JPS60168504A - Brine desalting operation in solar energy power generation electrodialytic apparatus - Google Patents

Abstract

PURPOSE:To utilize the varied output of a solar cell in the operation of an electrodialytic apparatus with high efficiency, by providing a fresh water tank and an intermediate concn. tank and desalting brine in the intermediate concn. tank, when the output of the solar cell is high, so as to reach an intermediate concn. while supplying brine to the intermediate concn. tank corresponding to quantity of solar radiation to regulate a salt concn. CONSTITUTION:Water with an intermediate concn., which was desalted to the intermediate concn. in the previous day, is transferred to a fresh water tank 6 in an amount corresponding to that of fresh water formed per a day and, when the output of a solar cell is low over a predetermined time from sunrise, the water in said fresh water tank 6 is transferred to an electrodialytic apparatus 2 and desalted to obtain fresh water. Next, water with an intermediate concn. in an intermediate concn. tank 5 is recirculated to the electrodialytic apparatus 2 and desalted. Because the output of the cell shows increase inclination until the southing time of the sun, a valve 11 is opened and raw water is supplied to the intermediate concn. tank 5 and conditioned so as to enhance a salt concn. Because the salt concn. is lowered with the lowering in the output of the cell from the southing time to sunset and the max. output condition of the cell is formed automatically, water with an intermediate concn. desalted in the fresh water tank 6 in the next day is obtained.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a method of operating salt water desalination using a photovoltaic electrodialysis device, and particularly to a method for controlling the output of a solar cell with high efficiency even when the amount of solar radiation changes. The present invention relates to a method of operating salt water or seawater desalination using a solar power generation electrodialysis device suitable for use in salt water desalination.

[Background of the invention]

Electrodialysis is a method in which a potential difference is applied to an electrolyte solution, such as seawater, and an ion exchange membrane that is selective to ions of opposite sign is used to concentrate and dilute the electrolyte. This method is
■Simple pretreatment of seawater (saltwater), ■High strength of the ion exchange membrane, and ■Low operating pressure. Are suitable.

In recent years, the performance of electrodialysis equipment for desalinating salt water (seawater) has significantly improved due to the establishment of high-temperature operation technology and the emergence of new technologies such as the development of new structures.

On the other hand, solar cells are seen as a promising new energy source and are being actively researched, with remarkable improvements in performance and reductions in manufacturing costs.

By the way, regions that are generally blessed with solar energy, such as the Middle East, are often not blessed with water resources, and the current situation is that they are struggling to take measures to secure water resources. Therefore, seawater desalination using solar energy is attracting attention in these regions. In particular, electrodialysis equipment that uses solar cells as a power source to desalinate seawater is considered to be a promising technology, reflecting recent technological innovations.

In a seawater desalination system that combines a solar cell and an electrodialysis device like this, there are two main features: ■ Direct current power is used as the separated energy for electrodialysis, so the output of the solar cells can be used directly; ■ The solar heat can be used. This has the advantage that power consumption can be reduced by operating the electrodialyzer at high temperatures. Therefore, there is an advantage that a process that utilizes solar heat and sunlight simultaneously can be established.

By the way, the output of a solar cell varies greatly as the amount of solar radiation changes from day to day. Efficiently utilizing fluctuating power in this way is a challenge not only for electrodialyzers but also for various types of devices that serve as a load for solar cells. Fortunately, desalination plants can store fresh water, so they can be operated only during the day. In particular, the electrodialysis method is easy to start and stop, and the ion exchange membrane is resistant to microorganisms in seawater, so there is no need to take special precautions even when the system is stopped at night. Therefore, the problem with current seawater desalination methods using photovoltaic electrodialysis equipment is how to efficiently utilize the output of solar cells, which fluctuates widely in response to daily changes in solar radiation.

Conventionally, as a method to solve this technical problem, a method has been proposed that uses lead-acid batteries to smooth out power fluctuations (
1981 Sunshine Project Commissioned Research Results Report ``Research on Solar Energy Systems'').

However, this conventional method requires a large amount of expensive lead-acid batteries, is not easy to maintain and manage, and has the problem of a large drop in power efficiency as the batteries are charged and discharged. Ta.

[Purpose of the invention]

An object of the present invention is to provide a method for operating salt water desalination using a solar power generation electrodialysis device, in which the output of solar cells, which fluctuates greatly during the day depending on the amount of solar radiation, can be used with high efficiency to operate the electrodialysis device. is to provide.

[Summary of the invention]

A feature of the present invention is that the salt concentration of the water to be desalinated is adjusted in accordance with the amount of solar radiation in consideration of the characteristics of the solar cell depending on the amount of solar radiation, and the electrodialysis apparatus is operated at the maximum output of the solar cell. The purpose is to operate and desalinate seawater.

That is, the present invention provides a method of operating an electrodialysis apparatus for desalinating salt water using a solar cell as a power source, in which two circulation tanks, a fresh water tank and an intermediate concentration tank, are provided for the electrodialysis apparatus, and the solar cell When the output is high, the intermediate concentration tank is used to desalinate the salt water to an intermediate concentration, and the intermediate concentration tank is used to adjust the electrical resistance of the electrodialysis device, which is the load, so that the maximum battery output can be obtained according to the fluctuating amount of solar radiation. Batch operation characterized in that the salt concentration is adjusted by supplying salt water to a concentration tank, and the intermediate concentration water that has been desalinated to a salt concentration in the intermediate concentration tank is desalted to a fresh water concentration using the fresh water tank. This is the method of operation.

Figure 1 is a power generation characteristic diagram showing the relationship between the output voltage and output current of the solar cell with respect to the amount of solar radiation, and Figure 2 is the equivalent circuit when an electrodialysis tank (electrical resistance R) is used as the load of the solar cell. In the figure, 1 is a solar cell, and solar cell 1
An electrodialysis tank 2 whose resistance R varies over a wide range is connected to the dialysis tank 2.

The voltage (E+) and current (I+) characteristics at various amounts of solar radiation are shown by solid lines in FIG. The broken lines in the figure are the conditions under which the maximum power can be obtained, and the intersections of the solid lines and the broken lines are the maximum output conditions (voltage and current values, ie, optimal load resistance values) for each amount of solar radiation.

As shown in FIG. 1, (E+) under the maximum output condition with respect to the solar cover is approximately constant for each amount of solar radiation, and the output current value (I+) varies greatly as the amount of solar radiation changes.

As mentioned above, in order to use solar cells efficiently,
It is necessary to maintain voltage-current conditions for maximum efficiency by changing the load resistance, that is, the electrical resistance R of the electrodialysis tank, depending on the amount of solar radiation.

FIGS. 3(A), 3(B), 3(C), and 3(D) are diagrams schematically illustrating conditions for obtaining maximum efficiency.

(A) shows an example of changes in the amount of solar radiation (W) over time. At times near sunrise and sunset when the amount of solar radiation (W) is low, the load resistance (electrical resistance R of the electrodialysis tank) is increased as shown in Figure (B).

On the other hand, at a time near noon when the amount of solar radiation W increases, the maximum output characteristic can be maintained only by reducing the load resistance R.

Figure 6 (C) and (D) show the voltage at the maximum output characteristic (
E+) and current (E+1) are shown. Suwachi,
To obtain maximum output efficiency, at each time R+=Et/
Electrical resistance of an electrodialysis tank that satisfies I+! It is necessary to realize this. The electrical resistance casing R1 of this electrodialysis tank determines the salt concentration (C) of the water to be desalinated which is circulated through the electrodialysis tank and desalinated.
depends on.

FIG. 4 is a line showing the relationship between the salt concentration (C) of the water to be treated, that is, the salt concentration (0%) of the liquid flowing in the electrodialysis tank, and the electrical resistance (11(,)) of the electrodialysis tank.

Here, the salt concentration (0%) of the water to be desalinated is precisely the logarithmic average value of the salt concentrations at the inlet and outlet of the electrodialysis tank.

This relationship diagram shows that the structure of the electrodialysis tank is one of the ion exchange membranes.
The effective area of the sheet is 0.237. The logarithm of the ion exchange membranes is 200 pairs, and the interval between the ion exchange membranes is 0.8.
This is an example of a case where an aqueous salt solution containing common salt as a main component is desalted at room temperature. The relationship between this salt concentration and the electrical resistance (几) of the electrodialysis device is uniquely determined by the structure of the electrodialysis tank. For example, in the process of desalinating seawater with a salt concentration of about 3.5% to fresh water with a salt concentration of 0.05%, the electrical resistance (R) of the electrodialysis tank changes greatly hyperbolically from 0.7Ω to 14Ω.

Therefore, as a method to operate the electrodialysis device at maximum efficiency, the salt concentration of the water to be desalinated that flows through the electrodialysis tank is changed to achieve the maximum output load resistance R shown in Figure 3 (B). Adjust the electrical resistance of the electrodialyzer to obtain the maximum efficiency characteristics of the solar cell. There are ways to do this. In this method, when the output of the solar cell is low, the demineralized water with a low salt concentration (i.e., the area of high electrical resistance of the electrodialysis tank) is passed through the electrodialysis tank, while when the output of the solar cell is high, the water to be desalinated is passed through the electrodialysis tank. Desalinated water (i.e. the area where the electrical resistance R of the electrodialyzer is low)
The purpose is to match the operating conditions of the stain air dialysis tank with the time fluctuations of the maximum output of the solar cells by flowing the electrolytic dialysis tank into the electrodialysis tank.

By the way, as a typical operating method for conventional electrodialysis equipment, there is a known method in which batchwise, ie, desalinated water is circulated through an electrodialysis tank many times through a circulation tank to obtain fresh water with a predetermined salt concentration. ing. In this operating method, the salt concentration of the water to be desalinated flowing through the electrodialysis tank changes over time, but the pattern of the change in salt concentration over time is completely unrelated to fluctuations in the output of the solar cells. Therefore, in this batch operation method, the electrodialysis tank is simply connected directly as a load to the solar cell, and the output of the solar cell that depends on the amount of solar radiation cannot be efficiently utilized.

In contrast, the present invention provides two circulation tanks, a fresh water tank and an intermediate concentration tank, in parallel to the electrodialysis tank, and uses the two circulation tanks separately when the solar cell is at low altitude and when the output is high. By adjusting the salt concentration and performing batch operation, the operating conditions of the electrodialysis tank and the time fluctuations of the solar cell output are matched to obtain maximum efficiency. Let me explain more specifically.

The intermediate concentration tank is used to desalinate salt water to an intermediate concentration in advance during the high output of the solar cells on the previous day, and the intermediate concentration tank is also used to desalinate salt water at the maximum efficiency of the electrodialysis device in response to fluctuations in the output of the solar cells. The salt concentration is adjusted by supplying salt water to the

Next, the intermediate concentration water desalinated using the intermediate concentration tank is transferred to a freshwater tank, and when the solar cell output is low (for example, after sunrise the next day), the freshwater tank is used to raise the freshwater concentration to the intermediate concentration water. Fresh water can be obtained by desalination.

FIG. 5 is an explanatory diagram showing an example of a flowchart of an electrodialysis apparatus used for carrying out the present invention.

Reference numeral 2 denotes an electrodialysis tank that serves as a load for the solar cell, and a flow path 3 that circulates the water to be desalinated into the desalination chamber of the electrodialysis tank 2.
, 4, and an intermediate concentration tank 5 and a freshwater tank 6 are connected in parallel to the tank 4. Further, pulps 7 to 10 are provided in the upper and lower pipes of the intermediate concentration tank 5 and the fresh water tank 6, respectively. Further, a supply pipe 12 for supplying raw water through the pulp 11 is provided above the intermediate concentration tank 5 . On the other hand, a pump 13 is provided in the middle of the common flow path 3 of the intermediate concentration tank 5 and the fresh water tank 6, and the water to be desalinated in the intermediate concentration tank 5 or the fresh water tank 6 is subjected to electrodialysis by opening and closing the pulps 7 to 10. It is configured so that it can be circulated to tank 2.

Further, the flow path 4 on the outlet side of the electrodialysis tank 2 is connected to an intermediate concentration tank 5 and a fresh water tank 6, and its extended end is connected to a fresh water tank 15 via a pulp 14. In addition, in the electrodialysis tank 2, the parts related to concentrated water and polar liquid are omitted.

Next, a salt water desalination method according to the present invention will be explained using the apparatus configured as described above.

FIGS. 6(A), 6(B), and 6(C) are diagrams illustrating an example of the operating method of the present invention along the passage of time from sunrise to sunset. In addition, in the figure, a is the sunrise time, b is the time when switching from the freshwater tank to the intermediate concentration tank, and C is the midday hour (12 o'clock).
and d is the sunset time.

In the figure, first of all, when the battery output is low and time has not passed since sunrise (point a in Figure 6), the intermediate concentration that has been desalted from raw water to an intermediate concentration in the intermediate concentration tank the previous day, as shown in Figure 5, is An amount of the concentrated water corresponding to the amount of fresh water produced per day is transferred to the fresh water tank 6, pulp 7.8 is closed, and pulp 9. 1O is opened and the pump 13 is operated to transfer the intermediate concentration water to the electrodialysis tank and desalinate it to obtain fresh water with a predetermined concentration.

When the output of the solar cells is low until a predetermined time (a-b) has elapsed from sunrise, intermediate concentration water with a low salt concentration (that is, the electrical resistance of the electrodialysis tank is high) is processed, so the third
As shown in the figure, high power usage efficiency can be obtained.

The fresh water obtained by the treatment is discharged into the fresh water tank 5 by closing the pulp 10 and opening the pulp 14 and operating the pump 13.

Next, the pulp 9.14 is closed, the pulp 7.8 is opened, and the intermediate concentration water in the intermediate concentration tank 5 is circulated to the stain dialysis tank by the pump 13 for desalination.

This period of operation is suitable for treating water with high battery output and high salt concentration.

Further, since the battery output tends to increase until the sun reaches its midpoint, the pulp 11 is opened and raw water is supplied to the intermediate concentration tank 5 to adjust the salt concentration to be high.

That is, between b and c, raw water is supplied in an amount exceeding the maximum capacity for desalination in the electrodialysis tank 2, and the salt concentration is increased over time. It is preferable that this change in salt concentration over time corresponds to an increase in the output of the battery.

Accordingly, the amount of raw water supplied can be optimally adjusted by changing the opening degree of the pulp 11 in conjunction with the battery output.

After midday (between C and D in FIG. 6), the salt concentration decreases as the battery output decreases, and the maximum battery output condition is automatically established. If the operation is continued until sunset in this manner, intermediate concentration water can be obtained for desalination treatment in the fresh water tank 6 the next day.

In addition, in this operation as well, raw water can be supplied as needed and optimal conditions can be strictly controlled.

A certain amount of intermediate concentration water obtained by the above operation is sent to the freshwater tank 6 by the pump 13 after opening the pulp 10 and closing the pulp 8, and is subjected to desalination treatment on the next day.

Hereinafter, the present invention will be explained in more detail using examples.

[Example 1] The method of the present invention was carried out using a DC power supply that simulated the output characteristics of a solar cell, and a 3.5% saline solution was heated to a salt concentration of s.
, oppm. As an electrodialysis tank, the ion exchange membrane has the same electrical resistance characteristics as the electrodialysis tank shown in Figure 4.The current carrying area per rod is 0.23 yr? An ion exchange membrane with a logarithm of 200 pairs was used. At the start of operation, 4.2 m'' of 0.35% saline solution was introduced into the fresh water tank, and 1.4 m'' of the same concentration saline solution was supplied to the intermediate concentration tank.

The maximum output of the DC power supply is 10kW, and the period is 16
The electrodialysis machine was operated for the first 8 hours with a sine wave of time.

FIG. 7 (A), (B), and (C) are diagrams showing electrodialysis characteristics with respect to cycle time, and (A) shows time, the amount of power generated by the solar cell (kW), and the power consumed for electrodialysis. (B) is a diagram showing the change in salt concentration of the salt water to be treated in the freshwater tank and the water concentration tank, and (C) is a diagram showing the power utilization efficiency of the electrodialysis tank.

As is clear from the figure, 1 hour and 55 minutes after the start of operation, the salt concentration of the water in the fresh water tank is 5001)I)m, and in the subsequent operation of the intermediate concentration tank, up to 4 hours (from the start of operation), the salt concentration is 3. 5
A saline solution was added in accordance with the DC power output. After 8 hours (from the start of operation), the salt concentration of the water in the intermediate concentration tank had decreased to 0.35%, the same as at the start of operation. The power usage efficiency during operation remained high, with an average of 91q, except for a drop immediately before the end of freshwater tank operation, as shown in Figure (C).
6 was obtained.

[Example 2] Using the same DC power output as in Example 1, the electrodialysis apparatus was operated in a conventional batch manner to desalinate a saline solution. In this batch operation, a desalination water tank and a concentration water tank are set up, and the salt solution is circulated from each tank to the desalination chamber and concentration chamber of the electrodialysis tank, respectively, until the salt concentration of the water in the desalination tank reaches 4 degrees of fresh water. When the water level decreases, we adopted a common method of extracting the fresh water and circulating new water to be treated. A 3.5% saline solution was introduced into the desalination water tank as raw water, and the freshwater concentration was 500.
Batch operation (6 times) was performed until ppln.

The results are shown in FIG. 7(j)(B).

During each batch operation, as shown in Figure 8 (13), the power usage efficiency always shows about 100% once, but because the time when the power usage efficiency is low is overwhelmingly long, the average over 8 hours of operation The power usage efficiency was 66 cm. It was found that the conventional batch method had significantly lower power utilization efficiency than the method of the present invention (Example 1).

〔Effect of the invention〕

As is clear from the above explanation, according to the method for desalinating salt water using solar power dialysis according to the present invention, it is possible to directly operate the electrodialysis apparatus with high efficiency using the output of the solar cells, which fluctuates greatly during the day. It has the remarkable effect of being able to.

[Brief explanation of the drawing]

Figure 1 is a voltage-current characteristic diagram showing the power generation characteristics of solar cells, and Figure 2 is the equivalent cycle i-3 of an electrodialysis device using solar cells.
The figure is a schematic diagram showing the usage conditions at maximum output of the solar cell, Figure 4 is a diagram showing the relationship between the salt concentration of the water to be treated circulating through the electrodialysis equipment and the electrical resistance of the electrodialysis tank, and Figure 5 is a flowchart of the electrodialysis apparatus according to the method of the present invention, and FIG. 6 (A
) (B) (C) are diagrams showing the operation details according to the present invention,
7(A), (B), and (C:) are diagrams showing the results of operation according to the embodiment of the present invention, and FIG. 8 is a diagram showing the results of operation according to the conventional batch method. DESCRIPTION OF SYMBOLS 1...Solar cell, 2...Electrodialysis tank, 5...Intermediate concentration tank 6...Freshwater tank, 7-10...Pulp, 13.
··pump. Agent Patent attorney Tatsuyuki Unuma 1 drawing, 2 drawings, 2 drawings, 3 sections (c) (D) Time and day drawing, electricity transmission town, Joshihiro street, spring salt concentration C (Karitoki i11, continuation of page 1 ■ Invention chopsticks Seiji Koike 3-1-1 Saiwai-cho, Hitachi City Hitachi, Ltd. Hitachi Research Institute Internal Procedures Amendment ζ Rikijin Δ11, 1980 Commissioner of the Japan Patent Office 2 Invention (D name ftfF Solar power generation electrodialysis device. Salt water Desalination Operation Method 3, Relationship with the Ministry Case for Amendment Name of Patent Applicant (51G) Hitachi, Ltd. 8. Contents of the amendment (1) Figure 7 will be corrected as shown in red attached sheet.

Claims (1)

[Claims] 16. In a method of operating an electrodialysis apparatus for desalinating salt water using a solar cell as a power source, the electrodialysis apparatus is provided with two circulation tanks, a freshwater tank 5ζ intermediate concentration tank,
When the output of the solar cell is high, the intermediate concentration tank is used to desalinate the raw water to an intermediate concentration, and the raw water is supplied to the intermediate concentration tank to adjust the salt concentration so that the battery output can be used with high efficiency. 1. A method for operating salt water desalination using a solar power generation electrodialysis device, characterized in that intermediate concentration water desalinated to an intermediate concentration is desalted to a fresh water concentration using the fresh water tank. 2. In claim 1, when the output of the solar cells is low at the start of each day's solar radiation, intermediate concentration water that has been desalinated to an intermediate concentration on the previous day is desalinated to a fresh water concentration using a freshwater tank, and then A method of operating salt water desalination using a solar-powered electrodialysis device, which is characterized by desalinating raw water to an intermediate concentration using a concentration tank.