that is connected to the inlet side of the pump 43. It is a chemical storage tank.

The first-stage concentrated water 16 of the first-stage RO device 12 is the first
It moves through the supply pipe 20 through the pressure regulating valve 28 and the valve 30 in order, and the supply water inlet 2 of the latter stage RO device 24
6, and is separated into the latter-stage permeated water 44 and the latter-stage concentrated water 46 by the latter-stage RO device 24. The second-stage permeated water 44 is taken out from the recovery line 48 and used for various purposes.

The second-stage concentrated water is discharged to the outside of the system through a discharge line 52 provided with a second pressure adjusting valve 50.

As the deposition inhibitor supplied from the deposition inhibitor injection line 32 to the supply pipe 20, an acid for pH adjustment or a dispersant is used, but a bactericide or the like may be added if necessary.

Specific examples of the acid include hydrochloric acid and sulfuric acid. Further, an acidic liquid or the like generated by the electrolysis device can also be used. Examples of the dispersant include organic phosphates such as sodium hexametaphosphate and sodium polyacrylate. The above-mentioned acid is used in the latter stage RO device 24.
The pH of the second-stage concentrated water 46 is 6 or less, preferably 4.0 or less.
The amount is adjusted to about 5.5, and by adjusting the pH within this range, silica precipitation can be reliably prevented even if the silica concentration in the latter-stage concentrated water becomes equal to or higher than the saturation concentration. It should be noted that acid may not be added between the pre-stage RO device and the post-stage RO device, and acid may be added to the feed water of the pre-stage RO device from the beginning so that the concentrated water in the post-stage RO device has a pH of 6 or less. It is conceivable, but this is not preferable because the purity of the permeated water obtained from the former-stage RO device decreases. Moreover, you may use an acid and a dispersing agent together as needed.

As the cleaning chemical supplied from the cleaning chemical supply line 34 to the supply pipe, an acid aqueous solution of hydrochloric acid, citric acid, oxalic acid or the like or an alkaline aqueous solution of caustic soda or the like is preferable.

The acid aqueous solution preferably has a pH of 1.5 to 3. The alkaline aqueous solution preferably has a pH of 10-11.

In addition, EDTA, a surfactant and an aqueous enzyme solution may be used.

In the present invention, as described above, the RO apparatus is divided into the front RO apparatus 12 and the rear RO apparatus 24 in which the decrease of the permeated water is apt to occur due to the deposition of silica scale or the like. Keeps operating the front-stage RO device 12 (thus, while continuing to produce the front-stage permeated water), stops the operation of the rear-stage RO device 24 to perform the rear-stage RO device 24.
The device 24 is cleaned.

Therefore, as shown in FIG. 1, a cleaning chemical supply line 34 is installed between the front RO device 12 and the rear RO device 24, and the rear RO device 24 is cleaned without stopping the front RO device 12. It can be so. When cleaning the rear RO device 24 with chemicals, close the valves 30, 38, 36,
40 may be opened. If such a valve operation is performed, even if the amount of permeated water decreases in the rear RO device 24, the front RO
Since the device 12 can be continuously operated, the permeated water can always be obtained from the pre-stage RO device, and troubles due to the rapid decrease in the amount of permeated water due to the high recovery rate are unlikely to occur.

In the present invention, while the part of the front RO device 12 is operated for the purpose of desalting, the rear RO device 2 uses the front concentrated water of the front RO device 12 as water supply.
The main purpose of 4 is to collect the former-stage concentrated water. That is, the water quality of the permeate of the normal rear RO device 24 is usually the front RO
The impurity concentration is higher than the permeated water of the device 12. Therefore, although it can be used as it is, if it can be used for purposes other than the pre-stage RO device, such as cooling water, miscellaneous water, environmental water, etc., the water utilization rate can be improved in the entire factory. In addition, if the permeated water of the latter RO device is mixed with the water supply of the former RO device and used, the amount of water such as industrial water purchased from outside the factory can be reduced. In this case, the latter stage R
As an RO membrane of O equipment, RO of performance that the permeated water concentration of the latter stage RO equipment is the same as or slightly lower than the concentration of industrial water.
It is desirable to employ a membrane.

How to divide according to the operating conditions of the front stage and the rear stage is as follows:
In the first stage, the concentration of concentrated water silica that can be normally operated without adding a chemical such as a dispersant, for example, is set to about 100 ppm, and in the second stage, the silica concentration is further increased to 300 to 500 ppm by adding a dispersant or adjusting the pH. It is desirable to set.

In order to economically carry out a high recovery rate operation, it is necessary to reduce the chemical costs of the RO membrane and the deposition preventive agent such as a dispersant. However, when the operating cost is examined in detail, as the cost of the dispersant and the like becomes higher, the
It was found that the cost of the RO membrane decreased and the cost of the RO membrane increased. This is because the dispersant concentration is operated in a state where the concentration in the concentrated water is constant, so that the amount of concentrated water decreases as the recovery rate increases, and as a result, the amount of dispersant added decreases. on the other hand,
The cost of RO membranes increases with higher recovery rates. This is because increasing the recovery rate increases the amount of permeated water, and in the case of the same reverse osmosis membrane, the amount of RO membrane used increases. Therefore, it was found that reducing the amount of RO membrane used is important in improving the economical efficiency of high recovery operation.

Generally, in the case of RO membranes of the same type, the amount of permeated water is proportional to the operating pressure. Therefore, the only way to increase the permeated water under the same operating pressure is to increase the membrane area, that is, to increase the number of RO membrane modules used.

On the other hand, there are many types of RO membranes, and there is a so-called loose RO membrane that can obtain a large amount of permeated water per unit membrane area even with the same operating pressure. That is, by using such a loose RO membrane, it is possible to increase the amount of permeated water while keeping the increase in membrane area to a minimum.

In the present invention, the "loose membrane" means a membrane which can obtain a larger amount of permeated water under the same pressure. In the present invention, not only loose RO membranes when new, but also RO membranes that have loose performance after use are included.

Generally, the separation performance of the RO membrane deteriorates when it becomes loose. Therefore, if the RO membrane of the entire membrane device is made into a loose membrane, the quality of the permeated water will be lowered, and the desalination performance, which is the original purpose of the device, will be lowered. Therefore, in the present invention, the RO membrane having a high separation performance is used in the pre-stage RO device whose main purpose is the original desalination. Further, it is desirable to adopt a loose RO membrane in the latter-stage RO device whose main purpose is to economically improve the recovery rate. Thereby, each permeated water can be taken out separately and used effectively.

As described above, the loose RO is installed in the latter RO device.
If a membrane is used, the amount of permeated water per unit membrane area increases at the same pressure, so the required membrane area of the RO membrane becomes smaller. In other words, the required number of RO modules can be reduced, while the membrane easily fouls and the amount of permeated water increases. Is likely to occur. For this reason, there are many opportunities to stop the operation of the latter-stage RO device and clean the RO film. Therefore, the configuration of the present invention, which is capable of cleaning the rear RO device with chemicals while operating the front RO device, can be utilized more effectively.

In the present invention, the RO membrane used in the pre-stage RO apparatus is preferably a high desalting RO membrane such as SU720, SC-3200 (Toray), NTR759HR (Nitto Denko), FT-30 (Dow). . As the loose RO film used for the latter RO device, SU220, SU6
20 (Toray), NTR725 (Nitto Denko), NF-70
(Dow) and the like.

By adding a pH adjusting agent and / or a dispersant between the front RO apparatus and the rear RO apparatus, the front R
Compared with the case where these chemicals are added to the water supplied to the O apparatus, it is possible to prevent the deterioration of water quality due to the extremely small amount of the dispersant or pH adjuster that permeates the RO membrane. That is, in the case of the present invention, at least the permeated water of the front RO apparatus is not affected by the pH adjuster and the dispersant. Further, even if the permeated water of the latter RO apparatus is used as the water supply for the former RO apparatus, the influence of the pH adjuster and the dispersant on the permeated water quality of the former RO apparatus can be minimized.

In the present invention, the front RO device and the rear R device
It is preferable to connect the O devices in series and operate with one pump. In this case, pressure adjusting means (see FIG. 1) is provided between the front RO device and the rear RO device and on the concentrated water side of the rear RO device.
It is desirable to provide the middle valves 28, 50) so that the pressures of the front RO device and the rear RO device can be adjusted individually. In this case, by selecting an RO membrane, a membrane that can obtain a permeated water amount three times or more at the same operating pressure as the RO membrane of the latter RO apparatus may be used as compared with the RO membrane of the former RO apparatus. In such a case, it is necessary to adjust the operating pressure of the latter-stage RO device to a considerably lower pressure than that of the former-stage RO device. In this case, the front stage R
If a pH adjusting agent and / or a dispersant is added downstream of the pressure adjusting means (valve 28 in FIG. 1) installed between the O apparatus and the RO apparatus at the latter stage, the injection of these chemicals will result in a decrease in pressure. Advantageously, the discharge pressure of the pump (injection pump 42 in FIG. 1) is low.

It is to be noted that the permeated water in the former stage can be used after further improving its purity by an electric desalting apparatus, an ion exchange apparatus, an ultrafiltration membrane apparatus or the like as described above.

[0037]

【Example】

Example 1 The following treatment was performed using the water producing apparatus having the configuration shown in FIG.

Industrial water, which is the water to be treated 2, was turbid at 5 tons / hour by the pretreatment device 4 consisting of a membrane turbidity device, and then hydrochloric acid was injected from the acid supply line 6 to adjust the pH to 6.0. After that, it was deaerated by the deaeration device 8, then pressurized by the high pressure pump 10 and sent to the pre-stage RO device 12. The first-stage concentrated water 16 is the first
The pressure was adjusted by the pressure adjusting valve 28 and the pressure was supplied to the rear RO device 24. The rear-stage permeated water 44 was taken out from the recovery line 48 separately from the front-stage permeated water 18. The second-stage concentrated water 46 was discharged to the outside through the second pressure adjusting valve 50.

The former-stage permeated water was taken out as desalted water from the take-out line 18.

Front stage RO device 12 and rear stage RO device 24
As the RO membrane, Toray SU720 was used as the RO membrane, and the respective operating pressures were set to 15 Kgf / cm ² and 13 Kgf / cm ² .

Hydrochloric acid as an anti-deposition agent was injected from the anti-deposition agent injection line 32 to maintain the pH of the latter-stage concentrated water at 5.5.

The former RO device 12 has a concentrated water silica concentration of 75.
Concentrated to ppm (recovery rate of 80%), post-stage RO device 24
Runs at a silica concentration of 300 ppm (recovery rate 75%),
A total recovery rate of 95% was obtained.

Since the amount of permeated water in the latter stage decreased with the lapse of the number of operating days, the valves 30, 38 were closed and the valves 36, 40 were opened while continuing to operate the front stage RO device 12. Aqueous hydrochloric acid solution (pH adjusted as a cleaning chemical in the cleaning chemical storage tank 45)
2) is injected from the cleaning chemical supply line 34 by the pump 43, and is made to flow through the concentrated water side of the post-stage RO device 24, and then circulates through the discharge line 52 to the flow path indicated by the dotted line P to make the post-stage RO device 24 Circulation washing was performed for 2 hours. After that, the pump 43 was stopped and the system was immersed for 1 hour while being filled with the hydrochloric acid aqueous solution. Next, the hydrochloric acid aqueous solution in the cleaning chemicals storage tank 45 is discharged to adjust the sodium hydroxide aqueous solution (pH 11) in this storage tank, and this sodium hydroxide aqueous solution is circulated and washed for 2 hours in the same manner as the above hydrochloric acid cleaning. After that, the pump 43 was stopped and it was immersed overnight. After that, normal operation was restored.

FIG. 2 shows the operation result of the above apparatus. Figure 2
Shows the change with time of the permeated water amount per unit membrane area as a ratio (permeated water amount ratio) when the initial permeated water amount is 1, and is shown for each of the front RO membrane and the rear RO membrane. As can be seen from the figure, the permeated water amount of the front RO membrane hardly decreased for about 5 months, and the performance of the rear RO membrane was recovered by chemical cleaning. You can see that you can drive stably. Embodiment 2 FIG. 3 shows the Toray SU220, which is an RO membrane looser than SU720, as the rear RO device 24 in the above embodiment.
The same device as above except that the RO device equipped with S was used and the operating pressure of this RO device was 9 kgf / cm ² .
The operation results when operating under the same conditions are shown.

Since the Toray SU220S is an RO membrane that can obtain a permeated water amount of about three times per unit membrane area under the same pressure as the SU720, in this embodiment, the membrane area of the latter RO device is equal to that of the SU720. The operation was performed so as to be 1/2 of that in Example 1.

As shown in FIG. 3, the membrane area of the latter RO membrane device was set to 1/2 of that of Example 1, and the amount of permeated water per unit membrane area was made twice as large as that of Example 1, so that the latter RO membrane was formed.
The decrease in the amount of permeated water of the device is more remarkable than in the case of Fig. 2,
Such a decrease in the amount of water is reliably restored to the initial state of operation by chemical cleaning.

Therefore, in the case of this embodiment, the latter RO
Since the membrane area of the membrane device can be reduced to 1/2, the number of membrane modules used or the number of membrane elements used can be reduced, and as a result, the cost required for water recovery is lower than that of the first embodiment. It is much lower than the case.

[0048]

EFFECTS OF THE INVENTION According to the present invention, a more stable and high recovery rate operation is possible in a desalination apparatus using an RO membrane that uses industrial water or the like as the water to be treated, and the economical efficiency of the high recovery rate operation is greatly improved. Be improved.

[Brief description of drawings]

FIG. 1 is a flow chart showing an embodiment of the present invention.

FIG. 2 is a graph showing a relationship between a permeated water amount ratio and an operating time in Example 1.

FIG. 3 is a graph showing a relationship between a permeated water amount ratio and an operating time in Example 2.

[Explanation of symbols]

 2 Water to be treated 4 Pretreatment device 6 Acid supply line 8 Degassing device 10 Pump 12 Pre-stage RO device 14 Pre-stage permeated water 16 Pre-stage concentrated water 18 Extraction line 20 Supply pipe 22 Pre-stage concentrated water outlet 24 Post-stage RO device 26 Post-stage treated water inlet 28 First Pressure Adjustment Valve 30 Valve 31 Concentrated Water Extraction Line 32 Deposit Prevention Agent Injection Line 34 Cleaning Chemical Supply Line 36 Valve 38 Valve 40 Valve 42 Injection Pump (for Deposition Agent) 43 Pump (For Cleaning Chemical Supply) 44 Permeate Permeation Water 45 Cleaning chemical storage tank 46 Second-stage concentrated water 48 Recovery line 50 Second pressure adjustment valve 52 Discharge line

Claims (4)

[Claims] 1. A front-stage reverse osmosis membrane device for treating water to be treated by reverse osmosis membrane separation into front-stage permeate water and front-stage concentrated water; and a supply pipe for supplying the front-stage concentrated water to the rear-stage reverse osmosis membrane device,
In a fresh water generator that separates the former-stage concentrated water supplied through a supply pipe into a latter-stage permeated water and a latter-stage concentrated water by reverse osmosis membrane treatment, a concentrated-water take-out line in the supply pipe,
An anti-sedimentation agent injection line, a cleaning chemicals supply line, and a flow path switching means for these lines are provided, and in normal operation, the concentrated water take-out line and the cleaning chemicals supply line are closed, and the deposition inhibitor injection line is also provided. Supply anti-deposition agent from the supply pipe to the supply pipe, and close the anti-deposition agent injection line during cleaning to stop the anti-deposition agent supply and remove the preceding concentrated water from the concentrated water extraction line and supply the cleaning chemical from the cleaning chemical supply line. Then, the desalination apparatus is characterized in that the latter stage reverse osmosis membrane device is washed while operating the former stage reverse osmosis membrane device. 2. The desalination apparatus according to claim 1, wherein the reverse osmosis membrane of the rear stage reverse osmosis membrane device is a reverse osmosis membrane looser than the reverse osmosis membrane of the front stage reverse osmosis membrane device. 3. The former-stage concentrated water outlet is directly connected to the feedwater inlet of the latter-stage reverse osmosis membrane device without a pump, and the latter-stage reverse osmosis membrane device is operated by the residual pressure of the concentrated water of the former-stage reverse osmosis membrane device. The fresh water generator according to claim 1. 4. The front osmosis water is obtained by treating the water to be treated with a reverse osmosis membrane device by a reverse osmosis membrane device to obtain pre-stage permeated water and pre-stage concentrated water, and the pre-stage concentrated water is obtained from the post-stage reverse osmosis membrane device. In the water production method in which the reverse osmosis membrane treatment is performed with the latter to separate the latter-stage permeated water and the latter-stage concentrated water, when cleaning the reverse osmosis membrane of the latter-stage reverse osmosis membrane device, the former-stage reverse osmosis membrane device is operated to take out the former-stage permeated water. At the same time, the method for producing water is characterized in that the operation of the latter-stage reverse osmosis membrane device is stopped and the reverse-osmosis membrane of the latter-stage reverse osmosis membrane device is washed.