JPH0244573B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electrodialysis device that has a high desalination rate or concentration rate per passing flow. In particular, in electrodialysis equipment that has a demineralization chamber and a concentration chamber with a long flow path for the liquid to be treated, electrodialysis can be performed at a high desalination rate or high concentration rate without causing harmful effects such as alkali scale formation. Provides electrodialysis equipment.

Conventionally, a cation exchange membrane and an anion exchange membrane are connected to electrodes through a chamber frame having a notch that forms a current-carrying surface, a communication hole that supplies and discharges the liquid to be treated, and a notch that forms a liquid supply groove. By arranging and tightening a large number in between, a large number of demineralization chambers and concentration chambers for the liquid to be treated (electrolyte) are alternately formed in the device, and communication holes are provided for supplying and discharging the liquid to these chambers. Electrodialyzers having flow channels are known and are widely used for desalting or concentrating solutions containing electrolytes. In particular, it is used on an industrial scale in the production of common salt by concentrating seawater, in the production of fresh water by desalination of brine, and in the desalination and reuse of industrial wastewater.

For example, when desalinating seawater using such an electrodialysis device, the desalination rate per overflow, that is, during one pass through the desalination chamber, is low. Depending on the method, desalination is carried out by circulating it through the electrodialysis machine multiple times,
Alternatively, a method is generally adopted in which a plurality of electrodialyzers are arranged in series and desalination is performed sequentially in multiple stages.

However, the former batch desalination method requires a circulation pump, circulation tank, and piping between them, and the latter method of arranging them in series also requires multiple dialysis machines, which increases equipment costs. The drawback is that not only does the amount of fuel increase dramatically, but the driving operation is also complicated.

The present inventors focused on the drawbacks of the above-mentioned electrodialysis method, and conducted studies on the development of an electrodialysis device that uses a single electrodialysis device to increase the desalting rate per flow. Generally, methods for increasing the desalination rate in a single electrodialysis device include increasing the current density applied to the electrodialysis device or decreasing the amount of fluid supplied. However, there is a limit to the current density that can be applied to an electrodialysis device, that is, a critical current density, and when electrodialysis is performed at a current density higher than the critical current density, water decomposition occurs and alkaline scale is deposited in the dialysis chamber. Furthermore, when the amount of the treated liquid to be supplied is reduced, the linear flow velocity on the surface of the ion exchange membrane is reduced, and therefore the critical current density is also reduced. Therefore, if the applied current density is kept constant and the amount of supplied liquid to be treated is reduced, water decomposition and alkali scale deposition will similarly occur. For these reasons, it is not preferable to increase the desalination rate simply by increasing the current density or decreasing the amount of supplied liquid to be treated.

Therefore, as a means of increasing the desalination rate in a single electrodialysis device, a method has been proposed in which electrodialysis is performed by forming a long channel for the liquid to be treated in order to lengthen the desalination time (hereinafter also simply referred to as the long channel method). ing. A typical example is the one made by Ionics Inc. (USA), which has a regularly curved flow path, but there are also other ways to create a U-shaped flow path, a spiral shape, a long straight path, etc. It has been known.

This long-channel method has the characteristic that it does not require a circulation tank, a circulation pump, or multiple electrodialysis devices and has low equipment costs, unlike the aforementioned batch method or serial multi-stage method. For example, when desalinating seawater, a phenomenon is observed in which alkaline scale forms in some concentration chambers. This alkaline scale causes blockage of the flow path or damage to the membrane, eventually leading to a situation in which dialysis is impossible.

The present inventors have discovered that the main cause of this phenomenon is the non-uniform distribution of the liquid to be treated into the demineralization chamber and/or the concentration chamber. In other words, normally the liquid to be treated is supplied to the desalination chamber or the concentration chamber through the liquid supply groove from the communication hole, but if there are more than 100 chambers, especially
It is nearly impossible to evenly distribute the liquid to be treated in the demineralization chambers or concentration chambers of a large-scale device with over 1,000 chambers.
In fact, in a typical electrodialysis machine, the distribution of the liquid to be treated is uneven, and there are chambers where the flow rate is 5 to 10% lower than the average flow rate. If desalination is continued in a state where such non-uniform distribution of the liquid to be treated exists, the concentration in the demineralization chamber where the amount of liquid to be supplied is small will be abnormally reduced compared to other demineralization chambers. As a result, it was found that water decomposition occurred in the demineralization chamber where the concentration had abnormally decreased, and alkali scale such as calcium carbonate was precipitated.

A more detailed study revealed that alkali scale precipitation occurs from the latter half of the path through which the liquid to be treated flows while undergoing electrodialysis treatment (hereinafter referred to as the "flow path"), as shown in Figure 1. It happened in
It was found that this was particularly noticeable after 3/5 of the liquid flow path.

Figure 1 shows the current density divided by the concentration of the desalting solution (i/c) depending on the position of the flow path in an electrodialysis device that desalinates seawater using the long flow path method to obtain a high desalination rate. (abbreviated)) shows how it changes. As shown in the figure, when entering the latter half of the flow path, i/
c shows an increasing tendency, and shows a particularly rapid increase after 3/5. On the other hand, I/C has a limit value (limit current density) unique to each electrodialysis device, and above that limit water decomposition occurs, leading to the precipitation of alkali scale, so I/C has a limit value. Must be set to less than or equal to the value. In this way, when attempting to obtain a high desalination rate using the high flow channel method, the limit value is exceeded due to a rapid increase in I/C in the latter half of the flow channel as shown in Figure 1, resulting in alkali formation due to the occurrence of water splitting. It can be understood that this leads to scale precipitation. This phenomenon becomes even more remarkable after 3/5 of the flow path.

The present inventors have developed a structure of an electrodialysis device that can obtain a high desalination rate without water splitting or alkaline scale formation in a single electrodialysis device, especially a single electrodialysis device with a long flow path. As a result of our research, we found that by collecting the liquid from multiple desalting chambers or concentration chambers in the latter half of the flow path of the liquid to be treated, mixing them, and then redistributing them and subjecting them to electrodialysis, we were able to As shown in the figure, it was discovered that desalination could be performed below the limit value, and the present invention was completed.

In the present invention, a large number of demineralization chambers and concentration chambers are alternately formed by alternately arranging and tightening cation exchange membranes and anion exchange membranes between electrodes via chamber frames. In an electrodialysis apparatus in which the liquid to be treated flows through the concentration chamber, a mechanism for collecting, mixing, and redistributing the liquid in the plurality of desalination chambers and/or concentration chambers is provided in the latter half of the flow path for the liquid to be treated. This is an electrodialysis device characterized by the following.

Hereinafter, the present invention will be explained in detail using the accompanying drawings.

FIG. 2 is a schematic diagram showing the configuration of a typical electrodialysis apparatus used conventionally. The cation exchange membrane 1 and the anion exchange membrane 2 are sequentially stacked via the chamber frame 3 and the chamber frame 4 in which the mesh spacer 5 is inserted into the notch, and when the appropriate number of layers is reached, the tightening frame 6 is tightened.
(the other clamping frame is not shown), one stack is formed as a handling unit. One or more of these stacks are placed between the electrodes and tightened using a hydraulic press or the like to form an electrodialysis device. Chamber frames 3 and 4
Generally has a thickness of 0.5 to 3 mm and has a notch in the center, so it is divided by a cation exchange membrane and an anion exchange membrane, and a demineralization chamber and a concentration chamber with a mesh spacer inside. (These are also collectively referred to as dialysis rooms) are formed alternately. The chamber frames forming the desalination chamber and the concentration chamber are called a desalination chamber frame and a concentration chamber frame, respectively. In addition, the desalination chamber frame and the concentration chamber frame each have a perforation 7 that forms a communication hole for supplying the liquid to be treated into the dialysis chamber or discharging it outside the dialysis chamber, and a distribution groove that connects the perforation 7 and the central notch. 8 and a flow collecting groove 9 are provided. Incidentally, at least one perforation 7 is required for the desalted liquid and one perforated for the concentrated liquid, and although a plurality of perforations 7 are generally provided at regular intervals, only one perforation is shown in the drawing. The same applies to the following drawings.

When desalination is performed using such an electrodialysis device, the desalination solution (liquid to be treated) is introduced into each desalination chamber through the communication hole 10 and further through the distribution groove 8 provided in the demineralization chamber frame. . The introduced desalting solution is dispersed in the desalting chamber and subjected to dialysis treatment, and then is discharged to the outside of the dialysis apparatus through the flow collecting groove 9 and further through the communication hole 11. On the other hand, the concentrated liquid is introduced into each concentration chamber through the communication hole 14 and further through the distribution groove 12 provided in each concentration chamber frame. The concentrated solution introduced into the concentration chamber is dispersed within the concentration chamber and subjected to electrodialysis treatment, and then is discharged to the outside of the dialysis apparatus through the flow collecting groove 13 provided in the concentration chamber frame and further through the communication hole 15.

FIG. 3 is a cross-sectional view taken along line A-A' of the device after the components shown in FIG. 2 are fastened between electrodes.

In the typical conventional dialysis equipment shown in Figures 2 and 3 above, the flow path of the liquid to be treated is short, so the dialysis rate per one excess flow, that is, one pass through the dialysis chamber, is increased. This is generally not possible. For example, if desalination is performed by forming a long flow path in the dialysis chamber, water decomposition, generation of alkali scale, etc. will occur as described above.

In order to solve this problem, the present invention provides a mechanism (hereinafter also simply referred to as a redistribution mechanism) for collecting, mixing, and redistributing the liquid to be treated in the latter half of the flow path for the liquid to be treated in the dialysis chamber. I solved it.

The redistribution mechanism may be any mechanism that is configured to once collect and mix the liquid in multiple desalination chambers or concentration chambers, and then redistribute it to a new desalination chamber or concentration chamber; The fourth preferred embodiment
This will be explained using the figure below.

FIG. 4 shows a schematic diagram of an electrodialysis apparatus having a structure in which the flow path of the liquid to be treated is long and linear, and the redistribution mechanism is composed of communication holes. Taking the case of desalination as an example, the liquid to be treated passes through the communication hole 10, is introduced into the desalination chamber through the distribution groove 8, is electrodialyzed, and exits from the flow collection groove 9 to the communication hole 11. I'm going, but
A communication hole 16, which is a redistribution mechanism, is newly provided at a position of about 3/4 in the latter half of the flow path of the liquid to be treated in the demineralization chamber. This communication hole 16 passes through a plurality of demineralization chambers, generally one stack, and has a liquid collection port for the liquid to be treated desalted in area A of the demineralization chamber, and is mixed in the communication hole. It has a redistribution port that redistributes the processed liquid to area B of the desalination chamber where further desalination is performed. In addition, a flow collection groove 17 is formed by the chamber frame between the A area demineralization chamber and the liquid collection port of the communication hole in order to facilitate the collection of the liquid to be treated, and similarly, the communication hole is redistributed. A flow distribution groove 18 is also formed between the mouth and the B area demineralization chamber to facilitate flow distribution.

Incidentally, FIG. 5 is a sectional view taken along the line BB' of the device after the components shown in FIG. 4 are fastened between the electrodes.

As described above, by newly providing the communication hole 16 in the latter half of the flow path, the liquid to be treated collected from the liquid collection ports corresponding to the number of desalination chambers is mixed in the communication hole and then sent from the redistribution port. Although it flows out into area B of the desalination room,
In order to more thoroughly mix the liquid to be treated within the communication hole and to achieve a uniform concentration composition, it is preferable to provide a mechanism in the communication hole 16 that further promotes the mixing. In general, it is best to have a structure in which a baffle plate is provided to form a curved flow and cause a turbulent flow state. For example, a plate-like body with small holes or multiple pores bored at regular intervals is placed on the liquid collection port side and the redistribution port side. It is preferable to adopt an aspect in which the opening is installed in the communicating hole so as to be separated from the outside.

FIG. 6 is a schematic diagram showing the configuration of an electrodialysis apparatus according to another embodiment of the present invention. In this embodiment, the communication holes are the liquid collection communication hole 19 and the redistribution communication hole 2.
0, and tighten these communicating holes with the tightening frame 6.
Mixing of liquids is performed by connecting them within the chamber. Note that the communication hole 21 and the communication hole 20 may be connected within a cutout of the liquid supply frame (not shown) when the liquid supply frame is provided separately.

FIG. 7 is a sectional view taken along the line C-C' of the device after the components shown in FIG. 6 have been fastened between the electrodes.

The mechanism for collecting, mixing, and redistributing the liquid to be treated from the latter half of the flow path onwards has been explained above in the case of desalination using Figures 4 to 7, but it can of course be similarly applied to the case of concentration. Needless to say.

Further, although the type of electrodialysis apparatus shown is a case in which the liquid to be treated flows almost linearly from the supply communication hole to the drainage communication hole, the present invention is not limited to this. Of course, the present invention can also be applied to an electrodialysis device having a long flow path.

For example, in Figure 8, the flow path of the liquid to be treated is horizontal,
A bent flow path is formed by connecting two U-shapes horizontally, and a redistribution mechanism is installed at a position of 3/4 of the flow path, that is, a position of 1/4 from the side of the drainage communication hole. A communication hole 21 is provided.

In addition, FIG. 9 also has a structure in which a bent flow path is formed in the horizontal direction as in FIG. 22 and a communication hole 23 are shown.

In the electrodialysis apparatus of the present invention, the redistribution mechanism for the liquid to be treated is installed from the latter half of the flow path, especially in the 3rd and 3rd half of the flow path.
It is preferable to set it as 5 or more. Further, the number of the mechanisms installed can be two or more in consideration of the desired salt removal rate, the length of the flow path, etc.

According to the electrodialysis apparatus of the present invention, the amount of the liquid to be treated that is supplied from the communication hole through the distribution groove to the dialysis chamber, for example, the demineralization chamber, is uneven, and the amount of liquid is small and the desalination rate is high. Even if a deionization chamber exists, the liquid to be treated is mixed with the liquid from other desalination chambers, preferably one stack of demineralization chambers, before reaching a low concentration that causes water decomposition, so that the liquid to be treated has a uniform concentration composition. Furthermore, since it is supplied to the subsequent desalination chamber, even with electrodialysis equipment with a high desalination rate, there is no alkali scale precipitation that can cause water decomposition in one overflow, and stable electricity with a high desalination rate is generated. It has the characteristic that dialysis is possible. Moreover, since the mechanism for collecting, mixing and redistributing the liquid to be treated is structurally simple, as typified by the communicating holes, there is an advantage that the equipment cost is low.

Example 1 An electrodialysis apparatus having a structure in which a flow path for a liquid to be treated is provided in a long straight line as shown in FIG. 4 was assembled.

As a notch in the center of the chamber frame, width 200mm x length
A 1740mm notch (forming the A area demineralization chamber) and a 200mm width x 580mm length notch (constituting the B area demineralization chamber) with an interval of 80mm between these notches.
50mm in width and 20mm in length to form a communication hole between them as a redistribution mechanism.
One mm cutout is formed for the desalted liquid and one for the concentrated liquid, and the liquid is supplied around the chamber frame.
Through a chamber frame (thickness 0.75 mm, width 260 mm x length 2640 mm) provided with notches that form two communication holes for discharge (one for desalinated liquid and one for concentrated liquid),
Cation exchange membrane [Product name: “Neoceptor CL-”
25T” (manufactured by Tokuyama Soda Co., Ltd.) Strongly acidic membrane with sulfonic acid as the exchange group] and anion exchange membrane [trade name “Neoseptor ACH-45T” (manufactured by Tokuyama Soda Co., Ltd.), with quaternary ammonium group as the exchange group] strong basic membranes] are arranged alternately and tightened between the electrodes to form the concentration chamber 201.
An electrodialysis device consisting of 200 demineralization chambers and desalination chambers was assembled. The cathode was a stainless steel plate, and the anode was a platinum-plated titanium plate.

A NaCl aqueous solution with a TDS of 3000 ppm was introduced from the bottom of the device at a flow rate of 6 cm/sec in the desalination chamber.
In addition, when electrodialysis was performed at an average current density of 0.95 A/dm ² with each supply being supplied so that the flow rate in the concentrate was 2 cm/sec, the
A desalinated solution containing 300 ppm NaCl was obtained at 6.1 m ³ /hr.
As a result, the salt removal rate was 90%. On the other hand, a concentrated solution containing 11,000 ppm of NaCl was obtained from the concentration chamber. The voltage at this time was 122V.

After continuing desalination for 2000 hours under these conditions, the electrodialysis machine was disassembled and no abnormalities were found.

Comparative Example 1 Chamber frame with a notch in the center and a notch on the periphery to form communication holes and distribution grooves for supplying and discharging liquid (thickness 0.75 mm, size 260 mm x 2560 mm, size of center notch An electrodialysis apparatus was assembled in the same manner as in Example 1, except that a sample (width 200 mm x length 2320 mm) was used.
The flow path length of the liquid to be treated in this dialysis apparatus is approximately 2.3 m from the length of the central notch in the chamber frame.

A NaCl aqueous solution with a TDS of 3000 ppm was introduced from the bottom of the device at a flow rate of 6 cm/sec in the desalination chamber.
In addition, when electrodialysis was performed at an average current density of 0.95 A/ ^dm2 with each supply being supplied so that the flow rate in the concentration chamber was 2 cm/sec, 300 ppm of NaCl was produced from the desalting chamber.
of desalinated liquid was obtained at 6.1 m ³ /hr. As a result, the salt removal rate was 90%. On the other hand, from the concentration room
A concentrated solution containing 11000 ppm of NaCl was obtained. The voltage at this time was 130V.

After electrodialysis was performed for 250 hours under these conditions, the device was disassembled and 23 cells were detected from the anode chamber side.
Calcium carbonate scale was deposited on the membrane surfaces of the concentration chamber side of the 126th, 36th, 83rd, 126th, and 146th anion exchange membranes. The location where scale was deposited was in the latter half of the flow path for both films.
The closer to the outlet distribution channel, the greater the amount of scale precipitated. This is thought to be because the flow rate of the demineralization chamber in contact with the membrane where these scales were generated decreased, resulting in an abnormal decrease in the concentration, which caused water decomposition and led to the generation of scales. Stable long-term electrodialysis is not possible under such conditions.

Example 2 In the communication hole (width 50 mm x length 20 mm) provided as the redistribution mechanism in Example 1, a baffle plate (width 50 mm x thickness 10 mm with a diameter of 30 mm in the center) was placed to promote mixing.
(with a hole of mm) was inserted to separate the liquid collection port side and the redistribution port side. When a NaCl aqueous solution with TDS of 3000 ppm was desalted under the same conditions as in Example 1, 6.1 m ³ of a desalted solution with NaCl of 300 ppm was obtained per hour. Meanwhile, a solution containing 11,000 ppm of NaCl was discharged from the concentration chamber. The voltage at this time was 120V. After continuing desalination for 2000 hours under these conditions, the dialysis machine was disassembled and no abnormalities such as scale precipitation were observed.

Example 3 As shown in FIG. 6, an electrodialysis apparatus was assembled in which the redistribution mechanism had a liquid collection communication hole and a redistribution communication hole connected within a notch of a clamping frame. In other words, a notch in the center of the chamber frame with a width of 200 mm and a length of
Create a 1740 mm notch (forming the A area demineralization chamber) and a 200 mm width x 580 mm length notch (constituting the B area demineralization chamber) so that these notches are 150 mm apart. A notch for forming two stages of communication holes with a diameter of 30 mm for the redistribution mechanism was formed in the interval between the two, and the other parts were the same as in Example 1. Frame (width 260mm x length
An electrodialysis apparatus was assembled in the same manner as in Example 1 using a dialysis machine (2710 mm). Note that the communication holes provided in two stages were connected through a notch in the tightening frame.

TDS3000ppm NaCl under the same conditions as Example 1.
When the aqueous solution was desalted, good results similar to those in Example 2 were obtained.

Example 4 An electrodialysis apparatus having a structure in which the flow path of the liquid to be treated was bent as shown in FIG. 8 was used. i.e. thickness 0.75
A notch was provided in the chamber frame with a width of 1000 mm and a length of 2200 mm to form a bent flow path with a width of 210 mm and a length of 8000 mm. Moreover, the 8000mm bending notch is 6000mm.
Divide into two parts with a length of 2000mm, and a width of 80mm between them.
A notch with a length of 30 mm was provided for a communication hole as a redistribution mechanism. In addition, cutouts were provided before and after the bent cutout to form communication holes for supplying and discharging liquid.

Using this chamber frame and the same ion exchange membrane as in Example 1, an electrodialysis apparatus consisting of 301 concentration chambers and 300 desalination chambers was assembled.

Seawater containing salt with a TDS of 34,000 ppm was supplied to the desalination chamber of this device at a flow rate of 6 cm/sec, and the same seawater was supplied to the concentration chamber at a rate of 5.0 cm/sec, and electrodialysis was performed at an average current density of 3.3/ ^dm2. As a result, 8.9 m ³ of desalted solution with TDS of 380 ppm was obtained from the desalting room per hour. This corresponds to a desalination rate of 98.9%. Meanwhile, a concentrated solution containing 68,000 ppm of NaCl was discharged from the concentration chamber. The voltage at this time was 220V. After electrodialysis was continued for 2000 hours under these conditions, the apparatus was disassembled and no abnormalities such as scale precipitation were observed.

Comparative Example 2 Without dividing the flow path into two by the chamber frame of Example 4,
Further, an electrodialysis apparatus was assembled in the same manner as in Example 4, except that a redistribution mechanism was not provided and a chamber frame provided with a notch for forming a continuous flow path with a width of 210 mm and a length of 8000 mm was used. Seawater electrodialysis was performed in the same manner as in Example 4 using this electrodialysis apparatus. The voltage at this time was 245V. From the desalination room
8.9 m ³ of desalted solution with TDS of 460 ppm was obtained per hour. This corresponds to a desalination rate of 98.6%. On the other hand, 68,000 ppm of concentrated liquid was discharged from the concentration chamber. After desalination continued for 200 hours under these conditions, the equipment was disassembled and the 5th, 86th, 124th, 216th, and 246th anion exchange membranes counted from the anode chamber were found. Calcium carbonate scale was deposited on the membrane surface on the concentration chamber side. The area where scale was deposited was located 5000mm from the desalination fluid supply distribution channel.

[Brief explanation of drawings]

FIG. 1 is a graph showing the relationship between the position of the flow path and current density/concentration. FIG. 2 is a schematic diagram showing the configuration of a typical electrodialysis device conventionally used.
FIG. 3 is a sectional view taken along the line A-A' of the device after the components shown in FIG. 2 have been tightened; FIG. The figure is a sectional view taken along the line B-B' of the device after the components shown in FIG. 4 have been tightened, FIG. The figure is a sectional view taken along the line C-C' of the device after the components shown in FIG. 6 are fastened between the electrodes, and FIG. 8 is a schematic diagram showing the configuration of an electrodialysis device showing still another embodiment of the present invention. and FIG. 9 are schematic diagrams of a chamber frame showing still another embodiment of the present invention. In the figure, 1... Cation exchange membrane, 2... Anion exchange membrane, 3, 4... Chamber frame, 5... Net spacer, 6... Tightening frame, 7... Perforation for forming a communication hole, 8... Distribution groove. , 9... Collecting groove, 10, 11... Desalting side communication hole,
12... Distribution groove, 13... Collecting groove, 14, 15... Concentration side communication hole, 16... Communication hole as redistribution mechanism, 1
7... Flow collection groove, 18... Distribution groove, 19... Communication hole for liquid collection, 20, 21, 22, and 23... Communication hole as a redistribution mechanism, respectively.

Claims (1)

[Claims] 1. A large number of demineralization chambers and concentration chambers are alternately formed by alternately arranging and tightening cation exchange membranes and anion exchange membranes between electrodes via chamber frames. In an electrodialysis apparatus in which the liquid to be treated flows through the demineralization chamber and the concentration chamber, the liquids in the plurality of demineralization chambers and/or concentration chambers are collected, mixed, and redistributed, respectively, in the latter half of the flow path of the liquid to be treated. An electrodialysis device characterized by being equipped with a mechanism. 2. The electrodialysis apparatus according to claim 1, wherein a mechanism for collecting, mixing and redistributing liquid is provided in 3/5 or more of the flow path. 3. The electrodialysis apparatus according to claim 1, wherein the mechanism for collecting, mixing and redistributing liquid is a communication hole having a liquid collection port and a redistribution port. 4. The electrodialysis apparatus according to claim 3, which is provided with a mechanism for mixing liquid within the communication hole. 5. In claim 1, the liquid collection, mixing and redistribution mechanism has a liquid collection communication hole and a redistribution communication hole connected within a notch of the clamping frame or the liquid supply frame. Electrodialysis equipment consisting of.