JP2003145160A - Treatment method of water in cooling water system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent corrosion in a cooling water system, thereby obtaining an excellent slime preventing effect by controlling the amount of a generated chlorine oxidizer within a proper range, in a treatment method of water in the cooling water system where slime generation in the system is prevented by supplying electrolyzed water containing the chlorine oxidizer generated by the electrolysis of cooling water. SOLUTION: In the treatment method of water in the cooling water system, the cooling water system is made to contain the electrolyzed water in which the chlorine oxidizer has been generated from chloride ions contained in the cooling water by applying a current between electrodes 4A, 4B dipped in the cooling water. The oxidation-reduction potential of the cooling water is measured, and applying current to the electrodes 4A, 4B is controlled based on the measured value.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cooling water-based water treatment method, and more specifically, to electrolytically process cooling water to produce a chlorine-based oxidizer such as hypochlorous acid from chloride ions in the cooling water. The present invention relates to a cooling water system water treatment method for preventing a slime problem of a cooling water system by this chlorine-based oxidizing agent.

[0002]

2. Description of the Related Art In a cooling water system, slimes are easily generated by microorganisms. In particular, in highly concentrated operation of the circulating cooling water system, the water quality of the cooling water is deteriorated, and slime, which is formed by mixing earth and sand and dust with microbial groups such as bacteria, mold, algae, etc., easily occurs, and the heat exchanger Cause deterioration of heat efficiency and deterioration of water flow. It also induces local corrosion of equipment and piping at the slime adhesion part.

In order to prevent such damage caused by slime, a chlorine-based agent or a non-chlorine-based microbial repellent is added to the circulating cooling water as a slime control agent. Also, as a method for preventing slime without adding such chemicals, chloride ions contained in cooling water are converted to chlorine-based oxidizers such as hypochlorous acid by electrolytic oxidation, and this chlorine-based oxidation is performed. The method of making an agent exist in cooling water is also performed.

[0004] That is, the tap water or industrial water used as make-up water for the cooling water system, usually several ^mg-Cl - / ^L~10
Since chloride ions of about mg-Cl ⁻ / L are contained, the chloride water in the makeup water is concentrated in the cooling water of the circulating cooling water system by the highly concentrated operation of 6 to 8 times. . Therefore, by electrolytically treating this cooling water,
Residual chlorine (free chlorine) having a slime preventing effect can be generated from chloride ions in cooling water. By returning the electrolytically treated water containing this residual chlorine to the cooling water system,
Slime disorders can be prevented.

In the electrolytic treatment apparatus for generating the chlorine-based oxidizing agent, a DC voltage is applied between the anode and the cathode by using an external power source, and cooling water is passed between both electrodes.
As a result, chloride ions in the cooling water are oxidized on the surface of the anode, and residual chlorine having a strong oxidizing power such as hypochlorous acid is generated. The generated residual chlorine sterilizes the microorganisms that cause slime or suppresses the growth thereof, so that the generation of slime in the circulating cooling water system can be effectively prevented.

[0006]

In order to surely prevent slime in the cooling water system, it is necessary to raise the residual chlorine concentration in the system to some extent, but in order to prevent corrosion of the metal material in the system. Should avoid excessively high residual chlorine concentration in the system.

For this reason, when residual chlorine is generated by electrolytic treatment and added to the cooling water system, it is necessary to control the amount of residual chlorine produced within an appropriate range.

However, since the generation rate of residual chlorine by an electrolytic treatment apparatus such as an electrolytic hypochlorous acid generator varies greatly depending on the water quality, it is easy to maintain the residual chlorine concentration in the cooling water system within a predetermined range by electrolytic treatment. However, the internal corrosion tends to occur due to excessive generation of residual chlorine, or the slime preventing effect tends to decrease due to insufficient residual chlorine.

The present invention solves the above-mentioned problems of the prior art, and by supplying electrolytically treated water containing a chlorine-based oxidant produced by electrolytically treating cooling water to the cooling water system, the generation of slime in the system is prevented. In a cooling water-based water treatment method to prevent, it is an object to control the amount of chlorine-based oxidizer generated within an appropriate range.

[0010]

The cooling water-based water treatment method of the present invention is an electrolytic treatment in which an electrode immersed in cooling water is energized to generate a chlorine-based oxidizer from chloride ions contained in the water. In a cooling water system water treatment method in which water is contained in cooling water system cooling water, an oxidation-reduction potential of the cooling water is measured, and energization to the electrode is controlled based on the measured value.

Chlorine in water has a redox potential (OR
P) is increased, and there is a correlation between the ORP and the residual chlorine concentration. When the residual chlorine concentration is high, the ORP is high,
If the residual chlorine concentration is low, the ORP will be low.

In the present invention, the energization of the electrolytic treatment apparatus is controlled based on the ORP of the cooling water. For example, when the ORP exceeds a predetermined value, the energization amount is reduced or the energization is stopped so that the ORP is lower than the predetermined value. If it also decreases, it is possible to keep the concentration of the chlorine-based oxidant in the cooling water within a predetermined range by increasing the amount of energization or restarting energization.

By the way, during the electrolytic treatment, chlorine is produced at the anode and hydrogen is produced at the cathode. Chlorine increases ORP, while hydrogen decreases ORP. Since the balance between chlorine and hydrogen generated by electrolytic treatment differs depending on the water quality and operating conditions, a correlation cannot be obtained between ORP and residual chlorine concentration in the presence of hydrogen.

Therefore, in the present invention, it is preferable to measure the ORP of the cooling water containing no hydrogen. For this reason, the dissolved gas such as hydrogen is dissolved by the cooling water from which the dissolved gas such as hydrogen has been removed. O of removed cooling water
It is preferred to measure RP.

In the present invention, it is possible to install an electrolytic treatment device in the cooling water circulation line and directly subject the circulating cooling water to electrolytic treatment. In this case, however, residual chlorine was excessively generated due to some condition change. In this case, the cooling water system is greatly affected, such as corrosion of the heat exchanger.

Accordingly, the cooling water is extracted from the cooling water system,
It is preferable to perform electrolytic treatment outside the system so that electrolytically treated water is returned. Further, in this case, it is preferable that the electrolytically treated water is returned to the pit of the cooling tower and diluted with water in the pit to adjust the concentration.

On the other hand, the ORP measurement is preferably performed on the cooling water from which hydrogen has been released by water sprinkling in the cooling tower, and therefore the O in the water in the pit of the cooling tower below the water spray plate.
It is preferable to measure RP, but if this ORP measurement location is close to the location where the electrolytically treated water is introduced, it will be affected by hydrogen in the electrolytically treated water. Therefore, in this case, it is preferable to measure the ORP of the cooling water below the water spray plate of the cooling tower, which is separated from the location where the electrolytically treated water is introduced into the cooling tower.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of a cooling water system water treatment method of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a system diagram showing an embodiment of a water treatment method for a cooling water system according to the present invention. In FIG. 1, the cooling tower is shown as a plan view from above.

A cooling tower 1 is provided with water spray plates 1A and 1B. The cooling water in the pit of the cooling tower 1 is pump P ₁
Thus, the return water is sent to the heat exchanger 2 through the pipe 11, the return water is returned to the cooling tower 1 through the pipe 12, the pipes 12A and 12B, and is sprayed from the water spray plates 1A and 1B. Reference numeral 3 denotes an electrolytic treatment device, an electrolytic bath 4, electrodes 4A and 4B provided in the electrolytic bath 4, and a power source 5 for applying a voltage to the electrodes 4A and 4B.
With.

In the electrolytic cell 4 of this electrolytic treatment apparatus 3, the cooling water in the pit of the cooling tower 1 is piped by the pump P _2.
And is electrolyzed in the electrolytic bath 4, and the electrolyzed water is returned to one side of the pit of the cooling tower 1 through the pipe 14.

An ORP measuring electrode of an ORP meter 6 is provided below the sprinkler plate 1B in the pit of the cooling tower 1 on the side opposite to the position where the electrolytically treated water is introduced (X in FIG. 1). ,
The ORP of the cooling water is measured at this position. Then, the energization of the electrolytic treatment apparatus 3 is controlled based on the measurement result of the ORP meter 6.

In the cooling water system of FIG. 1, when the ORP measurement value exceeds a predetermined value based on the measurement value of the ORP meter 6, the power source 5 is turned off, and the energization to the electrodes 4A and 4B is stopped to perform the electrolytic treatment. If the ORP measurement value is below the specified value,
The residual chlorine concentration in the cooling water is kept within a predetermined range by turning on the power source 5 and energizing the electrodes 4A and 4B to restart the electrolytic treatment.

It should be noted that the amount of electricity supplied to the power source 5 may be increased or decreased instead of such an ON / OFF operation of the power source.
Is less than a predetermined value, the energization amount of the power source 5 is reduced to reduce the amount of residual chlorine generated in the electrolytic treatment, and when the ORP is less than the predetermined value, the energization amount of the power source 5 is increased to perform the electrolytic treatment. It is also possible to increase the amount of residual chlorine generated in step. In addition, when the ORP measurement value falls below a predetermined value,
The power supply 5 may be turned on for a predetermined time to carry out the electrolysis treatment for a predetermined time, or conversely, when the ORP exceeds a predetermined value, the power supply 5 may be turned off for a predetermined time to interrupt the electrolysis treatment for a predetermined time.

In the energization control based on the ORP predetermined value, the cooling water below the sprinkler plate 1B,
That is, the OR of the cooling water in which hydrogen in the water has been diffused
Since P is measured, it is not affected by hydrogen generated by electrolytic treatment. Moreover, since the installation position of the ORP meter 6 is separated from the position X where the electrolyzed water is introduced, it is not affected by the electrolyzed water containing hydrogen generated by the electrolysis, and is correlated with the residual chlorine. It is possible to accurately measure the ORP value, and based on this measured value, it is possible to carry out good energization control and keep the residual chlorine concentration in the system within a predetermined range.

The electrolytic treatment device 3 may be directly provided in the cooling water circulation pipe 11 or the like to directly subject the circulating cooling water to electrolytic treatment. In this case, however, as described above, there may be some variation in conditions. When the residual chlorine is excessively generated, the heat exchanger 2 and the like are corroded, which has a great influence on the cooling water system.

Therefore, the cooling water is extracted from the cooling water system,
It is preferable to perform electrolytic treatment outside the system so that electrolytically treated water is returned. In this case, as shown in FIG.
By returning the electrolytically treated water to the pit of the cooling tower, the electrolytically treated water can be immediately diluted with the water in the pit to adjust the residual chlorine concentration, which is preferable in terms of stabilizing the residual chlorine concentration in the system.

There are no particular restrictions on the position of withdrawing the cooling water, and it is possible to withdraw it from the circulation pipe 12. In particular, when considering the case of applying the present invention to an existing cooling water system, FIG. As shown in the drawing, it is preferable from the viewpoint of piping work that the cooling water in the pit of the cooling tower 1 is extracted, electrolyzed and then returned.

The relationship between the voltage control and the ORP measurement value is appropriately determined according to the water quality of the cooling water, the capacity of the electrolytic treatment apparatus, the suitable residual chlorine in the system, etc. In general, the ORP measurement value is To be in the range of 100 to 600 mV, that is, OR
When the measured P value is less than 100 mV, the electrolytic treatment is restarted or the electrolytic treatment amount is increased, and the measured ORP value is 600 mV.
If it exceeds, it is preferable to stop the electrolytic treatment or reduce the electrolytic treatment amount.

As described above, it is preferable to measure the ORP at a location that is not affected by hydrogen generated by the electrolytic treatment. Therefore, in FIG. 1, the ORP is separated from the location where the electrolytically treated water is introduced into the cooling tower 1. The measurement electrode of the ORP meter 6 is provided below the water spray plate 1B of the cooling tower 1, and the cooling water is ORed in this portion.
Although P is measured, the following method can also be adopted as a method for measuring ORP while preventing the influence of hydrogen generated by electrolytic treatment.

Gas-liquid separation is performed at the outlet of the electrolytic cell of the electrolytic treatment apparatus. This gas-liquid separation may be carried out by installing an appropriate gas-liquid separator, or by introducing it into a storage tank and stirring the electrolytically treated water. According to this method, the electrolytically treated water from which hydrogen has been removed is returned to the cooling water system, so that good measurement results can be obtained regardless of the location of the cooling water system, not limited to the pit of the cooling tower. Obtainable.

The electrolytically treated water is returned to the water spray plate of the cooling tower to spray water. In this case, since hydrogen in the electrolyzed water is released by water sprinkling, a good measurement result can be obtained not only in the pit of the cooling tower but also in any place of the cooling water system provided with the ORP meter. .

The electrolyzed water is sent to the circulation pump of the cooling tower without being brought into contact with the measurement electrode of the ORP meter and sent to the circulation pipe. In this case, since the return water is sprinkled by the sprinkling plate of the cooling tower to remove hydrogen, a good measurement result can be obtained by the ORP meter provided in the pit of the cooling tower.

Although the chloride ion concentration of the cooling water varies depending on the concentration ratio of the water system, it is generally 3
It is about 0 to 100 mg / L. Therefore, by electrolytically treating the cooling water having such a chloride ion concentration, for example, electrolytically treated water having a hypochlorous acid concentration of about 1 to 10 mg / L can be obtained.

The material of the electrodes 4A and 4B used in the electrolytic treatment apparatus 3 is not particularly limited, but as the anode, for example,
A material having good production efficiency of hypochlorous acid, which is obtained by coating a corrosion-resistant material such as titanium with a simple substance of a platinum-based element such as platinum or iridium and / or an oxide thereof, can be preferably used. As the cathode, for example, stainless steel, aluminum, silver or the like can be used, but the cathode and the anode can be the same type. In addition, the direction of the current does not have to be fixed in particular, and the positive and negative of the current can be periodically or arbitrarily reversed to carry out electrolysis while inverting the cathode and the anode (polarity conversion). By this polarity conversion, since it is possible to operate while peeling off the scale such as calcium carbonate attached to the cathode, it is possible to prevent a decrease in electrolysis efficiency. In this case, if both electrodes are of the same type, a constant hypochlorous acid generation efficiency can be obtained.
In this case, the electrode used may be, for example, a titanium-based material coated with platinum or iridium. The frequency of polarity conversion is 0.5 to 6 hr
Once is preferable.

In the present invention, the DC voltage applied for electrolysis is not particularly limited, but is preferably 2 to 40V, and more preferably 10 to 20V. If the applied voltage is less than 2 V, the generation efficiency of residual chlorine may decrease. If the applied voltage exceeds 40 V, there is a danger that the human body may be in danger. In the method of the present invention, there is no particular limitation on the value of the electric current supplied for electrolysis, but it is 0.
It is preferably from 01 to 0.1 A.

As described above, the cooling water has a sufficiently high chloride ion concentration. Therefore, the cooling water is treated by the electrolytic treatment apparatus 3 without supplementing the chloride ion, and a sufficient amount of residual chlorine is obtained. Although electrolytically treated water having a concentration can be obtained, salt (NaCl) or the like may be added to cooling water to increase the chloride ion concentration to about 100 to 300 mg / L, if necessary.

In the present invention, in order to prevent corrosion in the cooling water system and obtain a good slime prevention effect, the electrolytic treatment water containing residual chlorine obtained in the electrolytic treatment apparatus 3 is contained in the cooling water system. It is preferable to keep the residual chlorine concentration in the cooling water in the cooling water system in the range of about 0.1 to 1.0 mg-Cl ₂ / L, and perform electrolytic treatment so that such a residual chlorine concentration can be maintained. It is preferable to appropriately set the amount of cooling water, the amount of electricity supplied to the electrolytic treatment apparatus, its control conditions, and the like.

[0039]

EXAMPLES The present invention will be described more specifically with reference to Examples and Comparative Examples below.

Example 1 With the apparatus shown in FIG. 1, cooling water (chloride ion concentration: 80 to 110 mg / L) was added to 3000 L / liter from a circulating cooling water system cooling tower (holding water amount: 3000 L) using tap water as makeup water.
Slime in the system was prevented by extracting with hr and performing electrolytic treatment with an electrolytic treatment apparatus and returning the electrolytically treated water to the cooling tower. Moreover, in order to confirm the degree of corrosion, a mild steel test piece (SPCC: 50 mm × 15 mm × 1 mm) and a copper test piece (C1220P: 50 mm × 15 mm)
Corrosion rate (mdd)
Was measured. As shown in FIG. 1, the cooling tower is provided with an ORP meter at a position distant from the place where the electrolytically treated water is introduced.
When the measured value of the meter was lower than 300 mV, the power of the electrolytic treatment apparatus was turned on, and when it was higher than 310 mV, the power of the electrolytic treatment apparatus was turned off. The specifications of the electrolytic treatment apparatus and the ORP meter used are as follows.

Electrolytic treatment device: "Electrolytic sodium hypochlorite generator" manufactured by Kurita Water Industries Ltd. Voltage = 15V Current = 70A Anode = Pt on the surface of Ti material (50 dm ² , thickness 1 mm)
Cathode = Pt on the surface of Ti material (50 dm ² , thickness 1 mm)
The distance between electrode plates = 3 mm ORP meter: MP8801 type manufactured by Okura Electric Co., Ltd.

As a result, during the operation period of 30 days, the residual chlorine concentration in the cooling water can be stably maintained within the range of 0.1 to 0.3 mg-Cl ₂ / L, which causes system corrosion. It was possible to obtain a good anti-slime effect.

After the operation was continued for 30 days in this way, the slime deposition rate was calculated from the amount of slime deposited on the water sprayed part in the system, which was 1 mg / dm ² , which indicates that slime was sufficiently prevented. confirmed. The corrosion rate is 9 mdd for SPCC and 0.5 for C1220P.
It was mdd.

Comparative Example 1 The same treatment as in Example 1 was carried out except that the ORP measuring electrode of the ORP meter was provided at the portion where the electrolytically treated water was introduced into the cooling tower (X in FIG. 1). However, the residual chlorine concentration in the cooling water had a large fluctuation range of 0.1 to 4.0 mg-Cl ₂ / L.

When the slime deposition rate was examined in the same manner as in Example 1, it was 0.7 mg / dm ² , and although the slime preventing effect was sufficient, SPCC and C122 were found.
It was confirmed that the 0P corrosion rates were as high as 50 mdd and 2 mdd, respectively. It is presumed that this is because the ORP was measured at the portion where the electrolyzed water was introduced, so that it was affected by hydrogen in the electrolyzed water, and the ORP measurement value correlated with the residual chlorine concentration could not be obtained. Was done.

[0046]

As described in detail above, according to the cooling water-based water treatment method of the present invention, the cooling water is electrolyzed to generate a chlorine-based oxidizer from chloride ions in the cooling water to generate a chlorine-based oxidizing agent. In preventing the generation of slime in the system by supplying electrolytically treated water containing an oxidant to the cooling water system, the amount of chlorine-based oxidant produced should be adjusted so that the concentration of chlorine-based oxidant in the cooling water is within the specified range. It can be controlled within an appropriate range, whereby a good slime prevention effect can be obtained while preventing corrosion in the system.

[Brief description of drawings]

FIG. 1 is a system diagram showing an embodiment of a water treatment method for a cooling water system according to the present invention.

[Explanation of symbols]

1 cooling tower 1A, 1B watering plate 2 heat exchanger 3 Electrolytic treatment equipment 4 electrolyzer 4A, 4B electrodes 5 power supplies 6 ORP meter

Front page continuation (51) Int.Cl. ⁷ Identification code FI theme code (reference) C02F 1/50 531 C02F 1/50 531P 540 540B 550 550D 560 560F 1/76 1/76 A F28C 1/16 F28C 1 / 16 G01N 27/416 G01N 27/46 341M // F28F 19/01 F28F 19/00 501B F Term (reference) 4D011 AA11 AB01 4D037 AA08 AB18 BA24 CA04 CA16 4D050 AA08 AB06 BB06 BD04 CA03 CA10 CA12 4D0637 EB04 EB04 DB10 DB05 DB10 DB04 ED12 FA03 FA16 GA08 GC12

Claims (4)

[Claims] 1. A water treatment of a cooling water system in which cooling water of a cooling water system contains electrolyzed water in which a chlorine-based oxidizing agent is generated from chloride ions contained in the water by energizing an electrode immersed in the cooling water. In the method, the oxidation-reduction potential of the cooling water is measured, and the energization to the electrode is controlled based on the measured value. 2. The water treatment method for a cooling water system according to claim 1, wherein the oxidation-reduction potential of the cooling water from which the dissolved gas has been removed is measured. 3. The water treatment method for a cooling water system according to claim 2, wherein the oxidation-reduction potential of the cooling water from which dissolved gas has been removed by water sprinkling in the cooling tower is measured. 4. The cooling water system water treatment method according to claim 3, wherein the electrolytically treated water is introduced into one side of the cooling tower, the side being opposite to a location where the electrolytically treated water is introduced into the cooling tower. Measuring the oxidation-reduction potential of the cooling water in the cooling tower of 1.