JP2001314862A - Slime preventing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a slime preventing method, capable of preventing the growth of microorganisms by generating an oxidizing agent by the electrolysis of chloride ions without the addition of an agent, and of easily and safely preventing the deposition of slime. SOLUTION: In this slime prevention method, voltage is applied to an electrode immersed in cooling water to generate and supply an oxidizing agent. At the preceding stage of applying the voltage to the electrode, water is made to pass through a hardness removing means.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a slime prevention method. More specifically, the present invention can prevent the growth of microorganisms by generating an oxidizing agent by electrolysis of chloride ions without adding a drug, and can stably and safely prevent slime adhesion. It relates to a slime prevention method.

[0002]

2. Description of the Related Art Cooling water is used in various industrial fields such as the petrochemical industry and the steel industry for the purpose of indirectly or directly cooling an object to be treated, or for air conditioning, cooling and heating of a building, and the like.
It is widely used in related devices. In recent years, from the viewpoint of water resources shortage and effective use, advanced use of cooling water has been performed, such as reduction of the amount of forced blow in the high concentration operation of open circulation cooling water systems, in order to reduce the amount of cooling water used. I have. When cooling water is used in this way, the quality of the circulating cooling water deteriorates due to the concentration of dissolved salts and nutrients, and soil, dust, etc. are mixed with microorganisms such as bacteria, molds and algae. Slime that is formed together is likely to be generated, causing a decrease in thermal efficiency and deterioration of water flow in the heat exchanger, and also causes local corrosion of equipment and piping below the slime attachment. Therefore, various antibacterial agents, for example, oxidizing antibacterial agents such as sodium hypochlorite and aqueous hydrogen peroxide have been used to prevent such slime-induced slime. These antibacterial agents are stored in a chemical tank and are injected at a constant rate into a cooling water system by a chemical injection pump. However, if an antibacterial agent is used to prevent slime, labor will be required for transportation, such as transporting lorries, moving containers, and moving cubies to higher altitudes. There is a problem that there is a danger that it takes time to check the remaining amount of the medicine and refill it periodically. For this reason, utilization of residual chlorine generated by electrolysis of chloride ions in water has been attempted. For example, JP-A-61-283391 discloses that
As a drinking water sterilization method of a beverage supply device that can perform sterilization without adding a piping configuration or providing a sterilization device, by disposing a pair of electrodes in contact with tap water in a water circuit, by applying a DC voltage 2. Description of the Related Art A drinking water sterilization method for converting chlorine ions contained in tap water into residual chlorine by performing electrolysis has been proposed. However, when a DC voltage is applied to the electrode to continue electrolysis for a long period of time, the electrolysis efficiency gradually decreases, and it becomes difficult to generate an oxidizing agent sufficient to prevent slime even when the applied voltage increases. Therefore, a method has been proposed in which a solution in which the chloride ion concentration is increased by adding a chemical such as sodium chloride is repeatedly electrolyzed to increase the residual chlorine concentration and sterilize the cooling water system. However, this method not only complicates the equipment, such as the necessity of a storage tank for salt water, but also requires labor for transporting and replenishing salt, as compared with conventional methods using antimicrobial agents. And there are few advantages. For this reason, there has been a demand for a slime prevention method that can more easily and safely generate an oxidizing agent stably by electrolysis and effectively prevent slime of cooling water.

[0003]

DISCLOSURE OF THE INVENTION The present invention provides an oxidizing agent generated by electrolysis of chloride ions to prevent the growth of microorganisms without adding a drug, and to easily, safely and stably adhere slime. The purpose of the present invention is to provide a slime prevention method capable of preventing slime.

[0004]

The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems. As a result, when the electrolysis is continued for a long period of time, the decrease in the electrolytic efficiency is caused by the hardness component in the electrode. It has been found that by removing the hardness before the electrolysis, the oxidizing agent can be generated stably for a long period of time and the slime can be effectively prevented. Was completed. That is, the present invention provides (1) a slime prevention method in which a voltage is applied to an electrode immersed in cooling water to generate an oxidizing agent from chloride ions in the water and supply the oxidizing agent. In the preceding stage, a slime prevention method characterized by passing water through the hardness removing means, (2) the hardness removing means is selected from an ion exchange device, a reverse osmosis membrane device, a crystallization means and a hardness removing means by electrolysis. 2. The method for preventing slime according to claim 1, comprising a seed or a combination thereof, and (3) the hardness removing means is provided only upstream of an electrolytic cell installed in a bypass line, and only for cooling water flowing through the electrolytic cell. The first to remove hardness
3. A method for preventing slime according to item 2 or 2.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION The slime prevention method of the present invention comprises the steps of: applying a voltage to an electrode immersed in cooling water to generate an oxidizing agent from chloride ions in the water and supplying the oxidizing agent; This is a slime prevention method in which water is passed through the hardness removing means before the voltage is applied to the electrodes.
In the method of the present invention, a pair of electrodes including an anode and a cathode is immersed in cooling water, and a voltage is applied between terminals of these electrodes using an external power supply. As a result, chloride ions in the cooling water are oxidized on the surface of the anode, and oxidizing species such as hypochlorite ions are generated, and slime is added in the same manner as when hypochlorite is added to the cooling water. Can be prevented. Although there is no particular limitation on the material of the electrode used in the method of the present invention, as the cathode, for example, stainless steel,
An electrode of aluminum, silver, or the like can be used. Further, as the anode, an electrode in which a metal material is coated with a simple substance or oxide of a platinum group element can be used. Examples of the platinum group element include ruthenium, rhodium, palladium, osmium, iridium and platinum, and among them, platinum, iridium and ruthenium can be particularly preferably used. By using an electrode coated with a simple substance or an oxide of a platinum group element as the anode, the efficiency of generating an oxidizing agent can be improved by the catalytic action of the platinum group element. The cathode and anode can be of different materials or of the same material. In the method of the present invention, the voltage applied to the electrode is not particularly limited, but is preferably 10 V or more from the viewpoint of the efficiency of oxidant generation, and is preferably 10 to 40 V in consideration of human safety. In addition, it is preferable to control the intensity of the current so that the concentration of the oxidant becomes a predetermined value while measuring the concentration of the oxidant in the cooling water. For example, when the water quality of the cooling water fluctuates greatly, it is necessary to stably maintain and manage the cooling water system by adding a system that automatically controls the current intensity from the measured value of the oxidant concentration. Can be.

[0006] In the method of the present invention, there is no particular limitation on the location of the electrode. For example, the electrode can be inserted and immersed in a pit of the cooling water system, or a bypass line is provided in the cooling water system, and the electrode is provided in the bypass line. It is also possible to install a flow-through type electrolysis cell incorporating, generate an oxidizing agent from chloride ions in the water, and then return it to the cooling water system. In the method of the present invention, the degree of removing the hardness from the cooling water can be appropriately selected according to the strength of the current flowing through the electrode and the flow rate of the cooling water in the electrolytic cell. It is preferably 0.1 mg CaCO ₃ / L or less in the cooling water circulating inside. By setting the calcium hardness in the cooling water to 0.1 mg CaCO ₃ / L or less, calcium carbonate is prevented from adhering to the electrode, and a predetermined voltage is applied to maintain a predetermined current intensity, thereby stably oxidizing the oxidizing agent. Can be generated. In the method of the present invention, before applying a voltage to the electrode immersed in the cooling water, the cooling water is passed through a hardness removing means to remove the hardness. There is no particular limitation on the hardness removal step, for example, the hardness can be removed from the entire amount of cooling water, or
The hardness can be removed only for the cooling water flowing through the electrolytic cell. When the hardness is removed from the entire amount of the cooling water, for example, the hardness of the makeup water to the cooling water system can be removed, or the cooling water can be taken in from the bypass line, the hardness can be removed, and then returned. When the hardness is to be removed only from the cooling water flowing through the electrolytic cell, for example, a hardness removing means can be provided on the upstream side of the electrolytic cell provided in the bypass line.

In the method of the present invention, there is no particular limitation on the hardness removing means, but an ion exchange device, a reverse osmosis membrane device, a crystallization device and a hardness removing device by electrolysis can be suitably used. As the ion exchange device, for example, an ion exchange column filled with a strong acidic ion exchange resin of Na type can be mentioned. As the reverse osmosis membrane device, for example, a device in which an aromatic polyamide hollow fiber is incorporated can be cited, but a device that allows chloride ions to leak, such as loose RO, is more preferable from the viewpoint of oxidizing agent generation efficiency. Examples of the crystallization means include a method in which a column is filled with a seed crystal such as calcium carbonate and water to be treated is passed through the column. Examples of the means for removing hardness by electrolysis include an electrodialyzer, an electric desalinator using an activated carbon electrode, and an electric desalinator filled with a cation exchange resin. One of these hardness removing means may be used alone, or two or more thereof may be used in combination. Further, the chloride ion concentration in the cooling water is 10 mg / L or more, more preferably the concentration ratio is about 2 to 5 times, and the chloride ion concentration is 20 to 80 mg.
/ L is desirable from the viewpoint of the efficiency of oxidant generation. If the concentration ratio is low, the concentration of salts other than the chloride ion concentration will also be low, the electrical resistance between the electrodes will be large, and a higher applied voltage will be required. If the chloride ion concentration is too high, problems such as corrosiveness occur. FIG. 1 is a process flow chart of an embodiment of the method of the present invention. All of the make-up water to the cooling tower 1 is passed to the cation exchange resin tower 2 to remove hardness. The cold water stored in the pit 3 of the cooling tower is sent to the heat exchanger 5 by the circulation pump 4. Some of the cold water
Water is divided into a bypass line 6 and is passed by a pump 7 to an electrolytic cell 8 having a pair of electrodes, whereby an oxidizing agent is generated from chloride ions. Cooling water containing the oxidant is returned to the cold water line. FIG. 2 is a process flow chart of another embodiment of the method of the present invention. The cold water stored in the pit 3 of the cooling tower 1 is sent to the heat exchanger 5 by the circulation pump 4. A part of the cold water is separated into a bypass line 6, and is passed through a reverse osmosis membrane device 9 by a pump 7, and after the hardness in the water is removed, the cold water is passed through an electrolytic cell 8 having a pair of electrodes. An oxidizing agent is generated from chloride ions. Cooling water containing the oxidant is returned to the cold water line. According to the method of the present invention, since the hardness component does not adhere to the electrode immersed in the cooling water, the conversion efficiency from chloride ions to the oxidizing agent does not decrease, and the slime is stably prevented over a long period of time. be able to. The method of the present invention is safer and more economical than a method of adding an oxidizing agent to cooling water, and can be applied to a wide range of water systems. In the present invention, it is not necessary to add a drug, but if necessary, a pH adjuster such as a scale inhibitor, an anticorrosive or an alkali agent can be added.

[0008]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, which should not be construed as limiting the present invention. In Examples and Comparative Examples, the slime prevention ability was evaluated in a cooling water system having a pilot-scale heat exchanger in the process shown in FIG. This cooling water system has a water volume of 300 L and an outer diameter of 19 mm.
Heat transfer area with SUS304 tube of 0.32
and a heat exchanger m ^2. Cooling water flow is 1,680
L / h, of which 300 L / h is drawn from the bypass line into an electrolytic cell provided with two platinum-coated stainless steel electrodes, while applying a DC voltage to generate hypochlorite ions, The operation was performed for 30 days. The makeup water is tap water having a chloride ion concentration of 10 mg / L and a calcium hardness of about 40 mg CaCO ₃ / L.
Doubled. In addition, the inlet temperature of the cooling water heat exchanger is 30 ° C,
The heat exchanger outlet temperature was kept at 50 ° C. After the operation for 30 days, the calcium hardness and the residual chlorine concentration of the cooling water were measured. Further, three 75 mm × 25 mm × 1.5 mm rubber plates were immersed in the cold water pit for 3 days from the 20th to 23rd days after the start of operation, and the slime adhered and grown was collected. After drying, the slime deposition rate was determined from the arithmetic average of the measured weights. Example 1 The entire amount of makeup water was passed through a cation exchange resin tower to remove hardness, and operation was performed for 30 days while maintaining the concentration of cooling water at twice and the current of the electrolytic cell at 3.0 A. The voltage required to maintain the current of 3.0 A is 21.
It was constant at 3V. On the 30th day, the calcium hardness of the cooling water was 0.1 mg CaCO ₃ / L or less, and the residual chlorine concentration was 0.1 mg.
53 mgCl / L. No slime adhered to the rubber plate immersed in the cold water pit. Comparative Example 1 Example 1 except that tap water was used as makeup water.
The operation was performed for 30 days in the same manner as described above. In order to maintain the current of the electrolytic cell at 3.0 A, it was necessary to gradually increase the voltage, and reached 32.1 V on the 30th day. On the 30th day, the calcium hardness of the cooling water was 82 mgCaCO ₃ / L, and the residual chlorine concentration was 0.42 mgCl / L. The slime deposition rate was 1 mg / dm ² / 3day. Comparative Example 2 Tap water was used as makeup water as it was, and the concentration of the cooling water was increased by 2 while maintaining the voltage applied to the electrolytic cell at 21.0 V.
The operation was carried out for 30 days. The current in the electrolysis cell gradually decreased to 2.1 A on the 30th day. The calcium hardness of the cooling water on the 30th day was 84 mgCaCO ₃ / L, and the residual chlorine concentration was 0.19 mgCl / L. The slime deposition rate was 7 mg / dm ² / 3day. Comparative Example 3 The cooling water was stopped from flowing through the electrolysis cell, and sodium hypochlorite was added so that the residual chlorine concentration was 0.5 mgCl / L. I drove. The calcium hardness of the cooling water on the 30th day is 80 mg CaCO ₃
/ L, and the residual chlorine concentration was 0.49 mgCl / L. No slime adhered to the rubber plate immersed in the cold water pit. Comparative Example 4 Cooling water was stopped flowing through the electrolytic cell, and operation was performed for 30 days at a concentration ratio of cooling water of 2 times without adding a chemical. The calcium hardness of the cooling water on the 30th day is 82 mg CaCO ₃
/ L, and the residual chlorine concentration was 0.05 mgCl / L. The slime deposition rate was 23 mg / dm ² / 3day.

Example 2 All of the make-up water was passed through a cation exchange resin tower to remove hardness, and the operation was performed for 30 days while maintaining the concentration of cooling water at 5 times and the current of the electrolytic cell at 5.0 A. Was. The voltage required to maintain the current of 5.0 A is 12.
It was constant at 6V. On the 30th day, the calcium hardness of the cooling water was 0.1 mg CaCO ₃ / L or less, and the residual chlorine concentration was 0.1 mg.
It was 63 mgCl / L. No slime adhered to the rubber plate immersed in the cold water pit. Comparative Example 5 Example 2 except that tap water was used as makeup water.
The operation was performed for 30 days in the same manner as described above. In order to maintain the current of the electrolytic cell at 5.0 A, it was necessary to gradually increase the voltage, and reached 28.8 V on the 30th day. On the 30th day, the cooling water had a calcium hardness of 155 mgCaCO ₃ / L and a residual chlorine concentration of 0.50 mgCl / L. The slime deposition rate was 1 mg / dm ² / 3day. Comparative Example 6 Tap water was used as makeup water as it was, and the concentration of the cooling water was increased by 5 while the voltage applied to the electrolytic cell was maintained at 13.0 V.
The operation was carried out for 30 days. The current in the electrolysis cell gradually decreased to 2.3 A on the 30th day. The calcium hardness of the cooling water on day 30 is 150 mgCaCO ₃ / L,
The residual chlorine concentration was 0.21 mgCl / L. The slime deposition rate was 12 mg / dm ² / 3day. Comparative Example 7 The cooling water was stopped from flowing through the electrolysis cell, and sodium hypochlorite was added so that the residual chlorine concentration became 0.6 mgCl / L. I drove. Calcium hardness of cooling water on the 30th day is 200mgCaCO
₃ / L, and the residual chlorine concentration was 0.62 mgCl / L. No slime adhered to the rubber plate immersed in the cold water pit. Comparative Example 8 The cooling water was stopped flowing through the electrolytic cell, and the operation was performed for 30 days at a concentration ratio of cooling water of 5 times without adding a chemical. Calcium hardness of cooling water on the 30th day is 145mgCaCO
₃ / L, and the residual chlorine concentration was 0.04 mgCl / L. The slime deposition rate was 30 mg / dm ² / 3day. Table 1 shows the results of Examples 1 and 2 and Comparative Examples 1 to 8.

[0010]

[Table 1]

As can be seen from Table 1, when the makeup water is passed through the cation exchange resin tower to remove the hardness, the concentration ratio becomes 2
In both Example 1 and Example 2 in which the concentration ratio was 5 times, the oxidizing agent could be generated from chloride ions through a predetermined current by applying a constant voltage. As in the case of adding sodium hypochlorite of Example 7, the adhesion of slime is prevented. On the other hand, if tap water is used as makeup water without removing hardness, it is necessary to gradually increase the voltage as in Comparative Examples 1 and 5 in order to keep the current constant, and the oxidation The generation amount of the agent is slightly small, and slime adheres slightly. Further, if tap water is used as makeup water without removing hardness and a constant voltage is continuously applied, the current flowing through the electrolytic cell decreases as in Comparative Examples 2 and 6, and the generation of the oxidizing agent occurs. The amount is reduced and slime adheres. When the electrodes were observed after the completion of the operation for 30 days, adhesion of scale was observed on the surfaces of the cathodes used in Comparative Example 1, Comparative Example 2, Comparative Example 5, and Comparative Example 6. Analysis of this scale revealed that the main component was calcium carbonate.

[0012]

According to the method of the present invention, an oxidizing agent is generated by electrolysis of chloride ions to prevent the growth of microorganisms without adding a drug, and to easily, safely and stably prevent slime from adhering. can do.

[Brief description of the drawings]

FIG. 1 is a process flow chart of an embodiment of the method of the present invention.

FIG. 2 is a process flow chart of another embodiment of the method of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Cooling tower 2 Cation exchange resin tower 3 Pit 4 Circulation pump 5 Heat exchanger 6 Bypass line 7 Pump 8 Electrolysis cell 9 Reverse osmosis membrane device

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI theme coat ゛ (reference) F28F 19/01 F28F 19/00 501B F-term (reference) 4D006 GA03 GA04 HA01 JA02Z KA12 KA72 KB01 KB11 KD01 KD23 MA01 MB02 MB07 MC54 PA01 PB06 PB07 PB27 PC80 4D025 AA02 AA06 AB02 AB19 BA08 BA09 BB02 BB07 BB18 DA05 DA06 DA08 4D061 DA03 DA05 DB02 DB03 DB05 DB07 DB10 EA03 EB04 EB14 EB19 EB27 EB28 EB30 GC06

Claims (3)

[Claims] A voltage is applied to an electrode immersed in cooling water,
A slime prevention method for generating an oxidizing agent from chloride ions in water and supplying the oxidizing agent, wherein water is passed through a hardness removing means before a voltage is applied to an electrode. 2. The slime prevention method according to claim 1, wherein the hardness removing means comprises one selected from an ion exchange apparatus, a reverse osmosis membrane apparatus, a crystallization means, and a means for removing hardness by electrolysis, or a combination thereof. 3. The hardness removing means is provided upstream of an electrolytic cell installed in a bypass line, and removes hardness only from cooling water flowing through the electrolytic cell.
The slime prevention method described.