JPH0791879A - Method for operating cooling tower - Google Patents

Abstract

PURPOSE:To restrict a salt concentration in circulating water from being increased and to reduce a blow down water amount by a method wherein either make-up water or the blow down water for a cooling tower is supplied to a diluting chamber in an electrical dialysis tank so as to be electrically processed and further supplied to the cooling tower after the salt concentration is reduced. CONSTITUTION:A cooling tower is operated such that water is contacted with air of which temperatures is lower than of water, a part of the water is evaporated into air, the water is cooled by discharging evaporating latent heat. This is widely used in various kinds of factories, plants and building air conditioning facilities requiring a large amount of cooling water. The circulating water at this cooling tower is apt to cause a salt concentration of NaCl, CaCo3 and MgCO3 etc., contained in the water to be increased. In view of this fact, either the make-up water or blow down water is supplied to an electrical dialysis tank in which a plurality of positive ion exchanging films and negative ion exchanging films are arranged alternatively between the electrodes, for example, so as to form a diluting chamber and a concentrating chamber and after salt concentration in the water is reduced through an electrical dialysis, thereafter the water is replenished to the cold water tower.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of operating a cold water tower, and more particularly to a method of operating a cold water tower capable of reducing blowdown water quantity and makeup water quantity.

[0002]

2. Description of the Related Art A cold water tower is one in which water is connected to air having a temperature lower than that of the water, a part of the water is evaporated into the air, and the latent heat of vaporization is released to cool the water. Widely used in factories, plants, building air conditioning equipment, etc.

Regardless of the method used in the cold water tower, a large amount of water is circulated and used for cooling. In the cooling process, a certain amount of water is generated due to an evaporation phenomenon depending on the temperature and humidity. Lost as evaporated water. As a result, the salt concentration of Na salt, Ca salt, K salt, etc. contained in the circulating water is increased, and if left unattended, corrosion of equipment such as pumps, pipes and heat exchangers of the cold water tower will occur. Absent. Therefore, it is necessary to always keep the salt concentration in the circulating water below a prescribed value. Therefore, it is necessary to take out a prescribed amount of water as blowdown water from the circulating water and replenish the circulating water with low salt concentration as makeup water. was there.

[0004]

It is obvious that when the amount of blowdown water taken out from the circulating water is small in the above, the amount of makeup water to be supplied to the circulating water can be reduced, but especially in recent years, due to environmental restrictions, blow with a large salt concentration is required. Disposal of down water has been a problem, while it has become increasingly difficult to obtain pure water with low salt concentration. Thus, there is a strong demand for reduction of the blowdown water and makeup water in the cold water tower.

[0005]

The present invention has been made to solve the above problems, and a method of operating a cold water tower according to the present invention is a makeup water corresponding to a total amount of evaporated water and blowdown water. In the method of operating a cold water tower that operates while supplying circulating water to the circulating water, the make-up water or blowdown water is supplied to the dilution chamber of the electrodialysis tank and subjected to energization treatment. It is characterized in that the makeup water or blowdown water that has been lowered is supplied to the circulating water.

The present invention will be described in more detail below. The cold water tower operated according to the present invention may be either a natural or forced draft tower, and the contact between water and air may be a countercurrent type or a crossflow type. Well, it can be applied to any type of cold water tower.
The cooling water obtained in these cold water towers is used in many of the above-mentioned devices, and the water whose temperature has risen due to use is returned to the cold water tower and cooled again before being circulated. In such circulating water, the concentration of salts such as NaCl, CaCO ₃ , MgCO ₃ , and Na ₂ SO ₄ contained therein increases due to the evaporation of water in the cold water tower, but such salt concentration is preferably 2000 ppm or less. Especially, it is necessary to control it to 1000 ppm or less. This is because if the concentration exceeds the above-mentioned level, problems such as equipment corrosion will occur.

In order to control the salt concentration in the circulating water, a part of the circulating water with an increased salt concentration is discharged as blowdown water to the outside of the system, and the decrease in circulating water lost by evaporation and blowdown is replenished. As a result, water with low salt concentration is newly supplied to the circulating water. Thus, when the amount of blowdown water is large, the amount of makeup water increases and the problem of discarding the blowdown water occurs.

In the present invention, the make-up water or blowdown water is electrodialyzed to reduce the amount of make-up water and blowdown water. In electrodialysis, make-up water or blowdown water is supplied to the diluting chamber of the electrodialysis tank to be energized. Among the above, when the make-up water is electrodialyzed according to the present invention, the tank voltage does not increase as the dialysis progresses as in the case of electrodialysis of blowdown water, so that the present invention is carried out more efficiently. be able to.

The electrodialysis tank used in the present invention comprises a cation exchange membrane and an anion exchange membrane, preferably a monovalent anion-selective anion exchange membrane, arranged between the electrodes, and a plurality of such chambers are provided. It is an electrodialysis tank in which concentration chambers are alternately formed. The cation exchange membrane preferably has a sulfonic acid group as a cation exchange group, and preferably has an ion exchange capacity of 0.5 to 10 meq / g dry resin and a thickness of 5
The thing of 0-500 micrometers is used. The cation exchange membrane may be either a homogeneous one or a heterogeneous one, but it is preferable to use a membrane having a styrene-divinylbenzene copolymer as a matrix. The cation exchange membrane may be reinforced with a woven or non-woven fabric such as polyolefin, polyvinyl chloride or polyester, if necessary.

As the anion exchange membrane, an anion exchange membrane having a quaternary ammonium group as an anion exchange group is preferably used, and in the case of a monovalent anion selective membrane, chlorine ion, nitrate ion and the like are used. Those having a property of selectively permeating monovalent anions as compared with polyvalent anions such as sulfate ions are used. In this case, the selectivity of monovalent anion / multivalent ion is preferably 2 times or more, particularly 5
Double or more is appropriate. The ion exchange capacity is preferably
0.5-10 meq / g dry resin, thickness 50-500
The one with μm is used. Anion exchange membrane is a homogeneous system,
Alternatively, either a non-homogeneous system can be used, but it is preferable to use a homogeneous one having a styrene-divinylbenzene copolymer as a matrix.

In the electrodialysis tank, preferably 10 to 600 cation exchange membranes and 10 to 600 cation exchange membranes are alternately arranged between the electrodes to form a dilution chamber and a concentration chamber. As means for assembling the electrodialysis tank, any of the known methods described in JP-A-54-1674, JP-A-55-24538, and JP-B-51-47663 can be used. In the present invention, the tightening type (filter press type) device is preferably used.

In the present invention, the make-up water or blowdown water is preferably contained in the dilution chamber of the electrodialysis tank in an amount of 5 to 50.
It is supplied in cm / sec. In the concentration chamber of the electrodialysis method, when the operation of the electrodialysis tank is started, cations and anions are sequentially transferred from the dilution chamber along with the movement of water, so it is not always necessary to supply the aqueous electrolyte solution. The blowdown water from the cold water tower is preferably 0.5 to 5 cm /
It is supplied in sec. In addition, since various suspensions are often mixed in the blowdown water, they are deposited on the ion exchange membrane of the electrodialysis tank, so that the concentration of the suspension is preferably 1 ppm or less. It is filtered when it is supplied to the electrodialysis tank.

The respective anode chambers and cathode chambers at both ends of the electrodialysis tank, in which the anodes and cathodes are housed, are the same as those supplied to an appropriate aqueous electrolyte solution, for example, the above-mentioned concentration chamber, according to a conventional method. An aqueous electrolyte solution is supplied.

Thus, the electrodialysis tank is energized at a current density not higher than the limiting current density, preferably 0.1-10 A / dm ² , and the salt in the make-up water or blowdown water supplied to the dilution chamber is supplied. The formed cations and anions are desalted by transferring to the concentration chamber through the cation exchange membrane and the anion exchange membrane, respectively. When a monovalent anion-selective membrane is used as the anion exchange membrane, SO
₄ ^2-, etc. as compared to the divalent or higher polyvalent anions Cl ^-,
It is particularly preferable that monovalent anions such as NO ₃ ⁻ which cause corrosion of equipment in a cold water tower or the like are almost selectively transferred to the concentration chamber and removed. In such a case, since the salt concentration allowed in the circulating water can be increased, it is more effective in reducing blowdown water, and by extension, make-up water.

Thus, according to the invention, the salt concentration in the make-up water or blowdown water is preferably 1000-2000 ppm, especially 200-500 p, by electrodialysis.
desalted to pm. Thus, the resulting reduced salt concentration water is added to the water circulating therein as make-up water for the cold water tower. On the other hand, water with an increased salt concentration is obtained from the concentrating chamber of the electrodialysis tank, and this is discarded as blowdown water outside the system.

[0016]

In the present invention, by electrodialyzing make-up water or blow-down water, the salt concentration in these water is reduced, and as a result, the amounts of make-up water and blow-down water are reduced. The mechanism is as follows.

When electrolyzing make-up water, the salt concentration in the water supplied to the circulating water can be reduced, so that even if a predetermined amount of water evaporates, the increase in the salt concentration in the circulating water can be controlled to be small. As a result, the amount of blowdown water can be reduced.

On the other hand, when the blowdown water is electrodialyzed, the blowdown water can be regenerated as water having a low salt concentration, and by reusing this as makeup water, the amount of makeup water can be reduced and discharged to the outside of the system. The amount of blowdown water to be used can be reduced.

[0019]

【Example】

Example 1 Circulating water amount is 5000 m ³ / day, evaporated water amount is 800 m ³ / day
Blowdown water (TDS 1000ppm, Na ⁺
150ppm, Ca ⁺⁺ 70ppm, Cl ^- 250pp
m) is 200 m ³ / day, make-up water (TDS 200 pp
m, Na ⁺ 30 ppm, Ca ⁺⁺ 14 ppm, Cl ^- 50
(ppm) 1000 m ³ / day The cold water tower was operated.

The blowdown water in the cold water tower was electrodialyzed. The following were used as the electrodialysis tank. Strongly acidic cation exchange membrane, "Selemion CMV" (manufactured by Asahi Glass Co., Ltd., styrene-divinylbenzene copolymer membrane having sulfonic acid groups, ion exchange capacity 3.4 meq / g dry resin, thickness 150 μm) and strong base Anion exchange membrane "Selemion AMV" (manufactured by Asahi Glass Co., Ltd., styrene-divinylbenzene copolymer membrane having a quaternary ammonium group, ion exchange capacity 3.4 meq / g dry resin, thickness 140 μm)
Filter press type electrodialysis tank Selemion DB-4 type (Asahi Glass Co., Ltd., effective membrane area 0.8 m ² ) assembled by alternately arranging 30 sheets and 30 sheets each between the cathode and the anode via polypropylene spacers did.

The blowdown water is supplied to the diluting chamber of the electrodialysis tank through a diluting solution tank by a circulating pump, and the concentrating chamber, the cathode chamber and the anode chamber are also supplied through the concentrating liquid tank and the polar liquid tank by a circulating pump. Circulates the same blowdown water as the
V was applied, electricity was supplied at a current of 80 A, and the operation was continued.

After the operation became stable after a while, the diluted solution and concentrated solution flowing out from the diluted solution tank and concentrated solution tank were as follows. That is, the diluent is TDS
200ppm, Na ⁺ 30ppm, Ca ⁺⁺ 14ppm,
Cl ^- 50 ppm, the concentrate is TDS 1800
ppm, Na ⁺ 270 ppm, Ca ⁺⁺ 126 ppm, C
l ^- has a 450ppm, none of the liquid volume 100m ³ /
It was a day. Thus, the diluted solution in the electrodialysis tank was added to the makeup water and supplied to the circulating water in the cold water tower. As a result,
Blowdown water, will only concentrate the electrodialysis cell, blowdown water becomes 100 m ³ / day, makeup water 100 m ³ / day can reduce became 900 meters ³ / day.

Example 2 In Example 1, 9% make-up water was used instead of blowdown water.
It was supplied to the dilution chamber of the electrodialysis tank at 00 m ³ / day and subjected to electrodialysis treatment in the same manner. Thus, when steady state operation was reached, analysis showed that the dilution chamber of the electrodialysis tank showed T
DS 588ppm, Na ⁺ 9ppm, Ca ⁺⁺ 4.2p
Diluted solution of pm, Cl ^- 14.7ppm was obtained at 850m ³ / day, TDS 2600ppm,
Na ⁺ 390ppm, Ca ⁺⁺ 182ppm, Cl ^- 65
A 0 ppm concentrate was obtained at 50 m ³ / day.

When the entire amount of the above-mentioned diluted solution was supplied to the cold water tower as make-up water for the cold water tower to operate, the blowdown water from the cold water tower had TDS of 1000 ppm, Na ⁺ 150 pp.
m, Ca ⁺⁺ 70 ppm, Cl ⁻ 250 ppm, the amount was 50 m ³ / day.

Example 3 In Example 2, a monovalent anion-selective anion exchange membrane "Selemion ASV" (manufactured by Asahi Glass Co., Ltd., having a quaternary ammonium group) was used as the anion exchange membrane instead of the usual anion exchange membrane. Styrene vinyl benzene copolymer, ion exchange capacity 3.4 meq / g dry resin, thickness 140 μm)
The electrodialysis treatment was carried out in the same manner as in Example 2 except that the water supplied to the dilution chamber was changed to 800 m ³ / day.

As a result, from the dilution chamber of the electrodialysis tank, T
DS 43ppm, Na ⁺ 11ppm, Ca ⁺⁺ 7pp
830 m ³ / day of a dilute solution of m, Cl ⁻ 3.6 ppm was obtained, and TDS 4543 ppm, Na ⁺ 5 was obtained from the concentration chamber.
48ppm, Ca ⁺⁺ 203ppm, Cl ^- 1333pp
m concentrated solution was obtained at 30 m ³ / day.

When the entire amount of the above-mentioned diluted solution was supplied to the cold water tower as make-up water for the cold water tower to operate, the blowdown water from the cold water tower was TDS 1200 ppm, Na ⁺ 304 pp.
^m, Ca ⁺⁺ 193ppm, Cl - has a composition of 100 ppm, the amount was only 30 m ³ / day.

Example 4 In Example 3, blowdown water (TDS 800, which was discharged from the cold water tower from the beginning of electricity supply to the concentration chamber of the electrodialysis tank, was used.
ppm, Na ⁺ 120 ppm, Ca ⁺⁺ 56 ppm, Cl
^- 200ppm) addition was supplied at 35m ³ / day,
Electrodialysis treatment was carried out in the same manner as in Example 3.

As a result, in the steady state, TDS was 33.5 ppm, Na ⁺ 5 p from the dilution chamber of the electrodialysis tank.
pm, Ca ⁺⁺ 2.4ppm, Cl ^- 8.4ppm diluted solution was obtained at 835m ³ / day, and TDS 3 was obtained from the concentration chamber.
^{400ppm, Na + 510ppm, Ca ++} 238pp
m, Cl ^- 850 ppm dilution was obtained at 50 m ³ / day. When the entire amount of the diluted solution was supplied as the make-up water for the cold water tower and operated, the make-up water supplied to the diluted room of the electrodialysis tank was balanced at 850 m ³ / day.

[0030]

EFFECTS OF THE INVENTION Reduction of blowdown water from a cold water tower, and hence reduction of makeup water, can be carried out extremely efficiently, which is extremely useful in terms of saving water resources and environmental measures.

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Claims (4)

[Claims] 1. In a method of operating a cold water tower, in which make-up water corresponding to the amount of evaporated water and blow-down water is supplied to circulating water for cooling, the make-up water or blow-down water is supplied to a dilution chamber of an electrodialysis tank. A method for operating a cold water tower, which comprises supplying and conducting electricity, and supplying make-up water or blowdown water having a reduced salt concentration obtained from the dilution chamber to the circulating water. 2. A monovalent anion selective permeable membrane is used as an anion exchange membrane in an electrodialysis tank to selectively remove chlorine ions from makeup water or blowdown water.
How to operate the cold water tower. 3. The method for operating a cold water tower according to claim 1, wherein a part of the blowdown water is supplied to the concentration chamber of the electrodialysis tank. 4. The method for operating a cold water tower according to claim 3, wherein a part of the blowdown water is filtered and then supplied.