JP2020157274A - Pure water production apparatus and pure water production method - Google Patents

Abstract

To provide a pure water production apparatus and a pure water production method that enable effective use of water when concentrated water generated by using a reverse osmosis membrane is reused as a cooling water for a cooling tower.SOLUTION: A pure water production apparatus 10, comprising: a raw water supply channel 2 through which raw water w1 flows; a first reverse osmosis membrane 3 that separates the raw water w1 supplied from the raw water supply channel 2 into a primary permeate water w2 and a primary concentrated water w3; a second reverse osmosis membrane 4 that separates the primary concentrated water w3 into a secondary permeate water w4 and a secondary concentrated water w5; a cooling water supply channel L18 that supplies the secondary permeate water w4 to a cooling tower 5 as cooling water; and returning means 6 that returns the surplus of the secondary permeate water w4 to the raw water supply channel 2 when the production of the secondary permeate water w4 in the second reverse osmosis membrane 4 exceeds the demand for the secondary permeate water w4 in the cooling tower 5.SELECTED DRAWING: Figure 2

Description

The present invention relates to a pure water production apparatus and a pure water production method.

Generally, a pure water production apparatus is provided with a reverse osmosis membrane for separating raw water into permeated water and concentrated water for the purpose of removing impurities. The permeated water that has permeated the reverse osmosis membrane is further subjected to ion exchange treatment and the like, and then supplied to the point of use as pure water. On the other hand, the concentrated water that has not permeated the reverse osmosis membrane is returned to raw water and reused for pure water production in order to make effective use of water, or it is used in a cooling device such as a cooling tower. It may be reused as cooling water.

As a technique for reusing concentrated water in a pure water production apparatus, Patent Document 1 states that concentrated water discharged from a first reverse osmosis membrane apparatus is treated with a second reverse osmosis membrane apparatus to obtain permeable water. , It is described that this permeated water is returned to the raw water tank. Further, in Patent Document 2, a first concentrated water is produced by medium pressure reverse osmosis, and a second permeated water is produced by treating the first concentrated water by high pressure reverse osmosis to produce a second permeated water. It is stated that water will be reused. Further, Patent Document 3 describes a method of using concentrated water using concentrated water generated by a reverse osmosis membrane treatment apparatus as circulating cooling water.

Impurities are concentrated in the concentrated water produced by the reverse osmosis membrane, so that components such as calcium and silica are contained at a higher concentration than the raw water. When such concentrated water is supplied to the cooling tower, calcium and silica may precipitate in the piping inside the cooling tower to cause clogging. Therefore, when the concentrated water generated by the reverse osmosis membrane of the pure water production apparatus is reused for the cooling tower, the concentrated water generated by the first-stage reverse osmosis membrane is used as described in Patent Documents 1 to 3. Treatment with a second-stage reverse osmosis membrane may reduce the impurity concentration, or adjustment of the concentration ratio in the reverse osmosis membrane may prevent clogging due to calcium or silica.

However, the demand for cooling water in the cooling tower often does not match the amount of concentrated water produced by the reverse osmosis membrane, and especially when the demand for cooling water is less than the amount of concentrated water produced, excess concentration is achieved. Water had to be discharged from the pure water production equipment, and the effective use of water in the pure water production equipment was not achieved.

Japanese Unexamined Patent Publication No. 2016-13529 JP-A-2018-86649 JP-A-2017-104787

The present invention has been made in view of the above circumstances, and is a pure water production apparatus and pure water that enable effective use of water when the concentrated water generated by the reverse osmosis membrane is reused as cooling water for a cooling tower. The subject is to provide a water production method.

In order to solve the above problems, the present invention adopts the following configuration.
[1] A raw water supply channel through which raw water flows and
A first reverse osmosis membrane that separates the raw water supplied from the raw water supply channel into primary permeated water and primary concentrated water.
A second reverse osmosis membrane that separates the primary concentrated water into secondary permeated water and secondary concentrated water.
A cooling water supply path that supplies the secondary permeated water to the cooling tower as cooling water, and
When the production amount of the secondary permeated water in the second reverse osmosis membrane exceeds the demand amount of the secondary permeated water in the cooling tower, the surplus of the secondary permeated water is returned to the raw water supply channel. A pure water production apparatus characterized in that it is provided with a return means.
[2] The return means includes a return path for returning the secondary permeated water to the raw water supply path and a return path.
The pure water production apparatus according to [1], which comprises a flow rate control means for controlling the flow rate of the secondary permeated water flowing through the cooling water supply path.
[3] A preheating means arranged in the middle of the raw water supply path to preheat the raw water, and
A heating means for heating the raw water after preheating, which is arranged in the middle of the raw water supply path, is further provided.
The preheating means according to [1] or [2], wherein the preheating means is a heat exchanger in which the secondary permeated water flowing through the cooling water supply path is a high temperature side fluid and the raw water is a low temperature side fluid. Pure water production equipment.
[4] A primary permeation channel through which the primary permeate water that has permeated the first reverse osmosis membrane flows.
A first decarboxylation means that is installed in the primary permeation channel and decarboxylates the primary permeate water.
When the primary permeated water is installed after the first decarboxylation means of the primary permeation channel and the primary permeate water after passing through the first decarboxylation means is deionized, the present invention is further provided [1]. ] To [3]. The pure water production apparatus according to any one of the items.
[5] The pure water production apparatus according to any one of [2] to [4], wherein the return path is provided with a second decarboxylation means for decarboxylating the secondary permeated water.

[6] A first reverse osmosis membrane separation step of separating raw water into primary permeated water and primary concentrated water by a first reverse osmosis membrane.
A second reverse osmosis membrane separation step of separating the primary concentrated water into secondary permeated water and secondary concentrated water by a second reverse osmosis membrane.
The secondary permeated water is supplied to the cooling tower as cooling water through the cooling water supply path, and the production amount of the secondary permeated water in the second reverse osmosis membrane is the secondary permeated water in the cooling tower. A secondary permeated water supply step in which the surplus of the secondary permeated water is returned as raw water by a return means when the demand amount is exceeded.
A pure water production method characterized by being provided with.
[7] The return means includes a return path for returning the secondary permeated water to the raw water.
The pure water production method according to [6], which comprises a flow rate control means for controlling the flow rate of the secondary permeated water flowing through the cooling water supply path.
[8] A preheating step of preheating the raw water before supply to the first reverse osmosis membrane, and
A heating step of heating the raw water after preheating is further provided.
[6] or [7], wherein the preheating step is performed by a heat exchanger in which the secondary permeated water flowing through the cooling water supply path is a high temperature side fluid and the raw water is a low temperature side fluid. Pure water production method.
[9] In the first decarboxylation step of decarboxylating the primary permeated water by the first decarboxylation means,
Any of [6] to [8], further comprising an electrodeionization step of deionizing the primary permeated water after the first decarboxylation step with an electrodeionizer. The pure water production method according to item 1.
[10] The item according to any one of [7] to [9], which includes a second decarboxylation step of decarboxylating the secondary permeated water flowing through the return path by a second decarboxylation means. Pure water production method.

According to the pure water production apparatus of the present invention, when the production amount of the secondary permeated water in the second reverse osmosis membrane exceeds the demand amount of the secondary permeated water in the cooling tower, the surplus amount of the secondary permeated water is taken. Since the return means for returning to the raw water supply channel is provided, excess secondary permeated water can be effectively used without being discarded.

Further, according to the pure water production apparatus of the present invention, the return means is a flow control means for controlling the flow rate of the secondary permeated water flowing through the return path for returning the secondary permeated water to the raw water supply path and the cooling water supply path. Since it is composed of, the amount of secondary permeated water supplied to the cooling tower and the amount of secondary permeated water returned to the raw water supply channel can be adjusted to the optimum ratio, and effective use of water can be achieved. Can be planned.

Further, according to the pure water production apparatus of the present invention, when the preheating means and the heating means for preheating the raw water are arranged in the middle of the raw water supply path, the preheating means is used as a heat exchanger to provide the cooling water supply path. By recovering the heat of the flowing secondary permeated water by the preheating means, the energy consumption in the heating means can be reduced and the secondary permeated water sent to the cooling tower can be cooled.

Furthermore, according to the pure water production apparatus of the present invention, the first decarboxylation means and the electrodeionization apparatus are further provided in the primary permeation channel through which the primary permeation water that has permeated the first reverse osmosis membrane flows. Therefore, the amount of impurities in the primary permeated water can be further reduced, and high-purity pure water can be produced.

Further, according to the pure water production apparatus of the present invention, the secondary permeated water and the return path for returning to the raw water supply channel are provided with a second decarboxylation means for decarboxylating the secondary permeated water. The carbonated secondary permeated water can be returned to the raw water supply channel, thereby reducing the carbonic acid concentration of the raw water and reducing the load on the first decarboxylation means arranged in the primary permeated water channel.

Next, according to the pure water production method of the present invention, when the production amount of the secondary permeated water in the second reverse osmosis membrane exceeds the demand amount of the secondary permeated water in the cooling tower, the secondary permeated water Since the secondary permeated water supply process for returning the surplus to the raw water supply channel is provided, the surplus secondary permeated water can be effectively used without being discarded.

Further, according to the pure water production method of the present invention, the return means is a flow rate control means for controlling the flow rate of the secondary permeated water flowing through the return path for returning the secondary permeated water to the raw water supply path and the cooling water supply path. Since it is composed of, the amount of secondary permeated water supplied to the cooling tower and the amount of secondary permeated water returned to the raw water supply channel can be adjusted to the optimum ratio, and effective use of water can be achieved. Can be planned.

Further, according to the pure water production method of the present invention, when a preheating step and a heating step for preheating the raw water are performed in the middle of the raw water supply path, the heat of the secondary permeated water flowing through the cooling water supply path is preheated by the preheating means. Since it is recovered, energy consumption in the heating process can be reduced, and the secondary permeated water sent to the cooling tower can be cooled.

Furthermore, according to the pure water production method of the present invention, the primary permeated water is subjected to the first decarbonization step and the electrodeionization step in sequence with respect to the primary permeated water that has permeated the first reverse osmosis membrane. The amount of impurities in the above can be further reduced, and high-purity pure water can be produced.

Further, according to the pure water production method of the present invention, when the secondary permeated water is returned to the raw water supply channel, the secondary decarboxylation step is performed on the secondary permeated water, so that the decarboxylated secondary water is subjected to. The permeated water can be returned to the raw water supply channel, thereby reducing the carbonation concentration of the raw water and reducing the load of the first decarboxylation step in the primary permeated water channel.

FIG. 1 is a schematic diagram illustrating a configuration of a pure water production apparatus according to a first embodiment of the present invention. FIG. 2 is a schematic diagram illustrating a configuration of a pure water production apparatus according to a second embodiment of the present invention. FIG. 3 is a schematic view illustrating the configuration of a pure water production apparatus according to a third embodiment of the present invention.

(First Embodiment)
The pure water production apparatus and the pure water production method according to the first embodiment of the present invention will be described with reference to FIG.

First, the overall configuration of the pure water production apparatus 1 will be described. The pure water production apparatus 1 of the present embodiment has a raw water supply path 2 through which the raw water w1 flows, a first back-penetrating film 3 that separates the raw water w1 into a primary permeated water w2 and a primary concentrated water w3, and a primary concentrated water w3. A second back-permeation film 4 that separates the secondary permeated water w4 and the secondary concentrated water w5, a cooling water supply path L8 that supplies the secondary permeated water w4 as cooling water to the cooling tower 5, and a secondary permeated water w4. A return means 6 for returning the surplus portion of the above water to the raw water supply channel 2 is provided. Further, the pure water production apparatus 1 is provided with primary permeation channels L3 and L4 through which the primary permeation water w2 flows, a first decarboxylation means 31, and an electric deionization apparatus 32. Further, a concentrated water tank 8 for storing the primary concentrated water w3 is provided between the first reverse osmosis membrane 3 and the second reverse osmosis membrane 4. Furthermore, a water quality adjusting means 42 for adjusting the water quality of the primary concentrated water w3 is provided between the concentrated water tank 8 and the second reverse osmosis membrane 4.

Further, as shown in FIG. 1, a pretreatment device 41 is provided in front of the raw water supply path 2. The pretreatment device 41 may or may not be included in the pure water production device 1.

The raw water supply channel 2 is composed of a raw water tank 2a, a water channel L1 connecting the pretreatment device 41 and the raw water tank 2a, and a water channel L2 connecting the raw water tank 2a and the first reverse osmosis membrane 3. ..

The return means 6 is composed of a return path L9 for returning the secondary permeated water w4 to the raw water supply path 2 and a flow rate control means 7. The flow rate control means 7 is composed of a flow rate adjusting valve 7a and a control device 7b.

Further, the pure water production apparatus 1 is provided with a water channel for flowing water between each apparatus and each means. That is, the raw water supply channel 2 has a water channel L1 and a water channel L2. Further, the first reverse osmosis membrane 3 and the first decarboxylation means 31 are connected by the primary permeation channel L3, and the first decarboxylation means 31 and the electrodeionizer 32 are connected by the primary permeation channel L4. Further, the electric deionization device 32 and the raw water tank 2a of the raw water supply path 2 are connected by a water channel L10. The water channel L10 is not limited to the raw water tank 2a, and may be connected to any of the water channels L1 and L2.

Further, the first reverse osmosis membrane 3 and the concentrated water tank 8 are connected by a water channel L5, and the concentrated water tank 8 and the second reverse osmosis membrane 4 are connected by a water channel L6 to adjust the flow rate with the second reverse osmosis membrane 4. The valve 7a is connected by a water channel L7, and the flow control valve 7a and the cooling tower 5 are connected by a cooling water supply path L8. Further, the return path L9 branches from the middle of the water channel L7. The return path L9 is connected to the raw water tank 2a. The return channel L9 is not limited to the raw water tank 2a, and may be connected to any of the water channels L1 and L2.

Next, each device and each means constituting the pure water production device 1 will be described.
The pretreatment device 41 reduces the amount of impurities in the raw water w1 to a predetermined concentration or less by performing coagulation sedimentation, filtration, ion exchange, etc. on the raw water w1 such as tap water and industrial water. The raw water w1 treated by the pretreatment device 41 is sent to the raw water tank 2a by the water channel L1.

The raw water tank 2a temporarily stores the raw water w1. Further, a water channel L10 and a return channel L9 are connected to the raw water tank 2a, and the water returned from these water channels L9 and L10 is also stored as raw water w1. The stored raw water w1 is sent to the first reverse osmosis membrane 3 by the water channel L2.

The first reverse osmosis membrane 3 separates the raw water w1 supplied from the raw water supply path 2 into the primary permeated water w2 and the primary concentrated water w3. The raw water w1 is passed through the first reverse osmosis membrane 3 to remove impurities and become the primary permeated water w2. The removed impurities are contained in the primary concentrated water w3. As the first reverse osmosis membrane 3, a spiral type module in which a permeable membrane (membrane) is layered and wound in a seaweed roll shape and housed in a container can be preferably used, but the first is not limited thereto.

The first reverse osmosis membrane 3 is connected to a primary permeation channel L3 through which the primary permeate water w2 flows and a channel L5 through which the primary concentrated water w3 flows.

Further, two or more first reverse osmosis membranes 3 may be provided in series. When two or more first reverse osmosis membranes 3 are provided in series, the permeated water of the reverse osmosis membrane in the front stage is provided so as to supply water to the reverse osmosis membrane in the subsequent stage.

The first decarboxylation means 31 decarboxylates the primary permeated water w2. The first decarboxylation means 31 is not particularly limited as long as it can mainly remove carbon dioxide dissolved in the primary permeated water w2 that has permeated the first reverse osmosis membrane 3. As the first decarboxylation means 31, for example, a membrane degassing device composed of a degassing membrane such as a hollow fiber membrane, a decarboxylation tower, or the like can be used. The first decarboxylation means 31 is connected to a primary permeation water channel L4 that sends the primary permeation water w2 to the electrodeionizer 32.

The electrodeionizer 32 is installed after the first decarboxylation means 31. The electrodeionizer 32 is for further removing the ionic substance remaining in the primary permeated water w2 by deionizing the primary permeated water w2. The removed ionic substance is concentrated in concentrated water w6. As the electrodeionizer 32, for example, an anode and a cathode are partitioned by an anion exchange membrane and a cation exchange membrane, and an anode chamber, a cathode chamber, a desalting chamber and a concentration chamber are formed.

Further, a water channel L10 is connected to the electric deionization device 32. The water channel L10 returns the concentrated water w6 to the raw water tank 2a. Further, a water channel L11 is connected to the electrodeionizer 32. The water channel L11 is connected to the use point, and the deionized primary permeated water w2 is supplied to the use point as pure water.

A concentrated water tank 8 is installed at the end of the water channel L5 connected to the first reverse osmosis membrane 3. The concentrated water tank 8 temporarily stores the primary concentrated water w3. Further, a water channel L6 for sending the primary concentrated water w3 to the second reverse osmosis membrane 4 is connected to the concentrated water tank 8.

A water quality adjusting means 42 for adjusting the water quality of the primary concentrated water w3 is connected in the middle of the water channel L6. The main purpose of adjusting the water quality of the primary concentrated water w3 is to prevent scale precipitation in the second reverse osmosis membrane 4 and prevent membrane blockage. Therefore, in the water quality adjusting means 42, the water quality of the primary concentrated water w3 is adjusted to be acidic, for example, pH 5.5 or less, and a scale dispersant is added. The pH is preferably adjusted by adding sulfuric acid or the like. The water quality adjusting means 42 is not limited to being installed in the middle of the water channel L6, and may be installed in the concentrated water tank 8.

The second reverse osmosis membrane 4 separates the primary concentrated water w3 whose water quality has been adjusted by the water quality adjusting means 42 into the secondary permeated water w4 and the secondary concentrated water w5. The primary concentrated water w3 is passed through the second reverse osmosis membrane 4 to remove impurities and become the secondary permeated water w4. The removed impurities are contained in the secondary concentrated water w5. As the second reverse osmosis membrane 4, a spiral type module in which osmosis membranes (membranes) are laminated in multiple layers and wrapped in a seaweed roll can be preferably used, but the second reverse osmosis membrane 4 is not limited thereto.

A water channel L7 through which the secondary permeated water w4 flows and a water channel L12 through which the secondary concentrated water w5 flows are connected to the second reverse osmosis membrane 4.

Further, two or more second reverse osmosis membranes 4 may be provided in series. When two or more second reverse osmosis membranes 4 are provided in series, the permeated water of the reverse osmosis membrane in the front stage is provided so as to supply water to the reverse osmosis membrane in the subsequent stage.

The return means 6 is composed of a return path L9 that branches from the middle of the water channel L7 and a flow rate control means 7. The flow rate control means 7 is composed of a flow rate adjusting valve 7a and a control device 7b. The flow rate adjusting valve 7a is arranged between the water channel L7 and the cooling water supply channel L8. The cooling water supply path L8 is connected to the cooling tower 5, and the secondary permeated water w4 is supplied to the cooling tower 5. In the cooling tower 5, the secondary permeated water w4 is used as the cooling water.

The flow rate adjusting valve 7a adjusts the flow rate of the secondary permeated water w4 in the cooling water supply path L8 in response to the command of the control device 7b. Further, the control device 7b monitors the usage amount of the cooling water (secondary permeated water w4) in the cooling tower 5, and controls the flow rate adjusting valve 7a when the supply amount of the secondary permeated water w4 is insufficient. The flow rate of the secondary permeated water w4 in the cooling water supply path L8 is increased, and conversely, when the supply amount of the secondary permeated water w4 is excessive, the flow rate adjusting valve 7a is controlled to control the secondary permeated water in the cooling water supply path L8. Reduce the flow rate of w4.

As a result of the flow rate control for the secondary permeated water w4 by the flow rate adjusting valve 7a and the control device 7b, when a surplus is generated in the secondary permeated water w4, the surplus secondary permeated water w4 is flowed to the return path L9 and the raw water supply path. It is sent to the raw water tank 2a of 2.

Next, the pure water production method of the present embodiment will be described with reference to FIG. The pure water production method of the present embodiment includes a first back-penetrating film separation step of separating raw water w1 into primary permeated water w2 and primary concentrated water w3 by a first back-penetrating film 3, and primary concentrated water w3. In the second back-permeation membrane separation step of separating the secondary permeation water w4 and the secondary concentrated water w5 by the second back-permeation film 4, and the secondary permeation water w4 as cooling water in the cooling tower 5. In addition to supplying the secondary permeated water, the secondary permeated water supply step of returning the surplus of the secondary permeated water w4 to the previous stage of the first back-penetrating film 3 is performed. Further, in the pure water production method of the present embodiment, the first decarboxylation step of decarboxylating the primary permeated water w2 by the first decarboxylation means 31 and the primary permeated water w2 after the first decarboxylation step are electrically operated. The deionization device 32 performs an electrodeionization step of deionizing.
Hereinafter, each step will be described.

First, the amount of impurities in the raw water w1 is reduced to a predetermined concentration or less by performing coagulation sedimentation, filtration, ion exchange, etc. on the raw water w1 such as tap water and industrial water by the pretreatment device 41. The raw water w1 treated by the pretreatment device 41 is sent to the raw water tank 2a by the water channel L1.

Next, in the first reverse osmosis membrane separation step, the raw water w1 supplied from the raw water tank 2a of the raw water supply path 2 is separated into the primary permeated water w2 and the primary concentrated water w3. Impurities are removed from the raw water w1 by the first reverse osmosis membrane 3 to obtain the primary permeated water w2. Further, the removed impurities are contained in the primary concentrated water w3. Then, the primary permeated water w2 is sent to the first decarboxylation means 31 via the primary permeated water channel L3. Further, the primary concentrated water w3 is sent to the concentrated water tank 8 via the water channel L5.

The primary concentrated water w3 sent to the concentrated water tank 8 is further sent to the second reverse osmosis membrane 4 via the water channel L6, but before that, the water quality of the primary concentrated water w3 is adjusted by the water quality adjusting means 42. Since the primary concentrated water w3 is water in which impurities are concentrated in the first reverse osmosis membrane separation step, it contains impurities such as calcium, silica, and carbonate ions at a relatively high concentration, and the water quality is such that scale is easily generated. It has become. In particular, when scale is generated in the second reverse osmosis membrane separation step, the scale causes membrane blockage. Therefore, the water quality of the primary concentrated water w3 is adjusted in advance. Specifically, the primary concentrated water w3 is adjusted to be acidic, for example, pH 5.5 or less, and a scale dispersant is added. By lowering the pH of the primary concentrated water w3, the precipitation of scale is suppressed. Further, by adding the scale dispersant, even if the scale is generated, the film is prevented from being blocked without aggregating the scale. If the possibility of scale formation in the primary concentrated water w3 is expected to be low, the water quality adjustment of the primary concentrated water w3 may be omitted.

Next, in the second reverse osmosis membrane separation step, the primary concentrated water w3 is separated into the secondary permeated water w4 and the secondary concentrated water w5. Impurities are removed from the primary concentrated water w3 by the second reverse osmosis membrane 4 to obtain the secondary permeated water w4. Further, the removed impurities are contained in the secondary concentrated water w5. Then, the secondary permeated water w4 is sent to the water channel L7. On the other hand, the secondary concentrated water w5 is discharged from the pure water production apparatus 1 via the water channel L12.

By separating the secondary permeated water w4 from the primary concentrated water w3 by the second reverse osmosis membrane separation step, the secondary permeated water w4 having a smaller amount of impurities than the primary concentrated water w3 can be obtained. Since the secondary permeated water w4 has a low impurity concentration and scale is difficult to precipitate, even if it is used as cooling water in the cooling tower 5, scale is not generated in the piping of the cooling tower 5 and clogging occurs. There is little risk of waking up.

Next, in the secondary permeated water supply step, the secondary permeated water w4 is supplied to the cooling tower 5 as cooling water, and the surplus of the secondary permeated water w4 is returned to the raw water tank 2a as raw water by the return means 6. The demand for cooling water in the cooling tower 5 varies seasonally, and in the summer when the temperature and water temperature are relatively high, the demand for cooling water in the cooling tower 5 increases, while in the winter when the temperature and water temperature are relatively low. The demand for cooling water in the cooling tower 5 is reduced. In addition, the production amount of the secondary permeated water w4 can also fluctuate due to various factors. Examples of such factors include restrictions on the intake of raw water w1 due to water shortage, a decrease in the amount of raw water w1 used for cost reduction, and a decrease in the amount of raw water w1 used for reducing the environmental load. Therefore, when the production amount of the secondary permeated water w4 in the second reverse osmosis membrane 4 exceeds the demand amount of the secondary permeated water w4 in the cooling tower 5, the surplus amount of the secondary permeated water w4 is returned by the returning means 6. Will be returned as raw water.

Specifically, the control device 7b monitors the amount of cooling water (secondary permeated water w4) used in the cooling tower 5. When the supply amount of the secondary permeated water w4 is insufficient, the control device 7b controls the flow rate adjusting valve 7a to increase the flow rate of the secondary permeated water w4 in the cooling water supply path L8. On the other hand, when the supply amount of the secondary permeated water w4 is excessive, the control device 7b controls the flow rate adjusting valve 7a to reduce the flow rate of the secondary permeated water w4 in the cooling water supply path L8.

When the flow rate of the secondary permeated water w4 is reduced, excess secondary permeated water w4 is generated. The surplus secondary permeated water w4 flows into the return channel L9 branching from the channel L7 and is sent to the raw water tank 2a. Since the return path L9 is on the upstream side of the flow rate adjusting valve 7a, when the flow rate adjusting valve 7a reduces the flow rate of the secondary permeated water w4, the secondary permeated water w4 also flows into the return path L9. ..

The secondary permeated water w4 returned to the raw water tank 2a is sent to the first reverse osmosis membrane 3 again as raw water w1, treated by the first reverse osmosis membrane separation step, and the primary permeated water w2 and the primary concentrated water w3. Is generated.

Next, the primary permeated water w2 separated in the first reverse osmosis membrane separation step is sent to the first decarboxylation means 31 via the primary permeated water channel L3. In the first decarboxylation means 31, the first decarboxylation step is performed. In the first decarboxylation step, carbon dioxide dissolved in the primary permeated water w2 is removed from the primary permeated water w2 by decarboxylating the primary permeated water w2.

Next, in the electrodeionization step, the remaining impurities are further removed by deionizing the primary permeated water w2 after the first decarboxylation step. In the electrodeionization step, the primary permeated water w2 is deionized to produce concentrated water w6 in which impurities are concentrated. The concentrated water w6 is returned to the raw water tank 2a via the water channel L10, sent again as raw water w1 to the first reverse osmosis membrane 3, and treated by the first reverse osmosis membrane separation step. On the other hand, the deionized primary permeated water w2 is sent to the use point via the water channel L11 and used as pure water.

As described above, according to the pure water production apparatus 1 of the present embodiment, the production amount of the secondary permeated water w4 in the second reverse osmosis membrane 4 determines the demand amount of the secondary permeated water w4 in the cooling tower 5. When the amount exceeds the limit, the return means 6 for returning the surplus of the secondary permeated water w4 to the raw water tank 2a is provided, so that the surplus secondary permeated water w4 can be effectively used without being discarded.

Further, according to the pure water production apparatus 1 of the present embodiment, the return means 6 has a return path L9 for returning the secondary permeated water w4 to the raw water tank 2a and a secondary permeated water w4 flowing through the cooling water supply path L8. Since it is composed of the flow control means 7 for controlling the flow rate, the supply amount of the secondary permeated water w4 to the cooling tower 5 and the return amount of the secondary permeated water w4 to the raw water tank 2a are set to the optimum ratio. It can be adjusted and effective use of water can be achieved.

Furthermore, according to the pure water production apparatus 1 of the present embodiment, the first decarboxylation means 31 and electrodeionization are carried out in the primary permeation channels L3 and L4 through which the primary permeation water w2 that has permeated the first reverse osmosis membrane 3 flows. Since the device 32 is further provided, the amount of impurities in the primary permeated water w2 can be further reduced, and high-purity pure water can be produced.

Next, according to the pure water production method of the present embodiment, when the production amount of the secondary permeated water w4 in the second reverse osmosis membrane 4 exceeds the demand amount of the secondary permeated water w4 in the cooling tower 5, the second Since the secondary permeated water supply step of returning the surplus of the secondary permeated water w4 to the raw water tank 2a is provided, the surplus secondary permeated water w4 can be effectively used without being discarded.

Further, according to the pure water production method of the present embodiment, the return means 6 returns the secondary permeated water w4 to the raw water tank 2a, and the flow rate of the secondary permeated water w4 flowing through the cooling water supply path L8. Since it is composed of the flow control means 7 for controlling the above, the supply amount of the secondary permeated water w4 to the cooling tower 5 and the return amount of the secondary permeated water w4 to the raw water tank 2a are adjusted to the optimum ratio. It is possible to make effective use of water.

Furthermore, according to the pure water production method of the present embodiment, the first decarboxylation step and the electrodeionization step are sequentially performed on the primary permeated water w2 that has permeated the first reverse osmosis membrane 3. The amount of impurities in the primary permeated water w2 can be further reduced, and high-purity pure water can be produced.

In particular, the demand for cooling water in the cooling tower 5 has seasonal fluctuations as described above, and the production amount of the secondary permeated water w4 may also fluctuate due to various factors as described above. In the pure water production apparatus 1 and the pure water production method of the present embodiment, the water is effectively used by the return means 6 or the secondary permeated water supply step, so that it is stable even if various external factors fluctuate. Pure water can be produced, and cooling water can be supplied to the cooling tower.

Further, the secondary permeated water w4 has a higher purity than the clean water, industrial water or the primary concentrated water w3, and has a lower purity than the primary permeated water w2 because it has a larger amount of impurities. For example, the electric conductivity of the raw water w1 after the pretreatment is about 100 μS / cm, the primary permeated water w2 after the reverse osmosis membrane permeation is about 1 to 10 μS / cm, and the primary concentrated water w3 is 200 to 600 μS / cm. The secondary permeated water w4 is about 10 to 40 μS / cm. Therefore, the corrosiveness to metals such as iron and copper constituting the pipes of the cooling tower 5 is lower in the secondary permeated water w4 than in the primary permeated water w2, and the secondary permeated water w4 corrodes the pipes and the like. It's hard to do. Further, clean water and industrial water may generate scale in piping and the like, while secondary permeated water w4 has a low possibility of generating scale. Therefore, the secondary permeated water w4 in the present embodiment can be suitably used as cooling water in the cooling tower 5.

Further, in the present embodiment, since the secondary permeated water w4 having a purity higher than that of the raw water w1 is returned to the raw water tank 2a, the amount of impurities in the raw water w1 stored in the raw water tank 2a can be reduced. The burden on the pure water production apparatus 1 can be reduced.

(Second Embodiment)
The pure water production apparatus and the pure water production method according to the second embodiment of the present invention will be described with reference to FIG. The difference between the pure water production apparatus 10 of the present embodiment and the pure water production apparatus 1 of the first embodiment is that the pure water production apparatus 10 of the present embodiment has a preheating means and a heating means. Hereinafter, this difference will be mainly described. Further, in FIG. 2, the same components as those shown in FIG. 1 are designated by the same reference numerals as those in FIG. 1, and the description thereof will be omitted or simplified.

The pure water production apparatus 10 of the present embodiment is provided with a preheating means 11 and a heating means 12 in a water channel L2 (raw water supply path 2) between the raw water tank 2a and the first reverse osmosis membrane 3. .. The preheating means 11 preheats the raw water w1 to raise the water temperature of the raw water w1, and the heating means 12 further heats the raw water w1 after the preheating to further raise the water temperature of the raw water.

A cooling water supply path L18 through which the secondary permeated water w4 flows is drawn into the preheating means 11. In the preheating means 11, heat exchange is possible between the raw water w1 and the secondary permeated water w4. As a result, the preheating means 11 is a heat exchanger in which the secondary permeated water w4 flowing through the cooling water supply path L18 is used as the high temperature side fluid and the raw water w1 is used as the low temperature side fluid.

The heating means 12 heats the raw water w1, and specifically, an electric heater or various heat exchangers can be used. Examples of the heat exchanger include heat exchangers in which a high-temperature fluid other than the secondary permeated water w4, for example, a fluid such as combustion gas, heated air, high-temperature oil, or high-temperature water is used as the high-temperature fluid, and raw water w1 is used as the low-temperature fluid. ..

The pure water production method of the present embodiment is the same as that of the first embodiment, that is, the first reverse osmosis membrane separation step, the second reverse osmosis membrane separation step, the secondary permeated water supply step, and the first decarbonation. By performing the step and the electrodeionization step, the primary permeated water w2 is produced and sent as pure water to the use point, and the secondary permeated water w4 is sent to the cooling tower 5.

Here, in the pure water production method of the present embodiment, the secondary permeated water w4 generated by the second reverse osmosis membrane separation step is sent to the preheating means 11 by the cooling water supply path L18, and the raw water and heat are sent in the preheating means 11. After the replacement, the water is sent to the cooling tower 5 again by the cooling water supply path L18. As a result, the raw water w1 is preheated by the preheating means 11.

Further, the raw water w1 after preheating is heated to a predetermined temperature by the heating means 12. After being heated, the raw water w1 is supplied to the first reverse osmosis membrane 3.

In this way, the water temperature of the raw water w1 can be adjusted by heating the raw water w1 by the preheating means 11 and the heating means 12. For example, when the water temperature of the raw water w1 becomes relatively low, the viscosity of the raw water w1 decreases, so that the effective pressure in the reverse osmosis membrane decreases, and the inhibition rate of impurities may decrease. Therefore, by preheating and heating the raw water w1, it is possible to prevent a decrease in the effective pressure and maintain a high blocking rate of impurities.

According to the pure water production method of the present embodiment, the secondary permeated water w4 can be obtained from the raw water w1 heated by the heating means 12, but the water temperature of the secondary permeated water w4 is high due to the influence of the heating of the raw water w1. It has become. Therefore, heat recovery is performed by exchanging heat between the secondary permeated water w4, which has a relatively high water temperature, and the raw water w1 in the preheating means 11. Further, since the water temperature of the secondary permeated water w4 after heat recovery is relatively low, it is suitable as the cooling water for the cooling tower 5.

As described above, according to the pure water production apparatus 10 and the pure water production method of the present embodiment, the preheating means 11 is used as a heat exchanger to recover the heat of the secondary permeated water flowing through the cooling water supply path L18. As a result, the energy consumption in the heating means 12 can be reduced, and the secondary permeated water w4 sent to the cooling tower 5 can be cooled.

(Third Embodiment)
The pure water production apparatus and the pure water production method according to the third embodiment of the present invention will be described with reference to FIG. The difference between the pure water production device 20 of the present embodiment and the pure water production devices 1 and 10 of the first or second embodiment is that the pure water production device 20 of the present embodiment has a second decarboxylation in the return path L9. The point is that it has means. Hereinafter, this difference will be mainly described. Further, in FIG. 3, the same components as those shown in FIGS. 1 and 2 are designated by the same reference numerals as those in FIGS. 1 and 2, and the description thereof will be omitted or simplified.

In the pure water production apparatus 20 of the present embodiment, the second decarboxylation means 21 is arranged in the middle of the return path L9. The second decarboxylation means 21 decarboxylates the secondary permeated water w4 being returned. The second decarboxylation means 21 is not particularly limited as long as it can mainly remove carbon dioxide dissolved in the secondary permeated water w4. As the second decarboxylation means 21, for example, a membrane degassing device composed of a degassing membrane such as a hollow fiber membrane, a decarboxylation tower, or the like can be used.

The pure water production method of the present embodiment is the same as in the case of the first or second embodiment, that is, the first reverse osmosis membrane separation step, the second reverse osmosis membrane separation step, and the secondary permeated water supply step. 1 By performing the decarbonization step and the electrodeionization step, the primary permeated water w2 is produced and sent as pure water to the use point, and the secondary permeated water w4 is sent to the cooling tower 5.

Here, in the pure water production method of the present embodiment, when the surplus of the secondary permeated water w4 generated by the second reverse osmosis membrane separation step is returned to the raw water tank 2a by the return path L9, the second decarboxylation is performed. As the carbonization step, the secondary permeated water w4 is decarboxylated by the second decarboxylation means 21. By returning the decarboxylated secondary permeated water w4 to the raw water tank 2a, the carbonic acid concentration of the raw water w1 stored in the raw water tank 2a is reduced.

As described above, according to the pure water production apparatus 20 and the pure water production method of the present embodiment, when the secondary permeated water w4 is returned to the raw water tank 2a, the secondary decarboxylation step is performed on the secondary permeated water w4. Therefore, the decarboxylated secondary permeated water w4 can be returned to the raw water tank 2a, whereby the carbonic acid concentration of the raw water w1 is reduced, and the load of the first decarboxylation step in the first decarboxylation means 31 is performed. Can be reduced.

The pure water production apparatus of the present invention is not limited to that shown in FIGS. 1 to 3, and for example, even if the second decarboxylation means 21 is applied to the pure water production apparatus 1 of FIG. Good.

1, 10, 20 ... Pure water production equipment, 2 ... Raw water supply path, 2a ... Raw water tank, 3 ... First reverse osmosis membrane, 4 ... Second reverse osmosis membrane, 5 ... Cooling tower, 6 ... Return means, 7 ... Flow control means, 7a ... Flow control valve, 7b ... Control device, 11 ... Heat exchanger (preheating means), 12 ... Heating means, 21 ... Second decarbonization means, 31 ... First decarbonization means, 32 ... Electrodeionizer, 41 ... Pretreatment device, L3, L4 ... Primary permeated water channel, L8, L18 ... Cooling water supply channel, L9 ... Return channel, w1 ... Raw water, w2 ... Primary permeated water, w3 ... Primary concentrated water, w4 ... secondary permeated water, w5 ... secondary concentrated water.

Claims (10)

The raw water supply channel through which raw water flows and
A first reverse osmosis membrane that separates the raw water supplied from the raw water supply channel into primary permeated water and primary concentrated water.
A second reverse osmosis membrane that separates the primary concentrated water into secondary permeated water and secondary concentrated water.
A cooling water supply path that supplies the secondary permeated water to the cooling tower as cooling water, and
When the production amount of the secondary permeated water in the second reverse osmosis membrane exceeds the demand amount of the secondary permeated water in the cooling tower, the surplus of the secondary permeated water is returned to the raw water supply channel. A pure water production apparatus characterized in that it is provided with a return means. The return means includes a return path for returning the secondary permeated water to the raw water supply path, and a return path.
The pure water production apparatus according to claim 1, further comprising a flow rate control means for controlling the flow rate of the secondary permeated water flowing through the cooling water supply path. A preheating means that is arranged in the middle of the raw water supply channel to preheat the raw water,
A heating means for heating the raw water after preheating, which is arranged in the middle of the raw water supply path, is further provided.
The first or second aspect of the present invention, wherein the preheating means is a heat exchanger in which the secondary permeated water flowing through the cooling water supply path is a high temperature side fluid and the raw water is a low temperature side fluid. Pure water production equipment. A primary permeation channel through which the primary permeate water that has permeated the first reverse osmosis membrane flows,
A first decarboxylation means that is installed in the primary permeation channel and decarboxylates the primary permeate water.
An electric deionization device that is installed after the first decarboxylation means of the primary permeation water channel and deionizes the primary permeation water after passing through the first decarboxylation means is further provided. The pure water production apparatus according to any one of claims 1 to 3, which is characterized. The pure water production apparatus according to any one of claims 2 to 4, wherein the return path is provided with a second decarboxylation means for decarboxylating the secondary permeated water. A first reverse osmosis membrane separation step of separating raw water into primary permeated water and primary concentrated water by a first reverse osmosis membrane.
A second reverse osmosis membrane separation step of separating the primary concentrated water into secondary permeated water and secondary concentrated water by a second reverse osmosis membrane.
The secondary permeated water is supplied to the cooling tower as cooling water through the cooling water supply path, and the production amount of the secondary permeated water in the second reverse osmosis membrane is the secondary permeated water in the cooling tower. A secondary permeated water supply step in which the surplus of the secondary permeated water is returned as raw water by a return means when the demand amount is exceeded.
A pure water production method characterized by being provided with. The return means includes a return path for returning the secondary permeated water to the raw water.
The pure water production method according to claim 6, further comprising a flow rate control means for controlling the flow rate of the secondary permeated water flowing through the cooling water supply path. A preheating step of preheating the raw water before supply to the first reverse osmosis membrane, and
A heating step of heating the raw water after preheating is further provided.
The sixth or seventh aspect of the present invention, wherein the preheating step is performed by a heat exchanger in which the secondary permeated water flowing through the cooling water supply path is used as a high temperature side fluid and the raw water is used as a low temperature side fluid. Pure water production method. In the first decarboxylation step of decarboxylating the primary permeated water by the first decarboxylation means,
Any of claims 6 to 8, further comprising an electrodeionization step of deionizing the primary permeated water after the first decarburization step with an electrodeionizer. The pure water production method according to item 1. The pure water according to any one of claims 7 to 9, further comprising a second decarboxylation step of decarboxylating the secondary permeated water flowing through the return path by a second decarboxylation means. Production method.

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