JPH0375203B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electrodialysis seawater desalination apparatus equipped with a stratified desalination water tank for preventing a decrease in dialysis efficiency due to mixing of treated liquid and untreated liquid in the electrodialysis apparatus. .

FIG. 1 shows a system of an electrodialysis apparatus according to the prior art. The device includes an electrodialysis tank 1, a desalinated liquid circulation tank 2, a concentrated liquid circulation tank 3, a desalted liquid circulation pump 4, a concentrated liquid circulation pump 5, piping 6, a circulation valve 7, a recovery valve 8, a replenishment valve 9, and a DC power supply 10, etc.

After a predetermined amount of the desalted solution and concentrated solution are replenished into tanks 2 and 3, each pump 4 and 5
The desalted solution is circulated through the electrodialysis tank 1 via the piping 6 and the circulation valve 7 until it reaches a predetermined concentration.

After the circulating fluid has been treated to a predetermined concentration, the dialyzer is stopped, and both the desalinated fluid and the concentrated fluid are collected through the collection valves 8.

When the recovery is completed, the recovery valve 8 is closed, and raw water is replenished into each tank 2, 3 from the replenishment valve 9, and the process is repeated again in order. Here, the DC power source is stopped during liquid recovery and replenishment.

In this way, conventional electrodialysis equipment desalinates raw water by performing batch circulation processing, but since the desalination liquid tank is an open mixing tank, the dialysis tank outlet, which has a low salt concentration, is The treated liquid and the untreated liquid remaining in the tank are mixed. Therefore, since the salt concentration of the mixed solution is lower than that of the untreated solution, there is a large electrical resistance in the electrodialysis tank, and the electrical energy required for dialysis is greater than when the salt concentration is not reduced, resulting in an increase in processing costs.

That is, in the case of desalting by electrodialysis, the current value is proportional to the width of change in salt concentration, so the current value for reaching a predetermined concentration is constant, while the current flow resistance value increases as the salt concentration decreases. Therefore, the lower the salt concentration, the higher the power consumption.

In addition, since the DC power source is stopped when recovering and replenishing the processing liquid, desalination operations are not possible, and the processing capacity (operating rate) is reduced. For this reason, the processing capacity per piece of equipment (dialysis membrane area, DC power supply capacity, etc.) becomes smaller.

The purpose of the present invention is to eliminate the drawbacks of the prior art as described above, and to mix the treated solution with a low salt concentration at the outlet of a dialysis tank with the untreated solution with a high salt concentration remaining in the desalination tank. To provide an electrodialysis seawater desalination device capable of reducing electrical resistance in a dialysis tank and reducing electrical energy required for dialysis by preventing the salt concentration of a desalinated solution supplied to the dialysis tank from decreasing. It is in.

That is, the present invention provides a rectifying plate 12 inside the desalinated liquid tank 2 of an electrodialysis apparatus to form a liquid stratification type tank 11, and prevents the treated liquid from the electrodialysis tank 1 from mixing with the untreated liquid. An electrodialysis device characterized by sequentially supplying untreated liquid to an electrodialysis tank,
It is.

In short, the present invention provides a liquid stratification type tank 11 with a rectifier plate 12 installed in the tank so that the treated desalinated liquid at the outlet of the electrodialyzer and the untreated liquid remaining in the tank do not mix in the desalted liquid tank. It is an electrodialysis device.

FIG. 2 shows an embodiment in which the desalted solution tank of the electrodialysis apparatus according to the present invention is of a stratified type. By providing the stratified tank 11 shown in FIG. 2 in place of the desalted solution tank 2 in the dialysis machine shown in FIG. Since the flow is rectified from the tank inlet (upper side in this figure) along the plate 12 and flows to the tank outlet, the desalted liquid is circulated without mixing with the untreated liquid remaining in the tank (lower liquid in this figure). It is circulated and supplied to the dialysis tank 1 by the pump 4. In addition to this embodiment, various methods of installing the rectifying plate 12 can be considered, such as vertically, etc., but in any case, a similar dialysis system can be realized by making the liquid in the tank a stratified flow (also called a piston flow). . The advantages of this system will be explained with reference to FIG.

In FIG. 3, the horizontal axis shows the number of circulations of the treatment liquid in the desalinated water tank, and the vertical axis shows the salt concentration of the liquid and the corresponding electrical resistance of the liquid. In the conventional method, since the salt concentration continuously decreases, the electrical resistance value also increases continuously. This state is shown by the straight line in FIG. On the other hand, according to the present invention, since the salt concentration decreases in a stepwise manner, the electrical resistance also increases in a corresponding stepwise manner, and this situation is shown by the stepwise straight line in FIG. What is important here is that the electrical resistance value of the present invention is always lower than that of the conventional method. In other words, it is possible to reduce dialysis power consumption.

Note that the number of circulations shown in FIG. 3 is an example, and is not limited to this. In reality, it is determined by the shape and volume of the stratified tank.

As a method to prevent mixing of the treatment liquid in the desalination tank, multiple dialysis tanks are installed in series, and the treatment liquid at the outlet of the first dialysis tank is directly transferred to the second dialysis tank (without the desalination tank). ) and perform desalination treatment. Furthermore, there is a so-called one-time treatment system that performs desalination treatment in series with a third and fourth according to the required amount of desalination. A transient treatment system has already been proposed and known as a method of compensating for the drawbacks of a conventional dialysis system using a mixed type desalted liquid tank. The present invention can achieve the same effects as this transient treatment system using only a single dialysis tank.

The following three effects can be mentioned as effects of the present invention.

1. It is possible to prevent concentration reduction due to mixing of the desalted solution with the untreated solution in the desalted solution tank in the conventional dialysis system.

2. Therefore, the increase in dialysis electrical resistance is suppressed to a low level, resulting in a reduction in power consumption.

3. Since the same effects as the one-time treatment system can be achieved using a single dialysis tank, the equipment can be configured compactly.

[Brief explanation of drawings]

FIG. 1 shows a system diagram of a conventional batch type electrodialysis apparatus. FIG. 2 shows a cross-sectional view of an embodiment of a liquid stratification type tank according to the present invention. FIG. 3 shows a graph showing the relationship between the concentration of liquid in the dialysis tank, electrical resistance, and circulation recovery in the conventional dialysis apparatus and the dialysis apparatus according to the present invention. 1... Dialysis tank, 2... Desalinated liquid tank, 3... Concentrated liquid tank, 4... Desalted liquid circulation pump, 5... Concentrated liquid circulation pump, 6... Piping, 7... Circulation valve, 8... Recovery valve, 9...
Supply valve, 10... DC source, 11... Stratified tank, 1
2... Rectifier plate.

Claims (1)

[Claims] 1. A rectifying plate 12 is provided inside the desalination liquid tank 2 of the electrodialysis machine to form a liquid stratification type tank 11, and the untreated liquid is sequentially transferred from the electrodialysis tank 1 while preventing the treated liquid from mixing with the untreated liquid. An electrodialysis device that supplies electricity to an electrodialysis tank.