JPH0757309B2 - Electrodialysis desalination method and device - Google Patents

Description

TECHNICAL FIELD The present invention relates to a desalination method by electrodialysis and an apparatus used for carrying out the method, and more particularly to a desalination method suitable for use of fluctuating electric power and It relates to a device therefor.

[Conventional technology]

A cation exchange membrane having selective permeability for cations and an anion exchange membrane having selective permeability for anions are alternately and repeatedly arranged in parallel to form a large number of compartments between the membranes.
When a direct current is applied from both ends of the membrane group while passing a saline solution through each compartment, the compartment concentration decreases every other compartment due to ion electrophoresis and the selective permeation action of the membrane. Increased concentration room. Fresh water is obtained by passing salt water such as seawater through the desalination chamber.

The above desalination method using electrodialysis (hereinafter referred to as electrodialysis desalination method) is easy to pretreat raw water (seawater, etc.) such as turbidity, has a large membrane durability, and has a high operating pressure. It is suitable for medium and small capacity desalination equipment because of its low temperature and easy operation and operation. In recent years, with respect to this method, new technology such as high temperature operation technology and new structure device has been developed, and remarkable improvement in performance is recognized.

By the way, in the electrodialysis desalination method, electric power is used as motive power, but if the variable electric power can be used for operation without being stored, a remarkable merit will occur.

For example, various fuel cells have been vigorously developed with the aim of diversifying energy sources, improving expression efficiency, and improving energy use efficiency. Since this power generation method is considered to be used on-site, it is important to match the amount of power generation and power consumption. In particular, when used in an area where the electric power system is not developed, it is impossible to connect with other electric power systems, and this problem is important. Therefore, if an electrodialysis desalination method that can effectively use fluctuating surplus power and a device that can implement the method (hereinafter referred to as an electrodialysis desalination device) are realized, the power output of the power generation device is maintained in an optimum range. / A co-water supply system becomes possible.

Further, recently, from the viewpoint of diversification of energy sources, the proportion of nuclear power generation and coal-fired power generation (for base load) in the power source composition has been increasing. On the other hand, fluctuations in power demand have become noticeable due to changes in the industrial structure and lifestyle. Therefore, the gap between the power supply capacity and the power demand is increasing. Therefore, if off-road power is used to produce fresh water, the effect of power load leveling is produced. By the way, the amount of surplus electric power fluctuates greatly depending on the time of day, day, week, month, season, etc., and effective utilization technology is required.

As is clear from the above example, if the variable electric power can be used in the electrodialysis desalination method, its effect is very large.

As a proposal for using variable power in the electrodialysis desalination method, regarding the method of using variable power of the solar cell, a single electrodialysis tank is used to proceed with desalination stepwise according to the battery output. There is the method of Sho 59-178364. This method is difficult to apply to a large-capacity desalination apparatus that uses large-capacity electric power, and is effective in reducing the storage battery capacity, but the extent of the reduction is limited.

[Problems to be solved by the invention]

It is an object of the present invention to provide an electrodialysis desalination method capable of directly using fluctuating power (without storing almost any electric power) and an electrodialysis desalination apparatus for carrying out the method.

[Means for solving problems]

 The above problems can be solved by the following method and device.

The electrodialysis desalination apparatus is composed of a plurality of electrodialysis tanks.

Operate multiple electrodialysis tanks in batches.

In each electrodialysis tank, raw water (eg, seawater) is not desalted all at once to fresh water (eg, drinking water level salt concentration), but raw water is desalted to an intermediate salt level (at least one type) between fresh water and raw water. Fresh water is obtained by a step of salting and storing in a storage tank (high-concentration operation) and a step of desalting intermediate salt-concentration water to fresh water (low-concentration operation).

By selecting a combination of the number of high-concentration operations and the number of low-concentration operations in a plurality of electrodialysis tanks operating at the same time, the power consumption of the entire apparatus is changed.

Therefore, in the electrodialysis desalination method of the present invention, in the electrodialysis desalination apparatus including a plurality of electrodialysis tanks, the plurality of electrodialysis tanks are operated in batches, and the electrodialysis tanks are operated in batches. At this time, one to a plurality of intermediate salt concentration levels are set between the salt concentration level of the raw water and the salt concentration level of the target fresh water, and the raw water is passed through the one or more intermediate salt concentration levels to obtain the target fresh water. Each of the electrodialysis tanks has a separate step of sequentially desalting to the next lower salt concentration level, and the desalting at each salt concentration level is performed simultaneously between the electrodialyzers operating at the same time. The feature is that the power consumption of the entire desalination apparatus is changed to a required value over time by appropriately selecting the ratio of the electrodialysis tank in which the process is performed.

Further, the electrodialysis desalination apparatus of the present invention is, in the electrodialysis desalination apparatus composed of a plurality of electrodialysis tanks, a means for operating each of the plurality of electrodialysis tanks in batch, and a batch operation of each electrodialysis tank. , 1 or more, each of which stores individually desalinated water up to one or more intermediate salt concentration levels set between the raw water salt concentration level and the target fresh water salt concentration level Of the intermediate-concentration water storage tank, means for circulatingly supplying the water of the intermediate-concentration water storage tank to any one of the electrodialysis tanks, and performing a desalting process to a salt concentration level one step lower, and an electric power source operating at the same time. Between the dialysis tanks, it has means for appropriately selecting the ratio of the electrodialysis tanks for performing the desalting step at each salt concentration level, and changes the power consumption of the entire desalination apparatus to a required value over time. It is possible to It is characterized in that the.

[Operation] The electric resistance of the electrodialysis tank changes depending on the concentration of the water to be treated, that is, the salt water flowing through the electrodialysis tank. Fig. 5 shows an effective area of 0.23 m ² per membrane, the number of membrane pairs is 200, and the membrane spacing is 0.8 mm.
Salt solution (to be exact, the logarithmic mean value of the salt concentration at the inlet and outlet of the electrodialysis tank) and electrodialysis obtained by desalting an aqueous salt solution containing salt as the main component in the electrodialysis tank The relationship with the tank electrical resistance is shown. For example, seawater (salt concentration 3.5
%) To desalination to fresh water (salt concentration 0.04%), the electric resistance of the electrodialyzer changes greatly from 0.7Ω to 16Ω. In the batch operation method, that is, the method in which the water to be treated is repeatedly circulated to the electrodialysis tank through the circulation tank for desalination, the salt concentration of the liquid circulating in the electrodialysis tank is high at the beginning of the batch operation, which is large. An electric current flows (consumes a large amount of electric power), and with the passage of time, desalination proceeds, the salt concentration decreases, and the electric current decreases accordingly (electric power consumption decreases). Therefore, in an electrodialysis tank, raw water (eg, seawater) is not desalted all at once to fresh water (eg, salt concentration at the level of drinking water), but raw water is desalted to an intermediate concentration level (at least one) of raw water and fresh water. If (high-concentration operation) is performed, the power consumption of this step becomes large, and if the generated intermediate-concentration water is desalted to fresh water (low-concentration operation), the power consumption of this step becomes small. If high-concentration operation or low-concentration operation is selected according to the amount of electric power that can be used in the operation of a plurality of electrodialysis tanks, it is possible to adjust the electric power consumption in a wide range as a whole. That is, the number of electrodialysis tanks that perform high-concentration operation is increased when high power can be used, and the number of electrodialysis tanks that are low-concentration operation is increased when only small power can be used. In the above method, it is possible to use the variable power and at the same time reduce the number of electrodialysis tanks that are out of operation as much as possible, so that the operating rate of the desalination apparatus can be maintained high.

〔Example〕

An embodiment of the present invention will be described with reference to FIGS. This example is based on the method of the present invention.
This is a combined electricity and water system that combines an air fuel cell and an electrodialysis desalination system. The power system of this system will be described with reference to FIG. The DC power of the acidic electrolyte type methanol-air fuel cell (hereinafter referred to as methanol fuel cell) 1 is
A part of the voltage is converted into an alternating current having a voltage suitable for the application by the inverter 2 and supplied to the load. As mentioned above, this load fluctuates depending on the time of day, day, and season. The load may be an electric device such as an ordinary household, factory, store, office, hospital, hotel, etc., but is not particularly limited. A part of the AC power is adjusted to an appropriate voltage by a transformer 4 or the like, if necessary, and supplied to an AC load 5 (auxiliary device such as pump, control / instrumentation device, etc.) of the electrodialysis desalination apparatus.
The other part of the DC power is supplied to the electrodialysis tank 8. Further, a part of the DC power is supplied to the load via the lead storage battery 7 in order to fill up a gap between the power generation amount and the load power amount, which will be described later, when the power consumption changes suddenly when the pump is started. The configuration and function of the electrodialysis desalination apparatus in this system will be described with reference to FIG. The desalination apparatus comprises a plurality of electrodialysis tanks 8, a raw water tank 9, a demineralized water circulation tank 10 corresponding to each electrodialysis tank, an intermediate concentration water storage tank 11, a fresh water storage tank 12, a pump 13, and the like. The raw water is sent to the raw water tank 9 after being subjected to a pretreatment such as turbidity if necessary. In each electrodialysis tank 8, the salt water is circulated by the pump 13 through the corresponding circulation tank 10 while the direct current power is supplied, and desalination is promoted. In this desalination process, the raw water is desalted to an intermediate salt concentration level between raw water and fresh water, and the intermediate concentration water storage tank
Two kinds are possible: a step of sending to 11 (high-concentration operation) and a step of desalting intermediate-concentration water to fresh water and sending it to the fresh water storage tank 12 (low-concentration operation). In each electrodialysis tank, either of them is selected. When the high-concentration operation is selected for all electrodialysis tanks, the maximum is selected, and when the low-concentration operation is selected for all electrodialysis tanks, the minimum is selected, and the power consumption can be adjusted by combining both steps. The relationship between the operating state of the electrodialysis tank and the power consumption pattern according to the above operating method will be described with reference to FIG. Fig. 3 shows the amount of electric power (variation) supplied to the AC load and the fluctuation of the AC load at each time of the day when constant power is supplied from the methanol fuel cell. The relationship between the amount of electric power consumed by the gasification device and the selected operation process (high concentration operation or low concentration operation) of each electrodialysis tank of the electrodialysis desalination device is shown. For example, from 0 o'clock to 6 o'clock at a time when the power consumption of the AC load is small, four of the five electrodialysis tanks select high-concentration operation and the remaining one selects low-concentration operation to output high power. Consume. The gap between the remaining power supply and power consumption is adjusted by charging / discharging (charging in this case) the lead storage battery.

When the power consumption increases from 7 o'clock to 11 o'clock, 2 units select high-concentration operation and the remaining 3 units select low-concentration operation to reduce the power consumption in the desalination system. From 19:00 to 21:00 when the power consumption peaks, only low-concentration operation is selected, and if the amount of power that can be supplied to the desalination device is still insufficient, the number of operated electrodialysis tanks is reduced. The operating rate of the electrodialysis tank throughout the day reaches 95% or more in this embodiment. That is, most of the power fluctuations can be absorbed by the combination of high-concentration operation and low-concentration operation. Further, since the electrodialysis tank is operated in batches, the power consumption of each electrodialysis tank changes with time as described above. This can be averaged for the entire desalination apparatus by shifting the timing of starting the batch operation in each electrodialysis tank.

Although the case where the methanol fuel cell is used as the power source has been described above, it goes without saying that a system using various power sources such as various fuel cells, engine generators, and commercial power sources is established. When a commercial power source is used, high concentration operation is required from late night to early morning when excess power is generated to store intermediate concentration water, and low concentration operation is increased during the daytime when power consumption is relatively high to obtain fresh water. As a result, fresh water can be obtained while leveling the power consumption.

Although the type of the intermediate concentration water is one in the above embodiment, the effect can be enhanced by increasing the number of types. The configuration and function of the electrodialysis desalination apparatus in the case of generating two types of intermediate concentration water will be described with reference to FIG. The difference between FIG. 4 and FIG. 1 is that two kinds of intermediate concentration water storage tanks, a primary intermediate concentration water storage tank 11a and a secondary intermediate concentration water storage tank 11b, are provided. If necessary, the raw water is subjected to pretreatment such as turbidity and then sent to the raw water tank 9, and in each electrodialysis tank 8, while circulating direct current, salt water is circulated by the pump 13 through the corresponding circulation tank 10 to remove the salt water. The progress of salt is the same as in the case of FIG. In the desalination process, the raw water is desalted to a salt concentration level between the raw water and fresh water and sent to the primary intermediate concentration water storage tank 11a (high concentration operation), and the primary intermediate concentration water is transferred to the primary intermediate concentration water and fresh water. Three types of processes: desalting to a certain intermediate salt concentration level and sending it to the secondary intermediate concentration water storage tank 11b (intermediate concentration operation), and desalting secondary intermediate concentration water to fresh water and sending it to the fresh water storage tank 12 (low concentration operation) There is. The power consumption decreases in the order of high concentration operation, intermediate concentration operation, and low concentration operation. For each electrodialysis tank, select one from the three. With the above method,
Since the degree of freedom in selecting the amount of power consumption in the electrodialysis tank is further increased, the amount of power that can be used in the desalination apparatus and the amount of power that is actually consumed can be matched more accurately.

The present invention is also applicable to effective use of solar cell output. In other words, solar cells have been developed and put into practical use as a clean power generation method using inexhaustible solar energy.
The biggest technical problem in using solar cells is time, day,
It is how to use the electric power that fluctuates according to the amount of solar radiation that fluctuates depending on the season. Usually, a method of storing electricity in a lead storage battery is adopted, but this causes an increase in power generation cost and a reduction in power use efficiency. The method of the present invention can effectively cope with the use of solar cell output.

Fig. 6 shows the power system, power generation, and power consumption pattern of the electrodialysis desalination system using the solar cell output. In FIG. 6, a part of the output of the solar cell 6 is converted into an alternating current by the inverter 2, and the auxiliary device 5 of the electrodialysis device and the like 5
And part of the other is supplied to the electrodialysis tank 8. Further, a part of the solar cell output is supplied to the load via the lead storage battery in order to fill the gap between the power generation amount and the power consumption amount.
Further, FIG. 6 shows the power generation and power consumption patterns when the six electrodialysis tanks are operated by a method of generating a kind of intermediate concentration water, that is, a method of selecting high concentration operation and low concentration operation. It is clear that the solar cell output and the power consumption can be matched fairly well at the time, and the power supplied to the storage can be considerably reduced.

〔The invention's effect〕

As described above, according to the present invention, it is possible to directly use the variable power with little storage and to operate the electrodialysis desalination apparatus while maintaining a high operating rate.
In addition, various fuel cells including methanol fuel cells,
An electric power / water combined supply system will be realized which uses an engine generator, a commercial power source, and the like as electric power sources, and maintains the output of these in an optimum range to produce fresh water with fluctuating surplus electric power.

[Brief description of drawings]

1 and 4 are the system flow of the electrodialysis desalination apparatus, FIG. 2 is the power system diagram, FIG. 3 is the relationship between the operating state of the electrodialysis tank and the power consumption pattern, and FIG. 5 is the electrodialysis tank. The relationship between the salt concentration of the circulating salt water and the electric resistance of the electrodialysis tank, FIG. 6 is a power generation and power consumption pattern when the electrodialysis tank is operated according to the present invention. 1 ... Methanol fuel cell, 2 ... Inverter, 3 ...
... AC load, 4 ... Transformer, 5 ... Electrodialyzer auxiliary equipment, 7 ... Lead storage battery, 8 ... Electrodialysis tank, 9 ... Raw water tank, 10 ... Demineralized water circulation tank, 11 ... Intermediate Concentrated water storage tank, 12 ...
… Fresh water storage tank, 13 …… Pump, 21 …… Methanol fuel cell power generation, 22 …… Conversion loss, 23 …… Electric dialysis tank auxiliary power, 24 …… Electrodialysis tank power consumption, 24H …… High concentration Operating power consumption, 24L …… Low concentration operating power consumption, 25 …… AC load power consumption, 26 …… Storage battery charging power, 27 …… Storage battery discharging power.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yukichi Takahashi 4026 Kuji Town, Hitachi City, Hitachi, Ibaraki Prefecture Hitachi Research Laboratory, Hitachi Ltd. (72) Ryota Doi 4026 Kuji Town, Hitachi City, Ibaraki Prefecture Nitate Works Ltd. Hitachi Research Laboratory (72) Inventor Toshio Ogawa 4026 Kuji-cho, Hitachi City, Ibaraki Prefecture Hitachi Research Laboratory, Hitachi, Ltd. (56) Reference JP-A-60-168504 (JP, A)

Claims (2)

[Claims] 1. An electrodialysis desalination apparatus comprising a plurality of electrodialysis tanks, wherein each of the plurality of electrodialysis tanks is operated in a batch operation, and when the electrodialysis tanks are operated in a batch operation, a salt concentration level of a raw water and an object are obtained. 1 to a plurality of intermediate salt concentration levels are set between the fresh water salt concentration levels, and the raw water passes through the 1 to a plurality of intermediate salt concentration levels to reach a desired fresh water salt concentration level, respectively. There is a separate step for sequentially desalting to one lower salt concentration level, and between the electrodialysis tanks operating at the same time, the ratio of the electrodialysis tank performing the desalting step at each salt concentration level is appropriately adjusted. An electrodialysis desalination method characterized in that the power consumption of the entire desalination apparatus is changed to a required value over time by selection. 2. An electrodialysis desalination apparatus comprising a plurality of electrodialysis tanks, wherein means for operating the plurality of electrodialysis tanks in batches and salt concentration levels of raw water by batch operations in each electrodialysis tank 1 to a plurality of intermediate-concentration water storage tanks for individually storing water desalinated to a salt concentration level of 1 to a plurality of intermediate salt concentration levels set between the target fresh water salt concentration level, and Means for circulating the water in the intermediate concentration water storage tank to any one of the electrodialysis tanks to further carry out a desalting step to a salt concentration level one step lower, and between the electrodialysis tanks operating simultaneously, Having means for appropriately selecting the ratio of the electrodialysis tank that performs the desalting step at the salt concentration level, and enabling the power consumption of the entire desalination apparatus to be changed over time to a required value. Characterized by electricity析淡 hydration apparatus.